Kidney allograft rejection is associated with an imbalance of B cells, regulatory T cells and differentiated CD28-CD8+ T cells: analysis of a cohort of 1095 graft biopsies.

Introduction: The human immune system contains cells with either effector/memory or regulatory functions. Besides the well-established CD4+CD25hiCD127lo regulatory T cells (Tregs), we and others have shown that B cells can also have regulatory functions since their frequency and number are increased in kidney graft tolerance and B cell depletion as induction therapy may lead to acute rejection. On the other hand, we have shown that CD28-CD8+ T cells represent a subpopulation with potent effector/memory functions. In the current study, we tested the hypothesis that kidney allograft rejection may be linked to an imbalance of effector/memory and regulatory immune cells. Methods: Based on a large cohort of more than 1000 kidney graft biopsies with concomitant peripheral blood lymphocyte phenotyping, we investigated the association between kidney graft rejection and the percentage and absolute number of circulating B cells, Tregs, as well as the ratio of B cells to CD28-CD8+ T cells and the ratio of CD28-CD8+ T cells to Tregs. Kidney graft biopsies were interpreted according to the Banff classification and divided into 5 biopsies groups: 1) normal/subnormal, 2) interstitial fibrosis and tubular atrophy grade 2/3 (IFTA), 3) antibody-mediated rejection (ABMR), 4) T cell mediated-rejection (TCMR), and 5) borderline rejection. We compared group 1 with the other groups as well as with a combined group 3, 4, and 5 (rejection of all types) using multivariable linear mixed models. Results and discussion: We found that compared to normal/subnormal biopsies, rejection of all types was marginally associated with a decrease in the percentage of circulating B cells (p=0.06) and significantly associated with an increase in the ratio of CD28-CD8+ T cells to Tregs (p=0.01). Moreover, ABMR, TCMR (p=0.007), and rejection of all types (p=0.0003) were significantly associated with a decrease in the ratio of B cells to CD28-CD8+ T cells compared to normal/subnormal biopsies. Taken together, our results show that kidney allograft rejection is associated with an imbalance between immune cells with effector/memory functions and those with regulatory properties.

Case Report: Long-term observations from the tacrolimus weaning randomized clinical trial depicts the challenging aspects for determination of low-immunological risk patients.

Whilst calcineurin inhibitors (CNI) are the cornerstone of immunosuppressive maintenance therapy in kidney transplantation, several studies have investigated the safety of CNI withdrawal in order to avoid their numerous side effects. In this context, we performed several years ago a clinical randomized trial evaluating CNI weaning in stable kidney transplant recipients without anti-HLA immunization. The trial was interrupted prematurely due to a high number of de novo DSA (dnDSA) and biopsy proven acute rejection (BPAR) in patients who underwent tacrolimus weaning, resulting in treatment for rejection and resumption of tacrolimus. We report here the long-term outcomes of patients included in this clinical trial. Ten years after randomization, all patients are alive with a functional allograft. They all receive tacrolimus therapy except one with recurrent cutaneous neoplasia issues. Long-term eGFR was comparable between patients of the two randomized groups (46.4 ml/min vs 42.8 ml/min). All dnDSA that occurred during the study period became non-detectable and all rejections episodes were reversed. The retrospective assessment of HLA DQ single molecule epitope mismatching determined that a majority of patients who developed dnDSA after tacrolimus withdrawal would have been considered at high immunological risk. Minimization of immunosuppression remains a challenging objective, mainly because of the issues to properly select very low immunological risk patients. Valuable improvements have been made the last decade regarding evaluation of the allograft rejection notably through the determination of numerous at-risk biomarkers. However, even if the impact of such tools still need to be clarify in clinical routine, they may permit an improvement in patients' selection for immunosuppression minimization without increasing the risk of allograft rejection.

Antibody-mediated allograft rejection is associated with an increase in peripheral differentiated CD28-CD8+ T cells - Analyses of a cohort of 1032 kidney transplant recipients.

