HLA polymorphisms and risk of red blood cell alloimmunisation in polytransfused patients with sickle cell anaemia

Association between HLA-DRB1*04, HLA-DQB1*03, and HLA-DQB1*06 with alloimmunization in transfusion-dependent patients with thalassemia: the first case-control study in Iran

Transfusion therapy is crucial for treating Transfusion-dependent thalassemia (TDT) patients. However, the production of Alloantibodies presents a substantial challenge for these individuals and impacts their quality of life. The Rh and Kell blood group antigens are particularly susceptible to alloantibody development. This study aims to establish the correlation between HLA-DRB1*04, HLA-DQB1*03, and HLA-DQB1*06 alleles and alloimmunzation in thalassemia patients from Iran. 98 thalassemic patients were recruited for this study (49 alloimmunized and 49 non-alloimmunized). Alloimmunized patients developed Rh and Kell specificities alloantibodies. The two groups were compared based on the results of HLA-DRB1 and HLA-DQB1 genotyping conducted using Sequence-Specific Primers (SSP-PCR). The findings from the antibody screening revealed that the predominant alloantibody detected was Anti-K (95.9%), Anti-E (65.3%), Anti-C (30.6%), Anti-D (28.6%), Anti-c (10.2%), Anti-e (2%), and Anti-k (2%). There was a notable difference in HLA-DQB1*03 between alloimmunized and non-alloimmunized groups, 41.8% vs. 58.2%, respectively. (iP = 0.001, OR = 0.135, CI = 0.036-0.499). There was not any notable relationship between HLA-DRB1*04 and HLA-DQB1*06 alleles and alloimmunization. Our findings indicate that HLA-DQB1*03 may have a protective role in preventing alloantibody production. Thus, HLA-typing, particularly focusing on DQB1*03, can significantly enhance the screening process, leading to improved blood transfusion management, reduced rejection of hematopoietic stem cell transplantation, and minimized blood transfusion complications.

The influence of HLA allele and haplotype on RhE alloimmunization among pregnant females in the Chinese Han population

BACKGROUND AND OBJECTIVES

Anti-E alloantibody is the most common and important red blood cell (RBC) alloantibody during pregnancy. The study aimed to determine the correlation between RhE alloimmunization and human leukocyte antigen (HLA) allele polymorphism, as well as haplotype diversity, among pregnant individuals in the Chinese Han population.

STUDY DESIGN AND METHODS

All individuals included in our study were RhE-negative pregnant women of Chinese Han ethnicity, confirmed through serological testing. Pregnancy could be the only potential stimulating factor in RBC alloimmunization. Given the serological testing, the participants were divided into anti-E (responders) and non-anti-E-producing group (non-responders). The class I and II classical HLA genotyping were determined using next-generation sequencing, and the HLA genotype and haplotype frequencies were compared between the responders and non-responders.

RESULTS

In total, 76 responders and 94 non-responders were enrolled in this study. Comparison results showed that all HLA class I alleles had no difference between the two groups. For HLA class II phenotypes, responders had higher frequencies of HLA-DRB1*09:01, HLA-DQA1*03:02 and HLA-DQB1*03:03 phenotypes than non-responders, and the differences were statistically significant (pc < 0.05). In addition, the haplotype frequency of HLA-DRB1*09:01-DQA1*03:02-DQB1*03:03 in the RhE responders was significantly higher than in the non-responders (31.58% vs. 12.77%; odds ratio, 3.154; 95% confidence interval, 1.823-5.456; pc value, 1.25 × 10-3).

CONCLUSION

Our findings indicated that HLA-DRB1*09:01, HLA-DQA1*03:02 and HLA-DQB1*03:03 might be susceptible alleles for RhE alloimmunization among Chinese Han pregnant females. These three susceptible alleles constituted the unique three-locus haplotype in the RhE responders and collaborated to RhE alloimmunization.

