Donor specific HLA antibody in hematopoietic stem cell transplantation: Implications for donor selection

The use of haploidentical stem cell transplant as an alternative donor source in patients with decreased access to matched unrelated donors

INTRODUCTION

The likelihood of finding HLA-matched unrelated donors for rare HLA types and non-white European ancestry continues to be a challenge with less than a 70% chance of finding a full match. Mismatched transplants continue to have high rates of transplant-related mortality. With the near-universal ability to find a haploidentical donor in families, haploidentical transplants have become of more critical importance in ethnic minority groups and patients with rare HLA types.

METHODS

Data was collected through clinical trials, review articles, and case reports published in the National Library of Medicine.

RESULTS

The use of improved lymphodepleting conditioning regimens, graft versus host disease (GVHD) prophylaxis using regimens such as post-transplant cyclophosphamide, mycophenolate, and tacrolimus have improved engraftment to nearly 100 percent and reduced transplant-related mortality to less than 20 percent. Attention to donor-specific antibodies (DSAs) with interventions using bortezomib, rituximab, and plasmapheresis has decreased graft failure rates.

CONCLUSION

With improved prevention of GVHD with interventions such as post-transplant cyclophosphamide and management of DSAs, haploidentical transplants continue to improve transplant-related mortality (TRM) compared to patients who received matched-related donor transplants. While TRM continues to improve, ongoing research with haploidentical transplants will focus on improving graft and donor immunosuppression and identifying the best regimens to improve TRM without compromising relapse-free survival.

Uniform Graft-versus-Host Disease Prophylaxis using Post-Transplantation Cyclophosphamide, Methotrexate, and Cyclosporine following Peripheral Blood Hematopoietic Stem Cell Transplantation from Matched and Haploidentical Donors for Transfusion-Dependent Thalassemia: A Retrospective Report from the Bone Marrow Failure Working Group of Hunan Province, China

Although the survival of patients with transfusion-dependent thalassemia (TD-TM) is reportedly inferior after haploidentical hematopoietic stem cell transplantation (HSCT), the heterogeneity of transplantation approaches in studies suggests the need to assess the effect of conditioning regimen on matched and haploidentical transplantation outcomes. A novel post-transplantation cyclophosphamide (PTCy)-based approach for patients with TD-TM undergoing haploidentical HSCT was reported in our prior study. Here we aimed to retrospectively evaluate the real-world efficacy and safety of graft-versus-host disease (GVHD) prophylaxis in patients with TD-TM after HSCT from matched donors and haploidentical donors (HIDs). In this retrospective multicenter study, among 238 patients with TD-TM who underwent HSCT, 160 underwent peripheral blood HSCT, using uniform GVHD prophylaxis with PTCy, methotrexate, and cyclosporine, at member centers of the Bone Marrow Failure Working Group of Hunan Province between 2019 and 2023. The median age of the cohort at transplantation was 6 years (95% confidence interval [CI], 6 to 7 years). The 160 donors included 99 (61.9%) haploidentical family members, 13 matched sibling donors, and 48 matched or mismatched unrelated donors. The engraftment rate was 98.8% (95% CI, 96.1% to 97.7%). HSCT from HIDs had a lower risk of mixed chimerism (HR, .078; P = .022). Within 100 days after transplantation, 31 patients (19.6%; 95% CI, 14.0% to 26.3%) had grade II-IV acute GVHD (aGVHD), 9 of whom had grade III-IV aGVHD (5.7%; 95% CI, 2.9% to 10.1%). HIDs were significantly associated with a higher risk of grade II-IV aGVHD (HR, 3.973; P = .009). Nineteen patients (11.9%; 95% CI, 7.6% to 17.6%) developed late aGVHD after a median of 516 days (95% CI, 407 to 709 days). Twenty-six patients (16.5%; 95% CI, 11.3% to 22.8%) exhibited any 1 of the diagnostic, distinctive, or atypical features of chronic GVHD (cGVHD) according to the 2014 National Institutes of Health (NIH) criteria after a median of 690 days (95% CI, 496 to 902 days). Among these 26 patients, 7 had NIH-defined cGVHD, 14 had only 1 distinctive sign with no histologic evidence, and 5 had only atypical cGVHD signs. Of the 26 patients, 5 were classified with overlap syndrome. Of 21 patients classified with NIH-defined and potential cGVHD, 3 had moderate cGVHD and 1 had severe cGVHD. Logistic regression analyses identified that grade II-IV aGVHD independently predicted subsequent cGVHD (HR, 3.920; P = .006). The rates of cGVHD were similar in the matched donor and HID groups. Thalassemia-free survival (TFS) and event-free survival (EFS) were 97.5% (95% CI, 94.2% to 99.2%) and 90.6% (95% CI, 85.4% to 94.4%), respectively, after a median of 690 days (95% CI, 496 to 902 days). TFS rates were similar in the matched donor and HID groups (P = .549). The EFS rate was significantly higher in the matched donor group compared to the HID group (P = .033). Our study suggests that when PTCy-based uniform GVHD prophylaxis is administered, HSCT from matched donors and HIDs results in a low incidence of severe GVHD and treatment-related mortality with satisfactory survival.

