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Human Leukocyte Antigen-G Expression After Heart Transplantation Is Associated With a Reduced Incidence of Rejection
Abstract
Human leukocyte antigen (HLA)-G, a nonclassic major histocompatibility complex class I molecule expressed in the extravillous cytotrophoblast at the feto-maternal interface, is known to protect the fetus from maternal cellular immunity. In a preliminary study, we showed that HLA-G is expressed in the hearts of some patients after heart transplantation.
In the present study, a larger number of patients was investigated to confirm this finding and to look for possible correlations between HLA-G expression and the number and types of rejection. Expression of HLA-G in endomyocardial biopsy specimens was investigated by immunohistochemical analysis, and detection of the soluble HLA-G in the serum was performed by immunoprecipitation followed by Western blot analysis. HLA-G was detected in the biopsy specimens and serum of 9 of 51 patients (18%). The number of episodes of acute rejection was significantly lower in HLA-G-positive patients (1.2+/-1.1) as compared with HLA-G-negative patients (4.5+/-2.8) (P<0.001). No chronic rejection was observed in HLA-G-positive patients, whereas 15 HLA-G-negative patients had chronic rejection (P<0.032). A longitudinal study of these patients reveals that the status of HLA-G expression was maintained after 6 months both in serum and in biopsy specimens. During this period, HLA-G-positive patients did not have chronic rejection.
There is a significant correlation between rejection and HLA-G expression in the heart after transplantation. HLA-G expression and its effect in reducing the incidence and severity of rejection seem to be stable throughout the evolution.
... It is now known that the molecule is expressed in various cell types and in a diverse array of pathological situations such as, autoimmune disease, viral infection, cancer and organ transplantation [6][7][8][9]. HLA-G's inhibitory effect on immune cells has attracted a wide range of research from the fields of oncology, immunology and transplantation, in the hopes that the molecule and its gene could be used as a diagnostic marker and/or potential therapy [10][11][12]. ...
... The presence of HLA-G in transplanted hearts identified in a laboratory in Paris, France, commenced our decade-long research in this field [12,25]. The molecule appeared to be associated with cellular rejection events and this intrigued the laboratory team to investigate the molecule in the context of transplantation [12]. ...
... The presence of HLA-G in transplanted hearts identified in a laboratory in Paris, France, commenced our decade-long research in this field [12,25]. The molecule appeared to be associated with cellular rejection events and this intrigued the laboratory team to investigate the molecule in the context of transplantation [12]. Post transplantation, the allograft heart is subject to immune attacks from the host immune system [26]. ...
The Human Leukocyte Antigen-G (HLA-G) is a MHC-class Ib molecule with robust immunomodulatory properties; in transplant, it inhibits cytotoxic activity of immune cells and thus has a pivotal role in protecting the allograft from immune attack. The present review details a 10-year experience investigating the influence of HLA-G on heart transplantation, allograft rejection and cardiac allograft vasculopathy development. Exploration of HLA-G in transplantation began with the initial findings of its increased expression in allograft hearts. Since then, HLA-G has been recognized as an important factor in transplant immunology. We discuss inducers of HLA-G expression, and the importance of HLA-G as a potential biomarker in allograft rejection and heart failure. We also highlight the importance of polymorphisms and how they may influence both HLA-G expression and clinical outcomes. There remains much to be done in this field, however we hope that findings from our group and other groups will ignite interest and facilitate further expansion of HLA-G research in transplantation.
... HLA-G expression is frequently observed in tumors as well as various autoimmune diseases, suggesting its potential involvement in the pathogenesis of these conditions. In the context of cancer, HLA-G has been shown to confer protection to cancer cells against the cytotoxic activity of natural killer cells and cytotoxic T lymphocytes, enabling tumor immune escape, promoting tumor proliferation, and correlating with reduced patient Maternal blood during pregnancy [36] Serum from heart-transplanted patients [37] HLA-G7 Soluble ...
... Body fluids (such as amniotic fluid and serum) [32] Trophoblasts [33] Thymus [10] Oocytes [34] Pre-implantation embryo [35] HLA-G6 Soluble Maternal blood during pregnancy [36] Serum from heart-transplanted patients [37] HLA-G7 Soluble Transfected cell supernatant [38] Maternal blood during pregnancy [39] Most studies have highlighted the crucial role of HLA-G as an immunomodulator in pregnancy [40]. During pregnancy, sHLA-G (HLA-G5 and HLA-G6) in the maternal circulation is mainly produced and secreted by trophoblast cells [41]. ...
Human leukocyte antigen-G (HLA-G) is a non-classical human major histocompatibility complex (MHC-I) molecule with the membrane-bound and soluble types. HLA-G is primarily expressed by extravillous cytotrophoblast cells located at the maternal–fetal interface during pregnancy and is essential in establishing immune tolerance. This review provides a comprehensive understanding of the multiple molecular mechanisms by which HLA-G regulates the immune function of NK cells. It highlights that HLA-G binds to microRNA to suppress NK cell cytotoxicity and stimulate the secretion of growth factors to support fetal growth. The interactions between HLA-G and NK cells also activate senescence signaling, promoting spiral artery remodeling and maintaining the balance of maternal–fetal immune responses. In addition, HLA-G can inhibit the function of decidual T cells, dendritic cells, and macrophages. Overall, the interaction between trophoblast cells and immune cells mediated by HLA-G plays a crucial role in understanding immune regulation at the maternal–fetal interface and offers insights into potential treatments for pregnancy-related diseases.
... In situations of transplantation, HLA-G has been shown to be associated with a lower occurrence of acute and chronic rejection in heart, lung, and kidney transplantation [5,11,12]. ...
... Here, we describe, for the first time, the kinetics of HLA-G plasma levels before and after LT, allowing us to describe a similar pattern of evolution. We found pre-LT HLA-G levels to be stable and reproducible (S4A Fig in S1 File), as previously reported for heart transplantation [11] and LT [15]. We did not find any significant differences in pre-or post-LT HLA-G levels depending on the aetiology of the liver disease prior to transplantation, as suggested by the study of Moroso et al. [15]. ...
Graft rejection is a critical risk in solid-organ transplantation. To decrease such risk, an understanding of the factors involved in low immunogenicity of liver allografts could potentially make it possible to transfer this tolerogenic property to other transplanted organs. HLA-G, a natural physiological molecule belonging to the Human Leukocyte Antigen class (HLA) Ib family that induces tolerance, is associated with fewer rejections in solid-organ transplantation. In contrast to HLA-G, HLA antigen incompatibilities between donor and recipient can lead to rejection, except in liver transplantation. We compared HLA-G plasma levels and the presence of anti-HLA antibodies before and after LT to understand the low immunogenicity of the liver. We conducted a large prospective study that included 118 patients on HLA-G plasma levels during a 12-month follow-up and compared them to the status of anti-HLA antibodies. HLA-G plasma levels were evaluated by ELISA at seven defined pre- and post-LT time points. HLA-G plasma levels were stable over time pre-LT and were not associated with patient characteristics. The level increased until the third month post-LT, before decreasing to a level comparable to that of the pre-LT period at one year of follow-up. Such evolution was independent of biological markers and immunosuppressive treatment, except with glucocorticoids. An HLA-G plasma level ≤ 50 ng/ml on day 8 after LT was significantly associated with a higher rejection risk. We also observed a higher percentage of rejection in the presence of donor specific anti-HLA antibodies (DSA) and an association between the increase in HLA-G plasma levels at three months and the absence of DSA. The low immunogenicity of liver allografts could be related to early elevated levels of HLA-G, which lead, in turn, to a decrease in anti-HLA antibodies, opening potential new therapeutic strategies using synthetic HLA-G proteins.
... Its inhibitory function is conveyed through the interaction with specific receptors on a diverse set of immune cells. HLA-G is thought to be involved in transplantation immune tolerance by protecting the organ from rejection (9). ...
... HLA-G expression was first investigated in heart transplantation in 2000 (9). Since then, its expression was detected in different solid organs after transplantation such as in heart, kidney, liver, lung, liver-kidney, kidney-pancreas transplantations. ...
Organ transplantation is a lifesaving option for patients with advanced diseases. Rejection is regarded as one of the most severe risk factors post-transplantation. A molecule that contributes to immune tolerance and resisting rejection is human leukocyte antigen (HLA)-G, which belongs to the non-classical major histocompatibility complex class (MHC) I family. HLA-G was originally found to play a role during pregnancy to maintain immune tolerance between mother and child. It is expressed in the placenta and detected in several body fluids as soluble factor as well as different membrane isoforms on cells. Recent findings on HLA-G show that it can also play multifaceted roles during transplantation. This review will explain the general characteristics and biological function of HLA-G and summarize the views supporting the tolerogenic and other roles of HLA-G to better understand its role in solid organ transplantation (SOT) and its complications. Finally, we will discuss potential future research on the role of HLA-G in prevention, diagnosis, and treatment in SOT.
... Historically, the relationship between HLA-G and graft acceptance/rejection was first observed in heart transplantation (54), and, over time, information on this subject has been expanded. These studies reported the presence of HLA-G in biopsies of transplanted heart tissue, where HLA-G was especially prevalent in patients with no or low rejection scores (55). ...
... These studies reported the presence of HLA-G in biopsies of transplanted heart tissue, where HLA-G was especially prevalent in patients with no or low rejection scores (55). In HLA-G-positive patients, the incidence of acute or chronic rejection was significantly decreased (p<0.001 and p<0.032, respectively) when compared with HLA-G-negative patients (54). ...
HLA-G is a non-classical HLA class I molecule with immunomodulatory properties. It was initially described at the maternal-fetal interface, and it was later found that this molecule was constitutively expressed on certain immuneprivileged tissues, such as cornea, endothelial and erythroid precursors, and thymus. The immunosuppressive effect of HLA-G is exerted through the interaction with its cognate receptors, expressed on immunocompetent cells, like ILT2, expressed on NK, B, T cells and APCs; ILT4, on APCs; KIR, found on the surface of NK cells; and finally, the co-receptor CD8. Because of these immunomodulatory functions, HLA-G has been involved in several processes, amongst which organ transplantation, viral infections, cancer progression, and autoimmunity. HLA-G neo-expression on tumors has been recently described in several types of malignancies. In fact, tumor progression is tightly linked to the presence of the molecule, as it exerts its tolerogenic function, inhibiting the cells of the immune system and favoring tumor escape. Several polymorphisms in the 3’UTR region condition changes in HLA-G expression (14bp and +3142C/G, among others), which have been associated with both the development and outcome of patients with different tumor types. Also, in recent years, several studies have shown that HLA-G plays an important role in the control of autoimmune diseases. The ability of HLA-G to limit the progression of these diseases has been confirmed and, in fact, levels of the molecule and several of its polymorphisms have been associated with increased susceptibility to the development of autoimmune diseases, as well as increased disease severity. Thus, modulating HLA-G expression in target tissues of oncology patients or patients with autoimmune diseases may be potential therapeutic approaches to treat these pathological conditions.
... HLA-G's induction of immune tolerance is exerted directly via HLA-G1's inhibitory interactions with nearly all immune cells and indirectly by inhibiting vascularization via the soluble HLA-G5 isoform, the combination of which is hypothesized to prevent self-antigen recognition and immune response 13 . Previous studies in autoimmunity have found that HLA-G expression reduced the incidence of acute and chronic heart transplant rejection in humans 32 and that a single injection of endogenously produced HLA-G could be used as a tolerogenic molecule in skin transplants in animal models 13 . These studies demonstrated that HLA-G inhibits T cell functions and may attenuate clinical rejection by influencing a shift in cytokine expression profiles toward Th2 and production of TNFA, IFN-γ, and IL-10, endogenous immunomodulatory cytokines with potent immunosuppressive functions 32,33 . ...
... Previous studies in autoimmunity have found that HLA-G expression reduced the incidence of acute and chronic heart transplant rejection in humans 32 and that a single injection of endogenously produced HLA-G could be used as a tolerogenic molecule in skin transplants in animal models 13 . These studies demonstrated that HLA-G inhibits T cell functions and may attenuate clinical rejection by influencing a shift in cytokine expression profiles toward Th2 and production of TNFA, IFN-γ, and IL-10, endogenous immunomodulatory cytokines with potent immunosuppressive functions 32,33 . Additionally, the combination of HLA-G1 and HLA-G5 was demonstrated to provide long-term immunosuppressive in corneal inflammation and vascularization of rabbits 14 . ...
