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Monoclonal antibodies for cancer therapy
Abstract
Monoclonal antibodies directed at tumor-associated antigens have been used clinically since 1981. In most of the completed clinical trials, the McAbs were of murine origin. Twenty-six of 184 patients (14%) receiving McAbs demonstrated a major clinical response, including 3 complete responders. Toxicities are primarily related to immune responses. The immune response triggering the toxic manifestations may be mediated by interactions between the administered McAb and the target tumor-associated antigens, or between the McAb and host antibodies made in response to its administration. Analysis of the mechanism of action, pharmacokinetics and toxicity of McAb administration should lead to improved design of clinical protocols, and provide a basis for the use of human McAbs and McAbs conjugated to radioisotopes, toxins or chemotherapeutic agents.
... A Mab is like a biological missile in the human body that is constantly looking for the receptor. 11 Once it finds a cancerous cell, cohesion, combination, and blocking the growth of the cancer cell take place. 12 As a result, the major therapeutic areas of Mabs are in cancer treatment, which accounts for more than 40% of Mab sales. ...
The technology of monoclonal antibodies (Mabs) has been developed since the 1990s and is attracting more and more attention in China during the 21st century. While foreign Mabs dominate the Chinese market domestic universities and companies are taking efforts to catch up with the strong support from Chinese government. The first monoclonal antibody product was introduced by the Chinese local producer in 1999, and presently seven products are listed, of which three are humanized products. There are several technical constraints that are affecting the development of monoclonal antibodies in China: limitations to the number of drug targets, restricted biological diffusion, limitations to administration routes, and species-specific issues, as well as China's own limitations in production and R&D capabilities. This article provides suggestions relevant for the Chinese development of monoclonal antibodies. In the long run China is expected to catch up with its own technology roadmap and market opportunity.
... Monoclonal antibodies (MoAb), by virtue of their tu mon specificity, may represent a new class of agents superior to conventional therapies (1). We have devel o_ MoAb 3F8 specific for the disialoganglioside GD2, an antigen expressed on the surface of a wide spectrum of human tumors including neuroblastoma (NB) and melanoma cells (2,3). ...
... The clinical use of naked rodent MAbs has so far largely focused on the treatment of cancer, and on suppression of immune responses involved in auto-immune disease, graft versus host disease (OVHD) and transplant rejection. Naked rodent MAbs have in general proven very ineffective in cancer therapy~with only 23 partial remissions and three complete remissions reported among the initial 185 patients included in 25 clinical trials (Catane and Longo, 1988). . This is partly because most of these MAbs were not directed against cell surface structures with functions required for tumour cell proliferation, partly because HAMA responses prevented repeated administration, and partly because most rodent antibodies are very inefficient at recruiting human immune effector mechanisms. . ...
For most MAb-based therapies single doses of MAbs or MAb conjugates will not be curative. Rodent MAbs are highly immonogenic in almost all patients. The HAMA response abrogates efficacy and can cause toxicity in organs of clearance, especially for MAb-cytotoxic agent conjugates. Humanization is the most promising generally applicable approach to overcoming the immunogenicity of rodent MAbs. Chimerization reduces immunogenicity in patients significantly, but not completely. Full humanization of rodent antibodies with retention of most of their antigen binding activity is now a routine procedure. The studies with 4D5 (Kelley et al., 1992), however, illustrate that even when antigen binding activity is retained, humanization may affect the overall conformation of the antibody in ways which influence its interaction with cells (for example when the antigen is internalized or involved in signal transduction) and hence its in vivo properties. As yet there are not sufficient data to judge whether full humanization will (in practical terms) completely overcome the immunogenicity problem in patients, but these data will be available within a year. Antibody fragments are the most promising general approach to manipulating the pharmacokinetics and biodistribution of therapeutic MAbs. Such fragments are clearly superior to whole IgGs for tumour detection and will very likely prove superior for tumour therapy also. MAb targeting of highly potent cytotoxic agents to tumours represents a much-needed approach to improving therapeutic ratios in cancer treatment. Radioisotopes and highly potent low molecular weight drugs are the most promising cell-killing agents for MAb targeting, and conjugation technology suitable for clinical use of some of the best of these agents has now been developed. Very encouraging data have already been obtained in clinical studies of haematopoietic malignancies with MAb-isotope conjugates. Tumour loading data from clinical studies suggest that killing of solid tumours in patients will be achievable in the near future with repeated administration of humanized antibody fragments carrying the superior isotopes or highly potent drugs which are now available.
... Among the first 185 patients treated with monoclonal antibodies in centers around the world, there were only 3 complete and 23 partial remissions (1). There are many reasons for this, as summarized by Pirofski et aL (this issue), including the difficulty in generating useful antibodies against weak antigens, the low affinity and inappropriate effector functions of many potentially useful monoclonals, and the immunogenicity of mouse monoclonals in man. ...
We have proposed a multichain model for the high-affinity interleukin-2 (IL-2) receptor involving two IL-2-binding peptides, a 70/75 kilodalton (kD) and a 55 kD, reactive with the anti-Tac monoclonal antibody, which are associated in a receptor complex. With the use of coprecipitation analysis, radiolabeled interleukin-2 cross-linking procedures, and flow cytometric resonance energy transfer measurements, a series of additional peptides of molecular weight 22,000, 35,000, 40,000, 75,000 (non-IL-2 binding), 95,000-105,000, and 180,000 has been associated with the two interleukin-2-binding peptides. In contrast to resting T cells, the abnormal T cells of patients with human T-cell lymphotropic virus I-associated adult T-cell leukemia, patients with select autoimmune disorders, and individuals rejecting allografts express the Tac peptide (p55) of the IL-2 receptor. To exploit this difference in Tac antigen expression, we have initiated therapeutic trials using unmodified anti-Tac, conjugates of anti-Tac with truncated Pseudomonas exotoxin PE-40, interleukin-2-truncated toxin fusion proteins, and alpha- and beta-emitting isotopic chelates of anti-Tac. Furthermore, by genetic engineering humanized hyperchimeric anti-Tac molecules have been prepared in which the molecule is entirely human IgG1, except for the small complementarity-determining regions that are retained from the mouse antibody. This "humanized" antibody manifested the ability to perform antibody-dependent cellular cytotoxicity absent in the original mouse monoclonal. The clinical application of anti-interleukin-2 receptor-directed therapy represents a new perspective for the treatment of certain neoplastic diseases and autoimmune disorders and for the prevention of allograft rejection.
... The hybridoma technique of KÃ ¶hler and Milstein (1) rekindled interest in the use of antibodies targeted to cell surface antigens to treat cancer patients. However, such monoclonal antibodies have been relatively ineffective (2,3). There have been a number of explanations presented for this observed low therapeutic efficacy. ...
