Polyclonal anti-thymocyte globulins for the prophylaxis of graft-versus-host disease after allogeneic stem cell or bone marrow transplantation in adults

Higher cyclosporine-A concentration increases the risk of relapse in AML following allogeneic stem cell transplantation from unrelated donors using anti-thymocyte globulin

Cyclosporine-A (CsA) is used to prevent acute graft-versus-host disease (aGvHD). European Society for Blood and Marrow transplantation (EBMT) recommends a CsA target serum concentration of 200-300 µg/L during the first month after allogeneic hematopoietic stem cell transplantation (HSCT). With this study, we investigated whether a median CsA concentration > 200 µg/L (CsAhigh) the first month after HSCT, compared to ≤ 200 µg/L (CsAlow), increased the relapse risk of acute myloid leukemia (AML), using unrelated donors (URD) and antithymocyte globulin (ATG). Data was collected from 157 patients with AML, transplanted 2010-2016. The cumulative incidence of relapse (CIR) at 60 months was 50% in the CsAhigh versus 32% in the CsAlow group (p = 0.016). In univariate analysis, CsAhigh versus CsAlow (p = 0.028), 10-unit increase of CsA as a continuous variable (p = 0.017) and high risk disease (p = 0.003) were associated with higher CIR. The results remained after adjusting for disease risk. Death following relapse occurred more frequently in the CsAhigh group (p = 0.0076). There were no significant differences in rates of aGvHD, chronic GvHD (cGvHD), EBV/CMV-infections or overall survival (OS) between the two groups. In conclusion, we found that a median CsA concentration > 200 µg/L, the first month after HSCT, results in higher CIR of AML when combined with ATG.

Polyclonal anti-thymocyte globulins for the prophylaxis of graft-versus-host disease after allogeneic stem cell or bone marrow transplantation in adults

BACKGROUND

Allogeneic haematopoietic stem cell transplantation (SCT) is an established treatment for many malignant and non-malignant haematological disorders. Graft-versus-host disease (GVHD), a condition frequently occurring after an allogeneic SCT, is the result of host tissues being attacked by donor immune cells. It affects more than half of the patients after transplant either as acute and or chronic GVHD. One strategy for the prevention of GVHD is the administration of anti-thymocyte globulins (ATGs), a set of polyclonal antibodies directed against a variety of immune cell epitopes, leading to immunosuppression and immunomodulation.

OBJECTIVES

To assess the effect of ATG used for the prevention of GVHD in patients undergoing allogeneic SCT with regard to overall survival, incidence and severity of acute and chronic GVHD, incidence of relapse, non-relapse mortality, graft failure and adverse events.

SEARCH METHODS

For this update we searched the CENTRAL, MEDLINE, Embase, trial registers and conference proceedings on the 18th November 2022 along with reference checking and contacting study authors to identify additional studies. We did not apply language restrictions.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) investigating the impact of ATG on GVHD prophylaxis in adults suffering from haematological diseases and undergoing allogeneic SCT. The selection criteria were modified from the previous version of this review. Paediatric studies and studies where patients aged < 18 years constituted more than 20 % of the total number were excluded. Treatment arms had to differ only in the addition of ATG to the standard GVHD prophylaxis regimen.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by the Cochrane Collaboration for data collection, extraction and analyses.