Non-infectious uveitis (NIU) is an intractable, recurrent, and painful disease that is a common cause of vision loss. Available treatments of NIU, such as the use of topical corticosteroids, are non-specific and have serious side effects which limits them to short-term use; however, NIU requires long-term treatment to prevent vision loss. Therefore, a single dose therapeutic that mediates long-term immunosuppression with minimal side effects is desirable. In order to develop an effective long-term therapy for NIU, an adeno-associated virus (AAV) gene therapy approach was used to exploit a natural immune tolerance mechanism induced by the human leukocyte antigen G (HLA-G). To mimic the prevention of NIU, naïve Lewis rats received a single intravitreal injection of AAV particles harboring codon-optimized cDNAs encoding HLA-G1 and HLA-G5 isoforms one week prior to the induction of experimental autoimmune uveitis (EAU). AAV-mediated expression of the HLA-G-1 and -5 transgenes in the targeted ocular tissues following a single intravitreal injection of AAV-HLA-G1/5 significantly decreased clinical and histopathological inflammation scores compared to untreated EAU eyes (p < 0.04). Thus, localized ocular gene delivery of AAV-HLA-G1/5 may reduce the off-target risks and establish a long-term immunosuppressive effect that would serve as an effective and novel therapeutic strategy for NIU, with the potential for applications to additional ocular immune-mediated diseases.
... Human leukocyte antigen (HLA)-G is a non-classical class Ib protein that exists in membrane-bound and various soluble isoforms due to alternative splicing [5,6]. It is expressed in placenta, leukocytes and allograft parenchymal cells [7,8], where it inhibits lymphocytes [9], promotes the induction of regulatory cells [7,10] and inhibits rejection [11,12]. Unlike most HLA molecules, it exhibits limited variation in the protein-coding region, but its expression is modified by single nucleotide polymorphisms (SNPs), many of which are located in regulatory upstream and downstream elements of the HLA-G locus [13]. ...
... In a similar vein, BURGIERE et al. [16] observed higher serum concentrations of HLA-G at 12 months post transplant in patients who went on to develop CLAD. In contrast, previous transplantation studies revealed that higher levels of sHLA-G in serum conferred a reduced risk [11,12]. However, WHITE et al. [14] also observed that elevated sHLA-G in BAL fluid was associated with acute rejection and CLAD. ...
Human Leukocyte Antigen (HLA)-G is a non-classical HLA that inhibits immune responses. Its expression is modified by single nucleotide polymorphisms (SNPs), which are associated with transplant outcomes. Our aim was to investigate the association of donor and recipient HLA-G SNPs with chronic lung allograft dysfunction (CLAD) and mortality after lung transplantation (LT).
In this single-centre study, we examined 11 HLA-G SNPs in 345 consecutive recipients and 297 donors of a first bilateral lung transplant. A multivariable Cox proportional hazards model assessed associations of SNPs with death and CLAD. Transbronchial biopsies (TBBx) and bronchoalveolar lavage (BAL) samples were examined using quantitative PCR, ELISA, and immunofluorescence.
Over a median of 4.75 years, 142 (41%) patients developed CLAD; 170 (49%) died. Multivariable analysis revealed donor SNP +3142 (GG+CG vs CC) was associated with increased mortality (HR 1.78 [1.12-2.84], p=0.015). In contrast, five donor SNPs -201(CC), -716(TT), SNP -56(CC), G*01:03(AA) and 14bp INDEL conferred reduced mortality risk. Specific donor-recipient SNP pairings reduced CLAD risk. Predominantly epithelial HLA-G expression was observed on TBBx without rejection. Soluble HLA-G was present in higher concentrations in the BAL of patients who later developed CLAD.
Specific donor SNPs are associated with mortality risk after LT, while certain donor-recipient SNP pairings modulated CLAD risk. TBBx demonstrated predominantly epithelial, and therefore presumably donor-derived, HLA-G expression in keeping with these observations. This study is the first to demonstrate an effect of donor HLA-G SNPs on LT outcome.
... Expression of HLA-G has previously been studied in relation to clinical cardiac transplantation where endomyocardial expression [6,7] and levels of soluble HLA-G were associated with graft acceptance [7,8]. Serum levels increased post-transplantation in patients with good graft function but were significantly decreased in those suffering from cardiac allograft vasculopathy [9]. ...
... Expression of HLA-G has previously been studied in relation to clinical cardiac transplantation where endomyocardial expression [6,7] and levels of soluble HLA-G were associated with graft acceptance [7,8]. Serum levels increased post-transplantation in patients with good graft function but were significantly decreased in those suffering from cardiac allograft vasculopathy [9]. ...
... In addition, some reports have suggested that HLA-G is expressed on the surface of many non-placental cells. Membrane-anchored HLA-G and its soluble form (sHLA-G) have been demonstrated to perform multiple functions that promote immune tolerance to allogeneic molecules [13][14][15]. In particular, the association between HLA-G and GVHD has become a central focus in HSCT [16][17][18][19]. ...
... The utility of rTM in treating complications following HSCT has been reported in both patients with VOD/TMA and aGVHD [26][27][28][29][30][31][32][33][34][35]. The pathogenesis of GVHD involves vascular endothelial vulnerability and endothelial dysfunction [13][14][15][16]53,54]. Specifically, endothelial cells become a target of CTLs, resulting in the induction of endothelial cell apoptosis [55,56]. ...
... 14 HLA-G expression has been previously associated with decreased CAV incidence after heart transplantation. 15 Vascular smooth muscle cells (SMC) have a pivotal role in CAV development, as they are the main generators of vascular compromise. According to previous studies, HLA-G molecules affect endothelial cell activity. ...
... The fact that HLA-G expression in biopsies and serum/plasma of transplant patients is associated with reduced episodes of rejection and CAV suggests that HLA-G might play a role within the coronary artery. 15,24 A similar inverse association between HLA-G expression and graft failure has been reported in other solid organ transplants. 10,11 However, no research examines the protective effect of HLA-G within the vasculature of these allografts. ...
Human Leukocyte Antigen‐G (HLA‐G) expression is modulated by immunosuppressant use and is associated with lower incidence of graft rejection and cardiac allograft vasculopathy (CAV). We examined if everolimus induces HLA‐G expression and inhibits human coronary artery smooth muscle cell (HCASMC) proliferation, a critical event in CAV. Also, we examined if TNFα‐stimulated neutrophil adhesion is inhibited by HLA‐G on human coronary artery endothelial cells (HCAECs). HLA‐G expression in HCASMCs following everolimus treatment was determined by Western‐blot densitometric analysis. HCASMCs proliferation following incubation with recombinant HLA‐G was determined by automated cell counter detecting 2‐10μm particles. Assessment of recombinant HLA‐G on neutrophil adhesion to HCAECs in response to TNF‐α induced‐injury was determined by non‐static adhesion assays. HLA‐G expression was upregulated in HCASMCs following everolimus exposure (1000ng/ml; p<0.05). HLA‐G (500,1000ng/ml; both p<0.05) reduced HCASMC proliferation and inhibited TNFα‐stimulated neutrophil adhesion to endothelial cells at all concentrations (0.1‐1ng/ml; all p<0.001). Our study reveals novel regulation of HLA‐G by everolimus, by demonstrating HLA‐G upregulation and subsequent inhibition of HCASMC proliferation. HLA‐G is a potent inhibitor of neutrophil adhesion to HCAECs. Findings support HLA‐G's importance and potential use in heart transplantation for preventative therapy or as a marker to identify patients high‐risk for developing CAV.
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... HLA-G is a non-classical class Ib protein existing in membrane-bound and various soluble isoforms due to alternative splicing [5,6]. It is expressed in placenta, leukocytes, and allograft parenchymal cells [7,8], where it inhibits lymphocytes [9], promotes the induction of regulatory cells [7,10], and inhibits rejection [11,12]. Unlike most HLA molecules, it exhibits limited variation in the protein-coding region, but its expression is modified by single nucleotide polymorphisms (SNPs), many of which are located in regulatory upstream and downstream elements of the HLA-G locus [13]. ...
... In a similar vein, Burgiere and colleagues [16] observed higher serum concentrations of HLA-G at 12 months post-transplant in patients who went on to develop CLAD. In contrast, previous transplantation studies revealed that higher levels of sHLA-G in serum conferred a reduced risk [11,12]. However, White, Floreth [14] also observed that elevated sHLA-G in BAL was associated with acute rejection and CLAD. ...
... Several studies have described a protective effect of HLA-G in human allotransplantation such as kidney, liver, heart and lung [6,[17][18][19]. In kidney transplant patients, increased soluble HLA-G level was significantly associated with better graft acceptance [8,18,[20][21][22][23]. ...
... The HLA-G molecule inhibits cytotoxic activity of NK cells and cytotoxic T cells, alloproliferative response of CD4 + T cells, dendritic cells maturation and activation of regulatory T cells [12]. In relation to these characteristics, a protective effect of HLA-G in human allotransplantation such as kidney, liver, heart and lung has been described [6,[17][18][19]. As gene polymorphism can influence protein expression level, the association between HLA-G 14 bp ins/del polymorphism in the 3´UTR, soluble HLA-G level and kidney graft acceptance in the Slovak population was analyzed. ...
Human leukocyte antigen G (HLA-G) is a non-classical HLA class I protein with various immunosuppressive functions. Besides its profound effect to induce fetal tolerance, HLA-G has been also found to enhance graft acceptance. The aim of the study was to analyse the association between HLA-G 14 bp insertion/deletion polymorphism, soluble HLA-G level and kidney graft outcome in the Slovak population. We investigated 69 kidney transplant recipients aged 27–65 years. Out of this group, 37 recipients developed acute rejection, confirmed by biopsy, and 32 patients had stable allograft function. Plasma was obtained from recipients at 1 day before transplantation and analyzed by ELISA. Genotyping of HLA-G polymorphism was performed by PCR. Significantly higher pre-transplantation levels of sHLA-G were found in the group with stable allograft function in comparison to group with acute rejection (P = 0.0409). In the homozygous −14/−14 recipients with stable allograft function, significantly higher values of sHLA-G were determined in comparison to the recipients with acute rejection (P = 0.0052). The study revealed an association between 14 bp deletion polymorphism and soluble HLA-G level that is proportional to kidney graft acceptance. It is suggested that pre-transplantation levels of soluble HLA-G should be monitored as additional marker to predict kidney graft outcome.
... Expression of transgenic HLA-E and HLA-G in endothelial cell lines was reported to significantly suppress macrophage-mediated cytotoxicity in a xenomodel [35,36]. Furthermore, expression of HLA-E and HLA-G was associated with a reduced rate of rejection in transplant recipients [37][38][39]. CD161 is primarily an inhibitory receptor, blockage of which promotes activation of T cells and cytotoxicity [40,41]. CD161 is a marker of pro-inflammatory NK cell function with high cytokine responsiveness [42]. ...
Acute cardiac rejection remains a significant challenge in the post-transplant period, necessitating meticulous monitoring and timely intervention to prevent graft failure. Thus, the goal of the present study was to identify novel biomarkers involved in acute cardiac rejection, paving the way for personalized diagnostic, preventive, and treatment strategies. A total of 809 differentially expressed genes were identified in the GSE150059 dataset. We intersected genes selected by analysis of variance, recursive feature elimination, least absolute shrinkage and selection operator, and random forest classifier to identify the most relevant genes involved in acute cardiac rejection. Thus, HCP5, KLRD1, GZMB, PLA1A, GNLY, and KLRB1 were used to train eight machine learning models: random forest, logistic regression, decision trees, support vector machines, gradient boosting machines, K-nearest neighbors, XGBoost, and neural networks. Models were trained, tested, and validated on the GSE150059 dataset (MMDx-based diagnosis of rejection). Eight algorithms achieved great performance in predicting acute cardiac rejection. However, all machine learning models demonstrated poor performance in two external validation sets that had rejection diagnosis based on histology: merged GSE2596 and GSE4470 dataset and GSE9377 dataset, thus highlighting differences between these two methods. According to SHAP and LIME, KLRD1 and HCP5 were the most impactful genes.
... This anti-immune property makes Muse cells useful not only in tissue repair but also in suppressing autoimmunity [49]. Human leukocyte antigen G (HLA-G) is a mechanism evolved by placental mammals to prevent immune rejection of the placenta and the fetus it nurtures [80,85,86]. Whereas Indoleamine 2,3-dioxygenase (IDO) inhibits the kynurenine pathway by promoting the degradation of tryptophan in T cells, thereby inhibiting T cell proliferation and inducing apoptosis [86]. ...