The efficacy, specificity, and toxicity of bismuth (212Bi) alpha particle-mediated radioimmunotherapy was evaluated in nude mice bearing a murine lymphoma transfected with the human CD25 [human Tac; interleukin 2 receptor alpha (IL-2R alpha)] gene. The therapeutic agent used was the tumor-specific humanized monoclonal antibody anti-Tac conjugated to 212Bi. The human IL-2R alpha-expressing cell line was produced by transfecting the gene encoding human Tac into the murine plasmacytoma cell line SP2/0. The resulting cell line, SP2/Tac, expressed approximately 18,000 human IL-2R alpha molecules/cell. Following s.c. or i.p. injection of 2 x 10(6) SP2/Tac cells into nude mice, rapidly growing tumors developed in all animals after a mean of 10 and 13 days, respectively. The bifunctional chelate cyclohexyldiethylenetriaminepentaacetic acid was used to couple 212Bi to the humanized anti-Tac monoclonal antibody. This immunoconjugate was shown to be stable in vivo. Specifically, in pharmacokinetic studies in nude mice, the blood clearance patterns of i.v. administered 205/206Bi-anti-Tac and coinjected 125I-anti-Tac were comparable. The toxicity and therapeutic efficacy of 212Bi-anti-Tac were evaluated in nude mouse ascites or solid tumor models wherein SP2/Tac cells were administered either i.p. or s.c., respectively. The i.p. administration of 212Bi-anti-Tac, 3 days following i.p. tumor inoculation, led to a dose-dependent, significant prolongation of tumor-free survival. Doses of 150 or 200 microCi prevented tumor occurrence in 75% (95% confidence interval, 41-93%) of the animals. In the second model, i.v. treatment with 212Bi-anti-Tac 3 days following s.c. tumor inoculation also resulted in a prolongation of the period before tumor development. However, prevention of tumor occurrence decreased to 30% (95% confidence interval, 11-60%). In both the i.p. and s.c. tumor trials, 212Bi-anti-Tac was significantly more effective for i.p. (P2 = 0.0128 50/100 microCi 212Bi-anti-Tac versus 50/100 microCi Mik beta; P2 = 0.0142 150/200 microCi anti-Tac versus 150/200 microCi Mik beta) and for s.c. tumors (P2 = 0.0018 100 microCi anti-Tac versus 100 microCi Mik beta; P2 = 0.0042 200 microCi anti-Tac versus 200 microCi Mik beta 1) than the control antibody Mik beta 1 coupled to 212Bi at comparable dose levels. In contrast to the efficacy observed in the adjuvant setting, therapy of large, established s.c. SP-2/Tac-expressing tumors with i.v. administered 212Bi-anti-Tac (at doses up to 200 microCi/animal) failed to induce tumor regression.(ABSTRACT TRUNCATED AT 400 WORDS)
Immunotherapy with therapeutic antibodies has shown a lack of durable responses in some patients due to resistance mechanisms. Checkpoint molecules expressed by tumor cells have a deleterious impact on clinical responses to therapeutic antibodies. Myeloid checkpoints, which negatively regulate macrophage and neutrophil anti-tumor responses, are a novel type of checkpoint molecule. Myeloid checkpoint inhibition is currently being studied in combination with IgG-based immunotherapy. In contrast, the combination with IgA-based treatment has received minimal attention. IgA antibodies have been demonstrated to more effectively attract and activate neutrophils than their IgG counterparts. Therefore, myeloid checkpoint inhibition could be an interesting addition to IgA treatment and has the potential to significantly enhance IgA therapy.
Antibody-based immunotherapy is a promising strategy in cancer treatment. Antibodies can directly inhibit tumor growth, induce complement-dependent cytotoxicity and induce Fc receptor-mediated elimination of tumor cells by macrophages and natural killer cells. Until now, however, neutrophils have been largely overlooked as potential effector cells, even though they are the most abundant type of immune cells in the circulation. Neutrophils display heterogeneity, especially in the context of cancer. Therefore, their role in cancer is debated. Nevertheless, neutrophils possess natural anti-tumor properties and appropriate stimulation, i.e. specific targeting via antibody therapy, induces potent tumor cell killing, especially via targeting of the immunoglobulin A Fc receptor (FcαRI, CD89). In this review we address the mechanisms of tumor cell killing by neutrophils and the role of neutrophils in induction of anti-tumor immunity. Moreover, possibilities for therapeutic targeting are discussed.
Background
Despite the success of immune checkpoint inhibitors against PD-L1 in the clinic, only a fraction of patients benefit from such therapy. A theoretical strategy to increase efficacy would be to arm such antibodies with Fc-mediated effector mechanisms. However, these effector mechanisms are inhibited or reduced due to toxicity issues since PD-L1 is not confined to the tumor and also expressed on healthy cells. To increase efficacy while minimizing toxicity, we designed an oncolytic adenovirus that secretes a cross-hybrid Fc-fusion peptide against PD-L1 able to elicit effector mechanisms of an IgG1 and also IgA1 consequently activating neutrophils, a population neglected by IgG1, in order to combine multiple effector mechanisms.
Methods
The cross-hybrid Fc-fusion peptide comprises of an Fc with the constant domains of an IgA1 and IgG1 which is connected to a PD-1 ectodomain via a GGGS linker and was cloned into an oncolytic adenovirus. We demonstrated that the oncolytic adenovirus was able to secrete the cross-hybrid Fc-fusion peptide able to bind to PD-L1 and activate multiple immune components enhancing tumor cytotoxicity in various cancer cell lines, in vivo and ex vivo renal-cell carcinoma patient-derived organoids.
Results
Using various techniques to measure cytotoxicity, the cross-hybrid Fc-fusion peptide expressed by the oncolytic adenovirus was shown to activate Fc-effector mechanisms of an IgA1 (neutrophil activation) as well as of an IgG1 (natural killer and complement activation). The activation of multiple effector mechanism simultaneously led to significantly increased tumor killing compared with FDA-approved PD-L1 checkpoint inhibitor (Atezolizumab), IgG1-PDL1 and IgA-PDL1 in various in vitro cell lines, in vivo models and ex vivo renal cell carcinoma organoids. Moreover, in vivo data demonstrated that Ad-Cab did not require CD8+ T cells, unlike conventional checkpoint inhibitors, since it was able to activate other effector populations.
Conclusion
Arming PD-L1 checkpoint inhibitors with Fc-effector mechanisms of both an IgA1 and an IgG1 can increase efficacy while maintaining safety by limiting expression to the tumor using oncolytic adenovirus. The increase in tumor killing is mostly attributed to the activation of multiple effector populations rather than activating a single effector population leading to significantly higher tumor killing.
Immunoglobulin A (IgA) is the most abundant antibody class present at mucosal surfaces. The production of IgA exceeds the production of all other antibodies combined, supporting its prominent role in host-pathogen defense. IgA closely interacts with the intestinal microbiota to enhance its diversity, and IgA has a passive protective role via immune exclusion. Additionally, inhibitory ITAMi signaling via the IgA Fc receptor (FcαRI; CD89) by monomeric IgA may play a role in maintaining homeostatic conditions. By contrast, IgA immune complexes (e.g., opsonized pathogens) potently activate immune cells via cross-linking FcαRI, thereby inducing pro-inflammatory responses resulting in elimination of pathogens. The importance of IgA in removal of pathogens is emphasized by the fact that several pathogens developed mechanisms to break down IgA or evade FcαRI-mediated activation of immune cells. Augmented or aberrant presence of IgA immune complexes can result in excessive neutrophil activation, potentially leading to severe tissue damage in multiple inflammatory, or autoimmune diseases. Influencing IgA or FcαRI-mediated functions therefore provides several therapeutic possibilities. On the one hand (passive) IgA vaccination strategies can be developed for protection against infections. Furthermore, IgA monoclonal antibodies that are directed against tumor antigens may be effective as cancer treatment. On the other hand, induction of ITAMi signaling via FcαRI may reduce allergy or inflammation, whereas blocking FcαRI with monoclonal antibodies, or peptides may resolve IgA-induced tissue damage. In this review both (patho)physiological roles as well as therapeutic possibilities of the IgA-FcαRI axis are addressed.