MAIN RESULTS

For this update we included seven new RCTs, leading to a total of ten studies investigating 1413 participants. All patients had a haematological condition which warranted an allogeneic SCT. The risk of bias was estimated as low for seven and unclear for three studies. ATG probably has little or no influence on overall survival (HR (hazard ratio) 0.93 (95 % confidence interval (CI) 0.77 to 1.13, nine studies, n = 1249, moderate-certainty evidence)). Estimated absolute effect: 430 surviving people per 1000 people not receiving ATG compared to 456 people surviving per 1000 people receiving the intervention (95 % CI 385 to 522 per 1000 people). ATG results in a reduction in acute GVHD II to IV with relative risk (RR) 0.68 (95 % CI 0.60 to 0.79, 10 studies, n = 1413, high-certainty evidence). Estimated absolute effect: 418 acute GVHD II to IV per 1000 people not receiving ATG compared to 285 per 1000 people receiving the intervention (95 % CI 251 to 331 per 1000 people). Addition of ATG results in a reduction of overall chronic GvHD with a RR of 0.53 (95 % CI 0.45 to 0.61, eight studies, n = 1273, high-certainty evidence). Estimated absolute effect: 506 chronic GVHD per 1000 people not receiving ATG compared to 268 per 1000 people receiving the intervention (95 % CI 228 to 369 per 1000 people). Further data on severe acute GVHD and extensive chronic GVHD are available in the manuscript. ATG probably slightly increases the incidence of relapse with a RR of 1.21 (95 % CI 0.99 to 1.49, eight studies,  n =1315, moderate-certainty evidence). Non relapse mortality is probably slightly or not affected by ATG with an HR of 0.86 (95 % CI 0.67 to 1.11, nine studies, n=1370, moderate-certainty evidence).   ATG prophylaxis may result in no increase in graft failure with a RR of 1.55 (95 % CI 0.54 to 4.44, eight studies, n = 1240, low-certainty evidence).  Adverse events could not be analysed due to the serious heterogeneity in the reporting between the studies, which limited comparability (moderate-certainty evidence) and are reported in a descriptive manner.   Subgroup analyses on ATG types, doses and donor type are available in the manuscript.

AUTHORS' CONCLUSIONS

This systematic review suggests that the addition of ATG during allogeneic SCT probably has little or no influence on overall survival. ATG results in a reduction in the incidence and severity of acute and chronic GvHD. ATG intervention probably slightly increases the incidence of relapse and probably does not affect the non relapse mortality. Graft failure may not be affected by ATG prophylaxis. Analysis of data on adverse events was reported in a narrative manner. A limitation for the analysis was the imprecision in reporting between the studies thereby reducing the confidence in the certainty of evidence.

Reduced risk of chronic GVHD by low-dose rATG in adult matched sibling donor peripheral blood stem cell transplantation for hematologic malignancies

The optimal rabbit anti-thymocyte globulin (rATG) graft-versus-host disease (GVHD) prophylaxis regimen in matched sibling donor peripheral blood stem cell transplantation (MSD-PBSCT) remains to be elucidated. In this prospective study, we used low-dose rATG for GVHD prophylaxis in patients or donors aged ≥ 40 years with hematological malignancies receiving MSD-PBSCT. rATG was administered to 40 patients at an intravenous dose of 5 mg/kg divided over day 5 and day 4 before graft infusion. No graft failure occurred. Median times to leukocyte engraftment and platelet engraftment were 11.0 days and 13.9 days. The cumulative incidence of grades 2–4 and grades 3–4 acute GVHD at day +100 was 30.0% and 2.6%. The 2-year cumulative incidence of extensive chronic GVHD and severe chronic GVHD was 11.4% and 14.7%. 93.5% (29/31) of patients had discontinued immunosuppressive medication within 3 years after transplantation. The 2-year cumulative incidence of transplant-related mortality (TRM) and relapse was 14.0% and 22.6%. The cumulative incidence of cytomegalovirus reactivation, Epstein–Barr virus reactivation, and fungal infection was 22.3%, 12.9%, and 12.5%. Kaplan–Meier estimates for overall survival, disease-free survival, and GVHD-free and relapse-free survival 3 years after transplantation were 68.9%, 68.9%, and 54.0%. rATG for GVHD prophylaxis is tolerable and efficacious at a 5 mg/kg total dose administered over 2 days (days −5 to −4) in patients receiving allogeneic MSD-PBSCT.

Acute Graft-Versus-Host Disease: A Brief Review

Graft‐versus‐host disease (GvHD) is an important complication that can be observed after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Acute GvHD (aGvHD) is seen after allo-HSCT and the incidence of aGvHD is around 30%-50%. aGvHD prophylaxis is essential in patients undergoing allo-HSCT. Initial therapy for aGvHD is steroids. Prognosis is poor in aGvHD patients not responding to steroids. In this article, the pathobiology, clinical findings, prophylaxis, and treatment of aGvHD will be summarized.

