The Influence of Clinical and Biological Factors on Transfusion-Associated Non-ABO Antigen Alloimmunization: Responders, Hyper-Responders, and Non-Responders

Common RBC antigens in O type Tunisian blood donors and their importance in alloimmunization

BACKGROUND

The presence of some red blood cell (RBC) antigens may affect the preference for using type O blood in emergency situations because they may induce complex or multiple alloimmunization in special circumstances.

METHODS

A subgroup of 77 type O blood Tunisian donors were genotyped for 19 common blood alleles using the single specific primer-polymerase chain reaction method. The statistical analysis was done using HaploView software.

RESULTS

The study showed the dominance of the alleles RH*5, KEL*2, FY*2, and CO*1 and the absence of the homozygous state of the KEL*1 and CO*2 alleles. Furthermore, a complete linkage disequilibrium between the RH*2/RH*4 and RH*3/RH*5 loci and the FY*Null/FY*Exp and FY*A/FY*B loci was detected. Additionally, it seems that sensitization to MNS:3, FY:1, and RH:3 may constitute a potential factor for alloimmunization after transfusion with O blood type units: the probabilities of simple alloimmunizations are 24.5 per 100, 18.5 per 100, and 18 per 100, respectively. Multiple alloimmunization against RH:1;KEL:1 or RH:1;KEL:1;RH:3 phenotypes may occur, with probabilities of 7 per 1000 and 2 per 1000, respectively.

CONCLUSION

Some O-type RBC units may contain blood with very immunogenic phenotypes, the use of which in an emergency requires great caution because it can be a step towards subsequent alloimmunization.

The Distribution Patterns of Rhesus (Rh) Antigens

INTRODUCTION

The determination of one's blood group is dictated by the inheritance-based diversity in the presence or absence of RBC antigens on the surface. Extended Rhesus (Rh) antigens are the most clinically relevant antigens of blood group systems after the ABO blood group system in transfusion medicine. The aim of this study was to serologically assess the prevalence of extended Rh antigens across diverse blood group systems.

METHODS

A total of 2043 samples were tested for the ABO blood group and Rh typing with monoclonal antisera. The Rh phenotyping (C, c, E, e ) was performed on all the samples.

RESULTS

The most frequently observed ABO blood group was O (36.5%), while AB (13.6%) was identified as the least prevalent. Positive Rh D antigen was found in 91.6% of tested samples, while 8.4% were Rh D-negative. The most frequently encountered antigen was e, followed by D, while the least prevalent was E.

DISCUSSION

Establishing a Rh phenotype repository for blood donors and conducting Rh phenotype assessments as part of pretransfusion testing before initiating the initial blood transfusion for each patient could significantly lower the patients' incidence of alloimmunization.

Association of HLA-DRB1 alleles with anti-D alloimmunization in RhD negative pregnant women in India

BACKGROUND

Human leukocyte antigen (HLA) restriction plays an important role in the susceptibility to alloimmunization against red blood cell (RBC) antigens. The prevalence of anti-D alloimmunization in RhD negative pregnancy is still quite high in our population. Thus, we planned this study to determine the association of HLA-DRB1 alleles with anti-D alloimmunization in RhD negative pregnant women.

MATERIAL AND METHODS

RBC antibody screen (ABS) was performed for RhD negative pregnant women attending the antenatal clinic our institute. Those with a negative result were included in the 'non-alloimmunized' (NAL) group ('Control' group), while those with anti-D alloantibody on performing antibody identification were included in the alloimmunized (AL) group of the study (n = 50 each). ABS and identification were done using column agglutination technique. The HLA-DRB1 typing was done by Luminex based reverse sequence specific oligonucleotide probing (SSOP) using commercial kits. The HLA-DRB1 allele frequency was compared in both the groups.

RESULTS

There was a significant difference between the two groups in terms of gravida (p < 0.001) and history of anti-D immunoprophylaxis (p < 0.001). The frequency of HLA-DRB1*03 and HLA-DRB1*04 alleles was significantly higher in the AL group than the NAL group: 40 % versus 18 % [Odds Ratio (OR): 3.04, 95 % CI: 1.21-7.6; p = 0.015] for HLA-DRB1*03 alleles and 18 % versus 4 % (OR: 5.27, 95 % CI: 1.08-25.78, p = 0.025) for HLA-DRB1*04 alleles.