Desensitization Strategies for Donor-Specific Antibodies in HLA-Mismatched Stem Cell Transplantation Recipients: What We Know and What We Do Not Know

In human leukocyte antigen (HLA)-mismatched allogeneic stem cell transplantation settings, donor-specific anti-HLA antibodies (DSAs) can independently lead to graft failure, including both primary graft rejection and primary poor graft function. Although several strategies, such as plasma exchange, intravenous immunoglobulin, rituximab, and bortezomib, have been used for DSA desensitization, the effectiveness of desensitization and transplantation outcomes in some patients remain unsatisfactory. In this review, we summarized recent research on the prevalence of anti-HLA antibodies and the underlying mechanism of DSAs in the pathogenesis of graft failure. We mainly focused on desensitization strategies for DSAs, especially novel methods that are being investigated in the preclinical stage and those with promising outcomes after preliminary clinical application.

A simple predictor for donor-specific anti-HLA antibody desensitisation in haploidentical haematopoietic stem cell transplantation

Donor-specific HLA antibody (DSA) has been recognised as an independent risk factor for graft failure in patients undergoing haploidentical haematopoietic stem cell transplantation (HID HSCT). Therapeutic plasma exchange (TPE), as a first-line strategy for DSA desensitisation, can promptly reduce serum DSA levels. This study aimed to investigate DSA characteristics and identify a biomarker predicting the efficacy of DSA desensitisation in patients proceeding to HID HSCT. We retrospectively enrolled 32 patients with DSA from April 2021 to January 2024, and analysed the mean fluorescence intensity (MFI) value of DSA at the different time points of desensitisation treatment. Compared with baseline DSA level before TPE, the median MFI of HLA class I DSA was reduced from 8178.6 to 795.3 (p < 0.001), and HLA class II DSA decreased from 6210.9 to 808.8 (p < 0.001) after TPE. The DSA level in 1:16 diluted pre-TPE serum correlated well with DSA value in post-TPE serum (class I, r = 0.85, p < 0.0001; class II, r = 0.94, p < 0.0001), predicting TPE efficacy in 84.4% of patients. Based on the degree of DSA reduction after TPE, patients were divided into complete responders (decreased by >70%), partial responders (decreased by 30 to 70%) and non-responders (decreased by <30%) and the percentages were 43.8%, 25% and 31.2%, respectively. Non-responders receiving aggressive immunotherapy had longer overall survival compared to those receiving standard strategies (p < 0.05). The 1:16 diluted pre-TPE serum may predict the efficacy of TPE and allow for more rational immunotherapy strategy for patients with DSA proceeding to HID HSCT.

Advances in hematopoietic stem cells ex vivo expansion associated with bone marrow niche

Hematopoietic stem cells (HSCs) are an ideal source for the treatment of many hematological diseases and malignancies, as well as diseases of other systems, because of their two important features, self-renewal and multipotential differentiation, which have the ability to rebuild the blood system and immune system of the body. However, so far, the insufficient number of available HSCs, whether from bone marrow (BM), mobilized peripheral blood or umbilical cord blood, is still the main restricting factor for the clinical application. Therefore, strategies to expand HSCs numbers and maintain HSCs functions through ex vivo culture are urgently required. In this review, we outline the basic biology characteristics of HSCs, and focus on the regulatory factors in BM niche affecting the functions of HSCs. Then, we introduce several representative strategies used for HSCs from these three sources ex vivo expansion associated with BM niche. These findings have deepened our understanding of the mechanisms by which HSCs balance self-renewal and differentiation and provided a theoretical basis for the efficient clinical HSCs expansion.

