Torque teno virus in patients undergoing allogeneic hematopoietic stem cell transplantation for hematological malignancies

Abstract

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LETTER TO THE EDITOR
Torque teno virus in patients undergoing allogeneic
hematopoietic stem cell transplantation for hematological
malignancies
Bone Marrow Transplantation (2016) 51, 440–442; doi:10.1038/
bmt.2015.262; published online 9 November 2015
Patients undergoing allogeneic hematopoietic stem cell trans-
plantation (HSCT) for hematological malignancies are at high risk
of infections.
1
The synergy of transplant conditioning and
allogeneic effect of the graft will destroy the patient’s immune
system and in particular antiviral immunity may be impeded for a
substantial period of time. Moreover, many patients may already
have slumbering viral infections at transplant because the disease
and its treatment have weakened their immune system.
Immunocompetence is difficult to quantify but surrogate markers
may help in assessing the degree of the patient’s immunodefi-
ciency. The number of CD4-positive T cells is such a marker but it
may be inaccurate in patients going through multiple periods of
chemotherapy-
2
or transplant conditioning-induced lymphopenia
because the number of T cells may normalize without restoring
immunity.
3
It is obvious that the level of the patient’s immuno-
competence is assessed best based on his genuine capacity to
defend himself against infections.
Torque teno virus (TTV) is a small non-enveloped, single-
stranded DNA Anellovirus that infects humans early in life.
4–6
Reports on the prevalence in the general population vary greatly,
most likely owing to the different thresholds of the PCR
techniques used for the detection of the viral genome.
6
It is
currently believed that 490% of the population is infected but
that the viral load in blood may remain undetectable because
genome replication is efficiently controlled by the immune
system. The latter is clearly illustrated by the fact that the viral
load increases greatly after immune suppression given to prevent
rejection of transplanted organs
7,8
and that high copy numbers
are present in the blood during secondary immune deficiencies in
patients with AIDS
9
or after HSCT.
10,11
As TTV is not sensitive to
current antiviral prophylaxis/therapy,
8
the number of viral copies
in the patient’s blood may be an appropriate parameter to
measure immunocompetence.
We have determined TTV-titers in 74 healthy blood donors
and in 121 adult patients receiving first allogeneic grafts for
hematological malignancies during the first 3–4 months of
transplantation. Patients were transplanted for AML (n= 58), ALL
(n= 15), myelodysplastic syndrome (MDS) (12), non-Hodgkin
lymphoma (NHL) (10), myeloproliferative syndrome (MPS) (6),
multiple myeloma (9), HL (5), CML (3), CLL (1), myelodysplastic/
myeloproliferative syndrome (MDPS) (1) or acute plasmacytoid
dendritic leukemia.
1
Further details such as (disease) status at
transplant or other parameters with a potential impact on the
patient’s immunity are shown in the Table 1.
We used a Taqman-based quantitative PCR with primers
described by Moen et al.
12
with a detection limit of 25 viral
copies/ml of plasma and a linear amplification range from 250 to
2.5 × 10
9
viral copies/ml. With this method, we detected TTV in
51/74 (69%) of healthy controls (median 170, range 0–5.4 × 10
4
copies/ml, left panel of the Figure 1). At transplant (blood sampled
at day 4.3 ± 5.4), the bulk of patients had TTV-titers in the same
range, but 30 patients (25%) harbored supranormal viral loads
(defined as 490th percentile of healthy controls (1.2 × 10
4
copies/
ml of plasma)). Three months later, all patients with normal TTV-
titers at transplant who were still available for follow-up (n= 77) had
high numbers of viral copies in their blood. These patients had
received different intensities of transplant conditioning (60%
reduced intensity), different type of grafts (81% partially T-cell
depleted) from HLA-identical siblings (35%), from matched
unrelated donors (45%) or from mismatched related (8%) or
unrelated (12%) donors but none of these parameters appeared to
have had an impact on the levels of viral copies in the blood (data
not shown). We did observe that TTV-titers in patients with GvHD
(black symbols) who received immune suppression including
prednisone tended to be higher than in patients without, but this
difference barely reached significance (P= 0.043). Patients with
normal TTV-titers at transplant remained so for a considerable time.
At 1 month after transplantation, only a few patients (14%)
harbored supranormal TTV-titers in their blood, whereas 56% did so
at two months (data not shown). This lag time of 41 month is very
similar to the one observed after the beginning of immunosuppres-
sion in organ transplantation.
7,8
Hence, at transplant, the majority of
patients still disposes of sufficient residual immunity to keep TTV in
check while others already have lost this capacity. Interestingly,
supranormal TTV-titers at transplant were strongly associated with
the type of disease (right panel of the Figure 1). Viral copy numbers
were high in patients with ALL or NHL while titers in patients with
other malignancies were in the normal range.
Different degrees of immunodeficiency in patients with cancer are
often attributed to the type of chemotherapy received
13
and it has
been argued that in particular the corticosteroids in the protocols
used to treat patients with ALL/NHL are accountable for their
reduced immunity. Others have argued that disease specific features
may be at least as important.
14
Although our cohort is too small to
evaluate these hypotheses conclusively, our results do give
substantial support to the latter. First, most patients with
malignancies other than ALL/NHL had TTV-titers in the normal
range at transplant although many had received chemotherapies
with comparable toxicity. Furthermore, patients having received
previous autologous transplants (21 non-ALL/NHL patients) were not
different from other non-ALL/NHL patients and we found no
correlations between TTV-titers and time between diagnosis and
transplant (not shown). Second, we found no association between
TTV-titers in ALL/NHL patients and the number of cycles (range
2–13) of chemotherapy they had received. In fact, four of six patients
with Philadelphia-positive ALL (black dots) who had received only 2–
3 cycles of chemotherapy harbored much higher viral copy numbers
in their blood than the nine Philadelphia-negative ALL patients who
had received an average of 10.6 ± 3.7 cycles. It is true that the
Philadelphia-positive patients also received the tyrosine kinase
inhibitor imatinib but it is unlikely that this drug would add much to
the immunosuppression already induced by the chemotherapy.
More importantly, none of the non-ALL/NHL patients who had
received tyrosine kinase inhibitors such as imatinib (n=5) or
sorafenib (n= 5) were TTV-positive at transplant. Furthermore, the
impact of corticosteroids also seemed negligible, because TTV-titers
Bone Marrow Transplantation (2016) 51, 440–442
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in (non-ALL/NHL) patients (2/20 TTV-positive) who had received
comparable long-term prednisone (defined as a median dose of
410 mg/day for at least 3 months) were not different from titers in
patients who had received chemotherapy without steroids (11/76
TTV-positive). Together, our findings would indeed suggest that the
type of disease has more impact on the patient’s immunity at
transplant than the treatment previously received and it is tempting
to speculate that lymphoid malignancies with large, destructive
8
10
6
4
2
Median
IQR
Ctrl at Tx 2-3m NHL OthersAML
124
25-1478
190
25-1224
3.105
2.104-2.107
ALL
2.104
605-2.105
3.105
8.104-2.106
170
25-1736
244
25-1.104
Log TTV copies/ml
P<0.0001 P<0.0001
P=0.0017
Figure 1. TTV-copy numbers per ml of plasma as determined by Taqman-based quantitative PCR adapted from Moen et al.
12
Depicted are
titers in healthy controls (Ctrl, n=74), in patients at transplant (at Tx, n=121) and the highest TTV-titer observed in patients at 2–3 months
after transplantation (2–3m, n=77) with (black symbols, n=15) or without (n=62, gray symbols) GvHD. The right panel shows TTV-titers at
transplant in patients with AML (n=58), with Ph
+
(n=6, black symbols) or Ph
−
(n=9, gray symbols) ALL, NHL (n=10) or other hematological
malignancies (n=38). Comparison between the patient groups and healthy controls were performed with the Mann–Whitney test.
Table 1. Patient characteristics
All patients ALL NHL AML Others
Patients (n) 121 15 10 58 38
Median age (years (range)) 50 (18–70) 40 (18–64) 50 (36–62) 52 (22–70) 49 (25–70)
Sex (n(%))
Male 67 (55.4) 11 (73.3) 9 (90) 32 (55) 15 (55.5)
Disease status at transplant (n(%))
Complete remission/partial remission 98 (81) 14 (93.3) 9 (90) 48 (82.8) 27 (71)
Progression/relapse 23 (19) 1 (6.6) 1(10) 10 (17.2) 11 (29)
Time since diagnosis (months median (IQR)) 10 (7–22) 8.3 (6–14) 36 (11–62) 9 (6–12) 16 (8–25)
Time since last treatment (months median (IQR)) 1.9 (1.3–3.5) 1.2 (0.7–2.2) 3.2 (1.8–4.6) 2.2 (1.6–3.4) 1.8 (1.1–3.7)
Therapy before transplantation
Chemotherapy cycles (median (IQR)) 5 (3–8) 7 (3–11) 9 (7–10) 5 (3–6) 3 (0–11)
Steroids (patients n(%)) 45 (37.2) 15 (100) 10 (100) 0 (0) 20 (52.6)
ASCT (patients n(%)) 30 (24.8) 1 (6.6) 8 (80) 6 (10.3) 15 (39.5)
TKI (patients n(%)) 16 (13.22) 6 (40) 0 (0) 5 (8.6) 5 (13.2)
Abbreviations: ASCT =autologous stem cell transplantation; IQR =interquar tile r ange; TKI =tyrosine kinase inhibitor.
Letter to the Editor
441
© 2016 Macmillan Publishers Limited Bone Marrow Transplantation (2016) 440 –442