CONCLUSION

The frequency of HLADRB1*03 and HLADRB1*04 alleles was significantly higher in RhD negative pregnant women alloimmunized with anti-D alloantibody.

Prevalence of blood group antigens among regular blood donors: A single center study from South India with a review of national literature

BACKGROUND AND OBJECTIVES

The antigen frequencies vary across different regions and ethnic groups. Hence, we aimed to study the prevalence of blood group antigens in our population and to systemize the zone-wise prevalence of the same across India.

MATERIALS AND METHODS

Regular voluntary O group blood donors were screened for 21 blood group antigens; C, c, E, e, K, k, Kpa, Kpb, Jka, Jkb, Fya, Fyb, Lea, Leb, Lua, Lub, P1, M, N, S, s, using commercially available monoclonal antisera by column agglutination technology. A literature search was performed to identify all the studies that reported blood group antigens prevalence to estimate the zone-wise prevalence of these antigens in the country.

RESULTS

A total of 521 participants of 9248 O group donors meeting all the inclusion criteria were included. Among the study group, the male-to-female ratio was 9:1 with a mean age of 32.6 years (±10.01) ranging from 18-60 years. The majority of the donors 446 (85.6%) were D positive. The most common phenotypes among Rh, Lewis, Kell, Duffy, Kidd, Lutheran and MNSs were CcDee (34.93%), Le(a-b+) (61.80%), K-k+(98.27%), Fy(a+b-) 43.19%, Jk(a+b+) 42.61%, Lu(a-b+) ( 99.61%), M+N+ (48.17%), S-s+ (45.29%) respectively. The prevalence of D and E antigens was significantly lower in the South zone compared to other zones of India.

CONCLUSION

Significant difference in the prevalence of blood group antigens is observed between the South and other zones of India. Zone-wise prevalence of blood group phenotypes is essential in the timely management of alloimmunized patients.

Future prospects for the clinical transfusion of pig red blood cells

Transfusion of allogeneic human red blood cell (hRBCs) is limited by supply and compatibility between individual donors and recipients. In situations where the blood supply is constrained or when no compatible RBCs are available, patients suffer. As a result, alternatives to hRBCs that complement existing RBC transfusion strategies are needed. Pig RBCs (pRBCs) could provide an alternative because of their abundant supply, and functional similarities to hRBCs. The ability to genetically modify pigs to limit pRBC immunogenicity and augment expression of human 'protective' proteins has provided major boosts to this research and opens up new therapeutic avenues. Although deletion of expression of xenoantigens has been achieved in genetically-engineered pigs, novel genetic methods are needed to introduce human 'protective' transgenes into pRBCs at the high levels required to prevent hemolysis and extend RBC survival in vivo. This review addresses recent progress and examines future prospects for clinical xenogeneic pRBC transfusion.

Phenotyping of clinically significant blood group antigens among the South Indian donor population

INTRODUCTION

Data on the prevalence of clinically significant antigens (Rh, Kell, Kidd, Duffy, MNSs, Lewis, P and Lutheran) among the Indian donor population is sparse.

OBJECTIVE

This prospective study was aimed at determining the prevalence of 21 clinically significant antigens for the first time in the South Indian donor population.

METHOD

A total of 672 regular O group blood donors were enrolled for Rh (C,c, E, e) and Kell (K) antigens typing. Of these, 188 donors were typed for other clinically significant antigens (k, Kpa, Kpb, Jka, Jkb, Fya, Fyb, M, N, S, s, P1, Lea, Leb, Lua and Lub).

RESULTS

Antigen frequencies were expressed in percentages. In our study, R1R1 and rr were the most common phenotypes among D+ and D- donors, respectively. Among the Rh antigens, the e antigen was expressed by 97.5% and 100% of D+ and D- donors, respectively. The K antigen was found in only 0.15% of donors. In the Duffy and Kidd blood group system, Fy (a+b+) and Jk (a+b+) were the most frequent phenotypes, respectively. In the MNSs blood group system, M+N+ and S-s+ were the most common phenotypes reported. The Le (a-b+) was found to be the phenotype with the highest prevalence in the Lewis blood group system. The Lu (a-b+) was the only phenotype found in the Lutheran blood group system.

CONCLUSION

Knowledge regarding the prevalence of antigens in a given population is essential in developing cost-effective in-house panels and a rare donor registry comprising donors typed negative for a high-frequency antigen or a combination of common multiple antigens.