Neutrophils represent the most abundant population of circulating cytotoxic effector cells. Moreover, their number can be easily increased by treatment with granulocyte‐colony stimulating factor or granulocyte macrophage‐colony stimulating factor, without the need for ex vivo expansion. Because neutrophils express Fc receptors they have the potential to act as effector cells during monoclonal antibody therapy of cancer. Additionally, since neutrophils play a role in the regulation of adaptive immune responses, exploiting neutrophils in mAb therapy may result in long term anti‐tumor immunity. There is limited evidence that neutrophils play a prominent role in current immunoglobulin G‐based immunotherapy. However, as IgA induces neutrophil recruitment, novel therapeutic strategies that aim to target the IgA Fc receptor FcαRI may fully unleash the potential of enlisting neutrophils as cytotoxic effector cells in antibody therapy of cancer.
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Monoclonal antibodies find broad application as therapy for various types of cancer by employing multiple mechanisms of action against tumors. Manipulating the Fc-mediated functions of antibodies that engage immune effector cells, such as NK cells, represents a strategy to influence effector cell activation and to enhance antibody potency and potentially efficacy. We developed a novel approach to generate and ascertain the functional attributes of Fc mutant monoclonal antibodies. This entailed coupling single expression vector (pVitro1) antibody cloning, using polymerase incomplete primer extension (PIPE) polymerase chain reaction, together with simultaneous Fc region point mutagenesis and high yield transient expression in human mammalian cells. Employing this, we engineered wild type, low (N297Q, NQ), and high (S239D/I332E, DE) FcR-binding Fc mutant monoclonal antibody panels recognizing two cancer antigens, HER2/neu and chondroitin sulfate proteoglycan 4. Antibodies were generated with universal mutagenic primers applicable to any IgG1 pVitro1 constructs, with high mutagenesis and transfection efficiency, in small culture volumes, at high yields and within 12 days from design to purified material. Antibody variants conserved their Fab-mediated recognition of target antigens and their direct anti-proliferative effects against cancer cells. Fc mutations had a significant impact on antibody interactions with Fc receptors (FcRs) on human NK cells, and consequently on the potency of NK cell activation, quantified by immune complex-mediated calcium mobilization and by antibody-dependent cellular cytotoxicity (ADCC) of tumor cells. This strategy for manipulation and testing of Fc region engagement with cognate FcRs can facilitate the design of antibodies with defined effector functions and potentially enhanced efficacy against tumor cells.
Clinical responses to anti-tumor monoclonal antibody (mAb) treatment have been regarded for many years only as a consequence of the ability of mAbs to destroy tumor cells by innate immune effector mechanisms. More recently, it has also been shown that anti-tumor antibodies can induce a long-lasting anti-tumor adaptive immunity, likely responsible for durable clinical responses, a phenomenon that has been termed the vaccinal effect of antibodies. However, some of these anti-tumor antibodies are directed against molecules expressed both by tumor cells and normal immune cells, in particular lymphocytes, and, hence, can also strongly affect the host adaptive immunity. In addition to a delayed recovery of target cells, lymphocyte depleting-mAb treatments can have dramatic consequences on the adaptive immune cell network, its rebound, and its functional capacities. Thus, in this review, we will not only discuss the mAb-induced vaccinal effect that has emerged from experimental preclinical studies and clinical trials but also the multifaceted impact of lymphocytes-depleting therapeutic antibodies on the host adaptive immunity. We will also discuss some of the molecular and cellular mechanisms of action whereby therapeutic mAbs induce a long-term protective anti-tumor effect and the relationship between the mAb-induced vaccinal effect and the immune response against self-antigens.
The immune system of the intestinal tract has been extensively studied. The lamina propria of adults is heavy populated with a variety of lymphoid cells: B- and T-lymphocytes, plasma cells, macrophages, mast cells, eosinophils and basophils. In normal subjects the majority of the B-cells are committed to IgA synthesis (90%), the residual 10% being represented (in order of decreasing frequency) by IgM, IgG, IgE and IgD producing plasma cells. These cells, which are located diffusely in the mucosa and more organized in Peyer’s patches, together with the an intact mucosal layer provide an effective barrier to the antigenic food load, that passes the bowel daily. Small amounts of antigen can transmigrate through the mucosa either by endo/pinocytic processes or via the tight junction complex. The production of antibodies to antigens penetrating the barrier is a physiological process that usually results in systemic tolerance. Changes in these immunological processes, caused by an altered mucosal barrier, an abnormal antigen-antibody or antigen-antigen presenting cell response, may play a role in the pathogenesis of Crohn’s disease.
Peptide growth factor receptors on the surface of malignant cells bind to their ligands with high affinity, resulting in intracellular responses which cause differentiation, growth, and the survival of these cells. Peptide growth factors, or monoclonal antibodies (mAbs) which target growth factor receptors, have been conjugated to drugs, toxins, radionuclides, or other mAbs that recognize/activate effector cells which can phagocytose or kill. These types of conjugated products, which have the ability to kill malignant cells, we call bispecific molecules (BsMol) and is the basis of this review article. The growth factors/receptors covered include α - and β-melanocyte stimulating hormone (MSH), bombesin/gastrin releasing peptide (BN/GRP), epidermal growth factor (EGF), HER-2/neu oncogene protein (p185(HER2), interleukin-2, and somatostatin. The preparation and biological use/activity of the following BsMol are discussed: β-MSH-daunomycin, [Nle4, D-Phe7]MSH-anti-CD3, 111In-DTPA-bis-α-MSH, DAB389-MSH, mAb22-Lys-BN, mAb22-Antag1, anti-EGFR/anti-CD3, DOXER2, DAB389EGF, 111In-DTPA-225, anti-p185(HER2)-SAP, 2B1, MDX-210, humAb4D5-8 x humAbUCHT1, DAB486IL-2, 111In-DTPA-octreotide (OctreoScan®), OX-26-NGF, and IVA039.1.
Immunoglobulin A (IgA) is the most prevalent antibody at mucosal sites, and has an important role in defense by preventing invasion of pathogens. Traditionally, IgA has been thought of as a non-inflammatory antibody that helps to maintain homeostasis in the mucosa. However, in the last decade it has become clear that IgA is a very potent stimulus to initiate pro-inflammatory cellular processes, especially after triggering the IgA Fc receptor (FcαRI) on neutrophils. It was furthermore described that FcαRI acts as a regulator between anti- and pro-inflammatory responses of IgA. Although neutrophil activation is beneficial in (mucosal) infections, abnormal or excessive IgA immune complexes can induce disproportionate neutrophil migration and in this way initiate a perpetuating neutrophil recruitment and activation loop, which will result in severe tissue damage. Increasing evidence on this process plays a detrimental role in several diseases, including autoimmune IgA blistering diseases, a subtype of rheumatoid arthritis and ulcerative colitis. Inhibiting FcαRI-mediated activation may dampen inflammation in these patients. This process also opens up the possibility of targeting FcαRI in antibody immunotherapy of cancer. Thus, interfering with IgA-mediated FcαRI activation may represent an attractive novel therapeutic strategy for multiple maladies.