Multilineage-differentiating stress-enduring (Muse) cells, a cell subgroup from mesenchymal stem cells (MSCs), are pluripotent cells with unique characteristics such as non-tumorigenic and pluripotent differentiation ability. After homing, Muse cells spontaneously differentiate into tissue component cells and supplement damaged/lost cells to participate in tissue repair. Importantly, Muse cells can survive in injured tissue for an extended period, stabilizing and promoting tissue repair. In addition, it has been confirmed that injection of exogenous Muse cells exerts anti-inflammatory, anti-apoptosis, anti-fibrosis, immunomodulatory, and paracrine protective effects in vivo. The discovery of Muse cells is an important breakthrough in regenerative medicine. The article provides a comprehensive review of the characteristics, sources, and potential mechanisms of Muse cells for tissue repair and regeneration. This review serves as a foundation for the further utilization of Muse cells as a key clinical tool in regenerative medicine.
... 13,14 Thus, due to its ability to inhibit innate and adaptive immune responses and its tolerogenic effects, HLA-G has become attractive to the fields of reproduction, infections, autoimmune diseases and organ transplantation. [15][16][17][18] HLA-G5, due to its unique structure, is a key molecular subtype in the HLA-G family that plays an immunosuppressive role. 19,20 Although studies have shown that the immunomodulatory functions of MSCs are mainly mediated by immunosuppressive molecules secreted by MSCs, the immunoregulatory mechanisms are still not fully elucidated. ...
Background
Acute graft-versus-host disease (aGVHD) initiated by intestinal barrier dysfunction and gut microbiota dysbiosis, remains one of the main obstacles for patients undergoing allogenic hematopoietic stem cell transplantation (allo-HSCT) to achieve good prognosis. Studies have suggested that mesenchymal stem cells (MSCs) can suppress immune responses and reduce inflammation, and human leukocyte antigen-G5 (HLA-G5) plays an important role in the immunomodulatory effects of MSCs, but very little is known about the potential mechanisms in aGVHD. Thus, we explored the effect of HLA-G5 on the immunosuppressive properties of human amnion MSCs (hAMSCs) and demonstrated its mechanism related to the gut microbiota at the intestinal barrier in aGVHD.
Methods
Patients undergoing allo-HSCT were enrolled to detect the levels of plasma-soluble HLA-G (sHLA-G) and regulatory T cells (Tregs). Humanized aGVHD mouse models were established and treated with hAMSCs or HLA-G5 overexpressing hAMSCs (ov-HLA-G5-hAMSCs) to explore the mechanism of HLA-G5 mediated immunosuppressive properties of hAMSCs and the effect of ov-HLA-G5-hAMSCs on the gut microbiota at the intestinal barrier in aGVHD.
Results
The plasma levels of sHLA-G on day +30 after allo-HSCT in aGVHD patients were lower than those in patients without aGVHD, and the sHLA-G levels were positively correlated with Tregs percentages. ov-HLA-G5-hAMSCs had the potential to inhibit the expansion of CD3+CD4+ T and CD3+CD8+ T cells and promote Tregs differentiation, suppress proinflammatory cytokine secretion but promote anti-inflammatory cytokines release. Besides, ov-HLA-G5-hAMSCs also could reverse the intestinal barrier dysfunction and gut microbiota dysbiosis in aGVHD.
Conclusion
We demonstrated that HLA-G might work with Tregs to create a regulatory network together to reduce the occurrence of aGVHD. HLA-G5 mediated hAMSCs to exert higher immunosuppressive properties in vivo and reverse the immune imbalance caused by T lymphocytes and cytokines. Furthermore, HLA-G5 overexpressing hAMSCs could restore gut microbiota and intestinal barriers, thereby ameliorating aGVHD.
... HLA-G was detected in immune-privileged organs and is related to reduction in inflammation and immune responses [59]; as well as present in placental mammals to avoid fetus and placenta rejection [60]. It has also been reported to support tolerance in heart transplantation [61]. For this reason, although HLA-G expression is lower after engrafting into the damaged area, it is suggested that HLA protects Muse cells from immunologic response [29]. ...
In recent years, several studies have been conducted on Muse cells mainly due to their pluripotency, high tolerance to stress, self-renewal capacity, ability to repair DNA damage and not being tumoral. Additionally, since these stem cells can be isolated from different tissues in the adult organism, obtaining them is not considered an ethical problem, providing an advantage over embryonic stem cells. Regarding their therapeutic potential, few studies have reported clinical applications in the treatment of different diseases, such as aortic aneurysm and chondral injuries in the mouse or acute myocardial infarction in the swine, rabbit, sheep and in humans. This review aims to describe the characterization of Muse cells, show their biological characteristics, explain the differences between Muse cells and mesenchymal stem cells, and present their contribution to the treatment of some diseases.
... The natural expression of HLA-G1 + has been measured in cardiac allograft recipient biopsies revealing 86% of HLA-G1 + grafts had no cellular rejection and correlated to a 0% risk of vasculopathy (39,62). HLA-G1 + expression in kidney, liver and FIGURE 7 | Skin fibroblasts derived from HLA-G + porcine cells increase phosphorylation of SHP-2 in various subsets of human PBMCs. ...
The human leukocyte antigen G1 (HLA-G1), a non-classical class I major histocompatibility complex (MHC-I) protein, is a potent immunomodulatory molecule at the maternal/fetal interface and other environments to regulate the cellular immune response. We created GGTA1⁻/HLAG1⁺ pigs to explore their use as organ and cell donors that may extend xenograft survival and function in both preclinical nonhuman primate (NHP) models and future clinical trials. In the present study, HLA-G1 was expressed from the porcine ROSA26 locus by homology directed repair (HDR) mediated knock-in (KI) with simultaneous deletion of α-1-3-galactotransferase gene (GGTA1; GTKO) using the clustered regularly interspersed palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) (CRISPR/Cas9) gene-editing system. GTKO/HLAG1⁺ pigs showing immune inhibitory functions were generated through somatic cell nuclear transfer (SCNT). The presence of HLA-G1 at the ROSA26 locus and the deletion of GGTA1 were confirmed by next generation sequencing (NGS) and Sanger’s sequencing. Fibroblasts from piglets, biopsies from transplantable organs, and islets were positive for HLA-G1 expression by confocal microscopy, flow cytometry, or q-PCR. The expression of cell surface HLA-G1 molecule associated with endogenous β2-microglobulin (β2m) was confirmed by staining genetically engineered cells with fluorescently labeled recombinant ILT2 protein. Fibroblasts obtained from GTKO/HLAG1⁺ pigs were shown to modulate the immune response by lowering IFN-γ production by T cells and proliferation of CD4⁺ and CD8⁺ T cells, B cells and natural killer (NK) cells, as well as by augmenting phosphorylation of Src homology region 2 domain-containing phosphatase-2 (SHP-2), which plays a central role in immune suppression. Islets isolated from GTKO/HLA-G1⁺ genetically engineered pigs and transplanted into streptozotocin-diabetic nude mice restored normoglycemia, suggesting that the expression of HLA-G1 did not interfere with their ability to reverse diabetes. The findings presented here suggest that the HLA-G1⁺ transgene can be stably expressed from the ROSA26 locus of non-fetal maternal tissue at the cell surface. By providing an immunomodulatory signal, expression of HLA-G1⁺ may extend survival of porcine pancreatic islet and organ xenografts.
... One alternative, of course, to all this and to reduce rejection, or even obviate the need to worry about it at all, is through genetically engineering the grafted cells so that they have a knockout of HLA-I/II proteins accompanied by an increased expression of HLA-G or E [80,81]. This increased expression of HLA-G or E could be useful to inhibit NK cell rejection of the grafted HLA-I/II knockout cells because they interact with the killer inhibition receptors of NK cells, hence preventing the rejection process mediated by these cells [82]. ...
Dopaminergic (DA) cell replacement therapies are a promising experimental treatment for Parkinson’s disease and a number of different types of DA cell-based therapies have already been trialled in patients. To date the most successful have been allotransplants of foetal ventral midbrain but even then, the results have been inconsistent. This coupled to the ethical and logistical problems with using this tissue has meant that an alternative cell source has been sought of which human pluripotent stem cells (hPSC) sources have proven very attractive. Robust protocols for making mesencephalic DA progenitor cells from hPSC now exist and the first in-human clinical trials have or are about to start. However, while their safety and efficacy are well understood, relatively little is known about their immunogenicity and in this review, we briefly summarise this with reference mainly to the limited literature on human foetal dopaminergic cells.
... This mechanisms is defined as trogocytosis and seems to play important role for the establishment of immune tolerance [133]. Several groups provides evidences about the role of HLA-G in kidney and heart transplantation [134][135][136]. In healthy conditions in adults, HLA-G is weakly expressed in liver, but it might be transmitted through transendothelial migration and/or trogocytosis from circulating cells under particular circumstances like cytokines, hypoxia etc. [137][138][139]. ...
The success of transplantation depends on multiple factors, but the establishment of immune tolerant milieu is of critical importance. Hepatic environment consists of different cellular populations with prominent capacity to tolerate a huge range of antigens. Among them, regulatory T cells (Tregs) play an important role. They control the strength of immune reactions against non-self antigens and were shown to have an impact on the establishment of immune tolerance in the post-transplantation period. Furthermore, they impact a particular state after transplantation – operational tolerance. The abundant data show that Tregs might be manipulated, which suggests their further implementation as a treatment strategy. Tregs are also a very attractive target as a biomarker in the monitoring of post-transplantation period. Here, we review the particular role of Tregs among the broad spectrum of immune tolerance mechanisms of the liver in the light of the current directions of medical research.
... As a molecule with immunosuppressive function, HLA-G plays a significant role in the development of immune tolerance following transplantation, especially in the field of solid organ transplantation [11]. The expression of HLA-G in heart and kidney transplant patients can reduce the occurrence of transplant rejection [50,51]. Therefore, the immunoregulatory and immunosuppressive activities of HLA-G have been widely concerned in the development of GVHD after hematopoietic stem cell transplantation in patients with hematologic diseases. ...
Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative therapeutic strategy to treat several hematological malignancies and non-hematological malignancies. However, graft-versus-host disease (GVHD) is a frequent and serious transplant-related complication which dramatically restrains the curative effect of allo-HSCT and a significant cause of morbidity and mortality in allogeneic HCT recipients. Effective prevention of GVHD mainly depends on the induction of peripheral immune tolerance. Human leukocyte antigen-G (HLA-G) is a non-classical MHC class I molecule with a strong immunosuppressive function, which plays a prominent role in immune tolerance. HLA-G triggers different reactions depending on the activation state of the immune cells and system. It also exerts a long-term immune tolerance mechanism by inducing regulatory cells. In this present review, we demonstrate the immunomodulatory properties of human leukocyte antigen-G and highlight the role of HLA-G as an immune regulator of GVHD. Furthermore, HLA-G could also serve as a good predictor of GVHD and represent a new therapeutic target for GVHD.
... Through these mechanisms, HLA-G may serve to dampen the specific immune response towards non-host targets. For instance, high levels of HLA-G have been associated with reduced rejection rate following heart (Lila et al., 2002), liver, and kidney transplantations (Creput et al., 2003). ...
Preeclampsia is a leading cause of maternal and offspring mortality and morbidity, and predicts increased future cardiovascular disease risk. Placental dysfunction and immune system dysregulation are likely key pathophysiological factors. Soluble human leukocyte antigen G (sHLA-G) may dampen the specific immune response towards placental trophoblasts. Previous studies have shown low sHLA-G levels in preeclampsia, but postpartum, levels are unknown. Furthermore, the relationship between sHLA-G and sFlt-1 and PlGF, placental function markers, is unknown. We hypothesized that low maternal sHLA-G during pregnancy would be associated with placental dysfunction, including preeclampsia, gestational hypertension, and dysregulated sFlt-1 and PlGF, and that sHLA-G would remain decreased following preeclampsia.
We included 316 pregnant women: 58 with early-onset preeclampsia (<34 weeks’ gestation), 81 with late-onset preeclampsia (≥34 weeks’ gestation), 25 with gestational hypertension, and 152 normotensive controls. Postpartum (1 or 3 years), we included 321 women: 29 with early-onset preeclampsia, 98 with late-onset preeclampsia, 57 with gestational hypertension, and 137 who were normotensive during their index pregnancies.
In pregnancy, plasma sHLA-G was significantly lower both in the early- and late-onset preeclampsia groups compared to controls. In women with preeclampsia or gestational hypertension, sHLA-G was inversely correlated with serum sFlt-1. Postpartum, plasma sHLA-G levels were significantly higher in women who had had early-onset preeclampsia compared to controls.