Transfusion Support in Hematopoietic Stem Cell Transplantation: A Contemporary Narrative Review

Hematopoietic stem cell transplantation (HSCT) is a cornerstone of modern medical practice, and can only be performed safely and effectively with appropriate transfusion medicine support. Patients undergoing HSCT often develop therapy-related cytopenia, necessitating differing blood product requirements in the pre-, peri-, and post-transplant periods. Moreover, ensuring optimal management for patients alloimmunized to human leukocyte antigens (HLA) and/or red blood cell (RBC) antigens, as well as for patients receiving ABO-incompatible transplants, requires close collaboration with transfusion medicine and blood bank professionals. Finally, as updated transfusion guidelines and novel blood product modifications emerge, the options available to the transplant practitioner continue to expand. Herein, we detail contemporary blood transfusion and transfusion medicine practices for patients undergoing HSCT.

Discovery of three HLA-DQB1*03:01:01 variants: HLA-DQB1*03:01:01:54, -DQB1*03:01:01:56 and -DQB1*03:01:01:58

Three nucleotide substitutions in intronic regions give rise to the novel alleles: HLA-DQB1*03:01:01:54, -DQB1*03:01:01:56, -DQB1*03:01:01:58.

Incidence and Role of Recipient-Specific Antibodies in Allogeneic Hematopoietic Cell Transplantation from Mismatched Related Donors

High titer of donor-specific antibodies (DSAs) increases the risk of graft rejection after mismatched related hematopoietic cell transplantation (HCT). There are no data regarding the incidence of anti-HLA recipient-specific antibodies (RSAs) and their role after transplantation. Here we aimed to identify the incidence of RSAs in a mismatched related hematopoietic cell donor population and their possible impact on immune-mediated complications, such as acute graft-versus-host disease (aGVHD), and complications resulting from endothelial injury, such as transplantation-associated thrombotic microangiopathy (TA-TMA) and veno-occlusive disease (VOD). We prospectively analyzed the incidence of anti-HLA antibodies in 28 mismatched related pairs of recipients and their donors who underwent HCT at our center between 2020 and 2022. In positive samples screened for anti-HLA class I and/or II antibodies, the specificity of the HLA antibodies was analyzed. All recipients had a hematologic malignancy and received a myeloablative conditioning regimen and immunosuppression consisting of post-transplantation cyclophosphamide, tacrolimus, and mycophenolate mofetil. Patients were tested for TA-TMA and aGVHD development during routine post-transplantation visits up to 100 days post-transplantation. We used modified Jodele criteria for TA-TMA diagnosis, and based aGVHD grading on the MAGIC criteria. VOD was assessed using the European Society for Blood and Marrow Transplantation. Anti-HLA antibodies were detected in 12 donors (43%) and in 9 recipients (32%). There were no significant differences between donors and recipients according to age (median, 42 years [range, 17 to 69 years] versus 39 years [range, 8 to 68 years]), sex, or pregnancy history. No transfusion history was noted in the donor group (P < .05). RSA antibodies were present more often than DSAs and were detected in 9 out of 12 (75%) anti-HLA-positive donors and in only 2 out of 9 (22%) recipients, respectively (P < .05). During the follow-up, 11 patients (39%) developed aGVHD, including grade I-II in 9 (32%) and grade III-IV in 2 (7%). Twelve patients (43%) met the criteria for TA-TMA, and only 1 patient (3.5%) was diagnosed with VOD by day 100 post-HCT. RSAs were detected significantly more often in the TA-TMA group; among 12 patients diagnosed with TA-TMA, 7 (58%) had RSAs (P < .05). We did not find a correlation between RSAs and aGVHD. The patient with VOD did not have an RSA-positive donor. There was no difference in membrane attack complex (MAC) concentration in the RSA-positive group on day 30 and day 60 post-HCT; however, there was a trend toward higher MAC concentration in the RSA-positive group on day 100 (median, 912 ng/mL [range, 788 to 1120 ng/mL] versus 616 ng/mL [range, 352 to 1244 ng/mL]; P = .055). Patients with RSA suffered more often from platelet and red blood cell decreases or transfusion refractoriness, and increased lactate dehydrogenase activity was observed in all RSA-positive cases. The donor immune status and the presence of RSA may be associated with higher rates of TA-TMA in mismatched HCT recipients. Antibody-mediated complement activation might be an additional factor influencing TA-TMA occurrence.

HLA diversity in ethnic populations can affect detection of donor-specific antibodies by single antigen beads

Introduction

In solid-organ transplantation, human leukocyte antigen (HLA) donor-specific antibodies (DSA) are strongly associated with graft rejection, graft loss, and patient death. The predominant tests used for detecting HLA DSA before and after solid-organ transplantation are HLA single antigen bead (SAB) assays. However, SAB assays may not detect antibodies directed against HLA epitopes that are not represented in the SAB. The prevalence and potential impact of unrepresented HLA epitopes are expected to vary by ethnicity, but have not been thoroughly investigated. To address this knowledge gap, HLA allele frequencies from seven ethnic populations were compared with HLA proteins present in SAB products from two manufacturers to determine unrepresented HLA proteins.