B Cell Reconstitution and Influencing Factors After Hematopoietic Stem Cell Transplantation in Children

B cell reconstitution after hematopoietic stem cell transplantation (HSCT) is variable and influenced by different patient, donor, and treatment related factors. In this review we describe B cell reconstitution after pediatric allogeneic HST, including the kinetics of reconstitution of the different B cell subsets and the development of the B cell repertoire, and discuss the influencing factors. Observational studies show important roles for stem cell source, conditioning regimen, and graft vs. host disease in B cell reconstitution. In addition, B cell recovery can play an important role in post-transplant infections and vaccine responses to encapsulated bacteria, such as pneumococcus. A substantial number of patients experience impaired B cell function and/or dependency on Ig substitution after allogeneic HSCT. The underlying mechanisms are largely unresolved. The integrated aspects of B cell recovery after HSCT, especially BCR repertoire reconstitution, are awaiting further investigation using modern techniques in order to gain more insight into B cell reconstitution and to develop strategies to improve humoral immunity after allogeneic HSCT.

A cure-rate model for Q-learning: Estimating an adaptive immunosuppressant treatment strategy for allogeneic hematopoietic cell transplant patients

Cancers treated by transplantation are often curative, but immunosuppressive drugs are required to prevent and (if needed) to treat graft-versus-host disease. Estimation of an optimal adaptive treatment strategy when treatment at either one of two stages of treatment may lead to a cure has not yet been considered. Using a sample of 9563 patients treated for blood and bone cancers by allogeneic hematopoietic cell transplantation drawn from the Center for Blood and Marrow Transplant Research database, we provide a case study of a novel approach to Q-learning for survival data in the presence of a potentially curative treatment, and demonstrate the results differ substantially from an implementation of Q-learning that fails to account for the cure-rate.

The Role of Anti-Thymocyte Globulin or Alemtuzumab-Based Serotherapy in the Prophylaxis and Management of Graft-Versus-Host Disease

Allogeneic hematopoietic stem cell transplant is an established treatment modality for hematologic and non-hematologic diseases. However, it is associated with acute and long-term sequelae which can translate into mortality. Graft-versus-host disease (GVHD) remains a glaring obstacle, especially with the advent of reduced-intensity conditioning. Serotherapy capitalizes on antibodies which target T cells and other immune cells to mitigate this effect. This article focuses on the utility of two such agents: anti-thymocyte globulin (ATG) and alemtuzumab. ATG has demonstrated benefit in prophylaxis against GVHD, especially in the chronic presentation. However, there is limited impact of ATG on overall survival and it has little utility in the treatment context. There may be an initial improvement, particularly in skin manifestations, but no substantial benefit has been elicited. Alemtuzumab has shown benefit in both prophylaxis and treatment of GVHD, but at the consequence of a more profound immunosuppressive phase, mandating aggressive viral prophylaxis. There remains heterogeneity in the doses and regimens of the agents, with no standardized protocol in place. Furthermore, it seems that once steroid-refractory GVHD has been established, there is little that can be offered to offset the ultimately dismal outcome. Here we present a systematic overview of ATG- or alemtuzumab-based serotherapy in the prophylaxis and management of GVHD.

Immune reconstitution and outcomes after conditioning with anti-thymocyte-globulin in unrelated cord blood transplantation; the good, the bad, and the ugly

Unrelated umbilical cord blood transplantation (UCBT) exhibits a low risk of graft-versus-host-disease (GvHD) and has unique potent anti-virus and anti-leukemia effects. Anti-thymocyte globulin (ATG) in the conditioning regimen for UCBT is successful in reducing graft rejection and GvHD. Nevertheless, this beneficial effect of ATG coincides with its detrimental effect on immune reconstitution. The latter directly relates to a high incidence of viral infections and leukemia relapses. ATG has been used in transplant patients for over 30 years. In recent years, the knowledge on the mechanisms of action of ATG and its implementation in the UCBT setting has increased dramatically. Important data became available showing the highly variable pharmacokinetics (PK) of ATG and its consequence on outcome measures. Here, we review the effects of ATG on immune reconstitution and subsequent outcomes after UCBT, and describe the mechanisms causing these effects. We highlight the importance of optimizing ATG exposure before and after UCBT and discuss strategies to maintain the 'good' and overcome the 'bad and ugly' effects of ATG on UCBT outcome.