Our results support that sHLA-G may be important for placental function. Unexpectedly, sHLA-G was elevated up to 3 years after early-onset preeclampsia, suggesting an excessively activated immune system following this severe preeclampsia form, potentially contributing to future cardiovascular disease risk.
... It was reported that HLA-G is upregulated in response to rejection of organ transplantation [33][34][35][36][37], and heart failure (HF) [38], suggesting a putative role to modulate the inflammatory condition [39,40]. ...
Aims
Immune endothelial inflammation, underlying coronary heart disease (CHD) related phenotypes, could provide new insight into the pathobiology of the disease. We investigated DNA methylation level of the unique CpG island of HLA-G gene in CHD patients and evaluated the correlation with cardiac computed tomography angiography (CCTA) features.
Methods
Thirty-two patients that underwent CCTA for suspected CHD were enrolled for this study. Obstructive CHD group included fourteen patients, in which there was a stenosis greater than or equal to 50% in one or more of the major coronary arteries detected; whereas subjects with Calcium (Ca) Score = 0, uninjured coronaries and with no obstructive CHD (no critical stenosis, NCS) were considered as control subjects (n = 18). For both groups, DNA methylation profile of the whole 5’UTR-CpG island of HLA-G was measured. The plasma soluble HLA-G (sHLA-G) levels were detected in all subjects by specific ELISA assay. Statistical analysis was performed using R software.
Results
For the first time, our study reported that 1) a significant hypomethylation characterized three specific fragments (B, C and F) of the 5’UTR-CpG island (p = 0.05) of HLA-G gene in CHD patients compared to control group; 2) the hypomethylation level of one specific fragment of 161bp (+616/+777) positively correlated with coronary Ca score, a relevant parameter of CCTA (p<0.05) between two groups evaluated and was predictive for disease severity.
Conclusions
Reduced levels of circulating HLA-G molecules could derive from epigenetic marks. Epigenetics phenomena induce hypomethylation of specific regions into 5'UTR-CpG island of HLA-G gene in CHD patients with obstructive non critical stenosis vs coronary stenosis individuals.
... Muse cells display immunosuppressive effects by activating regulatory T cells, suppressing dendritic cell differentiation and expressing HLA-G [26]. HLA-G has been shown to promote graft tolerance in heart transplantation [27], which may protect Muse cell from immunologic attack in the early phase of integration. ...
Multilineage differentiating stress enduring cells (Muse cells), double positive for SSEA-3 and CD105, can be isolated by fluorescence-activated cell sorting (FACS) or sever cellular conditions from dermal fibroblasts, bone marrow stem cells (BMSCs), adipose tissue derived stem cells (ADSCs), fresh bone marrow and liposuction fat. When cultured in a single-cell suspension, Muse cells can grow into characteristic cell clusters. Muse cells maintain pluripotency as evidenced by pluripotent markers in vitro. Besides, Muse cells have no tumorigenesis up to 6 months in SCID mice. Muse cells differentiate into cells representative of all three germ layers both spontaneously and under specific induction. In comparison to mesenchymal stem cells (MSCs), Muse cells show higher homing and migration capabilities to damaged sites which is predominantly attributed to S1P–S1PR2 axis. The regenerative effects of Muse cells have been demonstrated by many models in vivo or in vitro, including stroke, intracerebral hemorrhage, myocardial infarction, aortic aneurysm, lung injuries, liver fibrosis, focal segmental glomerulosclerosis, osteochondral defects and skin ulcer. In general, migration, differentiation and paracrine play a pivotal role in the regeneration capability. Here we review the isolation, core properties, preclinical studies as well as the underling molecular and cellular details to highlight their regenerative potential.
... As a result of its tolerogenic properties, HLA-G has been extensively studied in the context of transplantation. In the case of heart transplants, HLA-G was detected in myocardial biopsies and serum samples of 18% of heart transplant patients [61]. These patients had a significantly lower incidence of acute rejection in comparison to the HLA-G-negative group. ...
HLA-G is a nonclassical MHC-Class I molecule whose expression, along the feto-maternal barrier contributes towards tolerance of the semiallogeneic fetus during pregnancy. In light of its inhibitory properties, recent research has established HLA-G involvement in mechanisms responsible for directing allogeneic immune responses towards tolerance during allogeneic situations such as organ transplantation. Here, we critically review the data supporting the tolerogenic role of HLA-G in organ transplantation, the various factors influencing its expression, and the introduction of novel humanized mouse models that are one of the best approaches to assess the utility of HLA-G as a therapeutic tool in organ transplantation.
... It has been previously reported that the presence of HLA-G in transplanted hearts was associated with cellular rejection events [21], that can occur as a cellular mediated process which is an inflammation caused by T-lymphocytes [22], or by an antibody mediated rejection process caused by antibodies created pre or post-transplant [23]. Myocardial biopsies were analyzed for HLA-G expression. ...
Infection is still a leading cause of death during the first year after heart transplantation. We evaluated the pre-transplant levels of HLA (Human Leukocyte antigen) - G molecules as a means of identifying heart recipients at risk of serious infections. We prospectively analyzed 122 adult heart transplant (HT) recipients. Serum samples were collected beforetransplantation and analyzed for sHLA-G levels by ELISA assay. The clinical follow-up period lasted 5 years. Clinical outcomes were bacterial infections requiring intravenous anti-microbial agents, cytomegalovirus (CMV) disease, and fungal infections requiring therapy. We found that 39 patients (32%) developed at least 1 serious bacterial infection. Higher pre-transplant sHLA-G levels were a risk factor for serious infection (above median value 5.4 ng/ml; relative risk 3.70; 95% confidence interval 1.03-12.64; p = 0.043). Patients with high levels of pre-transplant sHLA-G are also characterized by a lower overall survival at 5 years (p = 0.017), with microbial infections as major causes of death. No association was observed with the development rejection episode. Early monitoring of sHLA-G molecules proved useful for the identification of heart recipients who are at risk of serious infections.
... Furthermore, soluble HLA-G1 can be generated by cleavage of membrane-bound HLA-G1 by metalloproteinase activity [22,23]. Thereby, both HLA-G5, HLA-G6 and sHLA-G1 can be detected in the blood [24][25][26]. Females and males show the same concentration levels in peripheral blood, while levels in women raise during the first trimester of pregnancy [27,28]. ...
The human major histocompatibility complex includes a group of non-classical HLA class I genes, HLA-E, -F and -G. While nearly all focus since the discovery of these class Ib molecules have been on basic biochemistry and molecular biology of HLA-G and HLA-E, as well as their expression patterns, functions in immune modulation and during pregnancy, and also possible implications in a range of diseases, in infertility and pregnancy complications, HLA-F has nearly been ignored. However, recent discoveries show that HLA-F can be expressed as both open conformers binding to a number of KIRs on primarily NK cells, as well as peptide-bound HLA-F binding to ILT2 and ILT4. Furthermore, a number of reports indicate a possible involvement of HLA-F in viral infections, in cancer immunology, and in fertility and reproduction, which may initiate more interest in this rather unknown HLA class I molecule. In this short review, we focus on recent discoveries that indicate a functional role for HLA-F in reproduction and during pregnancy, and the role of HLA-F in relation to HLA-G.
... While compulsory immunosuppression can impair myocardial function, some pharmacotherapies (including some immunosuppressants) retain their ability to induce a protected cardiac phenotype. Myocardial and/or soluble human leukocyte antigen-G (HLA-G) expression has been shown in several studies to reduce cardiac allograft rejection and vasculopathy post-HTx [228,229]. Expression of HLA-G appears more prominent in HTx recipients receiving everolimus (a PSI) compared to mycophenolate mofetil (MMF), and this expression is not affected by CsA treatment [230]. Alternatively, the antioxidant properties of MMF can reduce the oxidative stress and DNA damage induced by TAC [231]. ...
Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.
... 7 Heart transplant patients with expression of HLA-G in myocardial cells and plasma have been shown to experience fewer acute rejection episodes, as well as no chronic allograft rejection, compared with HLA-G-negative patients. 6 In kidney transplant patients, expression of HLA-G was associated with low-level production of alloantibody, immune tolerance, and better graft acceptance. Alloantibodies have an important role in pathogenesis of both acute and chronic rejection in recipients. ...
Objectives:
Human leukocyte antigen-G is an immuno-modulatory factor that affects acute allograft rejection and autoimmune diseases such as type 1 diabetes mellitus. In this study, possible associations between human leukocyte antigen-G 14-bp insertion/deletion polymorphism and acute pancreas rejection were investigated.
Materials and methods:
Human leukocyte antigen-G genotyping was assessed in 102 Iranian pancreas transplant recipients (including 41 with acute rejection and 61 with nonacute rejection). Results were compared with 100 individuals in a normal control group.
Results:
No significant differences in genotype frequencies of human leukocyte antigen-G 14-bp insertion / deletion were observed in recipients who had acute rejection episodes. On the other hand, the insertion / insertion genotype was a risk factor for susceptibility to type 1 diabetes mellitus (odds ratio = 3.82, 95% confidence interval, 1.37- 11.22; P = .005).
Conclusions:
Our results provided evidence revealing that the human leukocyte antigen-G insertion / insertion genotype might be involved in the pathogenesis of type 1 diabetes mellitus.
... The expression ratio in Muse cells was remarkably high compared with that of other stem cells; undifferentiated human embryonic stem and induced pluripotent stem cells do not express HLA-G, 36,37 and <20% of adult BM-MSCs express HLA-G. 38 Because HLA-G is suggested to promote graft tolerance in heart transplantation, 39 the high expression of HLA-G together with the immunomodulatory effects of allograft and xenograft Muse cells may contribute to their escape from immunologic attack in the early phase of integration. The mechanism of how these cells could survive in the host tissue after differentiation into cardiomyocytes at the late phase (6 months) of AMI remains to be investigated. ...
Rationale:
Muse cells, pluripotent marker SSEA-3+cells, are non-tumorigenic endogenous pluripotent-like stem cells obtainable from various tissues including the bone marrow (BM). Their therapeutic efficiency has not been validated in the acute myocardial infarction (AMI).
Objective:
To clarify the efficiency of intravenously infused rabbit autograft, allograft, and xenograft (human) BM-Muse cells in a rabbit AMI model and their mechanisms of tissue repair.
Methods and Results:
In vivo dynamics of Nano-lantern-labeled Muse cells showed preferential homing of the cells to the post-infarct heart at 3 days and 2 weeks, with ~14.5% of injected GFP-Muse cells estimated to be engrafted into the heart at 3 days. The migration and homing of the Muse cells was confirmed pharmacologically (S1P receptor 2 [S1PR2]-specific antagonist JTE-013 co-injection) and genetically (S1PR2-siRNA-introcuded Muse cells) to be mediated through the S1P-S1PR2 axis. They spontaneously differentiated into cells positive for cardiac markers, such as cardiac troponin-I, sarcomeric α-actinin, and connexin43, as well as vascular markers. GCaMP3-labeled Muse cells that engrafted into the ischemic region exhibited increased GCaMP3 fluorescence during systole and decreased fluorescence during diastole. Infarct size was reduced by ~52% and the ejection fraction was increased by ~38% compared with vehicle injection at 2 months, ~2.5 and ~2.1 times higher, respectively, than induced by mesenchymal stem cells. These effects were partially attenuated by the administration of GATA4-gene silenced-Muse cells. Muse cell allografts and xenografts efficiently engrafted and recovered functions, and allografts remained in the tissue and sustained functional recovery for up to 6 months without immunosuppression.
Conclusions:
Muse cells may provide reparative effects and robust functional recovery, and may thus provide a novel strategy for the treatment of AMI.
... HLA-G is induced during transplantation [25,26], viral infection [27] and malignancies [28,29] and its expression correlates with the size and aggressiveness of solid tumor [30,31]. HLA-G is also expressed by immune cells in the tumor microenvironment by trogocitosis, thereby restricting their local proliferation and cytotoxicity [32]. ...
In this study, we tested whether polymorphisms in human leukocyte antigen G (HLA-G) were associated with event-free survival (EFS) in pediatric Hodgkin's lymphoma (HL). We evaluated the association of HLA-G 3′-UTR polymorphisms with EFS in 113 pediatric HL patients treated using the AIEOP LH-2004 protocol. Patients with the +3027-C/A genotype (rs17179101, UTR-7 haplotype) showed lower EFS than those with the +3027-C/C genotype (HR= 3.23, 95%CI: 0.99-10.54, P=0.012). Female patients and systemic B symptomatic patients with the HLA-G +3027 polymorphism showed lower EFS. Multivariate analysis showed that the +3027-A polymorphism (HR 3.17, 95%CI 1.16-8.66, P=0.025) was an independent prognostic factor. Immunohistochemical analysis showed that HL cells from patients with the +3027-C/A genotype did not express HLA-G. Moreover, HLA-G +3027 polymorphism improved EFS prediction when added to the algorithm for therapeutic group classification of pediatric HL patients. Our findings suggest HLA-G +3027 polymorphism is a prognostic marker in pediatric HL patients undergoing treatment according to LH-2004 protocol.