BACKGROUND: CD28-CD8+ T cells represent a differentiated CD8+ T cell subset that is found to be increased in various conditions associated with chronic antigenic stimulation such as aging, chronic viral infections, autoimmune diseases, cancers, and allotransplantation. METHODS: Using multivariate models, we analyzed a large cohort of 1032 kidney transplant patients in whom 1495 kidney graft biopsies were performed concomitant with a peripheral blood leukocyte phenotyping by flow cytometry. We investigated the association between the level of CD28-CD8+ T cells in the blood and the diagnosis of graft rejection according to the recent Banff classification of renal allograft pathology. FINDINGS: We found that antibody-mediated rejection (ABMR) was associated with a significant increase in the percentage as well as the absolute number of CD28-CD8+ T cells in the peripheral blood of kidney transplant patients at the time of biopsy. The confounder-adjusted mean difference of log percentage and log absolute value between the ABMR group and the normal/subnormal histology group were 0.29 (p=0.0004) and 0.38 (p=0.0004), respectively. Moreover, we showed that CD28-CD8+ T cells from the patients diagnosed with ABMR responded more rigorously to TCR and FcγRIIIA (CD16) engagement compared to their CD28+ counterparts as evidenced by an increase in the expression of IFNγ, TNFα, and CD107a. INTERPRETATION: Collectively, our data suggest that differentiated CD28-CD8+ T cells, with increased frequency, number, and function, may participate in the pathobiology of ABMR. Further studies are warranted to clarify the immunological role of this T cell subset in kidney graft rejection. FUNDING: Agence nationale de la recherche (France).

The MHC class I MICA gene is a histocompatibility antigen in kidney transplantation.

The identity of histocompatibility loci, besides human leukocyte antigen (HLA), remains elusive. The major histocompatibility complex (MHC) class I MICA gene is a candidate histocompatibility locus. Here, we investigate its role in a French multicenter cohort of 1,356 kidney transplants. MICA mismatches were associated with decreased graft survival (hazard ratio (HR), 2.12; 95% confidence interval (CI): 1.45-3.11; P < 0.001). Both before and after transplantation anti-MICA donor-specific antibodies (DSA) were strongly associated with increased antibody-mediated rejection (ABMR) (HR, 3.79; 95% CI: 1.94-7.39; P < 0.001; HR, 9.92; 95% CI: 7.43-13.20; P < 0.001, respectively). This effect was synergetic with that of anti-HLA DSA before and after transplantation (HR, 25.68; 95% CI: 3.31-199.41; P = 0.002; HR, 82.67; 95% CI: 33.67-202.97; P < 0.001, respectively). De novo-developed anti-MICA DSA were the most harmful because they were also associated with reduced graft survival (HR, 1.29; 95% CI: 1.05-1.58; P = 0.014). Finally, the damaging effect of anti-MICA DSA on graft survival was confirmed in an independent cohort of 168 patients with ABMR (HR, 1.71; 95% CI: 1.02-2.86; P = 0.041). In conclusion, assessment of MICA matching and immunization for the identification of patients at high risk for transplant rejection and loss is warranted.

Occurrence of De novo Donor-Specific Antibodies After COVID-19 in Kidney Transplant Recipients Is Low Despite Immunosuppression Modulation.

Introduction: Decreased immunosuppression has been proposed for kidney transplant recipients infected with coronavirus disease 2019 (COVID-19), but the impact on the alloreactive immune response during and after infection has been poorly investigated. We evaluated the occurrence of antihuman leukocyte antigen (HLA) donor-specific antibodies (DSAs) (post-COVID-19) and rejection episodes after COVID-19 with particular focus on immunosuppression modulation. Methods: Kidney transplant recipients from 2 French institutions had anti-HLA antibody screening before and after COVID-19. Management of immunosuppression, rejection episodes, COVID-19 severity, inflammatory markers, and antiviral therapies were recorded. Results: From 251 recruited patients, 72 were excluded because of COVID-19-related death (n = 25) and incomplete immunologic follow-up (n = 47). Among the remaining 179 included patients, almost half were hospitalized (49.2%). Antimetabolites were interrupted in 47% of patients (82% in hospitalized, median time of resumption of 23 days and in 15% nonhospitalized, median time of resumption of 7 days). Calcineurin inhibitors were interrupted in 12% of patients (all hospitalized, median time of resumption of 11 days). The incidence of post-COVID-19 DSA was 4% (8% and 0% in hospitalized and nonhospitalized, respectively). Allograft rejection occurred in 3 patients (1.7%) and all were hospitalized. Younger age, transplantation <1 year, and preexisting DSA were more frequently observed in patients with post-COVID-19 DSA, whereas inflammatory markers, lymphopenia, and use of antiviral therapies were not. Conclusion: The incidence of post-COVID-19 DSA among COVID-19-positive kidney transplant recipients was low (4%) despite a significant decrease in immunosuppression and was mainly restricted to high-risk immunologic patient's status. COVID-19 severity was not associated with post-COVID-19 DSA and/or rejection.