Pharmacokinetics, Pharmacodynamics, and Pharmacogenomics of Immunosuppressants in Allogeneic Hematopoietic Cell Transplantation: Part II

Part I of this article included a pertinent review of allogeneic hematopoietic cell transplantation (alloHCT), the role of postgraft immunosuppression in alloHCT, and the pharmacokinetics, pharmacodynamics, and pharmacogenomics of the calcineurin inhibitors and methotrexate. In this article (Part II), we review the pharmacokinetics, pharmacodynamics, and pharmacogenomics of mycophenolic acid (MPA), sirolimus, and the antithymocyte globulins (ATG). We then discuss target concentration intervention (TCI) of these postgraft immunosuppressants in alloHCT patients, with a focus on current evidence for TCI and on how TCI may improve clinical management in these patients. Currently, TCI using trough concentrations is conducted for sirolimus in alloHCT patients. Several studies demonstrate that MPA plasma exposure is associated with clinical outcomes, with an increasing number of alloHCT patients needing TCI of MPA. Compared with MPA, there are fewer pharmacokinetic/dynamic studies of rabbit ATG and horse ATG in alloHCT patients. Future pharmacokinetic/dynamic research of postgraft immunosuppressants should include '-omics'-based tools: pharmacogenomics may be used to gain an improved understanding of the covariates influencing pharmacokinetics as well as proteomics and metabolomics as novel methods to elucidate pharmacodynamic responses.

Reduced platelet transfusions and earlier platelet engraftment using alemtuzumab-based conditioning regimen in allogeneic stem cell transplantation

PURPOSE

In patients undergoing allogeneic stem cell transplantation, conditioning regimens containing alemtuzumab instead of anti-thymocyte globulin (ATG) may result in an earlier platelet engraftment and a reduced number of platelet transfusions.

METHODS

We performed a retrospective, single-center, case-control study analyzing time to engraftment and transfusion needs using alemtuzumab in comparison with ATG as part of conditioning protocol.

RESULTS

Median values for time to platelet engraftment, number of transfused platelet concentrates and number of transfused red cell concentrates were 12 versus 19.5 days (p < 0.001), 2 versus 14 (p < 0.001) and 6 versus 14.5 (p = 0.003) in the alemtuzumab and ATG group. Time to leukocyte engraftment did not differ with median 15 days in both groups. Patients in the ATG group showed a significant higher decrease in platelet count during conditioning (68 vs. 29 %, p = 0.001), leading to significant lower median platelet counts at the day of stem cell infusion (38 vs. 95.5 Gpt/l, p = 0.008), and higher values for median C-reactive protein after first antibody infusion (69.0 vs. 43.6 mg/l, p = 0.001) compared with alemtuzumab group. Test for significance was done by using Wilcoxon rank-sum test. Subgroup analysis considering the type of ATG used (Thymoglobulin vs. ATG Fresenius) revealed that differences between alemtuzumab and ATG group were more due to effects of ATG Fresenius than Thymoglobulin.

CONCLUSIONS

The use of alemtuzumab in comparison with ATG as part of the conditioning regimen may be an approach to reduce the number of transfused platelet and red cell concentrates after allogeneic stem cell transplantation.

Population pharmacokinetic modeling of Thymoglobulin(®) in children receiving allogeneic-hematopoietic cell transplantation: towards improved survival through individualized dosing

BACKGROUND AND OBJECTIVES

To prevent graft-versus-host disease and rejection in hematopoietic cell transplantation (HCT), children receive Thymoglobulin(®), a polyclonal antibody acting mainly by depleting T cells. The therapeutic window is critical as over-exposure may result in delayed immune reconstitution of donor T cells. In this study, we describe the population pharmacokinetics of Thymoglobulin(®) as a first step towards an evidence-based dosing regimen of Thymoglobulin(®) in pediatric HCT.

METHODS

Serum active Thymoglobulin(®) concentrations were measured in all pediatric HCTs performed between 2004 and 2012 in two pediatric HCT centers in The Netherlands. Population pharmacokinetic analysis was performed using NONMEM(®) version 7.2.

RESULTS

A total of 3,113 concentration samples from 280 pediatric HCTs were analyzed, with age ranging from 3 months to 23 years old. The cumulative Thymoglobulin(®) dose was 10 mg/kg in 94 % of the patients given in 4 consecutive days. A model incorporating parallel linear and concentration-dependent clearance of Thymoglobulin(®) was identified. Body weight [for linear clearance (CL) and central volume of distribution] as well as lymphocyte count pre-Thymoglobulin(®) infusion (for CL) were important covariates. As such, the current dosing regimen results in higher exposure in children with a higher bodyweight and/or a lower lymphocyte count pre-Thymoglobulin(®) infusion.