The Development and Consequences of Red Blood Cell Alloimmunization

While red blood cell (RBC) transfusion is the most common medical intervention in hospitalized patients, as with any therapeutic, it is not without risk. Allogeneic RBC exposure can result in recipient alloimmunization, which can limit the availability of compatible RBCs for future transfusions and increase the risk of transfusion complications. Despite these challenges and the discovery of RBC alloantigens more than a century ago, relatively little has historically been known regarding the immune factors that regulate RBC alloantibody formation. Through recent epidemiological approaches, in vitro-based translational studies, and newly developed preclinical models, the processes that govern RBC alloimmunization have emerged as more complex and intriguing than previously appreciated. Although common alloimmunization mechanisms exist, distinct immune pathways can be engaged, depending on the target alloantigen involved. Despite this complexity, key themes are beginning to emerge that may provide promising approaches to not only actively prevent but also possibly alleviate the most severe complications of RBC alloimmunization.

Somatic mutations show no clear association with red blood cell or human leukocyte antigen alloimmunization in de novo or therapy-related myelodysplastic syndrome

BACKGROUND

Myelodysplastic syndrome (MDS) is a marrow failure disease. As patients often require chronic transfusion, many develop red blood cell (RBC) alloimmunization or immune-mediated platelet refractoriness. MDS represents a spectrum of diseases with specific categorizations and genetic abnormalities, and we set out to determine if these characteristics predispose patients to antibody formation.

STUDY DESIGN AND METHODS

A natural language search identified MDS patients with pre-transfusion testing from 2015 to 2020. Marrow reports, cytogenetic results, and next-generation sequencing panels were gathered. Transfusion history and testing were collected from the laboratory information system.

RESULTS

The group consisted of 226 biopsy-proven MDS patients. The prevalence of RBC alloimmunization was 11.1% (25 of 226). Half (23 of 46) of all RBC alloantibodies were against Rh (C, c, E, e) and Kell (K) antigens. There was a relative enrichment for JAK2 positivity among the RBC alloimmunized group. A total of 7.1% (16 of 226) of patients had immune-mediated platelet refractoriness and had increased transfusion requirements (p ≤ 0.01). No disease type or genetic abnormality was significantly associated with alloimmunization or immune-mediated platelet refractoriness.

DISCUSSION

While JAK2 specific mutations were enriched among RBC alloimmunized patients, this association failed to reach statistical significance in our single-center cohort. Further study using larger patient cohorts is warranted. Overall, this cohort of MDS patients had very similar RBC alloimmunization prevalence and anti-RBC antibody specificities as other recent literature. Our data reinforce the finding that MDS patients are at greater risk for alloimmunization and support the use of extended phenotype matching for these at-risk patients.

Features of the distribution of the antigens of Kell, Duffy, Kidd, MNS, Lewis, Lutheran blood group systems in blood donors in the Kirov region

The frequency of occurrence of antigens of the Kell (Kpa, Kpb), Kidd, Duffy, MNS and Lutheran systems in donors of the Kirov region corresponds to the distribution of antigens characteristic of white Europeans. Antigens K (Kell system) and Lea (Lewis system) are detected in the population of the region much less frequently, antigen Leb (Lewis system) - more often than in the population of Europe. The presence of a registry of donors typed according to a wide range of red blood antigens is a prerequisite for the immunohematological safety of blood transfusions.

Following targeted routine antenatal anti-D prophylaxis, almost half of the pregnant women had undetectable anti-D prophylaxis at delivery

INTRODUCTION

In September 2016, a nationwide targeted routine antenatal anti-D prophylaxis program was implemented in Norway. The prophylaxis (anti-D immunoglobulin) aims to cover the whole third trimester and is administered in gestational week 28 to RhD-negative women who carry RhD-positive fetuses. However, in many women, antibody screening at delivery does not detect anti-D immunoglobulin. The goal of this study was to investigate the presumable role of dose and timing of antenatal anti-D immunoglobulin administration in non-detectable prophylaxis at the time of delivery.

MATERIAL AND METHODS

In this retrospective observational study, RhD-negative pregnant women who gave birth at Oslo University Hospital and Akershus University Hospital between January 2017 and December 2019 were analyzed. Women who received antenatal anti-D immunoglobulin (1500 IU at Oslo University Hospital and 1250 IU at Akershus University Hospital) when fetal RHD genotyping at gestational week 24 predicted an RhD-positive fetus were included if an antibody screen at delivery was available. Data from the blood bank, maternity information systems, and electronic patient records were used.