Immunoglobulin A (IgA) is the most prevalent antibody class at mucosal surfaces. In addition to protecting mucosal surfaces by preventing invasion of pathogens, IgA can interact with multiple IgA receptors by binding to the Fc tail, carbohydrate side chains, or accessory molecules. The best characterized IgA Fc receptor is FcαRI (CD89), which acts as a regulator between anti- and proinflammatory responses of IgA. Furthermore, the Fcα/μR, polymeric Ig receptor, transferring receptor, and asialoglycoprotein receptor have been described, as well as IgA receptors on M cells, T cells, natural killer cells, and dendritic cells. However, the significance of several of these receptors is still unclear. The neonatal Fc receptor for IgG, furthermore, plays a role in transporting IgG across epithelial cells, whereas Fc receptors for IgE are involved in parasitic infections, allergies, and asthma. The focus of this chapter is therefore the role of Fc receptors in mucosal immunology.
All clinically approved antibodies are of the IgG isotype and mediate the clearance of target cells via binding to Fcγ receptors and complement (C1q). Even though IgA can elicit powerful cytotoxic action via FcαRI receptor binding, IgA antibodies have not been amenable to therapeutic development. Here, we report the engineering of a "cross-isotype" antibody, IgGA, which combines the effector functions of both IgG and IgA. IgGA binds to FcαRI with an affinity comparable to that of IgA, and to the activating Fcγ receptors, FcγRI and FcγRIIa, with high affinity, and displays increased binding to C1q compared to IgG. Unlike trastuzumab-IgG, trastuzumab-IgGA potently activates both neutrophils and macrophages to kill Her2(+) cancer cells. Furthermore, IgGA mediates greater complement-dependent cytotoxicity than IgG1 or IgA antibodies. The multitude of IgGA effector functions could be important for therapeutic purposes and highlights the concept of engineering antibodies that combine effector functions from multiple antibody isotypes.
Copyright © 2014 Elsevier Ltd. All rights reserved.
Fifteen novel monoclonal antibodies (mAbs) against S102, an established hepatocellular carcinoma cell line from a Thai patient, were tested at 50-500 μg/ml concentration for cell proliferation inhibitory activity against various types of commercial human cancer cell lines i.e., HepG2 (liver), Chago (lung), A375 (melanoma), Kato-III (gastric) and SW 620 (lymph node). To compare these inhibitory activity effects, we also verified them against a normal liver cell line, Chang liver, as well as against two of the established hepatocellular carcinoma cell line from Thai patients, S102 and R12 at the same mAbs concentration. The viability of cells after exposure to these 15 novel mAbs was determined by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) colori-metric methods. The result showed that, at their IC 50 concentration against S102, only 4 of them (Hep20: IC 50 = 100 μg/ml, Hep44: IC 50 = 300 μg/ml, Hep88: IC 50 = 100 μg/ml and Hep94: IC 50 = 200 μg/ml mAbs) illustrated cell proliferation inhibitory activity against the hepatocellular carcinoma cell lines including HepG2, S102 and R12. Interestingly, Hep88 mAb inhibited S102 and R12 cell growth by approximately 70 and 95%, respectively, at 100 μg/ml, whereas it gave a tumoricidal effect to the HepG2 cell line at the same concentration. It had no effect on the normal liver cell line, Chang liver. Moreover, when compared with the effect from an anti-oncogenic cytokine, an interferon alfa-n1 (IFN) at its IC 50 concentration (IC 50 = 1,000 U/ml), Hep88 mAb showed lesser cytotoxicity on the normal liver cell line. These results suggest that Hep88 mAb might play an important role not only in inhibitory effects but also in lethal effects on hepatocellular carcinoma cells without disturbing normal cells. Accordingly, this antibody may be a promising tool for the therapeutic era of hepatocellular carcinoma in the next decade.
The advancement of medical research in molecular biology and genetic engineering has given rise to the development of new drugs aimed at blocking different pathways of cellular immune responses. Biological therapy is a new therapeutic option for progressive chronic disease management. In chronic lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), diffuse parenchymal lung disease (DPLD) and lung cancer, treatment with biologics has made important advances in the understanding of these diseases, and in some cases, due to their effectiveness, has contributed to the improvement in life quality of patients who suffer them. Due to the increasing number of biological therapy drugs and their therapeutic application in chronic inflammatory diseases and cancer, it is relevant to review their current status in the management of chronic lung diseases.
The prospects for developing improved liposome based anti-cancer drug formulations are great, particularly when considering the potential role of lipid-based formulations for delivery of biopharmaceuticals. It is important however, to pursue improved formulations with an expectation of what the improvements are designed to achieve and an understanding of the pharmaceutical issues involved in development of such a drug. Our efforts in this area have focused on the important role of liposome extravasation in defining therapeutic activity of intravenously administered liposomal anticancer drugs. We have developed targeting strategies based on two key assumptions. First, cell specific targeting is an attribute required after the passive extravasation of a drug-loaded carrier. Accordingly, if targeting is to be of potential therapeutic value it is important that the targeting features do not interfere with the tendency of the carrier to move from the blood compartment to an extravascular site. Second, it is critical to demonstrate that liposomes that have extravasated are available for targeting. As part of this effort we have identified a need to develop simple, pharmaceutically viable, procedures for the preparation of stable protein conjugated liposomes.
With the majority of HIV infections resulting from mucosal transmission, induction of an effective mucosal immune response is thought to be pivotal in preventing transmission. HIV-specific IgA, but not IgG, has been detected in the genital tract, seminal fluid, urethral swabs, urine, and vaginal wash samples of HIV-negative sex workers and HIV-status discordant couples. Purified mucosal and plasma IgA from some individuals with highly exposed, persistently seronegative status can neutralize infection and present cross-clade neutralization activity, though present at low levels. We generated a CD4-induced human mAb, F425A1g8, and characterized the impact of its isotype variants on HIV neutralizing activity. The result showed that, in contrast to little neutralization by the F425A1g8 IgG1 in the absence of sCD4, the IgA1 variant of the Ab displayed significant independent neutralization activity against a range of HIV clade B isolates in the absence of sCD4. Studies of the neutralizing function of IgA isotypes, and the functional relationship between different antigenic epitopes and IgA Abs, may also suggest strategies for the intervention of virus transmission and spread within the mucosa of the host, as well as serve to inform the design of vaccine strategies that may be more effective at preventing mucosal transmission. This research clearly suggests that IgA isotype, because of its unique molecular structure, may play an important role in HIV neutralization.
Thiol 2-mercaptoethanol (2-ME) has been reported to enhance growth in lymphocytes by various investigators. Some have used 50 μM for growing hybridomas in vitro. Concentrations of 50 and 5 μM in 5% FBS supplemented D-MEM were tested to determine their effects on the growth of 5 monoclonal antibody secreting mouse B cell hybridomas and the myeloma Sp2/O-Ag14. Viability after 24 and 48 h exposure was determined by Trypan blue exclusion. Analysis by one-way ANOVA confirmed that 50 μM 2-ME has a significant negative impact (p<0.05) on hybridoma as well as on myeloma growth, whereas no significant difference (p>0.05) between the control and the 5 μM treatment group was observed after 48 h. Also, no significant difference (p>0.05) in the mortality rates between the control and the treatment groups was found. When combined with the observed protracted doubling time in the 50 μM treatment group, these results indicate that the impact of 2-ME is due to inhibition of cell division. The degree of inhibition was observed to vary between the different hybridomas as well as the myeloma. Although the impact of 2-ME on mitosis has been demonstrated in organisms such as the ciliated protozoan Tetrahymena pyriformis, the yeast Saccharomycess cerevisiae, and the egg of the echinoid the sand dollar Dendraster excentricus, this work demonstrates for the first time that 2-ME impedes the growth of mouse B cell hybridomas. We conclude that adding 2-ME to mouse B cell hybridoma growth media may not be beneficial.