CONCLUSION

This model can be used to develop an individual dosing regimen for Thymoglobulin(®), based on both body weight and lymphocyte counts, once the therapeutic window has been determined. This individualized regimen may contribute to a better immune reconstitution and thus outcome of allogeneic HCT.

Intestinal Blautia Is Associated with Reduced Death from Graft-versus-Host Disease

The relationship between intestinal microbiota composition and acute graft-versus-host disease (GVHD) after allogeneic blood/marrow transplantation (allo-BMT) is not well understood. Intestinal bacteria have long been thought to contribute to GVHD pathophysiology, but recent animal studies in nontransplant settings have found that anti-inflammatory effects are mediated by certain subpopulations of intestinal commensals. Hypothesizing that a more nuanced relationship may exist between the intestinal bacteria and GVHD, we evaluated the fecal bacterial composition of 64 patients 12 days after BMT. We found that increased bacterial diversity was associated with reduced GVHD-related mortality. Furthermore, harboring increased amounts of bacteria belonging to the genus Blautia was associated with reduced GVHD lethality in this cohort and was confirmed in another independent cohort of 51 patients from the same institution. Blautia abundance was also associated with improved overall survival. We evaluated the abundance of Blautia with respect to clinical factors and found that loss of Blautia was associated with treatment with antibiotics that inhibit anaerobic bacteria and receiving total parenteral nutrition for longer durations. We conclude that increased abundance of commensal bacteria belonging to the Blautia genus is associated with reduced lethal GVHD and improved overall survival.

Successful desensitization of a patient with aplastic anemia to antithymocyte globulin

Antithymocyte globulin (ATG) is a polyclonal gamma immunoglobulin derived from either rabbit or equine serum that serves as therapy for aplastic anemia; however, ATG causes serum sickness in up to 70% and anaphylaxis in up to 5% of recipients. Intradermal (ID) skin testing has been the primary technique used to evaluate for a preexisting Gell and Coombs type I hypersensitivity reaction to ATG. There are no data reporting the predictive value of delayed reactions to ID testing on the risk of serum sickness. This study was designed to establish the importance of epicutaneous and ID skin testing before the administration of ATG through a case report and literature discussion. We report a patient with severe aplastic anemia that was successfully desensitized to ATG after a negative epicutaneous skin test and positive ID skin test. The patient had neither systemic nor localized reactions during the desensitization. Desensitization to ATG in patients with positive epicutaneous skin testing has been shown to be associated with serious and potentially life-threatening complications and should only be considered when the benefits outweigh the risks. Epicutaneous skin testing should be considered in conjunction with ID skin testing when screening for potential sensitivity to ATG. Because of the serious risk of anaphylaxis, desensitization should be performed in an intensive care unit setting in conjunction with a physician familiar with drug desensitization and the management of anaphylaxis.

Graft-versus-host disease prophylaxis after transplantation: a network meta-analysis

BACKGROUND

Graft-versus-host Disease (GvHD) prophylaxis after allogeneic hematopoietic stem-cell transplantation (HSCT) is an ongoing effort but relative effects of different policies are not systematically explored.

METHODS

We systematically reviewed 30-year evidence on GvHD prophylaxis and quantified the relative effect of different policies using a network meta-analysis. We searched PubMed and the Cochrane Library for randomized studies on the topic. The primary outcome of interest was grade II-IV acute GvHD over 0 or I (with odds ratio OR <1 denoting benefit).

FINDINGS

Thirty-three eligible studies that enrolled 3,440 patients (published up to June 2014), provided data on seven immunosuppressive drugs namely cyclosporin A (CsA), methotrexate (MTX), anti-thymocyte globulin (ATG), mycophenolate mofetil (MMF), tacrolimus, sirolimus or corticosteroids and their combinations to calculate 14 direct and 21 indirect effects. The majority of trials (32/33) referred to myeloablative conditioning and sibling transplants (25/33). Tacrolimus/MTX (OR 0.44; 95% 0.27-0.70, number needed to treat to benefit, i.e. to avert a case of II-IV GvHD, NNTB = 5) and ATG/CsA/MTX (OR 0.45; 95%CI 0.26-0.78; NNTB = 5) were superior over CsA/MTX. ATG/CsA/MTX did not differ from tacrolimus/MTX (indirect evidence). Sirolimus-based prophylaxis outperformed CsA/MTX (OR 0.10; 95%CI 0.02-0.49, NNTB = 4) and marginally outperformed tacrolimus/MTX (OR 0.22; 95%CI 0.05-1.11). Add-on corticosteroids had no benefit over CsA/MTX.