HLA-EPI: A new EPIsode in exploring donor/recipient epitopic compatibilities.

The HLA system plays a pivotal role both in transplantation and immunology. While classical HLA genotypes matching is made at the allelic level, recent progresses were developed to explore antibody-antigen recognition by studying epitopes. Donor to recipient matching at the epitopic level is becoming a trending topic in the transplantation research field because anti-HLA antibodies are epitope-specific rather than allele-specific. Indeed, different HLA alleles often share common epitopes. We present the HLA-Epi tool (hla.univ-nantes.fr) to study an HLA genotype at the epitope level. Using the international HLA epitope registry (Epregistry.com.br) as a reference, we developed HLA-Epi to easily determine epitopic and allelic compatibility levels between several HLA genotypes. The epitope database covers the most common HLA alleles (N = 2976 HLA alleles), representing more than 99% of the total observed frequency of HLA alleles. The freely accessible web tool HLA-Epi calculates an epitopic mismatch load between different sets of potential recipient-donor pairs at different resolution levels. We have characterized the epitopic mismatches distribution in a cohort of more than 10,000 kidney transplanted pairs from European ancestry, which showed low number of epitopic mismatches: 56.9 incompatibilities on average. HLA-Epi allows the exploration of epitope pairing matching to better understand epitopes contribution to immune responses regulation, particularly during transplantation. This free and ready-to-use bioinformatics tool not only addresses limitations of other related tools, but also offers a cost-efficient and reproducible strategy to analyze HLA epitopes as an alternative to HLA allele compatibility. In the future, this could improve sensitization prevention for allograft allocation decisions and reduce the risk of alloreactivity.

[Relevance of antibodies in hematopoietic stem cell transplantation: Antibodies anti-HLA, anti-platelets, anti-granulocytes, anti-erythrocytes and anti-MICA. Guidelines from the Francophone Society of Bone Marrow Transplantation and Cellular Therapy (SFGM-TC)]. / Importance des anticorps dans la prise en charge de la greffe de cellules souches hématopoïétiques : anticorps anti-HLA, anti-plaquettes, anti-granuleux, anti-érythrocytes et anti-MICA. Recommandations de la Société francophone de greffe de moelle et de thérapie cellulaire (SFGM-TC).

The presence of allo-antibodies in the serum of a recipient awaiting hematopoietic stem cell transplantation (HSCT) may have an impact on transfusion efficiency and/or donor choice, especially in the absence of an identical sibling donor. Prior to transplantation, donor specific anti-HLA (Human Leukocyte Antigen) antibodies (DSA) have a recognized effect on transplant outcome, correlated with the increasing MFI value and with the ability of such antibody to fix the complement fraction. Anti-platelet antibodies (anti-HLA class I and anti-HPA [Human Platelet Antigen]) are better involved in transfusion inefficiency and can be responsible for refractory status. ABO incompatibilities require a specific treatment of the graft in presence of high titer to avoid hemolytic adverse effects. Investigations of these antibodies should be carried out on a regular basis in order to establish appropriate transfusion recommendation, select an alternative donor when possible or adapt the source of cells. After transplantation, in case of delayed recovery or graft rejection, long term aplasia, persistent mixed chimerism or late release, and after elimination of the main clinical causes, a biological assessment targeted on the different type of antibodies will have to be performed in order to orient towards the cause or the appropriate therapy. Further studies should be carried out to determine the impact of anti-MICA antibodies and recipient specific anti-HLA antibodies, on the outcome of the transplantation.

Terminally Differentiated Effector Memory CD8+ T Cells Identify Kidney Transplant Recipients at High Risk of Graft Failure.