HLA Class II regulation of immune response in sickle cell disease patients: Susceptibility to red blood cell alloimmunization (systematic review and meta-analysis)

BACKGROUND AND OBJECTIVES

Sickle cell disease (SCD) patients are commonly treated with red blood cell (RBC) transfusion. Pretransfusion tests commonly involve limited serological antibody testing. RBC alloimmunization to RBC antigens is a frequently encountered complication seen in chronically transfused patients. Genetic factors such as the human leukocyte antigen (HLA) are known to influence and regulate immune responses. HLAs are highly polymorphic and play an essential role in regulating immune responses, including RBC alloimmunization. The aim of this study was to conduct a systematic review and meta-analysis to evaluate the association between HLA Class II allelic polymorphisms with the possible risk of developing RBC alloantibodies.

MATERIALS AND METHODS

Four databases were systematically searched for relevant studies between the years 2000 and 2021 following the PRISMA guidelines. Four articles met the eligibility and quality criterion, and three alleles, HLA-DRB1*04, HLA-DRB1*15 and HLA-DQB1*03, that were found to be potentially associated with an increased risk in alloantibody formation were included.

RESULTS

The primary outcome measure was alloimmunization by RBC antigen exposure in multiply transfused SCD patients. The total estimate of alloimmunization of the SCD patients was 2.33 (95% CI, 1.58-3.44), demonstrating susceptibility to RBC alloantibody formation. Heterogeneity between the studies was insignificant, suggesting the differences associated with random sampling errors. The results showed that SCD patients carry an increased risk of producing RBC alloantibodies.

CONCLUSION

A strategy to prevent RBC alloimmunization is genotyping for genetically susceptible SCD patients receiving multiple transfusions. Early identification of genetic variants that can potentially increase the risk of RBC alloimmunization could aid in the screening process and selection of phenotypically matched RBC units.

An overview of red blood cell and platelet alloimmunisation in transfusion

Post-transfusion alloimmunisation is the main complication of all those observed after one or more transfusion episodes. Alloimmunisation is observed after the transfusion of red blood cell concentrates but also of platelet concentrates. Besides alloimmunisation due to antigens carried almost exclusively by red blood cells such as those of the Rhesus-Kell system, alloimmunisation often raises against HLA antigens; the main responsibility for that, apart from platelet transfusions, lies with residual leukocytes in the products transfused, hence the central importance of effective leukoreduction right from the blood product preparation stage. Alloimmunization is not restricted to transfusion, but it is also observed during pregnancies, carrying out microtransfusions of blood from the fetus immunizing the mother through the placenta (in a retrograde way). Preexisting maternal-fetal immunization can complicate a transfusion program and intensify the creation of alloantibodies in several blood and tissue group systems. The occurrence of autoantibodies, created by several pathogenic reasons, can also interfere with the propensity of certain recipients of blood components to produce alloantibodies. The genetic condition of individuals is in fact strongly linked to the ability or not to recognize antigenic variants foreign to their own biological program and mount an alloimmune response. Some hemoglobin diseases, in carriers of which transfusions can be iterative and lifelong, are complicated by frequent alloimmunizations and amplification of the complications of these alloimmunizations, imposing even stricter transfusion rules. This review details the mechanisms favoring the occurrence of alloimmunization and the immunological principles for the production of molecular and cellular tools for alloimmunization. It concludes with the main preventive measures available to limit the occurrence of these frequent complications of varying severity but sometimes severe.

Screening for new red blood cell alloantibodies after transfusion in patients with sickle cell disease

BACKGROUND

Patients with sickle cell disease (SCD) are frequent recipients of red blood cell (RBC) transfusions and are at risk for RBC alloimmunization. RBC alloimmunization is diagnosed by identifying RBC alloantibodies as part of pre-transfusion testing, but this testing fails to detect alloantibodies that have evanesced. It may be beneficial to screen for new RBC alloantibody development after transfusion before possible antibody evanescence.