Background. Monoclonal antibodies have not been evaluated in metastasizing endocrine tumors, even though these lesions may induce severe morbidity of hormone excess in absence of considerable tumor burden.
Methods. A murine monoclonal antibody of the IgG2a subtype was generated by immunization with dispersed tumor cells from an endocrine pancreatic carcinoma associated with liver and peritoneal metastases as well as a therapy-resistant Verner-Morrison's syndrome.
Results. Immunohistochemical staining disclosed selective tissue reactivity of the antibody and conspicuous immunostaining on the surface of the tumor cells. Infusion of 100 mg antibody over 2 days into the common hepatic artery of the patient was accompanied by reduced diarrhea volume until death 6 weeks later and transient elevation of total plasma immunoreactivity for vasoactive intestinal peptide due to large molecular forms of the peptide. Postmortem examination demonstrated disappearance of peritoneal metastases as well as absence of immunostaining for the injected antibody and the transferrin receptor within residual hepatic tumors.
Conclusion. The results substantiate that symptomatic alleviation and perhaps interference with tumor cell mass may be obtained with monoclonal antibodies in patients with endocrine tumors and that the antiidiotypic immunoglobulin response may play a role herein. Cancer 1994; 73:1346–52.
Neutrophils potently kill tumour cells in the presence of anti-tumour antibodies in vitro. However, for in vivo targeting, the neutrophils need to extravasate from the circulation by passing through endothelial barriers. To study neutrophil migration in the presence of endothelial cells in vitro, we established a three-dimensional collagen culture in which SK-BR-3 tumour colonies were grown in the presence or absence of an endothelial barrier. We demonstrated that - in contrast to targeting FcγR on neutrophils with mAbs - targeting the immunoglobulin A Fc receptor (FcαRI) instead triggered neutrophil migration and degranulation leading to tumour destruction, which coincided with release of the pro-inflammatory cytokines interleukin (IL)-1β and tumour necrosis factor (TNF)-α. Interestingly, neutrophil migration was enhanced in the presence of endothelial cells, which coincided with production of significant levels of the neutrophil chemokine IL-8. This supports the idea that stimulation of neutrophil FcαRI, but not FcγR, initiates cross-talk between neutrophils and endothelial cells, leading to enhanced neutrophil migration towards tumour colonies and subsequent tumour killing.
Immunoglobulin A (IgA) is commonly recognized as the most prevalent antibody (Ab) at mucosal sites with an important role in defense by shielding mucosal surfaces from invasion by pathogens. However, its potential to both actively dampen excessive immune responses or to initiate potent proinflammatory cellular processes is less well known. Interestingly, either functional outcome is mediated through interaction with the myeloid IgA Fc receptor FcαRI (CD89). Monomeric interaction of IgA with FcαRI triggers inhibitory signals that block activation via other receptors, whereas multimeric FcαRI crosslinking induces phagocytosis, reactive oxygen species production, antigen presentation, Ab-dependent cellular cytotoxicity, and cytokine release. Thus, FcαRI acts as a regulator between anti- and proinflammatory responses of IgA. As such, the biology of FcαRI, and its multifaceted role in immunity will be the focus of this review.
Neutrophils are the most abundant circulating FcR-expressing WBCs with potent cytotoxic ability. Currently, they are recognized as promising effector cells for Ab-mediated immunotherapy of cancer, because their capacity to kill tumor cells is greatly enhanced by tumor Ag-specific mAbs. The FcαRI represents the most potent FcR on neutrophils for induction of Ab-mediated tumor cell killing. However, the mechanisms of cell death that are induced are poorly understood. Because these mechanisms can be used for modulation of anticancer treatment, we investigated the tumor cell death induced by neutrophil-mediated Ab-dependent killing via FcαRI. Human mammary carcinoma cells were efficiently killed when incubated with human neutrophils and tumor-specific FcαRI bispecific or IgA Abs. Interestingly, we observed characteristics of autophagy such as autophagic structures by electron microscopy and LC3B(+) autophagosomes in different human epithelial carcinoma cells, which resulted in tumor cell death. To a lesser extent, necrotic features, such as cellular membrane breakdown and spillage of intracellular content, were found. By contrast, apoptotic features including fragmented nuclei, Annexin V-positivity, and presence of cleaved caspase-3 were not observed. These findings indicate that neutrophils mainly facilitate autophagy to induce tumor cell death rather than the more commonly recognized apoptotic cell death mechanisms induced by NK cells or cytotoxic T cells. This knowledge not only reveals the type of tumor cell death induced in neutrophil-mediated, Ab-dependent cellular cytotoxicity, but importantly opens up additional perspectives for modulation of anticancer therapy in, for example, apoptosis-resistant tumor cells.
In preparing for testing a pharmaceutical grade preparation of chimeric (mouse/human) antibody CGP 47,439 in HIV-1 infected individuals, it was administered to Macaca fascicularis (cynomolgus) monkeys to study tolerability, immunogenicity and pharmacokinetics. Four groups of monkeys, three males and three females per group, received respectively four infusions of 0, 1.43, 4.3, and 14.3 mg of CGP 47,439/kg body weight at one-week intervals. The chimeric antibody induced no fever, was tolerated well throughout the 50-day observation period, elicited no tissue damage and no anti-antibody response. The pharmacokinetic profile was similar at all dose levels with a mean T1/2 alpha of 14.2 h (range 11.8-19.3 h) and a mean T1/2 beta of 172.6 h (range 137.2-220.5h). Following four successive antibody infusions serum concentrations of CGP 47,439 increased without reaching a steady state, and its measured concentrations were comparable to the simulated values. Collectively the study has provided safety and pharmacokinetic data that would allow human studies with this antibody in AIDS patients.
Immunologic changes may play a role in the pathogenesis of Crohn's disease. Whether these changes are the primary cause of the disease or secondary to the inflammatory response remains unknown. Activated T helper cells probably play a pivotal role in Crohn's disease, although no causative antigen has been identified. Possible targets for immunomodulating therapy should include neutralization of the antigens, deletion of reactive activated T cells or, less specifically, interference with the antigen-presenting process. New, humanized, monoclonal antibodies that interfere with the antigen-presenting process are now available for clinical investigation. In particular, CD4 antibody treatment seems of interest, in view of the predominant role of T cells in Crohn's disease. Finally, because tumor necrosis factor is necessary for granuloma formation, inhibition of this factor may be expected to improve disease activity in Crohn's disease.