BACKGROUND: Identifying biomarkers to predict kidney transplant failure and to define new therapeutic targets requires more comprehensive understanding of the immune response to chronic allogeneic stimulation. METHODS: We investigated the frequency and function of CD8+ T cell subsets-including effector memory (EM) and terminally differentiated EM (TEMRA) CD8+ T cells-in blood samples from 284 kidney transplant recipients recruited 1 year post-transplant and followed for a median of 8.3 years. We also analyzed CD8+ T cell reactivity to donor-specific PBMCs in 24 patients who had received living-donor kidney transplants. RESULTS: Increased frequency of circulating TEMRA CD8+ T cells at 1 year post-transplant associated with increased risk of graft failure during follow-up. This association remained after adjustment for a previously reported composite of eight clinical variables, the Kidney Transplant Failure Score. In contrast, increased frequency of EM CD8+ T cells associated with reduced risk of graft failure. A distinct TEMRA CD8+ T cell subpopulation was identified that was characterized by expression of FcγRIIIA (CD16) and by high levels of proinflammatory cytokine secretion and cytotoxic activity. Although donor-specific stimulation induced a similar rapid, early response in EM and TEMRA CD8+ T cells, CD16 engagement resulted in selective activation of TEMRA CD8+ T cells, which mediated antibody-dependent cytotoxicity. CONCLUSIONS: At 1 year post-transplant, the composition of memory CD8+ T cell subsets in blood improved prediction of 8-year kidney transplant failure compared with a clinical-variables score alone. A subpopulation of TEMRA CD8+ T cells displays a novel dual mechanism of activation mediated by engagement of the T-cell receptor or of CD16. These findings suggest that TEMRA CD8+ T cells play a pivotal role in humoral and cellular rejection and reveal the potential value of memory CD8+ T cell monitoring for predicting risk of kidney transplant failure.

Tacrolimus- versus sirolimus-based immunosuppression after simultaneous pancreas and kidney transplantation: 5-year results of a randomized trial.

Tacrolimus, the cornerstone immunosuppression after simultaneous pancreas and -kidney (SPK) transplantation, may exert nephrotoxic and diabetogenic effects. We therefore prospectively compared in an open-label, randomized, monocentric, 5-year follow-up study, a tacrolimus- and a sirolimus-based immunosuppressive regimen. Randomization using the block method allowing a blind allocation was done at the time of surgery. All patients received anti-thymocyte globulin and maintenance therapy with tacrolimus, mycophenolate mofetil, and steroids. At month 3, tacrolimus was continued or replaced by sirolimus. The primary endpoint was kidney and pancreas graft survival at 1 and 5 years. Fifty patients were included in the final analysis in each group. At 1 year, differences for kidney and pancreas graft survival between sirolimus and tacrolimus were 0% (90% confidence interval -4.61% to 4.61%) and 6% (90% confidence interval -6.32% to 18.32%), respectively. There was no difference in renal and pancreas graft survival at 5 years. Thirty-four patients (68%) in the sirolimus group vs three (6%) in the tacrolimus group needed definitive withdrawal of the study drug. Despite noninferiority of sirolimus compared to tacrolimus for kidney and pancreas graft survival, the high rate of sirolimus discontinuation does not favor its use as cornerstone therapy after SPK transplantation (NCT00693446).

[Haploidentical hematopoietic stem cell transplant: How to choose the best donor? Guidelines from the Francophone Society of Bone Marrow Transplantation and Cellular Therapy (SFGM-TC)]. / Greffe de cellules souches hématopoïétiques haplo-identiques avec cyclophosphamide en post-greffe : comment choisir le meilleur donneur en 2019 ? Recommandations de la Société francophone de greffe de mœlle et de thérapie cellulaire (SFGM-TC).

Haploidentical hematopoietic stem cell transplantation has been growing steadily since 2012. The SFGM-TC has twice published guidelines concerning T-cell repleted haploidentical grafts with high dose cyclophosphamide post-transplantation. The 2013 workshop recommended using the non-myeloablative Baltimore protocol with bone marrow and developed prospective protocols to evaluate these transplantations. The 2015 workshop reported improved results of reduced conditioning regimens in Hodgkin's lymphoma and intensive conditioning in myeloid hemopathies, and a similar outcome with 10/10 HLA matched donor with the same disease-risk score thus raising the question of the qualifier "alternative" for haploidentical transplants. The current work concerns the criteria for selecting the donor. The main criterion remains the absence of anti-HLA antibodies directed against the donor present in the recipient sera (DSA - Donor Specific Antibodies). In case of DSA and in the absence of an alternative donor, desensitization protocols exist. The other criteria are impossible to prioritize: age, sex, CMV, and blood type. The degree of relatedness and the number of HLA incompatibilities do not seem to be a criterion of choice. The 'ideal' donor would be a young man, CMV-matched, without major ABO incompatibility with a marrow transplant. There is insufficient data for the KIR-ligand and NIMA/NIPA mismatch. Peripheral stem cell grafts appear to yield more acute GVHD than bone marrow grafts after intensive conditioning, but with comparable survival rates. Based on the literature review, the comparison of haploidentical with unrelated donors encourages inclusion in existing national protocols randomizing these different donors.