STUDY DESIGN AND METHODS

Our institution started a new initiative for episodically transfused patients with SCD to obtain at least one antibody screen 2-6 months after transfusion as part of their clinical care. A database was created to prospectively track all transfused patients for 1 year and their post-transfusion antibody screen results. Patients received prophylactically CEK-matched RBC units.

RESULTS

During the study year, 138 patients with SCD received a total of 242 RBC transfusions. Patients with a history of an RBC alloantibody (n = 13, 9.4%) had previously received more RBC units than non alloimmunized patients (median 11 vs. 2 RBC units, p = .0002). A total of 337 post-transfusion antibody screens were obtained in 127 patients (92.0%) with 110 patients (79.7%) having at least one antibody screen 2-6 months post-transfusion. With this prospective testing, two new RBC alloantibodies (anti-C and -M) were identified in two patients.

CONCLUSION

It is feasible to test for new RBC alloantibody development in most episodically transfused patients with SCD as part of their routine care. The yield of this screening appears low with CEK matching, but it could still provide important information for individual patients.

Back to base pairs: What is the genetic risk for red bloodcell alloimmunization?

Red blood cell (RBC) alloimmunization is a serious complication of blood transfusions, challenging selection of compatible units for future transfusions. Genetic characteristics may be associated with the risk of RBC alloimmunization and may therefore serve to identify high-risk patients. The aim of this systematic review was to summarize the available evidence on genetic risk factors for RBC alloimmunization. Electronic databases were searched up to April 2020 for studies (Search terms included transfusion, alloimmunization and genetic). A total of 2581 alloimmunized cases and 26,558 controls were derived from 24 studies. The alleles that were most frequently studied and that demonstrated significant associations in a meta-analysis with alloimmunization to the Duffy^a antigen were HLA-DRB1*04 (Odds Ratio 7.80 (95%CI 4.57-13.33)), HLA-DRB1*15 (OR 3.76 (95%CI 2.14-6.59)), and HLA-DRB1*03 (OR 0.12 (95%CI 0.05-0.29)). Furthermore, significant associations with anti-K formation was found for the alleles HLA-DRB1*10 (OR 2.64 (95%CI 1.41-4.95)), HLA*DRB1*11 (OR 2.11, (95%CI 1.34-3.32)), and HLA-DRB1*13 (OR 1.71 (95%CI 1.26-2.33)). Overall, the available evidence was of moderate to low quality, hampering interpretation of reported results. There is an urgent need for high quality evidence on genetic risk factors for RBC alloimmunization.

The cause and pathogenesis of hemolytic transfusion reactions in sickle-cell disease

PURPOSE OF REVIEW

The current review aims to summarize the epidemiology, cause, pathophysiology, and management of hemolytic transfusion reactions in sickle-cell disease (SCD).

RECENT FINDINGS

Patients undergoing occasional, isolated transfusions have been shown to have a higher risk of developing this condition. Despite the identification of well known risk factors, including alloimmunization, the pathophysiology of this syndrome remains unclear, as very severe forms with hyperhemolysis may develop in the absence of detectable antibodies, or with antibodies that are not considered to be clinically significant. Complement plays a crucial role in this reaction, particularly in cases of intravascular hemolysis. Complement triggers the reaction, but it also amplifies the inflammatory response and aggravates tissue damage. Free heme and hemoglobin are released and interact with complement, causing tissue damage.

SUMMARY

Hemolytic transfusion reactions are the most feared complications of blood transfusion in patients with SCD. This reaction is underdiagnosed because it mimics a vaso-occlusive crisis. Alloimmunization against red blood cell antigens is known to be a major trigger of this reaction, but abnormal complement activation and the underlying condition in patients with chronic hemolysis, may amplify the reaction. There is an urgent need to develop evidence-based approaches for preventing and treating this reaction.

