Prevalence and risk factors of antibodies to human leukocyte antigens in haploidentical stem cell transplantation candidates: A multi-center study

Donor-derived anti-HLA antibodies in a haploidentical hematopoietic cell transplant recipient shortly after transplant

A pediatric patient with acute myeloid leukemia was referred to our institution for investigational therapy after disease relapse following a mismatched unrelated donor hematopoietic cell transplant (HCT). Prior to second HCT, the patient's serum was negative for antibodies to class I and class II HLA. Eight days after receiving a maternal donor haploidentical transplant, the patient became platelet refractory and highly sensitized to multiple class I HLA. Serum from the patient's mother was positive for the strongest antibodies present in the patient, suggesting the antibodies were donor-derived. Patient sera showed magnified and expanded sensitization over time in the context of 100% donor chimerism and despite undetectable circulating B cells. Escalating sensitization suggests active transfer of rituximab-resistant antibody-producing passenger lymphocytes from a haploidentical donor to a transplant recipient at the time of progenitor cell infusion. Evaluation of donor sensitization status may be a consideration prior to HLA mismatched HCT.

The Role of Pre-existing Anti-HLA Antibodies in Severe Aplastic Anemia Patients Undergoing Allogenic Hematopoietic Stem Cell Transplantation

The objective is to underscore the significance of pre-existing anti-HLA Abs in the context of allogeneic hematopoietic stem cell transplantation (allo-HSCT) for SAA. A retrospective analysis was conducted using data from 244 SAA patients who underwent allo-HSCT between January 2016 and October 2022. The patient cohort was divided into 2 groups based on the presence of pre-existing anti-HLA Abs. Out of 244 SAA patients, 82 were tested positive for anti-HLA Abs. Seventeen patients were tested with DSA in haplo-HSCT. We found that the presence of pre-existing anti-HLA Abs did not influence neutrophil engraftment (P = .600); however, it resulted in delayed platelet recovery (P = .006). Comparatively, patients with anti-HLA Abs demonstrated lower overall survival (OS) compared to their counter parts without anti-HLA Abs (P = .001), with a correspondingly elevated transplant-related mortality (TRM) in the former group (P = .002). Multivariate analysis established pre-existing anti-HLA Abs as an independent risk factor for impaired platelet recovery (HR 1.67, 95% CI 1.16 to 2.44, P = .006) and OS (HR 2.19, 95% CI 1.03 to 4.67, P = .043). However, there were no differences between DSA and non-DSA patients after desensitization in haplo-HSCT. In summary, the presence of pre-existing anti-HLA Abs in SAA patients undergoing allo-HSCT appears to detrimentally affect platelet recovery and overall prognosis.

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.

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.

[Incidence and clinical significance of platelet transfusion refractoriness after allogeneic hematopoietic stem cell transplantation in patients with chronic myelomonocytic leukemia]

Objective: To retrospectively analyze the incidence and clinical significance of platelet transfusion refractoriness (PTR) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) in patients with chronic myelomonocytic leukemia (CMML) . Methods: A cohort of 55 CMML patients received allo-HSCT at Peking University Institute of Hematology during 2004-2021 were retrospectively assessed. The incidence of PTR within 30 days after allo-HSCT was retrospectively analyzed, and the impact on clinical outcomes and bleeding event were compared between patients with platelet transfusion refractoriness (PTR) or effective platelet transfusion (EPT) . Results: The incidence of PTR after allo-HSCT in CMML patients was 25.5% (14/55) . PTR patients had a lower rate of platelet engraftment than EPT patients (28.6% vs 100%) , and the median time of engraftment was 67 (33-144) days and 21 (9-157) days respectively (P<0.010) . There was no significant difference between two groups in acute graft-versus-host disease (aGVHD) and chronic graft-versus-host disease (cGVHD) (P=0.183, P=0.455) . After following-up a median of 684 (24-3978) days, the 1-year overall survival (OS) and 1-year leukemia free survival (LFS) in PTR and EPT patients were (35.4±13.9) % vs (75.1±7.8) % (P=0.037) and (28.1±13.3) % vs (65.3±8.2) % (P=0.072) , respectively. The transplant-related mortality (TRM) were (48.2±2.4) % and (9.0±0.25) %, respectively (P=0.009) . Bleeding events occurred in five patients (35.7%) of PTR and 2 patients (4.9%) of EPT (P=0.009) . Conclusion: In CMML patients with allo-HSCT, the incidence of PTR is 25.5%, which was associated with delayed platelet engraftment, increased bleeding events, inferior OS and increased TRM.

Prevalence and risk factors of antibodies to HLA according to different cut-off values of mean fluorescence intensity in haploidentical allograft candidates: A prospective study of 3805 subjects

The importance of anti-HLA antibodies in transplantation settings, such as HLA-mismatched or haploidentical hematopoietic stem cell transplantation and platelet refractoriness, is widely recognized. In previous reports, it was mentioned that several cut-off values of donor-specific anti-HLA antibodies mean fluorescence intensity (MFI) were related to graft rejection in the environment of HLA mismatched stem cell transplantation and the aim of this study was to investigate the prevalence and risk factors of anti-HLA antibodies according to those cut-off values of MFI. A total of 3805 patients with hematologic disease were prospectively enrolled and analyzed. When using MFI of anti-HLA antibodies ≥500, ≥1000, ≥1500, ≥2000, ≥5000, and ≥ 10,000 as cut-off values for positivity, the prevalence of class I or II anti-HLA antibodies ranged from 4.6% to 20.2% in all cases. When the MFI cut-off value was ≥500 for positivity, multivariate analysis indicated that platelet transfusion, underlying disease, and pregnancy were the most important risk factors for the presence of anti-HLA antibodies for the total patients. Subgroup analysis according to age, gender, and underlying disease showed that pregnancy was the most important risk factor for the presence of anti-HLA antibodies. For all patients (n = 3805), when anti-HLA antibody positivity was defined according to different MFI cut-off values, including ≥1000, ≥1500, ≥2000, ≥5000, and ≥ 10,000, an association of platelet transfusion and pregnancy with anti-HLA antibodies was also demonstrated. Our results suggest that pregnancy and platelet transfusion are the main risk factors for the prevalence of anti-HLA antibodies in haploid allograft candidates, providing evidence for guiding the evaluation of anti-HLA antibodies and helping donor selection for HLA-mismatched transplant candidates.