CXCR5+PD1+ICOS+ Circulating T Follicular Helpers Are Associated With de novo Donor-Specific Antibodies After Renal Transplantation.

Donor-specific anti-HLA antibodies (DSAs) are a major risk factor associated with renal allograft outcomes. As a trigger of B cell antibody production, T follicular helper cells (Tfhs) promote DSA appearance. Herein, we evaluated whether circulating Tfhs (cTfhs) are associated with the genesis of antibody-mediated rejection. We measured cTfh levels on the day of transplantation and 1 year after transplantation in blood from a prospective cohort of 237 renal transplantation patients without DSA during the first year post-transplantation. Total cTfhs were characterized as CD4+CD45RA-CXCR5+, and the three following subsets of activated cTfh were analyzed: CXCR5+PD1+, CXCR5+PD1+ICOS+, an CXCR5+PD1+CXCR3-. Immunizing events (previous blood transfusion and/or pregnancy) and the presence of class II anti-HLA antibodies were associated with increased frequencies of activated CXCR5+PD1+, CXCR5+PD1+ICOS+, and CXCR5+PD1+CXCR3- cTfh subsets. In addition, ATG-depleting induction and calcineurin inhibitor treatments were associated with a relative increase of activated cTfh subsets frequencies at 1 year post-transplantation. In multivariate survival analysis, we reported that a decrease in activated CXCR5+PD1+ICOS+ at 1 year after transplantation in the blood of DSA-free patients was significantly associated with the risk of developing de novo DSA after the first year (p = 0.018, HR = 0.39), independently of HLA mismatches (p = 0.003, HR = 3.79). These results highlight the importance of monitoring activated Tfhs in patients early after transplantation and show that current treatments cannot provide early, efficient prevention of Tfh activation and migration. These findings indicate the need to develop innovative treatments to specifically target Tfhs to prevent DSA appearance in renal transplantation.

HLA-DRB3/4/5 mismatches are associated with increased risk of acute GVHD in 10/10 matched unrelated donor hematopoietic cell transplantation.

Matching for HLA-A, -B, -C, and -DRB1 loci (8/8 match) is currently the gold standard for unrelated donor hematopoietic cell transplantation (HCT). In Europe, patients are also matched at the HLA-DQB1 loci (10/10 match). However, there is increasing evidence that matching at HLA-DRB3/4/5 loci may help to lower transplant-related morbidity and mortality. We therefore investigated the impact of HLA-DRB3/4/5 mismatches on outcomes in 1975 patients who received a first 10/10 matched unrelated donor (MUD) HCT in France from 2000 to 2012 for a hematological malignancy. High-resolution typing was performed at HLA-A, -B, -C, -DRB1, -DQB1, -DPB1, and -DRB3/4/5 loci for all donor/recipient pairs. Compared with DRB3/4/5-matched pairs, patients who received a MUD HCT from a DRB3/4/5 mismatched donor had a significantly increased risk of grade II-IV acute graft-versus-host disease (aGVHD) (Adjusted Hazard Ratio (HR) 1.43 (1.07 to 1.90)) associated with lower graft-versus-host disease-free and relapse-free survival (GRFS) (Adjusted HR 1.20 (1.02 to 1.42)). Conversely, we observed no differences in terms of chronic GVHD, nonrelapse mortality, relapse and overall survival. However, we believe that patients stand to benefit from DRB3/4/5 loci being considered for unrelated donor selection to improve GRFS and then quality of life after unrelated HCT.

[Polymorphism in HLA and KIR genes and the impact on hematopoietic stem cell transplantation outcomes and unrelated donor selection: Guidelines from the Francophone Society of Bone Marrow Transplantation and Cellular Therapy (SFGM-TC)]. / Polymorphisme des gènes HLA et KIR et l'impact sur le devenir de la greffe et le choix du donneur non apparenté de cellules souche hématopoïétiques : recommandations de la Société francophone de greffe de moelle et de thérapie cellulaire (SFGM-TC).