CONCLUSIONS

Tacrolimus/MTX and ATG/CsA/MTX were the outperformers over CsA/MTX, but sirolimus-based regimens showed also potential. More randomized data are needed for reduced-intensity conditioning, as well as for MMF and sirolimus-containing regimens.

Population pharmacokinetic/dynamic model of lymphosuppression after fludarabine administration

PURPOSE

Quantitative relationships between 9-β-D-arabinofuranosyl-2-fluoroadenine (F-ara-A) concentrations and lymphosuppression have not been reported, but would be useful for regimen design. A population pharmacokinetic/pharmacodynamic model was constructed in this study using data from 41 hematopoietic cell transplant (HCT) recipients conditioned with busulfan in combination with fludarabine (total dose 120 mg/m², Protocol 1519) or with fludarabine (total dose 250 mg/m²) with rabbit antithymocyte globulin (rATG, Protocol 2041).

METHODS

Individual pharmacokinetic parameters were fixed to post hoc Bayesian estimates, and circulating absolute lymphocyte counts (ALC) were obtained during the 3 weeks prior to graft infusion. A semi-physiological cell-kill model with three lymphocyte transit compartments was applied and aptly characterized the time course of suppression of circulating ALC by fludarabine administration. Drug- and system-specific parameters were estimated using a maximum likelihood expectation maximization algorithm, and the final model was qualified using an internal visual predictive check.

RESULTS

The final model successfully characterized the time course and variability in ALC. Pharmacodynamic parameters exhibited considerable between subject variability (38.9-211 %). The HCT protocol was the only covariate associated with the pharmacodynamic parameters, specifically the lymphocyte kill rate, the transit rate between lymphocyte compartments, and the baseline ALC.

CONCLUSIONS

This model can be used to simulate the degree of lymphosuppression for design of future fludarabine-based conditioning regimens.

The biology of graft-versus-host disease: experimental systems instructing clinical practice

The last 6 decades have seen major advances in the understanding of immunologic diseases, driven by preclinical animal models. Indeed, bone marrow transplantation (BMT) has its genesis in rodent models dating back to the 1950s. Allogeneic BMT and its major complication, graft-versus-host disease (GVHD), represent a paradigm for the translation of preclinical concepts into clinical practice. The appreciation that GVHD can be thought of as a stepwise escalation in immune activation characterized by eventual massive target tissue apoptosis has allowed the design of rational approaches to better manage patients. Here, we describe the pathophysiology of GVHD as defined in preclinical models, focusing on the successes and failures of this research to instruct and translate clinical practice. We also provide a commentary on the limitations of these models so that they may be better appreciated and addressed in future studies. Notable preclinical successes include the definition of modern immune suppression, reductions in conditioning intensity, posttransplant cyclophosphamide, and the promotion of regulatory T-cell reconstitution. New strategies including naïve T-cell depletion, focused cytokine and chemokine inhibition, and the blockade of costimulation now also appear highly promising and very likely to translate into patients in the near future.

Rabbit antithymocyte globulin induces rapid expansion of effector memory CD8 T cells without accelerating acute graft versus host disease

Rabbit antithymocyte globulin (Thymoglobulin(®)) is commonly used as graft-versus-host disease (GvHD) prophylaxis. Since we found similar total CD8 T cell numbers in patients with and without Thymoglobulin(®) therapy within the first six months after allogeneic hematopoietic stem cell transplantation, we have analyzed the reconstitution of the CD8 T cell compartment in detail. After T cell-depletion, higher and more sustained proliferative capacity of memory CD8 T cells resulted in their rapid expansion, whereas the fraction of naive CD8 T cells decreased. Importantly, this shift towards effector memory CD8 T cells did not accelerate the incidence of GvHD.