RESULTS

Analysis of the 984 RhD-negative women at the two hospitals revealed that 45.4% had non-detectable anti-D at delivery. A significant difference between the two hospitals was observed: 40.5% at Oslo University Hospital (n = 509) and 50.7% at Akershus University Hospital (n = 475) (p = 0.001). The proportion with non-detectable anti-D increased to 56.0 and 75.3%, respectively (p = 0.008) in the group of women who gave birth 12 weeks after routine antenatal anti-D prophylaxis. Significantly fewer women had detectable anti-D at delivery when the lower anti-D immunoglobulin dose (1250 IU) was administered antenatally. Multiple logistic regression indicated that the time interval between routine antenatal anti-D prophylaxis and delivery, in addition to anti-D dose, were significantly associated with detectable anti-D at delivery (p < 0.001).

CONCLUSIONS

We do not know which RhD-negative pregnant women, despite antenatal anti-D prophylaxis, are at risk of RhD alloimmunization, when antibody screening is negative at delivery. Administration of antenatal prophylaxis should probably be moved closer to delivery, since the risk of fetomaternal hemorrhage is higher during the last weeks of the third trimester.

Alloimmunization in transfused patients with constitutional anemias in Norway

BACKGROUND AND OBJECTIVES

The status of red blood cell alloimmunization in patients with constitutional anemias including hemoglobinopathies is not known in Norway. The study objective was to investigate the impact of a strategy based on phenotype-matching for C, c, E, e, K, Jka, Jkb, Fya, Fyb, S and s on alloimmunization.

MATERIALS AND METHODS

We reviewed transfusions of 40 patients retrospectively using the computerized blood bank management system and medical records; including diagnosis, age at start of transfusion therapy, gender, number and age of packed red blood cell units transfused, follow-up time, phenotypes of the donors and patients, antigen-negative patients exposed to antigen-positive packed red blood cell units, transfusion reactions and alloantibody specificities.

RESULTS

Forty patients received 5402 packed red blood cell units. Alloimmunization frequency was 20 % for the whole group, being 7%, 25 % and 30 % in patients with sickle cell disease (n = 14), thalassemia (n = 16) and other conditions (n = 10), respectively. The alloantibodies detected were anti-E, -c, -C, -Cw, -K, -Jka and -Lua.

CONCLUSION

Good communication between the clinicians and the transfusion services is essential for successful management of patients with constitutional anemias. Providing full phenotype-matched units was not always possible. Extended pheno-/genotyping before the first transfusion and providing antigen-negative units for antigen-negative patients for at least C, c, E and K in every red cell transfusion would probably have reduced the alloimmunization rate. Non-phenotype-matched transfusions seem to be the main reason for alloimmunization. Finding markers for identifying responders prone to alloimmunization will ensure targeted transfusion strategies.

Non-ABO red cell antibodies and risk of COVID-19

It is not known whether non-ABO antibodies confer any protective effect against SARS-CoV-2 infection or COVID-19 severe illness alone or in conjunction with O blood group. This cohort study included 413 576 persons in Ontario, Canada with known ABO blood group and non-ABO antibody screen status, who subsequently underwent SARS-CoV-2 viral RNA polymerase chain reaction testing between January and November 2020. The risk of SARS-CoV-2 infection or COVID-19 severe illness was not associated with the presence of non-ABO antibodies, even among persons with O blood group.

A locus on chromosome 5 shows African ancestry-limited association with alloimmunization in sickle cell disease