HLA Homozygosity and Likelihood of Sensitization in Kidney Transplant Candidates

Background.

Homozygosity for HLAs has been associated with adverse outcomes after viral infection as well as pregnancy-induced HLA sensitization. We sought to assess the relationship between HLA locus homozygosity and the level of HLA antibody sensitization.

Methods.

We measured sensitization using the calculated panel reactive antibody value for a large cohort of 147 461 patients added to the US OPTN/United Network for Organ Sharing kidney transplant waitlist between December 2014 and December 2019. We used multinomial logistic modeling to compare 62 510 sensitized patients to 84 955 unsensitized controls.

Results.

We found that the number of homozygous HLA loci was strongly associated with the level of sensitization. Within mildly, highly, or extremely sensitized candidates, women displayed a higher relative abundance of HLA homozygosity at multiple HLA loci as compared with men, with attenuation of this effect in Black candidates. In a multivariable logistic model, the number of homozygous HLA loci interacted with female sex but not with other factors associated with sensitization, including recipient ethnicity and a history of prior kidney transplant.

Conclusions.

This study shows that HLA homozygosity is an innate genetic factor that affects the likelihood of HLA sensitization. Further research is needed to identify the immunologic mechanisms that underlie this observation.

Transfusions in Aplastic Anemia Patients Cause HLA Alloimmunization: Comparisons of Current and Past Cohorts Demonstrate Progress

Transfusions are the mainstay of supportive therapy in patients with aplastic anemia (AA) and may lead to anti- HLA alloimmunization, thereby also increasing the risk for donor-specific antibodies in the setting of HLA-mismatched transplantation. Historically, AA patients were thought to be at particularly high risk for HLA alloimmunization. In past decades, blood product manufacturing (leukoreduction) and HLA antibody testing have improved significantly by single antigen bead (SAB) technology. It is currently unknown how those developments have impacted HLA alloimmunization and treatment outcome in patients with AA. We retrospectively investigated 54 AA patients treated by immunosuppressive therapy or allogeneic hematopoietic cell transplantation after the introduction of the SAB assay at our center. We compared the HLA antibody results to a historical AA cohort (n = 26), treated before introduction of leukoreduced blood products from 1975 to 1995. HLA alloimmunization was detected in 43 of 54 (80%) recently treated patients. Past pregnancy, female gender, disease severity, age, and a history of other transfusions were significantly associated with a larger number or higher intensity (mean fluorescence intensity) of HLA antibodies. Treatment outcome including bleeding episodes, response to treatment, engraftment, graft-versus-host disease, and overall survival was not associated with HLA alloimmunization. In the historical cohort a significantly higher number of HLA antibodies (P < .01) with a higher mean fluorescent intensity (P < .01) was observed. HLA alloimmunization remains frequent in AA tested by current techniques, but it has significantly decreased since prior decades and does not affect treatment outcome. © 2021 American Society for Blood and Marrow Transplantation. Published by Elsevier Inc. All rights reserved.

Prevalence and risk factors of having antibodies to class I and II human leukocyte antigens in older haploidentical allograft candidates

The effect of donor-specific anti-human leukocyte antigen (HLA) antibodies (DSAs) has been recognized as a factor in graft failure (GF) in patients who underwent umbilical cord blood transplantation (UBT), matched unrelated donor transplantation (MUDT), or haploidentical stem cell transplantation (haplo-SCT). Presently, we know little about the prevalence of and risk factors for having anti-HLA antibodies among older transplant candidates. Therefore, we analyzed 273 older patients with hematologic disease who were waiting for haplo-SCT. Among all patients, 73 (26.7%) patients had a positive panel-reactive antibody (PRA) result for class I, 38 (13.9%) for class II, and 32 (11.7%) for both. Multivariate analysis showed that females were at a higher risk for having a PRA result for class II (P = 0.001) and for having antibodies against HLA-C and HLA-DQ. Prior pregnancy was a risk factor for having a PRA result for class I (P < 0.001) and for having antibodies against HLA-A, HLA-B and HLA-DQ. Platelet transfusions were risk factors for the following: having a positive PRA result for class I (P = 0.014) and class II (P < 0.001); having antibodies against HLA-A, HLA-B, HLA-C, HLA-DP, HLA-DQ, and HLA-DR; and having higher mean fluorescence intensity (MFI) of PRA for class I (P = 0.042). In addition, previous total transfusions were at high risk for having higher numbers of antibodies to specific HLA loci (P = 0.005), and disease course (7.5 months or more) (P = 0.020) were related to higher MFI of PRAs for class I. Our findings indicated that female sex, prior pregnancy, platelet transfusions and disease courses are independent risk factors for older patients with hematologic disease for having anti-HLA antibodies, which could guide anti-HLA antibody monitoring and be helpful for donor selection.