... Both cell-associated and soluble HLA-G have immunosuppressive properties in pregnancy [11], transplantation [12] and malignancy [13]. Induction of HLA-G expression has been found in both monocytes [14] and T cells following HIV infection [14,15], although HIV-1 has also been reported to downregulate cell surface HLA-G expression [16]. ...
... Higher levels of HLA-G expression on peripheral blood CD4+ T lymphocytes were found among renal transplant recipients with stable function compared to recipients with rejection [160]. The detection of HLA-G in the serum and tissues of cardiac transplant recipients was also associated with a lower risk of acute and chronic rejection [161]. The administration of immunosuppressive drugs (including cyclosporin, tacrolimus, and corticosteroids) prompted a notable increase in soluble HLA-G levels which was associated with improved graft acceptance [162][163][164]. ...
... The role of HLA-G in mediating immune tolerance further extends well beyond pregnancy. Detection of soluble HLA-G in patients receiving heart [26], liver [27], or kidney [28], transplants is associated with enhanced graft acceptance and human muscle cell lines transiently transfected with HLA-G1 and HLA-G5 expression constructs elicit reduced human cytotoxic T-cells responses and undergo less NK cell induced lysis [29]. Based on the ability of HLA-G to inhibit multiple mechanisms associated with immune rejection, we were interested to find out whether expression of different H2-Bl isoforms could facilitate transplantation of human and mouse ES-cells in immune competent mice. ...
Universal embryonic stem cell donor lines would greatly facilitate stem cell based regenerative medicine and permit facile testing of human pluripotent stem cell derived grafts in xenogeneic settings. Because HLA-G overcomes immune cell mediated attack of foetal tissues during pregnancy and inhibits T-cell responses and dendritic cell antigen maturation in vitro and in vivo, it is an attractive candidate molecule for achieving this goal. Here we investigated whether enforced expression of either the soluble or the membrane bound form of the HLA-G mouse homologue, H2-Bl, in human and mouse ES cell lines would allow engraftment in immunocompetent mice. Despite evidence for robust expression of soluble or membrane bound H2-Bl molecules and effective inhibition of CD8+ T-cell proliferation by all H2-Bl engineered ES cell lines, all failed to generate teratomas in immunocompetent mice, despite doing so in NOD-SCID mice. We conclude that expression of H2-Bl in human and mouse embryonic stem cells alone is insufficient to overcome xenogeneic rejection.
Multilineage-differentiating stress-enduring (Muse) cells are a type of pluripotent cell with unique characteristics such as non-tumorigenic and pluripotent differentiation ability. After homing, Muse cells spontaneously differentiate into tissue component cells and supplement damaged/lost cells to participate in tissue repair. Importantly, Muse cells can survive in injured tissue for an extended period, stabilizing and promoting tissue repair. In addition, it has been confirmed that injection of exogenous Muse cells exerts anti-inflammatory, anti-apoptosis, anti-fibrosis, immunomodulatory, and paracrine protective effects in vivo. The discovery of Muse cells is an important breakthrough in the field of regenerative medicine. The article provides a comprehensive review of the characteristics, sources, and potential mechanisms of Muse cells for tissue repair and regeneration. This review serves as a foundation for the further utilization of Muse cells as a key clinical tool in regenerative medicine.
Human leukocyte immunoglobulin (Ig)-like receptors (LILR) are a family of 11 innate immunomodulatory receptors, primarily expressed on lymphoid and myeloid cells. LILRs are either activating (LILRA) or inhibitory (LILRB) depending on their associated signalling domains (D). With the exception of the soluble LILRA3, LILRAs mediate immune activation, while LILRB1-5 primarily inhibit immune responses and mediate tolerance. Abnormal expression and function of LILRs is associated with a range of pathologies, including immune insufficiency (infection and malignancy) and overt immune responses (autoimmunity and alloresponses), suggesting LILRs may be excellent candidates for targeted immunotherapies. This review will discuss the biology and clinical relevance of this extensive family of immune receptors and will summarise the recent developments in targeting LILRs in disease settings, such as cancer, with an update on the clinical trials investigating the therapeutic targeting of these receptors.
Gynaecological tumours that threaten the health of women, especially when advanced and recurrent, have remained mostly intractable to existing treatments. Therefore, new therapeutic targets are urgently needed. Human leukocyte antigen-G (HLA-G) is a nonclassical major histocompatibility complex class I molecule typically expressed in foetuses for protection against destruction by the maternal immune system. HLA-G is also expressed under pathological conditions, such as in solid tumours, and may participate in tumour development and serve as a novel immune checkpoint in cancer. Furthermore, it is expressed in most gynaecological tumours. Therefore, inhibiting HLA-G and its receptors to block the immune escape pathway could represent a new strategy in cancer immunotherapy. To the best of our knowledge, this review is the first to summarize recent research findings on HLA-G in gynaecological oncology. We highlight the fact that HLA-G is expressed in gynaecological tumour tissues, wherein it inactivates immune effectors involved in tumour progression. Further studies on HLA-G in gynaecological oncology are needed to incorporate HLA-G into the design and evaluation of immunotherapy for malignant gynaecological diseases.
Despite the growing interest in the role of regulatory B cells (Bregs) in autoimmunity, their distinct role and function in kidney transplant outcomes remain elusive. Here, we retrospectively analyzed the proportion of Bregs, transitional Bregs (tBregs) and memory Bregs (mBregs) and their capacity to produce IL-10 in non-rejected (NR) versus rejected (RJ) kidney transplant recipients. In the NR group, we observed a significant increase in the proportion of mBregs (CD19+CD24hiCD27+) but no difference in tBregs (CD19+CD24hiCD38+), as compared to the RJ group. We also observed a significant increase in IL-10-producing mBregs (CD19+CD24hiCD27+IL-10+) in the NR group. As our group and others have previously reported a potential role of the human leukocyte antigen G (HLA-G) in human renal allograft survival, notably through IL-10, we then investigated possible crosstalk between HLA-G and IL-10+ mBregs. Our ex vivo data suggest a role of HLA-G in enhancing IL-10+ mBreg expansion upon stimulation, which further decreased CD3+ T cell proliferation capability. Using RNA-sequencing (RNA-seq), we identified potential key signaling pathways involved in HLA-G-driven IL-10+ mBreg expansion, such as the MAPK, TNF and chemokine signaling pathways. Together, our study highlights a novel HLA-G-mediated IL-10-producing mBreg pathway that may serve as a therapeutic target to improve kidney allograft survival.
Purpose
To describe the evolution of the serum levels of soluble HLA-G (s-HLA-G) during the first 12 months after heart transplantation (HT) and to correlate it with clinical outcomes.
Methods
Observational study based in a single-center cohort of 59 patients who underwent HT between December-2003 and March-2010. Soluble HLA-G levels were measured from serum samples extracted before HT, and 1, 3, 6 and 12 months after HT. The cumulative burden of s-HLA-G expression during the first post-transplant year was assessed by means of the area under the curve (AUC) of s-HLA-G levels over time and correlated with the acute rejection burden –as assessed by a rejection score–, the presence of coronary allograft vasculopathy (CAV) grade ≥ 1 and infections during the first post-transplant year; as well as with long-term patient and graft survival. Mean follow-up was 12.4 years.
Results
Soluble HLA-G levels decreased over the first post-transplant year (p = 0.020). The AUC of s-HLA-G levels during the first post-transplant year was higher among patients with infections vs. those without infections (p = 0.006). No association was found between the AUC of s-HLA-G levels and the burden of acute rejection or the development of CAV.
Overall long-term survival, long-term survival free of late graft failure and cancer-free survival were not significantly different in patients with an AUC of s-HLA-G levels higher or lower than the median of the study population.
Conclusions
Soluble HLA-G levels decreased over the first year after HT. Higher HLA-G expression was associated with a higher frequency of infections, but not with the burden of acute rejection or the development of CAV, neither with long-term patient or graft survival.
The HLA-G gene is classified as one of the non-classical HLA class I genes because of its low level of polymorphism, and its expression restricted to particular cell types. Although classified as non-classical, the HLA-G protein appears to play a role as an immune checkpoint molecule in pregnancy immunity, suppressing immune responses during organ transplantation, immune escape of tumors and viruses, and developing autoimmune diseases. The gene is known to be not highly polymorphic, but it has been recently reported that 14 bp insertion/deletion polymorphism (rs66554220) and one SNP (rs1063320) located in the 3’UTR of the HLA-G gene are associated with the risk of acute graft versus host disease and overall survival. We report here the determination of 22 full-length HLA-G allele sequences in the Japanese population, including the regions such as 3’UTR that are absent from the allele sequences released from the IPD-IMGT/HLA database.
The aim of this study was to evaluate the relation of Human Leukocyte Antigen-G (HLA-G) 14 bp ins/del (insertion/deletion) polymorphism and soluble HLA-G (sHLA-G) level with rejection in kidney transplant recipients.
The study was planned as a case-control study involving two hundred fifty kidney transplant recipients. The case group consisted of 125 (female/male:56/69) kidney transplant recipients diagnosed with acute (n=52) and chronic rejection (n=73). The control group consisted of one hundred twenty-five kidney transplant patients with no acute or chronic rejection matched by gender and age in the case group. The sHLA-G level in the recipient's plasma (at the time of rejection for the case, the same time as the case after the transplant for control) was analyzed by Enzyme-Linked Immunosorbent Assay (ELISA). HLA-G 3' untranslated region (3’UTR) polymorphism of recipient and donor was determined using agarose gel electrophoresis and DNA sequencing method.
In our study, it was shown that acute rejection rate increased 1.06 times and chronic rejection rate increased 1.14 times in kidney transplant recipients with low serum sHLA-G levels. The rejection patients with the HLA-G 14 bp del/del genotype had higher sHLA-G levels post-transplantation. The frequency of acute rejection was lower in patients with HLA- G 14 bp del/del polymorphism than those with ins/ins and ins/del polymorphisms.
This study proposes that HLA-G 3'UTR polymorphism and sHLA-G level might be useful in prediction of rejection in kidney transplant recipients.
The immunosuppressive non-classical human leukocyte antigen-G (HLA-G) promotes transplant tolerance as well as viral immune escape. HLA-G expression is associated with regulatory elements targeting certain single nucleotide polymorphisms (SNPs) in the HLA-G 3' untranslated region (UTR). Thus, we evaluated the impact of HLA-G 3'UTR polymorphisms as surrogate markers for BK polyomavirus (BKPyV) replication or nephropathy (PyVAN) and acute cellular and antibody mediated rejection (ACR/AMR) in 251 living-donor kidney-transplant recipient pairs. After sequencing of the HLA-G 3'UTR, fourteen SNPs between +2960 and +3227 and the 14 bp insertion/deletion polymorphism, which arrange as UTR haplotypes, were identified. The UTR-4 haplotype in donors and recipients was associated with occurrence of BKPyV/PyVAN compared to the other UTR haplotypes. While the UTR-4 recipient haplotype provided protection against AMR, the UTR-2 donor haplotype was deleteriously associated with ACR/AMR. Deduction of the UTR-2/4 haplotypes to specific SNPs revealed that the +3003C variant (unique for UTR-4) in donors as well as in recipients is responsible for BKPyV/PyVAN and also provides protection against AMR; whereas the +3196G variant (unique for UTR-2) promotes allograft rejection. Thus, HLA-G 3'UTR variants are promising genetic predisposition markers both in donors and recipients that may help to predict susceptibility to either viral infectious complication of BKPyV or allograft rejection.
Background: Human leukocyte antigen G (HLA-G) belongs to nonclassical HLA I molecule involving in the suppression of immune response. Besides its profound effect to induce fetal tolerance, HLA-G expression has been associated with allograft acceptance. For the regulation of HLA-G levels, polymorphic sites within the 3′ untranslated region (3′UTR) are of crucial importance. The aim of the study was to analyze the association between several HLA-G 3′UTR variants (+3003T/C, +3010C/G, +3027C/A, +3035C/T, +3142G/C, +3187A/G, and +3196C/G), soluble HLA-G (sHLA-G) level, and kidney graft outcome in the Slovak Caucasian population.