Immunization with tumor cells or tumor extracts preventing the growth of subsequently grafted cells provided the proof for immunogenicity of some animal tumors. The demonstration of antigenicity of experimental tumors and the beneficial effects of immunotherapy in animal models generated great expectations for cancer treatment. Active specific immunotherapy in patients was attempted by several investigators using various vaccines such as irradiated autologous tumor cells allogeneic or extracts of the corresponding histologic type. This chapter discussesthe potential of the combined treatment modalities including tumor debulking, followed by active immunization with tumor material, and by administration of cytokines, other biological response modifiers (BRMs), and antitumor antibodies in various combinations. The new ideas for immunotherapy propose readministration of autologous tumor–reactive T cells transfected with cytokine–encoding genes, and the use of encapsulated cytokines directed by antibodies to the tumor cells. These may home in on the tumor tissue and deliver large quantities of cytokines. The therapeutic efficacy of these two modalities is not yet known.
Dormancy in the murine BCL1 lymphoma can be induced by several strategies including cytoreductive therapy of mice with large tumor burdens and challenge of allogeneic chimeric mice or idiotype-immunized mice with BCL1 tumor. Dormant tumor cells were isolated from the spleens of the chimeric mice and the majority were shown to be noncycling. In idiotype-immunized mice that had lost dormancy, tumor growth occurred at a relatively rapid rate. A proportion of idiotype-immunized mice that had lost dormancy spontaneously regressed and then again relapsed; in these mice, the serum antiidiotypic levels were inversely related to the tumor burden.
Despite impressive progress in understanding the biology of breast cancer, mechanisms of host defense, and the pathophysiology of the metastatic process, this burgeoning fact bank has made little impact on the management of patients with breast cancer. There are many interesting ideas for improved diagnosis and therapy in various stages of development, but few have actually translated into improved survival of patients with breast cancer. Potentially useful biological agents include cytokines, monoclonal antibodies, immunotoxins, vaccines, and adoptive cellular therapies. Therapies targetting growth factor receptors and the cellular machinery required for metastasis may become useful, especially when used in combination with other cytotoxic agents. Colony-stimulating factors may allow a test of the hypothesis that augmented dose-intensity of cytotoxic chemotherapy will cure more patients. Though we are not yet sure precisely how to use all of these new tools, there can be little doubt that their application will make a significant impact on the management of patients with breast cancer and other malignancies in the next decade.
One factor that is critical to the potential effectiveness of radioimmunotherapy is the design of radiometal-chelated antibodies that will be stable in vivo. Stability in vivo depends on the condition that both the chelate linkage and radiolabeling procedures not alter antibody specificity and biodistribution. In addition, synthesis and selection of the chelating agent is critical for each radiometal in order to prevent inappropriate release of the radiometal in vivo. In the present study, we compare the in vivo stability of seven radioimmunoconjugates that use different polyaminocarboxylate chelating agents to complex yttrium-88 to the mouse anti-human interleukin-2 receptor monoclonal antibody, anti-Tac. Chelate linkage and radiolabeling procedures did not alter the immunospecificity of anti-Tac. In order to assess whether yttrium was inappropriately released from the chelate-coupled antibody in vivo, iodine-131-labeled and yttrium-88 chelate-coupled antibodies were simultaneously administered to the same animals to correlate the decline in yttrium and radioiodinated antibody activity. The four stable yttrium-88 chelate-coupled antibodies studied displayed similar iodine-131 and yttrium-88 activity, indicating minimal elution of yttrium-88 from the complex. In contrast, the unstable yttrium-88 chelate-coupled antibodies had serum yttrium-88 activities that declined much more rapidly than their iodine-131 activities, suggesting loss of the radiolabel yttrium-88 from the chelate. Furthermore, high rates of yttrium-88 elution correlated with deposition in bone. Four chelating agents emerged as promising immunotherapeutic reagents: isothiocyanate benzyl DTPA and its derivatives 1B3M, MX, and 1M3B. All four isothiocyanate agents showed prolonged yttrium-88 vascular survival which was essentially identical to that of their iodine-131 activity with only minimum accumulation (1.4-1.8%/g) of the yttrium-88 injected dose into bone. Thus, these four chelating agents were very stable in vivo and suitable for yttrium-monoclonal antibody radioimmunotherapy.
Human T-cell lymphotropic virus I (HTLV-I)-induced adult T-cell leukemia (ATL) cells constitutively express interleukin-2 (IL-2) receptors identified by the anti-Tac monoclonal antibody (MoAb), whereas normal resting cells do not. This observation provided the scientific basis for a trial of intravenous anti-Tac in the treatment of nine patients with ATL. The patients did not suffer untoward reactions and did not have a reduction in the normal formed elements of the blood, and only one of the nine produced antibodies to the anti-Tac MoAb. Three patients had transient mixed, partial, or complete remissions lasting from 1 to more than 8 months after anti-Tac therapy, as assessed by routine hematologic tests, immunofluorescence analysis of circulating cells, and molecular genetic analysis of HTLV-I provirus integration and of the T-cell receptor gene rearrangement. The precise mechanism of the antitumor effects is unclear; however, the use of a MoAb that prevents the interaction of IL-2 with its receptor on ATL cells provides a rational approach for the treatment of this malignancy.
The murine IgG3 monoclonal antibody (MoAb) 3F8, specific for the ganglioside GD2, activates human complement, is active in antibody-dependent cell-mediated cytotoxicity (ADCC), and can target specifically to human neuroblastoma in patients with metastatic disease. In a phase I study, 3F8 was administered intravenously (IV) to 17 patients with metastatic GD2 positive neuroblastoma or malignant melanoma at doses of 5, 20, 50, and 100 mg/m2. Serum 3F8 levels achieved were proportional to the dose of 3F8 infused. However, serum antimouse antibody levels did not increase with the amount of 3F8 administered. Toxicities included pain, hypertension, urticaria, and complement depletion. All acute side effects were controllable with symptomatic therapy. No long-term side effects were detected in patients observed for more than 14 months. None of the 17 patients received any antitumor therapy postantibody treatment. Antitumor responses occurred in seven of 17 patients. These ranged from complete clinical remissions to mixed responses. The murine monoclonal antibody (MoAb) 3F8 has clinical utility for the diagnosis and therapy of neuroblastoma and melanoma.
Recent studies have suggested that ICAM-1 (CD54) is involved in the pathogenesis of human multiple myeloma. A monoclonal antihuman CD54 antibody has been generated by immunizing BALB/c mice with human myeloma cell lines. SCID mice injected with human ARH-77 myeloma cells develop disseminated myeloma which is similar in several respects to multiple myeloma in humans. The mice have monoclonal gammopathy and succumb to hind leg paralysis caused by infiltration of tumor cells into the thoracolumbar vertebrae, resulting in compression of the spinal cord. In the absence of treatment, the mean paralysis time of the SCID/ARH-77 mice is 29 days. When the SCID/ARH-77 mice received four consecutive daily i.v. injections of anti-CD54 mAb commencing 1 day after tumor inoculation, they survived for 150 days, at which time the experiment was terminated. Histopathological analyses indicated that prior to death all control SCID/ARH-77 mice had myeloma cells in the vertebrae and skull. At this time, the anti-CD54-treated mice had no evidence of tumor. High levels of human immunoglobulin were detected in the sera of control, but not treated mice. F(ab')2 fragments of the anti-CD54 antibody also had similar, albeit, slightly less antitumor activity in vivo, suggesting that antibody effector function may account for some, but not all the antitumor activity of anti-CD54. In vitro studies indicate that anti-CD54 does not inhibit homotypic adhesion, the binding of myeloma cells to murine bone marrow stromal cells, or cell proliferation. By exclusion, we propose that the CD54-mediated homing of these ARH-77 cells to certain anatomical sites is crucial for their growth in vivo.