Materials

Allele frequencies were obtained from the Common, Intermediate, and Well Documented HLA catalog v3.0, and frequencies of unrepresented HLA types were calculated. Next-generation sequencing was used to determine HLA types of 60 deceased solid-organ donors, and results were used to determine if their HLA-A, -B, -C, and -DRB1 proteins were not present in SAB reagents from two vendors. Unrepresented HLA proteins were compared with the most similar protein in SAB assays from either vendor and then visualized using modeling software to assess potential HLA epitopes.

Results

For the seven ethnic populations, 0.5% to 11.8% of each population had HLA proteins not included in SAB assays from one vendor. Non-European populations had greater numbers of unrepresented alleles. Among the deceased donors, 26.7% (16/60) had at least one unrepresented HLA-A, -B, -C, or -DRB1 protein. Structural modeling demonstrated that a subset of these had potential HLA epitopes that are solvent accessible amino acid mismatches and are likely to be accessible to B cell receptors.

Discussion

In conclusion, SAB assays cannot completely rule out the presence of HLA DSA. HLA epitopes not represented in those assays vary by ethnicity and should not be overlooked, especially in non-European populations. Allele-level HLA typing can help determine the potential for HLA antibodies that could evade detection.

Antibody-mediated pathogenesis of chronic GVHD through DBY/HLA class II complexes and induction of a GVL effect

Chronic graft-versus-host disease (cGVHD) is a multiorgan syndrome with clinical features resembling those of autoimmune diseases. Thus, understanding commonalities in the pathophysiology of cGVHD and autoimmune diseases, such as the presence of disease-risk HLA alleles, is imperative for developing novel therapies against cGVHD. Alloantibodies against H-Y antigens encoded on the Y-chromosome are well-described risk factors for cGVHD in female-to-male transplantation. However, because H-Y antigens generally localize intracellularly in the male reproductive organs, how they emerge at affected organ levels remains elusive. Here, by analyzing nationwide registry data stratified per donor-recipient sex, we identified specific HLA class II alleles that contributed to susceptibility to male cGVHD after transplantation from HLA-identical female siblings (HLA-DRB1∗15:02: hazard ratio, 1.28; 95% confidence interval, 1.03-1.58; P = .025). Coexpression of HLA-DRB1∗15:02 efficiently transported full-length H-Y antigens, especially DBY, to the surface. The presence of alloantibodies against DBY/HLA class II complexes significantly predicted the occurrence of cGVHD (68.8% vs 31.7% at 1 year; P = .002). Notably, the ability of HLA class II molecules to transport and present DBY to alloantibodies was closely associated with the susceptibility of HLA class II alleles to cGVHD. DBY specifically colocalized with HLA class II molecules on the dermal vascular endothelium in cGVHD and provoked complement-dependent cytotoxicity. Moreover, these complexes were observed in some male leukemic cells. Altogether, these findings suggest that vascular endothelial cells facilitate alloantibody-mediated cGVHD and highlight that alloantibodies against DBY/HLA class II complexes could be common targets for cGVHD and a graft-versus-leukemia effect.

Applying Rituximab During the Conditioning Regimen Prevents Epstein-Barr Virus Infection Following Allogeneic Hematopoietic Stem Cell Transplant in a Children's Cohort: A Retrospective Case-Control Study

INTRODUCTION

Since hematopoietic stem cell transplant (HSCT) is an important therapy for malignant and non-malignant pediatric diseases, improving transplant-related mortality remains a challenge. Currently, rituximab, a monoclonal antibody of anti-CD20, is widely used for several post-HSCT complications. However, few studies have focused on the application of rituximab before HSCT.

METHODS

We conducted a retrospective case-control study from January 2019 to July 2021 to determine this effect in a single center. Forty-eight patients were included in the rituximab group, with a one-to-one ratio matched to the control group.

RESULTS

Both the occurrence rate and cumulative incidence rate of Epstein-Barr virus (EBV) infection were significantly lower in the rituximab group than in the without-rituximab group (10.4% vs. 33.3%, p = 0.014 and 12.2% vs. 39.3% p = 0.0026, respectively). Furthermore, without the application of rituximab was identified as a risk factor for post-HSCT EBV infection via both univariate [hazard ratio (HR) = 4.17, 95%CI (1.52-11.43), p = 0.005] and multivariate analyses [HR = 4.65, 95%CI (1.66-13.0), p = 0.003]. Although the overall survival (OS) probability of the rituximab group was comparable to the without-rituximab group, a markedly improved OS of the rituximab group was found in the malignant disease subgroup (78.9% vs. 42.1%, p = 0.032). The outcomes of graft-versus-host disease, neutrophil and platelet engraftment, other viral infections, and the reconstitution of lymphocytes showed no significant differences between the two groups.