Red blood cell (RBC) transfusion remains a critical therapeutic intervention in sickle cell disease (SCD); however, the apparent propensity of some patients to regularly develop RBC alloantibodies after transfusion presents a significant challenge to finding compatible blood for so-called alloimmunization responders. Predisposing genetic loci have long been thought to contribute to the responder phenomenon, but to date, no definitive loci have been identified. We undertook a genome-wide association study of alloimmunization responder status in 267 SCD multiple transfusion recipients, using genetic estimates of ancestral admixture to bolster our findings. Analyses revealed single nucleotide polymorphisms (SNPs) on chromosomes 2 and 5 approaching genome-wide significance (minimum P = 2.0 × 10^-8 and 8.4 × 10^-8, respectively), with local ancestry analysis demonstrating similar levels of admixture in responders and nonresponders at implicated loci. Association at chromosome 5 was nominally replicated in an independent cohort of 130 SCD transfusion recipients, with meta-analysis surpassing genome-wide significance (rs75853687, P _meta = 6.6 × 10^-9), and this extended to individuals forming multiple (>3) alloantibodies (P _meta = 9.4 × 10^-5). The associated variant is rare outside of African populations, and orthogonal genome-wide haplotype analyses, contingent on local ancestry, revealed genome-wide significant sharing of a ∼60-kb haplotype of African ancestry at the chromosome 5 locus (Bayes Factor = 4.95). This locus overlaps a putative cis-acting enhancer predicted to regulate transcription of ADRA1B and the lncRNA LINC01847, both members of larger ontologies associated with immune regulation. Our findings provide potential insights to the pathophysiology underlying the development of alloantibodies and implicate non-RBC ancestry-limited loci in the susceptibility to alloimmunization.

Pathophysiology of Alloimmunization

Introduction

Alloimmunization is caused by exposure to erythrocytes from a donor that expresses blood group antigens other than those of the recipient and is related to processes that alter the balance of the immune system. Knowing the pathophysiology of alloimmunization process is essential to understand clinical complications associated with this process.

Patients and Methods

From October 2016 to April 2017, irregular antibody screening was performed in 1,434 polytransfused (compatible with the ABO and D system) patients by means of agglutination techniques using erythrocytes of a known phenotype of 44 patients with a positive alloantibody screening. Non-alloimmunized (control) subjects were matched for age, gender, pathology, and treatment group with alloimmunized patients. The subsets of B, T, and Treg lymphocytes were determined by flow cytometry.

Results

The results of screening for alloantibodies in patients by specificity of antibodies were as follows: nonspecific (30%), followed by anti-Di^a (13%), anti-e (9%), anti-S (9%), anti-I (7%), anti-K (7%), and anti-P (7%). A lower percentage of CD4+ T lymphocytes and an increase of CD8+ T lymphocytes were observed in alloimmunized patients, as well as a low CD4/CD8 ratio (0.7 vs. 1.6, p = 0.003), a higher percentage of B lymphocytes versus the control group (30 vs. 20%, p = 0.003), and a decrease of Treg CD4+ lymphocytes versus the control group (3 vs. 12 cells/μL, p = 0.043). These observations suggest that alloimmunized patients have important alterations in the number of some lymphocyte subsets that can be translated into clinical immune dysregulation.

Conclusion

A decreased CD4/CD8 ratio, increased B lymphocytes, and Treg lymphocyte deficiency are the most significant changes observed in alloimmunized patients.

Red Blood Cell Alloimmunization in Korean Patients With Myelodysplastic Syndrome and Liver Cirrhosis

Red blood cell (RBC) alloimmunization varies across human populations and ethnic groups. We evaluated the characteristics of RBC alloimmunization and compared the risk of alloimmunization in Korean patients with myelodysplastic syndrome (MDS) and liver cirrhosis (LC), two representative diseases in which chronic transfusion is required. In total, 115 MDS patients and 202 LC patients transfused with RBCs between 2013 and 2015 were retrospectively included. Twenty patients (6.3%) were newly alloimmunized (five MDS patients, 4.3%; 15 LC patients, 7.4%). The median number of RBC units transfused in alloimmunized patients was nine (interquartile range, 4–15 units). As the number of transfused RBC units increased, the cumulative risk of alloimmunization was higher in LC than in MDS patients (P=0.001). The most common alloantibody detected in patients was anti-E (45%), followed by anti-c (17%), anti-e (10%), anti-C (7%), anti-Fy^b (7%), and anti-Jk^a (7%). The present data indicate the need for matching of extended RBC antigens (Rh, Duffy, and Kidd systems) for chronically transfused patients with MDS and LC in Korea.

A Conceptual Framework for Optimizing Blood Matching Strategies: Balancing Patient Complications Against Total Costs Incurred

Alloimmunization is currently the most frequent adverse blood transfusion event. Whilst completely matched donor blood would nullify the alloimmunization risk, this is practically infeasible. Current matching strategies therefore aim at matching a limited number of blood groups only, and have evolved over time by systematically including matching strategies for those blood groups for which (serious) alloimmunization complications most frequently occurred. An optimal matching strategy for controlling the risk of alloimmunization however, would balance alloimmunization complications and costs within the entire blood supply chain, whilst fulfilling all practical requirements and limitations. In this article the outline of an integrated blood management model is described and various potential challenges and prospects foreseen with the development of such a model are discussed.