Methods: We investigated 69 kidney transplant recipients (45 males, 24 females) of age 27–65 years. Out of this group, 37 recipients developed acute rejection that was biopsy proven. Recipient’s plasma was obtained at 1 day before transplantation and analyzed by ELISA. The HLA-G 3′UTR polymorphisms were typed by direct sequencing.
Results: In the recipients with stable allograft function, significantly higher values of sHLA-G were found in the homozygous +3010GG, +3142CC, +3187GG, and +3196CC carriers in comparison to the acute rejection recipients (P = 0.01-0.05).
Conclusion: The study demonstrated genetic association between HLA-G 3′UTR variants and sHLA-G level in kidney recipients leading to graft acceptance. We suggest to monitor the pretransplantation sHLA-G level as additional marker to predict kidney graft outcome. Abbreviations: AMR: Antibody-mediated rejection; APC: antigen-presenting cell; CD: cluster of designation; del: deletion; HLA: human leukocyte antigen; ILT: immunoglobulin-like transcript; ins: insertion; KIR: killer-cell immunoglobulin-like receptor; NK: natural killer; sHLA-G: soluble HLA-G; SNP: single nucleotide polymorphism; TCMR: T cell-mediated rejection; URR: upstream regulatory region; UTR: untranslated region
Human leucocyte antigen G (HLA-G) is a non-classical HLA-class I antigen that exerts immunoregulatory functions. The polymorphisms 14-base pair (bp) insertion/deletion (ins/del) (rs1704) and +3142C > G (rs1063320) could modify the expression level of HLA-G.
We genotyped 175 kidney recipients (41 with acute rejection and 134 without rejection) and additionally the corresponding donors for both polymorphisms in order to assess their impact on acute rejections one year after transplantation. In addition, we analyzed soluble HLA-G (sHLA-G) levels in sera of 32 living kidney donors and compared the sHLA-G levels in terms of the present genotype.
In kidney transplant recipients we did not observe an impact of the 14-bp ins/ins and the +3142GG genotypes on acute rejection. In contrast, we found a higher frequency of these genotypes in the donors of the no-rejection collective compared to the rejection collective (4.9% vs. 24.6%; p = 0.010; 9.8% vs. 31.3%; p = 0.006). Soluble HLA-G levels were highest in healthy kidney donors homozygous for the 14-bp insertion.
We conclude that the HLA-G polymorphisms of the donor are of importance for susceptibility of acute rejection in kidney transplantation. We suggest that the 14-bp ins/ins and the +3142GG genotypes are protective against kidney transplant rejection.
The dynamics and actions of Muse cells at a time of physical crisis are unique and highly remarkable compared with other stem cell types. When the living body is in a steady state, low levels of Muse cells are mobilized to the peripheral blood, possibly from the bone marrow, and supplied to the connective tissue of nearly every organ. Under conditions of serious tissue damage, such as acute myocardial infarction and stroke, Muse cells are highly mobilized to the peripheral blood, drastically increasing their numbers in the peripheral blood within 24 h after the onset of tissue injury. The alerting signal, sphingosine-1-phosphate, attracts Muse cells to the damaged site mainly via the sphingosine-1-phosphate receptor 2, enabling them to preferentially home to site of injury. After homing, Muse cells spontaneously differentiate into tissue-compatible cells and replenish new functional cells for tissue repair. Because Muse cells have pleiotropic effects, including paracrine, anti-inflammatory, anti-fibrotic, and anti-apoptotic effects, these cells synergistically deliver long-lasting functional and structural recovery. This chapter describes how Muse cells exert their reparative effects in vivo.
Classical and non-classical MHC class I (MHC I) molecules displayed at the cell surface are essential for the induction of innate and adaptive immune responses. Classical MHC I present endogenously derived peptides to CD8⁺ T cells for immunosurveillance of infected or malignant cells. By contrast, non-classical MHC I, in particular HLA-G, also display peptides, but primarily act as immunomodulatory ligands for the innate immune response and are an important component for extravillous trophoblast invasion to form the placenta in pregnancy. Endoplasmic Reticulum AminoPeptidase 1 (ERAP1), which trims peptides in the ER to generate ligands for MHC I loading, is a key regulator of the peptide repertoire and has a significant impact on the formation of stable MHC I at the cell surface. ERAP1 also plays a role in angiogenesis, cell cycle progression and migration, events that are shared between tumour cells and placenta formation. Here we discuss the similarities between tumour and extravillous trophoblast cells in their immune modulatory, invasion, migration and proliferation properties in the context of ERAP1 and its role in establishment of solid tumours and placenta formation.
Umbilical cord blood is medical waste and common allograft cellular source for bone marrow transplantation. It contains a special mesenchymal stem cells, whose cardiomyogenic transdifferentiation efficiency was about 100 times higher than well known marrow-derived mesenchymal stem cells. In this section, we would like to introduce the potential of umbilical cord blood derived mesenchymal stem cell for cardiac stem cell therapy.
The nonpolymorphic soluble HLA-G1 (sHLA-G1) isoform has been reported to be secreted by trophoblast cells at the ma- terno-fetal interface, suggesting that it may act as immuno- modulator during pregnancy. In this paper, we report that affinity-purified b2-microglobulin-associated sHLA-G1 trig- gered apoptosis in activated, but not resting CD81 peripheral blood cells. We demonstrate by Western blotting that sHLA-G1 enhanced CD95 ligand expression in activated CD81 cells. Cytotoxicity was inhibited by preincubation of the cells with a CD95 antagonist mAb (ZB4) or a soluble recom- binant CD95-Fc, indicating that apoptosis is mediated through the CD95/CD95 ligand pathway. Finally, we show that such sHLA-G1-induced apoptosis depends on the interaction with CD8 molecules, with cell death being blocked by various CD8 mAbs. The Journal of Immunology, 2000, 164: 6100 - 6104.
Considering the well established role of nonclassical HLA-G class I molecules in inhibiting natural killer (NK) cell function, the consequence of abnormal HLA-G expression in malignant cells should be the escape of tumors from immunosurveillance. To examine this hypothesis, we analyzed HLA-G expression and NK sensitivity in human malignant melanoma cells. Our analysis of three melanoma cell lines and ex vivo biopsy demonstrated that (i) IGR and M74 human melanoma cell lines exhibit a high level of HLA-G transcription with differential HLA-G isoform transcription and protein expression patterns, (ii) a higher level of HLA-G transcription ex vivo is detected in a skin melanoma metastasis biopsy compared with a healthy skin fragment from the same individual, and (iii) HLA-G protein isoforms other than membrane-bound HLA-G1 protect IGR from NK lysis. It thus appears of critical importance to consider the specific role of HLA-G expression in tumors in the design of future cancer immunotherapies.
Experiments in various models have indicated that immunological tolerance can result from the physical elimination (deletion) of reactive lymphocytes as well as from anergy. We have previously reported that mature CD4-CD8+ T cells when confronted with their antigen can proliferate extensively but are finally eliminated or become intrinsically anergic such that remaining cells are refractory to stimulation by any T cell receptor ligands, even in the presence of exogenous interleukin 2. Here we show that in vivo the anergy can be reversed in the absence of antigen, such that the cells are then able to proliferate extensively in vivo to a new challenge with the antigen in question.
We have investigated the protective role of the membrane-bound HLA-G1 and HLA-G2 isoforms against natural killer (NK) cell cytotoxicity. For this purpose, HLA-G1 and HLA-G2 cDNAs were transfected into the HLA class I-negative human K562 cell line, a known reference target for NK lysis. The HLA-G1 protein, encoded by a full-length mRNA, presents a structure similar to that of classical HLA class I antigens. The HLA-G2 protein, deduced from an alternatively spliced transcript, consists of the alpha1 domain linked to the alpha3 domain. In this study we demonstrate that (i) HLA-G2 is present at the cell surface as a truncated class I molecule associated with beta2-microglobulin; (ii) NK cytolysis, observed in peripheral blood mononuclear cells and in polyclonal CD3(-) CD16(+) CD56(+) NK cells obtained from 20 donors, is inhibited by both HLA-G1 and HLA-G2; this HLA-G-mediated inhibition is reversed by blocking HLA-G with a specific mAb; this led us to the conjecture that HLA-G is the public ligand for NK inhibitory receptors (NKIR) present in all individuals; (iii) the alpha1 domain common to HLA-G1 and HLA-G2 could mediate this protection from NK lysis; and (iv) when transfected into the K562 cell line, both HLA-G1 and HLA-G2 abolish lysis by the T cell leukemia NK-like YT2C2 clone due to interaction between the HLA-G isoform on the target cell surface and a membrane receptor on YT2C2. Because NKIR1 and NKIR2, known to interact with HLA-G, were undetectable on YT2C2, we conclude that a yet-unknown specific receptor for HLA-G1 and HLA-G2 is present on these cells.
HLA-G is the only class I determinant of the major histocompatibility complex (MHC) expressed by the trophoblasts, the fetal cells invading the maternal decidua during pregnancy. A unique feature of this nonclassical HLA molecule is its low polymorphism, a property that has been postulated to play an important role in preventing local activation of maternal alloreactive T and natural killer cells against the fetus. Yet, the mechanisms by which fetal HLA-G can be recognized as a self-MHC molecule by the maternal immune system remain unclear. Here we report the novel observation that HLA-G is expressed in the human thymus. Expression is targeted to the cell surface of thymic medullary and subcapsular epithelium. Thymic epithelial cell lines were generated and shown to express three alternatively spliced HLA-G transcripts, previously identified in human trophoblasts. Sequencing of HLA-G1 transcripts revealed a few nucleotide changes resulting in amino acid substitutions, all clustered within exon 3 of HLA-G, encoding for the alpha2 domain of the molecule. Our findings raise the possibility that maternal unresponsiveness to HLA-G-expressing fetal tissues may be shaped in the thymus by a previously unrecognized central presentation of this MHC molecule on the medullary epithelium.
HLA-G is a nonclassical major histocompatibility complex class I molecule selectively expressed on cytotrophoblasts at the feto-maternal interface, where it may play an important role in maternal tolerance of the fetus. We provide direct evidence under physiological conditions that supports the role of HLA-G in protecting cytotrophoblasts against natural killer (NK) cytolysis in 6 semiallogenic combinations of maternal uterine NK cells and their own trophoblast counterparts, as well as in 20 allogenic combinations of maternal uterine NK cells and trophoblasts from different mothers. We show that, in all cases studied, this HLA-G-mediated protection was abolished by treatment of cytotrophoblasts with an HLA-G-specific mAb. The HLA class I-negative K562 cell line transfected with the predominant HLA-G1 isoform results in similar protection and abolition from maternal uterine NK lysis. Because maternal uterine NK cells express killer inhibitory receptors for HLA-G, we conclude that their interactions contribute to the survival of the fetal semiallograft by confering immunological tolerance to its tissues.
Nonclassical MHC class I HLA-G antigen expression is tissue specific and is thought to play a role in tolerance of the semiallogeneic fetus by the maternal immune system. Ectopic expression of HLA-G by tumor cells provides them with an additional mechanism of escape from immunosurveillance by host cytotoxic effector mechanisms. The aim of this study was to assess the expression of nonclassical HLA-G antigens in ex vivo human melanoma biopsies. HLA-G mRNA levels corresponding to both membrane-bound and soluble protein isoforms were analyzed in tumor specimens obtained from primary or metastatic melanomas of 23 patients. High levels of HLA-G transcription were detected in tumor specimens in 5 of 23 patients and found to be comparable in both lymph node and skin metastases. HLA-G mRNA transcript levels at tumor sites in 18 of these patients were compared with those in samples of their own healthy skin and were higher in the tumor tissue in 12 patients. Differential expression of mRNA transcripts corresponding to soluble and membrane-bound HLA-G was also observed in some tumor biopsies. HLA-G protein expression was detected in tumors that exhibited high levels of HLA-G transcription by immunofluorescence of frozen sections and Western blot analysis of both tumor and healthy skin biopsies, using anti-HLA-G-specific monoclonal antibodies. This work provides evidence that HLA-G gene transcription and protein expression can be up-regulated ex vivo in melanoma. Our finding that several of the tumors studied expressed high levels of HLA-G provides additional clues as to how a tumor can be selected in vivo to escape from cytotoxic antitumor responses, constituting a new parameter to be considered in the design of therapeutic approaches aimed at enhancing antitumor immune responses.