HLA diversity in Brazil

Brazil is the fifth largest country in the world in area and the fifth most populous. The Brazilian voluntary Bone Marrow Donor Registry is the third largest in terms of number of donors in the world, being a valuable source of HLA genetics to characterize the donor population of Brazil as well. The genetic background of the Brazilian population is quite heterogeneous, resulting from 5 centuries of admixture among Native Americans, Europeans and Africans, making the Brazilian population unique in terms of genetic ancestry. The unique characteristics of populations in different Brazilian regions make them an exciting focus for genetic diversity studies. Studies on HLA genetic diversity of Brazilian populations have been conducted since the late 1980s and, in this review, we highlight the main findings from studies carried out in Brazil based on classical HLA. In addition, we calculated the genetic distance from the molecular data of the studies included in this review in order to have a broader view of the HLA diversity in Brazilian populations. We emphasize that characterization of HLA diversity is not only important for transplantation programs, but can shed a light on ancestry, history and other demographic patterns with or without association with autoimmune disease.

Optimized Antigen-Matched in Sickle Cell Disease Patients: Chances and Challenges in Molecular Times - the Brazilian Way

The development of red blood cell (RBC) alloantibodies and autoantibodies complicates transfusion therapy in sickle cell disease (SCD) patients. In an effort to reduce the risk of alloimmunization, some strategies have been used to provide antigen-matched RBC transfusions to patients with SCD in Brazil, including molecular matching in 3 levels: RH and K matching; extended matching (RH, KEL, FY, JK, MNS, DI), and extended matching including RHD and RHCE variant alleles. Molecular matching has shown clinical benefits to the patients with SCD, contributing significantly to reduce the rates of alloimmunization. Improvements in the clinical outcomes of the patients have also been observed as shown by an increase in their hemoglobin levels and reduction in their percentage of hemoglobin S as well as better in vivo RBC survival and diminished frequency of transfusions. However, prevention of RBC alloimmunization still remains a challenge in Brazil due to the difficulty to fulfill all transfusion requests of the patients with antigen-matching units, inaccuracy of RBC phenotyping, RBC transfusions outside the institution where the patient is treated, advanced age of some patients, the RBC antigen discrepancy between donors and recipients, and the presence of RH variants.

A unique major histocompatibility complex Class II-binding register correlates with HLA-DR11-associated immunogenicity of the major K blood group antigen

BACKGROUND

Kell is a glycoprotein expressed on red blood cells (RBCs). Its K and k variants contain either Met (K antigen) or Thr (k antigen) at Position 193, respectively. Development of anti-K after K-mismatched antigen exposure via blood transfusions or pregnancy can destroy RBCs, leading to hemolytic transfusion reactions and hemolytic disease of the fetus and newborn. The immunogenicity of overlapping 15-mer Kell peptides with M193 or T193 at every possible position was investigated previously. Interestingly, Peptide W179 to M193, with the polymorphic M193T residue at the peptide's C-terminus, was the most effective at stimulating CD4 T cells from a series of K-immunized women.

STUDY DESIGN AND METHODS

This study investigates the basis for HLA restriction of anti-K immune responses. Major histocompatibility complex Class II (MHCII)-binding prediction algorithms and quantitative peptide-MHCII-binding assays were employed to determine the binding registers; anchor residues; and affinities of wild-type, truncated, and sequence-modified K and k peptides. Predictions were generated using Immune Epitope Database and ProPred algorithms. Competitive peptide-MHCII-binding assays utilized 12 recombinant HLA-DR proteins, K and k peptides, and high-affinity MHCII-restricted reference peptides.

RESULTS

The peptide-MHCII-binding assays identified a unique K peptide-binding register (W179-S187) restricted to HLA-DRB1*11:01, in addition to partially overlapping binding registers that included the K/k M193T polymorphic site and that bound promiscuously to multiple HLA-DR proteins.

CONCLUSION

Three partially overlapping MHCII-binding motifs for HLA-DRB1*11:01 result in high-avidity K-peptide binding, which may contribute to HLA-DR11-restricted immunogenicity associated with the K allele.