Red blood cell alloimmunization: new findings at the bench and new recommendations for the bedside

PURPOSE OF REVIEW

To summarize recent discoveries from clinical studies and animal models that contribute to understanding the alloimmune response to non-ABO blood group antigens.

RECENT FINDINGS

Several studies have confirmed high rates of alloimmunization among patients requiring chronic red blood cell (RBC) transfusion. Moreover, 'triggers' for alloantibody development in the transfusion setting have been identified, with a number of investigations linking recipient inflammation to a higher likelihood of alloimmunization. Additional associations between human leukocyte antigen expression and CD4 T-cell markers in 'responder' or 'nonresponder' humans have been revealed. Recent animal studies have described novel mechanistic properties by which the alloimmune response is governed, including the critical role played by dendritic cells in transfusion-associated alloimmunization. New light has also been shed on the properties of alloantibodies developed as a result of pregnancy, as well as mechanisms through which such alloimmunization may be prevented.

SUMMARY

Many of the clinical/biological factors that contribute to the RBC alloimmune response have been further elucidated. This knowledge will be applied to identify individuals most likely to mount an immune response to RBC antigens, such that appropriate resources and strategies for preventing alloimmunization (or mitigating its harmful effects) can be implemented.

Association of IL-6 C-572G Gene Polymorphism with Anti-E Production

Background

Interleukin 6 (IL-6) is involved in regulation of immunoglobulin production. The aim of this study was to investigate the association between IL-6 single nucleotide polymorphisms (SNPs) in the IL-6 promoter and anti-E in red blood cell (RBC) transfusion recipients.

Methods

50 healthy subjects, 54 patients with RBC alloantibody anti-E (responders), and 45 patients without alloantibody (non-responders) were recruited. All patients were E antigen-negative.

Results

All healthy subjects and patients had GG at -174 position of IL-6 gene. In our healthy subjects, the frequency of the -572 CC genotype was 58%, that of the -572 CG genotype 38%, and that of the -572 GG genotype 4%. The frequency of G allele of -572 SNP in responders was significantly higher than that in non-responders, (31.5 vs. 16.7%; p = 0.020). The frequency of -572 G-positive genotypes (CG and GG) in responders was also significantly higher than that in non-responders, (55.6 vs. 31.1%; p = 0.016). The relative risk of RBC alloimmunization for patients with the -572 G-positive genotype was significantly higher than that of patients with the -572 CC genotype, (1.771 vs. 0.640; p = 0.016).

Conclusion

IL-6 C-572G gene polymorphism is significantly associated with anti-E production, with the allele G as a risk allele.

Nonclassical FCGR2C haplotype is associated with protection from red blood cell alloimmunization in sickle cell disease

Red blood cell (RBC) transfusions are of vital importance in patients with sickle cell disease (SCD). However, a major complication of transfusion therapy is alloimmunization. The low-affinity Fcγ receptors, expressed on immune cells, are important regulators of antibody responses. Genetic variation in FCGR genes has been associated with various auto- and alloimmune diseases. The aim of this study was to evaluate the association between genetic variation of FCGR and RBC alloimmunization in SCD. In this case-control study, DNA samples from 2 cohorts of transfused SCD patients were combined (France and The Netherlands). Cases had a positive history of alloimmunization, having received ≥1 RBC unit. Controls had a negative history of alloimmunization, having received ≥20 RBC units. Single nucleotide polymorphisms and copy number variation of the FCGR2/3 gene cluster were studied in a FCGR-specific multiplex ligation-dependent probe amplification assay. Frequencies were compared using logistic regression. Two hundred seventy-two patients were included (130 controls, 142 cases). The nonclassical open reading frame in the FCGR2C gene (FCGR2C.nc-ORF) was strongly associated with a decreased alloimmunization risk (odds ratio [OR] 0.26, 95% confidence [CI] 0.11-0.64). This association persisted when only including controls with exposure to ≥100 units (OR 0.30, CI 0.11-0.85) and appeared even stronger when excluding cases with Rh or K antibodies only (OR 0.19, CI 0.06-0.59). In conclusion, SCD patients with the FCGR2Cnc-ORF polymorphism have over a 3-fold lower risk for RBC alloimmunization in comparison with patients without this mutation. This protective effect was strongest for exposure to antigens other than the immunogenic Rh or K antigens.