CONCLUSIONS

The administration of rituximab before HSCT may prevent EBV infection following HSCT.

Case report: Curing a rare, unstable hemoglobin variant Hb Bristol-Alesha using haploidentical hematopoietic stem cell transplantation

Unstable hemoglobinopathies are a rare, heterogeneous group of diseases that disrupt the stability of hemoglobin (Hb), leading to chronic hemolysis and anemia. Patients with severe phenotypes often require regular blood transfusions and iron chelation therapy. Although rare, studies have reported that hematopoietic stem cell transplantation (HSCT) seems to be an available curative approach in transfusion-dependent patients with unstable hemoglobinopathies. Here, we describe successful haploidentical HSCT for the treatment of an unstable Hb variant, Hb Bristol-Alesha, in a 6-year-old boy with severe anemia since early childhood. Two years after transplantation, he had a nearly normal hemoglobin level without evidence of hemolysis. DNA analysis showed complete chimerism of the donor cell origin, confirming full engraftment with normal erythropoiesis.

High-Dose immunoglobulin Intervention as an effective and simple strategy for donor specific Anti-HLA antibody desensitization in haploidentical transplant

Donor-specific anti-HLA antibody (DSA) is a significant obstacle to successful haploidentical hematopoietic stem cell transplantation (haplo-HSCT) and is associated with poor engraftment rates. DSA strongly positive patients with a mean fluorescence intensity (MFI) over 5000 have a primary poor graft function (PGF) rate of over 60%. Currently, there is no consensus on the desensitization of DSA, and existing strategies are complex and have limited effectiveness. To address this issue, we conducted a retrospective study on 19 patients with strongly positive DSA (MFI over 5000) who underwent haplo-HSCT and were treated with intravenous immunoglobulin (IVIg)-based therapy. We also included 38 baseline-matched patients with DSA-negative as controls. Our findings revealed that the cumulative incidence of engraftment, PGF, graft-versus-host disease (GVHD), virus infection, overall survival (OS), disease-free survival (DFS), relapse, and non-relapse mortality (NRM) in the DSA strongly positive group after desensitization were comparable to those in the DSA negative group (P > 0.05). Our multivariable analysis showed that disease remission was a protective factor against PGF (P = 0.005, OR = 0.019, 95% CI 0.001-0.312). Subgroup analysis revealed that the desensitization efficacy was equal regardless of DSA type against HLA-I or II, and MFI value over 5000 or not. In conclusion, we propose a simple and effective DSA desensitization strategy based on immunoglobulin to ensure successful engraftment and improve patient prognosis.

Treatment with the combination of rituximab and intravenous γ globulin is effective in promoting engraftment in donor specific antibody positive patients receiving myeloablative conditioning haploidentical stem cell transplantation

BACKGROUND

Donor-specific anti-HLA antibodies (DSAs) are a major cause of engraftment failure in patients receiving haploidentical stem cell transplantation (HaploSCT). Effective procedures are needed for those who demand urgent transplantation and have no other donor options.

OBJECTIVE

We here retrospectively analyzed 13 patients with DSAs successfully treated with desensitization of rituximab and intravenous γ globulin prior to HaploSCT from March 2017 to July 2022.

STUDY DESIGN

All 13 patients were with DSA MFI >4000 of at least one loci before desensitization. Of the 13 patients, 10 patients were with the initial diagnosis of malignant hematological diseases, and 3 were diagnosed with aplastic anemia. Patients were treated with one (n=3) or two(n=10) doses of rituximab (375mg/m² for one dose). All patients receive the same total dose of 0.4g/kg of intravenous γ globulin (IVIg) within 72 hours before haploidentical stem cell administration to neutralize the remaining DSA.

RESULTS

All patients achieved neutrophil engraftment and 12 patients achieved primary platelet engraftment. The patient with primary platelet engraftment failure received purified CD34 positive stem cell infusion nearly 1 year after transplantation and achieved platelet engraftment thereafter. The estimated 3-year overall survival (OS) is 73.4%.

CONCLUSION

Although further studies on larger numbers of patients are needed, it is clear that the combination of IVIg and rituximab is an effective way to clear DSA and has a strong effect on promoting engraftment and survival for patients with DSA. It is a practical and adaptable combination of treatment options.