In an attempt to harmonize clinical practices among French hematopoietic stem cell transplantation centers, the Francophone Society of Bone Marrow Transplantation and Cellular Therapy (SFGM-TC) held its sixth annual workshop series in September 2015 in Lille. This event brought together practitioners from across the country with the purpose of offering careful analysis of published studies on clinical practice issues that remain to be disputed. This article addresses the impact of HLA and KIR gene polymorphism on the outcome of the transplantation in order to optimize unrelated donor selection.

Fetal and neonatal alloimmune thrombocytopenia: predictive factors of intracranial hemorrhage.

BACKGROUND: In Caucasians, fetal/neonatal alloimmune thrombocytopenia (FNAIT) is most frequently caused by maternal alloimmunization against the human platelet antigen HPA-1a. The most serious complication of severe FNAIT is intracranial hemorrhage (ICH). ICH mainly occurs in utero; therefore, there is a need to identify noninvasive predictive factors of ICH to facilitate early identification of this condition and to determine response to maternal therapy. STUDY DESIGN AND METHODS: We studied gynecologic and immunogenetic variables of severe cases of anti-HPA-1a FNAIT within three groups: Group I, FNAIT without ICH; Group II, FNAIT with ICH; and Group III, suspected FNAIT cases without detectable maternal anti-HPA-1a alloantibodies. RESULTS: ICH was associated with a poor outcome because it led to death in 59% of cases. Multigravida (two or more pregnancies) was overrepresented in Group II, consistent with the high concentrations of maternal HPA-1a alloantibody and the frequent detection of a strong newborn-specific HLA class I antibody response at delivery. The proportion of HLA-DRB4*01:01P (*01:01 or *01:03) women was similar in Groups I and II, but this allele was overrepresented in Group III, in which FNAIT was less severe than in the other two groups. Finally, antenatal intravenous immunoglobulin therapy tended to be more effective in HLA-DRB3*01:01(+)/HLA-DRB4*01:01P(+) women than for HLA-DRB3*01:01(+)/HLA-DRB4*01:01P(-) women. CONCLUSION: The number of gestations is a predictive factor of ICH in anti-HPA-1a-alloimmunized women. Maternal immunogenetic variables should be investigated in the context of maternal immunization and may predict response to maternal therapy in subsequent pregnancies.

Donor Immunization Against Human Leukocyte Class II Antigens is a Risk Factor for Graft-versus-Host Disease.

The sensitization to HLA antigens is caused mainly by pregnancy and transfusions; however, anti-HLA antibodies also may be detected in nulliparous females and nontransfused males, and thus specifically in hematopoietic stem cell transplantation (HSCT) donors. In such cases, the impact on HSCT outcome is known only for platelet transfusion refractoriness. This study addresses the impact on graft-versus-host disease (GVHD) of anti-HLA antibodies detected in voluntary unrelated donors. Among 100 donor/recipient (D/R) pairs, 33 and 82 showed at least 1 HLA class I and class II mismatch, respectively. Because class II mismatches were more frequent, we focused our detection on anti-class II antibodies, using the Luminex assay. Among 82 HLA class II mismatched D/R pairs, 26 donors (32%) had at least 1 anti-HLA class II antibody detected in peripheral blood. Recipients of a graft from an anti-class II immunized donor had a higher cumulative incidence for a first episode of either acute or chronic GVHD (2- year cumulative incidence, 88% versus 67%; P = .03), which was confirmed in multivariate analysis (hazard ratio, 1.7; P = .04). In particular, according to the National Institutes of Health classification scheme, the cumulative incidence of chronic GVHD was higher in recipients of immunized donors (multivariate hazard ratio, 2.5; P = .02). Identifying specificities of anti-class II antibodies revealed that 13 of 26 alloimmunized donors had recipient-specific antibodies, directed mainly against mismatched HLA-DPB1 alleles. Donor-derived anti-HLA antibodies could be detected in recipients up to at least 6 months post-HSCT, supporting their association with chronic GVHD. Donor immunization against foreign HLA antigens is a new parameter to predict the occurrence of GVHD after HSCT from HLA-mismatched unrelated donors.