Medical and economic implications of strategies to prevent alloimmunization in sickle cell disease

BACKGROUND

The pathogenesis of alloimmunization is not well understood, and initiatives that aim to reduce the incidence of alloimmunization are generally expensive and either ineffective or unproven. In this review, we summarize the current medical literature regarding alloimmunization in the sickle cell disease (SCD) population, with a special focus on the financial implications of different approaches to prevent alloimmunization.

STUDY DESIGN AND METHODS

A review of EMBASE and MEDLINE data from January 2006 through January 2016 was conducted to identify articles relating to complications of SCD. The search was specifically designed to capture articles that evaluated the costs of various strategies to prevent alloimmunization and its sequelae.

RESULTS

Currently, there is no proven, inexpensive way to prevent alloimmunization among individuals with SCD. Serologic matching programs are not uniformly successful in preventing alloimmunization, particularly to Rh antigens, because of the high frequency of variant Rh alleles in the SCD population. A genotypic matching program could offer some cost savings compared to a serologic matching program, but the efficacy of gene matching for the prevention of alloimmunization is largely unproven, and large-scale implementation could be expensive.

CONCLUSIONS

Future reductions in the costs associated with genotype matching could make a large-scale program economically feasible. Novel techniques to identify patients at highest risk for alloimmunization could improve the cost effectiveness of antigen matching programs. A clinical trial comparing the efficacy of serologic matching to genotype matching would be informative.

Red blood cell minor antigen mismatches during chronic transfusion therapy for sickle cell anemia

BACKGROUND

Red blood cell (RBC) alloimmunization occurs at a high frequency in sickle cell anemia (SCA) despite serologic matching for Rh (C/c, E/e) and K antigens. RBC minor antigen genotyping allows for prediction of antigens and RH variants that may lead to alloimmunization.

STUDY DESIGN AND METHODS

RBC antigen genotyping was performed on chronically transfused pediatric SCA patients, using PreciseType human erythrocyte antigen (HEA), RHCE, and RHD BeadChip arrays. All patients received C/c, E/e, and K serologically matched units (Category 1); patients with prior RBC antibodies were also matched for Fy^a , Jk^b , and any antibodies (Category 2). The RBC genotypes of all leukoreduced (LR) units transfused over a 12-month period were determined by the prototype HEA-LR BeadChip assay.

RESULTS

There were 2320 RBC units transfused to 90 patients in 1135 transfusion episodes. Thirty-five (38.9%) patients had homozygous or compound heterozygous RH variants. Seven new alloantibodies were detected, with alloantibody incidence of 0.706 in 100 units for Category 2 transfusions and 0.068 in 100 units for Category 1 (p = 0.02). Three patients on Category 2 transfusions formed new anti-Js^a and had a higher rate of exposure to Js^a than those who did not form anti-Js^a (20.4 vs. 8.33 exposures/100 units, p = 0.02). The most frequent mismatches were S (43.9%), Do^a (43.9%), Fy^a (29.2%), M (28.4%), and Jk^b (28.1%).

CONCLUSIONS

Alloimmunization incidence was higher in those with prior RBC antibodies, suggesting that past immunologic responders are at higher risk for future alloimmunization and therefore may benefit from more extensive antigen matching beyond C/c, E/e, K, Fy^a , and Jk^b .

Association of HLA-DRB1 and HLA-DQB1 with red-blood-cell alloimmunization in the Czech population

BACKGROUND AND OBJECTIVES

Alloimmune antibodies against red-blood-cell (RBC) antigens induced in susceptible individuals (responders) by transfusion, pregnancy or transplantation may have serious clinical consequences. The aim of this study was to investigate association of alloimmunization against selected RBC antigens with HLA-Class II.

MATERIALS AND METHODS

A total of 230 responders (106 monoresponders and 124 multiresponders) were enrolled into the study. HLA-DRB1 and HLA-DQB1 variants were determined by PCR-SSO and their frequencies compared between the patients (patient subgroups) and 375 ethnically and regionally matched controls.

RESULTS

Development of multiple RBC antibodies was associated with HLA-DRB1*15 and HLA-DQB1*06 allelic groups in the patients, with the relationship being particularly apparent in those with anti-C+D antibodies. Furthermore, DRB1*13 and DQB1*06 were more frequent in multiresponders with anti-E+c antibodies and DRB1*03 and DQB1*02 in those with anti-E+Cw.