An attractive approach to the therapy of solid tumors is to attack the endothelial cells of the tumor vascular bed rather than the tumor cells themselves, which circumvents the problem of poor penetration of tumor masses by monoclonal antibodies and other macromolecules. In this review, we will discuss the drawbacks of targeting solid tumors and the advantages of the 'vascular targeting' approach, describe the validation of the concept in a mouse model and summarize the properties of tumor endothelial cell markers, which are candidates for vascular targeting in humans.
We have obtained equilibrium and rate constants for the interaction of monoclonal IgG and its monovalent Fab fragment with a hapten (fluorescein) attached to the surface of a liposome. Binding was detected at nanomolar hapten concentrations by the quenching of the hapten's fluorescence on antibody binding. The binding parameters were computed from nonlinear least squares fits, using mass-action models. Crypticity of the hapten was observed and interpreted as an equilibrium between two states, extended and sequestered, the latter representing haptens associated with the membrane surface. Depending on the lipid composition of the liposomes, the fraction of sequestered hapten ranged from 0.25 to 0.975; transitions between the two states took place on the time scale of minutes. Fab interactions with extended hapten on the membrane were similar to interactions with water-soluble hapten. The ability of IgG to bind bivalently to membrane gave it an avidity two to six times the affinity for purely monovalent binding. However, the equilibrium constant for the monovalent-bivalent binding equilibrium was effectively four to five orders of magnitude less than that for the initial binding step. This probably reflects steric penalties for the simultaneous binding of two haptens on a membrane.
Antibody-drug conjugates utilize the targetting potential of antibodies to improve the potential of cytostatic or cytocidal drugs. One such murine monoclonal antibody, CTM01 (mCTM01), which recognizes an epitope on breast epithelial mucin, has potential for the treatment of breast and ovarian cancers. We examine in this paper the comparative properties of mCTM01 against a number of other anti-mucin antibodies. We then describe the humanization and high level re-expression of humanized CTM01 (hCTM01), a process designed to avoid the immune response to administered murine antibodies in human patients and to produce sufficient material for clinical studies. We show that the humanized form has properties superior to mCTM01 in terms of binding affinity to antigen presented on tumour cells.
Monoclonal antibodies have not been evaluated in metastasizing endocrine tumors, even though these lesions may induce severe morbidity of hormone excess in absence of considerable tumor burden.
A murine monoclonal antibody of the IgG2a subtype was generated by immunization with dispersed tumor cells from an endocrine pancreatic carcinoma associated with liver and peritoneal metastases as well as a therapy-resistant Verner-Morrison's syndrome.
Immunohistochemical staining disclosed selective tissue reactivity of the antibody and conspicuous immunostaining on the surface of the tumor cells. Infusion of 100 mg antibody over 2 days into the common hepatic artery of the patient was accompanied by reduced diarrhea volume until death 6 weeks later and transient elevation of total plasma immunoreactivity for vasoactive intestinal peptide due to large molecular forms of the peptide. Postmortem examination demonstrated disappearance of peritoneal metastases as well as absence of immunostaining for the injected antibody and the transferrin receptor within residual hepatic tumors.
The results substantiate that symptomatic alleviation and perhaps interference with tumor cell mass may be obtained with monoclonal antibodies in patients with endocrine tumors and that the antiidiotypic immunoglobulin response may play a role herein.
The pharmacokinetics of mouse V/human C (gamma 1, kappa) chimeric monoclonal antibody CGP 47 439 specific for the principal neutralizing determinant of human immunodeficiency virus type 1 (HIV-1) was studied in patients with stage IV HIV-1 disease in an open-labeled phase I/IIA trial. Twelve male patients were enrolled and nine completed the study. Patients were divided into three groups according to the extent of CGP 47 439 to bind to gp120 from their viral isolates: undetectable for group 1, modestly reactive for group 2, and strongly reactive for group 3. A first dose of 1, 10, or 25 mg was administered by intravenous infusion to group 1, group 2 and group 3 patients, respectively. The patients then received seven doses of 50, 100, or 200 mg, respectively, every three weeks. CGP 47 439 serum concentrations were determined by an ELISA using monoclonal antibody AB19-4 specific for the idiotope of CGP 47 439. Half an hour after infusion only 25.5-36.1% of the administered antibody was found in the serum, reflecting its rapid distribution in the extravascular space and possibly binding to gp120 antigen in some of the patients. The terminal elimination half-life (T1/2) was 16.2 days in group 1 patients, 9.7 days in group 2 and in group 3 patients 7.5 days and 9.1 days. An antibody response to CGP 47 439 was not a factor in determining elimination rates, because only very low and transient responses were found in three patients. These results suggest that the reactivity of CGP 47 439 with HIV-1 gp120 contributed to its elimination in HIV-1 infected patients.
Epidural neuroblastoma xenografts in nude rats causing paraparesis were treated with intravenous injection of an anti-GD2 monoclonal antibody 3F8. Metastatic or primary epidural tumors in humans cause rapid neurologic compromise. Treatment is often unsatisfactory. An animal model was established to study antibody targeted therapy of epidural tumor. Human neuroblastoma was xenotransplanted into the thoracic epidural space of nude rats. When paraparesis developed, animals were treated intravenously with an anti-GD2 monoclonal antibody, 3F8, either alone or radiolabeled with 131Iodine. Improvement in neurologic function occurred in 2 of 20 (10%) animals receiving no treatment or control antibody, 14 of 17 (82%) animals receiving 3F8 alone and all 9 animals receiving 131I-3F8 (p < 0.0001 for 3F8 or 131I-3F8 vs. control). Six animals treated with 3F8 alone recovered normal neurologic function and remained well until sacrifice 10 days later. Four animals treated with 3F8 alone had no tumor evident on pathologic examination. The percent injected dose of 131I-3F8/g tumor in 5 samples ranged from 0.73% to 3.8%. These observations demonstrate that neoplastic epidural compression of the spinal cord in the rat can be treated successfully with intravenous unmodified monoclonal antibody and that signs of neurologic dysfunction can be reversed. The potential of this approach in treating patients with epidural tumors and other neoplasms, especially those that are not sensitive to chemotherapy or radiotherapy, deserves to be explored.
Immune intervention began almost two centuries ago when Jenner introduced vaccination with cowpox as a means of protecting
against smallpox. This form of immune intervention plays a dominant role in the prevention of human disease. Furthermore,
immunological approaches including radioimmunoassays, enzyme-linked immunoassays, microfluorometry, and modern molecular immunogenetics
are critical in clinical diagnosis.