HLA-G plays an essential role in feto-maternal tolerance by inhibiting lysis by maternal NK cells. The factors that allow tissue-specific activation of HLA-G gene expression in trophoblasts remain to be characterized. We investigated the potential effect of IL-10, a cytokine which is secreted in placenta, on HLA-G gene transcription in trophoblasts. Using Northern blot, RNase protection assay and RT-PCR analysis, we demonstrated that IL-10 enhances steady-state levels of HLA-G transcription in cultured trophoblast cells. We further tested the effect of IL-10 on HLA-G gene transcription and protein expression in peripheral blood monocytes, showing that IL-10 can up-regulate HLA-G cell surface expression in this cell type. This effect of IL-10 is selective, since classical MHC class I products and MHC class II are down-regulated in monocytes following IL-10 treatment. Induction of HLA-G expression by IL-10 on monocytes may thus play a role in down-regulation of the immune response. We propose that IL-10 secretion by trophoblasts during pregnancy may also influence the HLA class I expression pattern at the feto-maternal barrier, thus protecting the fetus from rejection. This should be taken into consideration in the design of treatment for pathologies of pregnancy.
Individual predictive clinical, immunological, or molecular features for definition of patients with lymph-node-positive melanoma who do not benefit from adjuvant postsurgery high-dose interferon alpha treatment are lacking. Expression analysis of classic and non-classic HLA molecules on melanoma cells metastatic to the locoregional lymph node may help select these patients before treatment.
The nonclassical HLA-G primary transcript is alternatively spliced to generate several mRNAs that have the capacity to encode four membrane bound isoforms, namely HLA-G1, -G2, -G3, and -G4 and two soluble isoforms HLA-G5 and -G6. We aimed at defining the capacity of full length and truncated soluble HLA-G transcripts to be translated in human cell lines. Our study of HLA-G alternative transcripts in various human tissues led us to identify a new splice variant of the HLA-G mRNA, named G7, in which open reading frame continues in intron 2. Due to the presence of a stop codon within intron 2, HLA-G7 transcripts retain the capacity to be translated as soluble truncated HLA-G proteins bearing the alpha1 domain linked to two specific aminoacids encoded by intron 2. Expression vectors containing cDNAs encoding HLA-G5, -G6, and -G7 isoforms were transfected into human cell lines. The presence of translated HLA-G5, -G6, and -G7 proteins was detected in protein extracts of transfected cells by Western blot and immunoprecipitation, but only the full length HLA-G5 soluble isoform could be clearly detected as a secreted protein in both transfected cells supernatants and body fluids.
Exquisitely regulated cytokine balance during early pregnancy is thought to be necessary for promoting survival of the fetal allograft. Our previous studies have demonstrated that membrane-bound human leukocyte antigen (mHLA-G) expressed on trophoblasts is one of the key factors in regulating cytokine balance by shifting the Th1/Th2 balance toward Th2 polarization, a favourable milieu for the maintenance of pregnancy. Given that trophoblasts secrete soluble HLA-G (sHLA-G), we examined its biological roles in comparison with mHLA-G. We cultured peripheral blood mononuclear cells (PBMC) with either the HLA-A and -B-deficient B lymphoblast cell line (721.221 cells) or the same cell line transfected with mHLA-G (721.221-G1 cells), in the presence or absence of recombinant sHLA-G. Cytokine concentrations in the culture media were determined by enzyme-linked immunosorbent assay. In contrast to mHLA-G protein, sHLA-G stimulated the release of tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma, whereas it reduced the release of interleukin (IL)-3, regardless of the presence of the presence of a stimulatory effect of the mHLA-G-expressing cells. Although mHLA-G reduced the release of IL-4, sHLA-G did not have any effect. Conversely, sHLA-G stimulated the release of IL-10 whereas mHLA-G was without effect. These results suggest that sHLA-G regulates the release of cytokines from PBMC chiefly by counterbalancing mHLA-G, and thereby may play a role in maintaining pregnancy.
HLA-G is a nonclassical MHC class I molecule that plays a major role in maternal-fetal tolerance. Four membrane-bound (HLA-G1 to -G4) and two soluble (HLA-G5, and -G6) proteins are generated by alternative splicing. Only HLA-G1 has been extensively studied in terms of both expression and function. We provide evidence here that HLA-G2, -G3, and -G4 truncated isoforms reach the cell surface of transfected cells, as endoglycosidase H-sensitive glycoproteins, after a 2-h chase period. Moreover, cytotoxicity experiments show that these transfected cells are protected from the lytic activity of both innate (NK cells) and acquired (CTL) effectors. These findings highlight the immunomodulatory role that HLA-G2, -G3, and -G4 proteins will assume during physiologic or pathologic processes in which HLA-G1 expression is altered.
We recently reported that the nonclassical HLA class I molecule HLA-G was expressed in the endomyocardial biopsies and sera of 16% of heart transplant patients studied. The aim of the present report is to identify cells that may be responsible for HLA-G protein expression during the allogeneic reaction. Carrying out mixed lymphocyte cultures in which the responder cell population was depleted either in CD4(+) or CD8(+) T cells, we found that soluble HLA-G5 protein but not the membrane-bound HLA-G isoform was secreted by allo-specific CD4(+) T cells from the responder population, which suppressed the allogeneic proliferative T cell response. This inhibition may be reversed by adding the anti-HLA-G 87G antibody to a mixed lymphocyte culture. That may indicate a previously uncharacterized regulatory mechanism of CD4(+) T cell proliferative response.
HLA-G plays an essential role in feto-maternal tolerance by inhibiting lysis by maternal NK cells. The factors that allow tissue-specific activation of HLA-G gene expression in trophoblasts remain to be characterized. We investigated the potential effect of IL-10, a cytokine which is secreted in placenta, on HLA-G gene transcription in trophoblasts. Using Northern blot, RNase protection assay and RT-PCR analysis, we demonstrated that IL-10 enhances steady-state levels of HLA-G transcription in cultured trophoblast cells. We further tested the effect of IL-10 on HLA-G gene transcription and protein expression in peripheral blood monocytes, showing that IL-10 can upregulate HLA-G cell surface expression in this cell type. This effect of IL-10 is selective, since classical MHC class I products and MHC class II are down-regulated in monocytes following IL-10 treatment. Induction of HLA-G expression by IL-10 on monocytes may thus play a role in downregulation of the immune response. We propose that IL-10 secretion by trophoblasts during pregnancy may also influence the HLA class I expression pattern at the feto-maternal barrier, thus protecting the fetus from rejection. This should be taken into consideration in the design of treatment for pathologies of pregnancy.
We have investigated HLA-G mRNA expression in cells and tissues expressing the gene. This analysis has demonstrated that the HLA-G primary transcript is alternatively spliced to yield at least three distinct mature mRNAs. Sequencing of the transcripts has shown that the largest mRNA is essentially that previously characterized, encoding a leader sequence, three external domains, a transmembrane region, and a cytoplasmic sequence. Of the two smaller messages, a 900-base mRNA does not include exon 3, resulting in a predicted protein sequence with the alpha 1 and alpha 3 external domains joined. The smallest mRNA results from splicing out exons 3 and 4, connecting the alpha domain directly to the transmembrane sequence. Alternative splicing of HLA-G mRNA was found in placental tissues and in eye tissue as well as in HLA-G-transfected cell lines. In term placental tissue the smallest mRNA appeared to be more abundant than the full-length form, while in a cell line derived from an earlier developmental stage the larger form predominated. Immunoprecipitation of [35S]methionine-labeled cell lysates showed that three different HLA-G proteins were present in transfected cells, with sizes corresponding to those predicted from the three alternative mRNA sequences. These findings are discussed in terms of potential functions of the alternative HLA-G proteins.
The alpha chain of the human histocompatibility antigen HLA-G was identified as an array of five 37- to 39-kilodalton isoforms by the use of two-dimensional gel electrophoresis. Both cell-associated and secreted HLA-G antigens are prominent in first trimester villous cytotrophoblasts and are greatly reduced in third trimester cytotrophoblasts. Allelic variation was not detected, an indication that HLA-G is not obviously polymorphic in cytotrophoblasts. Among the following choriocarcinoma cell lines studied, HLA-G is expressed in JEG but not in Jar or BeWo. Expression of endogenous HLA-G genes has not been found in normal lymphoid cells. Thus, HLA-G is subject to both cell type-specific and developmental regulation and is expressed in early gestation human cytotrophoblasts.
We studied exercise performance before and after conversion of atrial tachycardia to sinus rhythm, atrial bradycardia, or junctional rhythm in 10 patients 9-25 years of age 8-20 years after congenital heart disease surgery (complete transposition of the great arteries, seven of 10 patients). The same maximal cycle (five of 10 patients) or treadmill (five of 10 patients) exercise protocol was performed in atrial tachycardia and sinus rhythm 1-232 days after atrial tachycardia (mean, 34 days). Electrocardiogram, heart rate, and pulmonary gas exchange were recorded. Sinus rhythm exercise increased peak VO2 (mean, 28.7 [sinus rhythm] vs. 24.7 [atrial tachycardia], p less than 0.01), exercise time (p less than 0.01), and O2 pulse at rest (p less than 0.01) and at peak exercise (NS). Mean resting heart rate decreased from 109 to 70 beats/min (p less than 0.01). In atrial tachycardia, peak exercise heart rate was low (80-163 beats/min) because of fixed conduction (six of 10 patients) or high as conduction approached 1:1 (176-252 beats/min) (four of 10 patients). In sinus rhythm, rest to peak exercise heart rate increased in six of 10 patients (p less than 0.05). The data show improved exercise performance in sinus rhythm primarily because of improved heart rate adaptation to exercise, by either permitting increased heart rate response or eliminating excessively high heart rate with inadequate diastolic filling.
To identify predictors of late acute rejection after orthotopic heart transplantation (OHT), 53 patients who received transplants between March 1984 and March 1987 and who survived at least 1 year postoperatively were followed up for 402-1,151 days (mean, 841 days). Fourteen patients experienced 22 moderate or severe rejection episodes more than 1 year after OHT (LR); 39 were nonrejectors (NR). Twelve of 14 (86%) LR and only 14 of 39 (36%) NR had two or more moderate or severe rejection episodes within the first year after OHT (p less than 0.001). The LR had significantly higher numbers of infections more than 1 year after OHT (2.0 vs. 0.9; p less than 0.05). Nine of 22 (40%) late acute rejection episodes followed within 1 month of infection. Human leukocyte antigen reactivity before OHT, follow-up hemodynamics, length of survival, incidence of diabetes mellitus, coronary artery disease 1 year after OHT, mean cyclosporine levels, and mean daily prednisone doses were similar in LR and NR patients. We conclude that 1) OHT recipients with two or more moderate or severe rejection episodes in the first year after OHT are at higher risk of developing late acute rejection and may require closer long-term rejection surveillance and more aggressive maintenance immunosuppression and 2) the possible relation between infection and subsequent acute rejection episodes in OHT recipients requires further investigation.
Previous studies of allograft rejection have focused on early episodes and risk factors from pretransplant variables.
This multiinstitutional study compared early (< 1 year) and late (> 1 year) rejection episodes and risk factors for recurrent rejection from variables both before and after transplantation among 1251 patients who underwent primary heart transplantation and available follow-up of greater than 1 year.
There were a total of 1882 rejection episodes over a mean follow-up of 26 +/- 0.3 months. The hazard function (instantaneous risk per patient per month) peaked at 1 month followed by a low constant risk of rejection after 12 months. By multivariable analysis, the most dominant risk factors for recurrent rejection during the first posttransplantation year were a shorter time interval since transplantation and a shorter time since a previous rejection episode. Other factors included young age, female gender, female donor, positive cytomegalovirus serology, prior infections, and OKT3 induction. In contrast, after the first year, the dominant risk factors for rejection were a greater number of rejections during the first year and the presence of prior cytomegalovirus infections.
These data show a striking time dependency for rejection episodes among heart transplant recipients. Factors that increase risk for rejection in the first year differ from risk factors for rejection in subsequent years. These data suggest that it may be possible to tailor rejection surveillance protocols and immunosuppression intensity, according to specific patient and time-related risk factors.