proliferations such as ALL and NHL have a more profound impact on
immunity than other hematological malignancies.
Since the last two decades, numerous studies have reported
that patients with reduced immunity harbor high copy numbers of
TTV in their blood. We believe that our data warrant further
investigation into the relevance of TTV-titers in patients under-
going HSCT. TTV-titers may complement current tests used to
assess the patient’s immunity. Furthermore, TTV allowed to
propagate in patients without sufficient adaptive immunity will
still be tracked by toll-like receptor 9 on cells of the innate
immune system and drive proinflammatory cytokine production
15
that may contribute to the severity of GvHD. This would make this
‘non-pathogenic’virus in patients with reduced immunity much
less innocuous in patients undergoing HSCT.
CONFLICT OF INTEREST
The authors declare no conflict of interest.
ACKNOWLEDGEMENTS
ER is supported by grants of the Swiss National Science Foundation and of the Swiss
Cancer Research foundation.
S Masouridi-Levrat
1
, A Pradier
2
, F Simonetta
1
, L Kaiser
3
,
Y Chalandon
1
and E Roosnek
2
1
Stem Cell Transplant Team, Division of Hematology, Geneva
University Hospital, Geneva, Switzerland;
2
Division of Hematology, Geneva University Hospital and Geneva
Medical School, Geneva, Switzerland and
3
Division of Infectious Diseases, Laboratory of Virology and
Division of Laboratory Medicine, University Hospital of Geneva,
Geneva, Switzerland
E-mail: eddy.roosnek@unige.ch
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Letter to the Editor
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Bone Marrow Transplantation (2016) 440 –442 © 2016 Macmillan Publishers Limited