Adult T-cell leukemia (ATL) is a malignancy of mature lymphocytes caused by the retrovirus human T-cell lymphotrophic virus-I (HTLV-I). It is an aggressive leukemia with an overall mortality rate of 50% within 5 months; no conventional chemotherapy regimen appears successful in inducing long-term disease-free survival in ATL patients. However, ATL cells constitutively express high-affinity interleukin-2 receptors (IL-2Rs) identified by the anti-Tac monoclonal antibody, whereas normal resting cells do not. To exploit this difference in receptor expression, we administered anti-Tac intravenously (IV) to 19 patients with ATL. In general the patients did not suffer untoward reactions, and in 18 of 19 cases did not have a reduction in normal formed elements of the blood. Seven patients developed remissions that were mixed (1 patient), partial (4 patients), or complete (2 patients), with partial and complete remissions lasting from 9 weeks to more than 3 years as assessed by routine hematologic tests, immunofluorescence analysis, and molecular genetic analysis of T-cell receptor gene rearrangements and of HTLV-I proviral integration. Furthermore, remission was associated with a return to normal serum calcium levels and an improvement of liver function tests. Remission was also associated in some cases with an amelioration of the profound immunodeficiency state that characterizes ATL. Thus the use of a monoclonal antibody that blocks the interaction of IL-2 with its receptor expressed on ATL cells provides a rational approach for treatment of this aggressive malignancy.
Anticancer antibodies have had a long history in the management of cancer, with major applications having been shown in the immunohistochemistry and immunoassay of tumor-associated antigen markers. With the advent of hybridoma-derived monoclonal antibodies, attempts to use these more reproducible reagents in vivo for cancer detection and therapy have intensified. Radiolabeled monoclonal antibodies appear to be gaining a role in the management of cancer by means of imaging methods to detect sites of increased radioactivity, and several products have been developed and tested clinically. In the area of radioimmunotherapy, a number of problems still need to be solved, including low tumor uptake of the radioimmunoconjugate, dose-limiting myelotoxicity, and the induction of an immune response to repeated doses of murine (foreign) immunoglobulins. Similar problems exist for toxin and drug immunoconjugates, but these also fail to benefit from the "bystander" effect of the ionizing radiation delivered with radioimmunoconjugates, and plant and bacterial toxin molecules appear to have additional immunogenicity that restricts repeated injections. Despite these limitations, recombinant engineering and other chemical approaches are making progress in developing second-generation immunoconjugates that may be more efficacious and less immunogenic as cancer-selective therapeutics. Although nonconjugated, "naked", murine monoclonal antibodies have shown limited success in the therapy of human neoplasms, human and "humanized" forms may be more effective, particularly in lymphatic tumors. Some evidence also suggests that anti-idiotype antibodies (antiantibodies) may serve as surrogate antigens in cancer vaccines. Thus, a number of promising immunologic approaches for cancer diagnosis, detection, and therapy have made important progress in recent years.
VIP-secreting tumours are rare, but they produce a dramatic clinical picture, the most prominent feature being profuse, watery diarrhoea and hypokalaemia. VIPomas are malignant and require sophisticated diagnostic and localization techniques in order to identify their presence. Delays in diagnosis are the rule rather than the exception. Improvements in the diagnosis of VIPomas appear to result in an increase in resectability rates. A definitive diagnosis is aided by the determination of plasma VIP concentrations through the use of sensitive radioimmunoassays. With heightened awareness of this syndrome, increasing numbers of patients can be identified and more effective treatments developed for the refractory and recurrent tumours.
3F8 is a murine IgG3 monoclonal antibody (MAb) selective for the ganglioside G(D2). Previous studies using 131I-3F8 have shown great potential in the imaging of neuroectodermal tumors and the therapy of human neuroblastoma. 131I is commonly used in radioimmunodiagnosis, but its relatively long half-life (8 days) and its high energy gamma-emission (364 KeV) are suboptimal for imaging purposes when compared with 99mTc (6 h and 140 KeV, respectively). To label 3F8 with 99mTc, the antibody was first coupled with a heterobifunctional linker, succinimidyl-6-hydrazinonicotinate hydrochloride (SHNH), obtaining a hydrazinonicotinamide-antibody conjugate. Using 99mTc-Tricine as the precursor complex, 3F8-SHNH was coupled efficiently to 99mTc, resulting in >90% radiometal incorporation, with a specific activity >10 mCi/mg and retaining full immunoreactivity. Immunoscintigraphy at 6, 22, and 46 h after intravenous injection of 1 mCi of 99mTc-3F8 showed selective neuroblastoma localization in xenografted nude mice, comparable to that obtained with the injection of 100 microCi of 131I-3F8. Biodistribution studies of 131I-3F8 and 99mTc-3F8 in mice demonstrated comparable %ID/g uptake in tumor (with a T/B ratio: approximately 2.5 at 24 h and approximately 3.5 at 48 h) and normal organs, including blood, except for spleen and liver which had about a three times higher uptake of the 99mTc conjugate. In conclusion, 99mTc can be coupled conveniently at high specific activity to 3F8 without compromising immunoreactivity. SHNH appears to be a useful linker for 99mTc in tumor diagnostic imaging and may have potential utility in coupling other radioisotopes (e.g., 94mTc) for positron imaging and therapy.
Cytokine receptors are exceptionally valuable targets for immunotherapy. For example, the high affinity IL-2 receptor is expressed by abnormal T cells in patients with certain lymphoid malignancies or autoimmune disorders and in individuals rejecting allografts whereas it is not expressed by normal resting cells.
To exploit this difference in receptor expression in normal resting cells and leukemic cells we have introduced different forms of IL-2 receptor directed therapy including an unmodified murine antibody to the alpha subunit of the IL-2 receptor (anti-Tac), humanized anti-Tac as well as this antibody armed with truncated Pseudomonas exotoxin or alpha- and beta-emitting radionuclides (e.g., 211At and 90Y). In particular, unmodified murine anti-Tac was used in the therapy of HTLV-I-associated adult T-cell leukemia (ATL).
Six of nineteen patients treated with this antibody underwent a partial (four) or complete (two) remission. In a subsequent clinical trial involving anti-Tac armed with 90Y over 50% of the patients with ATL treated underwent a partial or complete remission.
New agents under development include humanized antibodies directed toward shared cytokine receptors such as IL-2/15R beta used by both IL-2 and IL-15 as well as to a shared signal transduction element Jak3 utilized by the T-cell stimulatory cytokines IL-2, IL-4, IL-7, IL-9 and IL-15. Thus our emerging understanding of cytokine receptors and their signaling pathways taken in conjunction with the ability to produce humanized antibodies armed with radionuclides or toxins are providing novel perspectives for the treatment of leukemia and lymphoma.
Affinity reagents capable of selective recognition of the different human immunoglobulin isotypes are important detection and purification tools in biotechnology. Here we describe the development and characterization of affinity proteins (affibodies) showing selective binding to human IgA. From protein libraries constructed by combinatorial mutagenesis of a 58-amino-acid, three-helix bundle domain derived from the IgG-binding staphylococcal protein A, variants showing IgA binding were selected by using phage display technology and IgA monoclonal antibodies (myeloma) as target molecules. Characterization of selected clones by biosensor technology showed that five out of eight investigated affibody variants were capable of IgA binding, with dissociation constants (K(d)) in the range between 0.5 and 3 microm. One variant (Z(IgA1)) showing the strongest binding affinity was further analyzed, and showed that human IgA subclasses (IgA(1) and IgA(2)) as well as secretory IgA were recognized with similar efficiencies. No detectable cross-reactivity towards human IgG, IgM, IgD or IgE was observed. The potential use of the Z(IgA1) affibody as a ligand in affinity chromatography applications was first demonstrated by selective recovery of IgA protein from a spiked Escherichia coli total cell lysate, using an affinity column containing a divalent head-to-tail Z(IgA1) affibody dimer construct as a ligand. In addition, efficient affinity recovery of IgA from unconditioned human plasma was also demonstrated.
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