Human placental trophoblasts lie at the maternal-fetal interface, a position in which they could play an important role in maternal tolerance of the fetal semi-allograft. Central to this hypothesis is their unusual MHC class I expression: they suppress class Ia production while expressing HLA-G, a class Ib molecule. We investigated human trophoblast HLA-G protein production in vivo and in vitro. We first used a synthetic peptide corresponding to the variable sequence of the alpha 1 domain to produce mAbs that recognized HLA-G. Ab specificity was demonstrated by immunoaffinity purification of a single protein with the same molecular mass (38 kDa) as HLA-G from choriocarcinoma cells. Use of these Abs to stain tissue sections of the maternal-fetal interface containing cytotrophoblasts in all stages of differentiation showed that HLA-G is expressed only by cytotrophoblasts that invade the uterus. Our previous in vitro studies showed that when early-gestation cytotrophoblast stem cells are cultured, they differentiate rapidly along the invasive pathway, as demonstrated by their expression of stage-specific markers. Here we show they also up-regulate HLA-G production. Cytotrophoblasts from term placentas, which have reduced invasive capacity in vitro, also had decreased ability to up-regulate HLA-G protein expression. We detected high levels of HLA-G mRNA in cytotrophoblasts isolated from first- and second-trimester placentas, but only trace amounts in term cells. Taken together, these results suggest that HLA-G production is a critical component of cytotrophoblast differentiation along the invasive pathway.
The HLA-G primary transcript is alternatively spliced to yield mRNAs encoding three alternative membrane bound proteins. In addition to these forms, a soluble HLA-G protein has been described which is not encoded directly by any of the three alternative mRNAs. To explain the process which might lead to the expression of a soluble HLA-G Ag, we investigated the potential roles proteolytic processing and additional alternative splicing of HLA-G RNA might play. By generating transfected cells with HLA-G cDNA expression driven by a retroviral promoter, it was possible to rule out proteolytic processing of the membrane-bound HLA-G as a mechanism of generating soluble HLA-G, resulting in our focus on alternative splicing as an explanation. Analysis of PCR-amplified cDNA revealed a relatively abundant transcript present in all samples examined which consisted of the full length HLA-G mRNA sequence interrupted by intron 4 sequence. The open reading frame in this mRNA continues into intron 4 terminating 21 amino acids after the alpha 3 domain, thus excluding the transmembrane encoding region and yielding a protein with a highly charged carboxyl terminus. Transfection of the intron 4 containing cDNA, inserted into a retroviral expression vector, into LCL .221 followed by comparison of the class I protein to native soluble G by two dimensional isoelectric focusing/SDS-PAGE analysis, demonstrated this message encoded the soluble HLA-G protein. In addition, a similar intron containing message derived from the HLA-G2 mRNA was found, suggesting the existence of a soluble form of this alternative HLA-G protein. These findings are discussed in relation to other soluble class I molecules and with regard to potential functions of the soluble HLA-G Ag.
The endomyocardial biopsy (EMB) in heart transplant recipients has been considered the "gold standard" for diagnosis of graft rejection (REJ). The purpose of this retrospective study is to develop long-term strategies (frequency and postoperative duration of EMB) for REJ monitoring. Between 1985 and 1992, 346 patients (mean age 44.5 years, female patients = 14%) received 382 heart grafts. For graft surveillance EMBs were performed according to a fixed schedule depending on postoperative day and the results of previous biopsies. In the first year the average number (no.) of EMBs/patient was 20 with 19% positive for REJ in the first quarter, dropping to 7% REJ/EMB by the end of the first year. The percentage of REJ/EMB declined annually from 4.7% to 4.5%, 2.2% and less than 1% after the fifth year. Individual biopsy results in the first 3 postoperative months had little predictive value. Patients with fewer than two REJ (group 1), vs patients with two or more REJ in the first 6 postoperative months (group 2), were significantly less likely to reject in the second half of the first year (group 1: 0.29 +/- 0.6 REJ/patient; group 2:0.83 +/- 1.3 REJ/patient; P < 0.001) and third postoperative year (group 1:0.12 +/- 0.33 REJ/patients; group 2:0.46 +/- 0.93 REJ/patient; P < 0.05). In conclusion, routine EMBs in the first 3 postoperative months have only limited predictive value, however the number of routine EMBs can be drastically reduced later depending on the intermediate postoperative REJ pattern.
An encounter of the mature immune system with Ag usually leads to an immune response. If Ag is administered with CD4- and CD8-specific mAbs, the outcome of the response can be tolerance. This form of tolerance is peripheral, Ag specific, and maintained lifelong, and is associated with the suppression of nontolerant cells by CD4 cells of the tolerant host. Here we demonstrate that the degree of suppression is dependent on the number of suppressor cells. A neutralizing anti-IL-4 Ab was partially able to inhibit suppression, indicating a role for IL-4 in the regulation of Th1 rejection responses.
Although the cDNA sequence of HLA-G antigens is compatible with their expression as soluble molecules (sHLA-G), the determination of native sHLA-G levels in body fluids has not yet been described. The lack of this information is likely to reflect the difficulties in developing an assay suitable to measure sHLA-G antigens in the presence of soluble HLA-A, -B and -C (sHLA-I) antigens, since most of the available anti-HLA-G mAb do not detect soluble beta2-m associated HLA-G antigens or crossreact with sHLA-I antigens. Therefore, we have developed a two-step assay which eliminates the interference of classical HLA class I antigens. In the first step, the sample is depleted of sHLA-I antigens and of HLA-E antigens with mAb TP25.99. Then, HLA-G antigens are captured with mAb W6/32 and detected with anti-beta2-m mAb in ELISA. Utilizing this assay, sHLA-G antigen levels were measured in EDTA plasma from 92 controls with known HLA types, 28 women at delivery and the corresponding cord bloods and in 50 amniotic fluids. Mean sHLA-G plasma levels did not differ between males (24.9+/-3.0 SEM ng/ml; n=42) and females (20.1+/-2.1 SEM ng/ml; n = 50). However, sHLA-G levels in HLA-A11 positive probands (mean: 13.0+/-4.4 SEM ng/ml; n=12) were significantly (P<0.05) lower than in HLA-A11 negative ones (mean: 24.5+/-2.0 SEM ng/ml; n=80). sHLA-G levels in women at delivery (mean: 22.9+/-2.2 SEM ng/ml; n=28) were in the range of controls but were significantly (P<0.001) reduced in the corresponding cord bloods (mean: 13.8+/-1.5 SEM ng/ml; n=28). sHLA-G levels in amniotic fluids (mean: 15.5 + 1.0 SEM ng/ml; n=50) were significantly (P<0.001) lower than in plasma. sHLA-G levels were 5 and 11% of those of sHLA-I antigens in plasmas and amniotic fluids, respectively. Individual sHLA-G levels were not correlated with sHLA-I levels. SDS-PAGE analysis of plasma sHLA-G antigens revealed two molecular variants with a 35 kD and a 27 kD MW corresponding to the sizes of sHLA-G1 and -G2 isoforms. In conclusion, our study has shown that the two-step assay we have developed is reliable in measuring sHLA-G antigen levels. This assay will facilitate the analysis of the biological and clinical significance of sHLA-G antigens in plasma.
HLA-G found in five of 31 heart-transplant recipients was associated with a decrease of acute and chronic rejection episodes.
Soluble isoforms of the HLA class Ib gene HLA-G have been identified at the maternal-fetal interface. Because soluble forms of other HLA class I antigens modulate T-cell reactivity and induce cellactivated apoptosis, our goal was to determine whether soluble HLA-G circulates in maternal or fetal blood and to identify the specific isoform.
Capture enzyme-linked immunosorbent assays with mouse monoclonal antibodies directed toward an epitope present on all isoforms of soluble HLA-G were constructed to identify soluble HLA-G in 44 serum samples from nonpregnant control subjects, 129 serum samples from pregnant women, and 10 samples of term cord blood. Distinguishing between soluble HLA-G1, which is composed of heavy chains complexed with light chains (beta(2)-microglobulin), and soluble HLA-G2, which consists only of heavy chains, was achieved by substituting a monoclonal antibody that requires beta(2)-microglobulin for binding (W6/32) in the capture phase of the enzyme-linked immunosorbent assay.
Capture enzyme-linked immunosorbent assays with mouse anti-soluble HLA-G showed that soluble HLA-G was present at all stages of gestation and that levels of soluble HLA-G were statistically significantly higher in serum samples from pregnant women than in serum samples from nonpregnant women. In contrast, W6/32 failed to detect soluble HLA-G in serum samples from pregnant women. Cord serum samples did not contain detectable soluble HLA-G.
Collectively, the data indicate that pregnancy is characterized by the presence of soluble HLA-G circulating in maternal blood and strongly suggest that the major isoform is soluble HLA-G2.
HLA-G is a non-classical MHC class 1 molecule, expressed primarily on human foetal trophoblast cells, which exhibits almost no genetic polymorphism. Because of these unusual features, HLA-G has been suggested to help prevent maternal immune attack of the semi-allogeneic foetus. The aim of these experiments was to investigate the effects of HLA-G on T-lymphocyte responses by using MHC class II-bearing HLA-G transfectants as stimulators of a mixed lymphocyte reaction. The presence of HLA-G, but not classical HLA class I, on the surface of stimulator cells markedly suppressed thymidine incorporation by peripheral blood mononuclear responder cells from a class I-similar, class II-dissimilar male. The suppressive effect of HLA-G on the mixed lymphocyte reaction persisted after depletion of phagocytes and CD8(+) T-cells from the responder population, but the mixed lymphocyte reaction was entirely abolished by depletion of CD4(+) T-cells. These results suggest that HLA-G exerts a direct suppressive effect on CD4(+) T-lymphocytes, even in the absence of the CD8(+) cells with which other human MHC class I molecules are thought to interact. Thus, HLA-G may allow the foetus to escape maternal immune attack by modulating CD4(+) T-cell activity.
Human leucocyte antigen (HLA) -G is expressed on trophoblast cells during pregnancy, suggesting a role in protection of the semiallogeneic fetus. Published data suggest that HLA-G protects a cell against natural killer cell lysis. It has been hypothesized that HLA-G may also protect the fetus by preventing allo-cytotoxic T lymphocyte (CTL) responses. To test this hypothesis, we assayed the effects of various concentrations of purified HLA-G on CTL response in a mixed lymphocyte culture (MLC) system. We found that concentrations > or =0.1 microg/ml of HLA-G suppressed the allo-CTL response by 30-100% over the control, but, paradoxically, concentrations of 0.01-0.05 microg/ml of HLA-G augmented the allo-CTL response by 25-50% over the control. Concentrations < or = 0.001 microg/ml HLA-G had no effect. Addition of HLA-G to preprimed allo-CTL effector cells did not affect their killing ability. Allo-CTL suppressive doses of HLA-G induced a T helper type 2 (Th2) cytokine response, whereas allo-CTL-enhancing doses of HLA-G induced a Th1-type cytokine response. HLA-G purified from first-trimester placenta does not affect allo-proliferative responses nor does it alter the percentage of CD4+ or CD8+ T cells in MLCs. These findings support a potential role for HLA-G-mediated suppression of allo-CTL formation in normal pregnancies. In addition, the effects observed at lower concentrations of HLA-G may have interesting implications for the condition of pre-eclampsia in which concentrations of this HLA class I molecule are reduced.
Soluble HLA-G (sHLA-G) molecules are found in the peripheral blood of healthy females and males, in cord blood and in amniotic fluids and discussed to be a mediator in maternal-fetal tolerance. In this study we investigated whether there are allele-specific differences in expression of sHLA-G molecules. For this, the sHLA-G plasma concentrations of 94 healthy unrelated individuals were measured by ELISA and correlated to their HLA-G genotypes, as determined by sequence analysis of exon 2 and 3 of the HLA-G gene. Mean sHLA-G levels in individuals with the most common HLA-G alleles G*01011 (27.0+/-2.1 SEM ng/ml, n=66), G*01012 (28.4+/-3.2 SEM ng/ml, n=34) were very similar. In contrast, individuals carrying the HLA-G*01013 (8.1+/-1.7 SEM ng/ml, n=17) or the "null" allele HLA-G*0105N (8.2+/-3.2 SEM ng/ml, n=7) presented significantly (P(c)=0.001 and P(c)<0.01, resp.) reduced sHLA-G levels. Furthermore, individuals with the HLA-G*01041 allele had significantly (P(c)=0.004) increased sHLA-G levels (42.5+/-4.6 SEM ng/ml, n=14). These results demonstrate that the generation of sHLA-G molecules is associated to certain HLA-G alleles and imply that sHLA-G levels are under genetic control. As low and high sHLA-G plasma levels did not segregate with HLA haplotypes including the HLA-G*01013 or *01041 allele, additional mechanisms may be involved in the regulation of the individual sHLA-G levels. Nevertheless, the existence of "low" and "high secretor" HLA-G alleles further suggests different levels of functionality in immune regulation.