CONCLUSION

For the first time, we confirmed the association of HLA-DRB1*15 with RBC antibody multiresponder status and found HLA-Class II associations for three frequent RBC antibody combinations. Our data support the concept that HLA restriction plays an important role in the response to RBC alloantigens.

Impact of antigenic exposures and role of molecular blood grouping in enhancing transfusion safety in chronically transfused thalassemics

Background:

Red cell alloimmunization is an acknowledged complication of blood transfusion. Current transfusion practices for thalassemia do not cater to this risk. Serological phenotyping is usually not reliable in these cases unless performed before the first transfusion. Under such circumstances, molecular blood grouping is an effective alternative.

Aim:

To perform molecular blood group genotyping in chronically transfused thalassemia patients and assess the risk of antigenic exposure and incidence of alloimmunization with current transfusion protocols.

Materials and Methods:

Molecular blood group genotyping was performed for 47 chronically transfused thalassemia patients. Their 1-year transfusion records were retrieved to assess the antigenic exposure and the frequency thereof.

Results:

Of 47 patients, 6 were already alloimmunized (3 with anti-E and 3 with anti-K) and were receiving the corresponding antigen negative units. We observed that random selection of ABO and Rh D matched units resulted in 57.7% ±8.26% chance of Rh and Kell phenotype matching also. Forty-four patients had received one or more antigenic exposures at least once. The 6 already alloimmunized patients were further exposed to antigens other than the ones they were immunized to. During the study period, only one patient developed an alloantibody, anti-E with exposure to antigens C (92%) and/or E (32%) at each transfusion.

Conclusion:

Several factors apart from mere antigen exposure may influence the development of alloimmunization as most of our patients received antigenic exposures but not alloimmunized. Our data provide an impetus for future large-scale studies to understand the development of alloimmunization in such patients.

Impact of azacitidine on red blood cell alloimmunisation in myelodysplastic syndrome

BACKGROUND

The incidence of alloimmunisation in myelodysplastic syndromes (MDS) during the era of supportive treatment ranges from 9 to 56%. However, it is unknown if the widespread use of hypomethylating agents has changed the risk of immunisation. The aim of this study is to evaluate the impact of azacitidine (AZA) therapy on red blood cell (RBC) alloimmunisation in transfused patients with MDS, myelodysplastic syndromes/myeloproliferative syndromes (MDS/MPS) and secondary acute myeloid leukaemia (AML).

MATERIAL AND METHODS

We have analysed retrospectively all patients with MDS, MDS/MPS and secondary AML from MDS, who received their first transfusion in our hospital between January 1995 and December 2014. We have assessed the impact of age, sex, RBC and platelets units transfused, and AZA treatment on developing alloantibodies.

RESULTS

In our study, the number of RBC units transfused increased the risk of developing alloantibodies. However aging and the treatment with AZA were associated with a lower rate of alloimmunisation.

DISCUSSION

Patients with MDS, MDS/MPS and secondary AML who received treatment with AZA developed RBC antibodies at a lower rate than control group. We suggest that aging and immunosuppression due to AZA therapy could develop an immunological tolerance with a weak response to allotransfusions.

Modifications to Blood Components: When to Use them and What is the Evidence?

Blood component modifications can be performed by the hospital blood bank for select clinical indications. In general, modification of blood components increases costs and may delay availability of the blood component because of the additional time required for some modification steps. However, the benefit of blood product modification may outweigh these concerns. Common modifications include leukoreduction, irradiation, volume reduction, splitting, and washing. Modification availability and selection practice may vary from hospital to hospital. In this article, available blood component modifications are described along with the benefits, drawbacks, and specific clinical indications supporting their use.

Rare and transient anti-D antibody response in D(-) liver transplant recipients transfused with D(+) red blood cells

A retrospective analysis was conducted on 20 D(-) liver transplant (LT) recipients transfused with D(+) RBCs perioperatively and screened for RBC antibodies between 2 and 6 months later. None developed anti-D detectable by the indirect antiglobulin test. Two patients produced weak anti-D that reacted only with papain-treated RBCs at 10 and 11 days without any sign of immune haemolysis. Antibodies became quickly undetectable. These data suggest an unusual pattern of alloimmunization in LT recipients with rapid, weak and transient antibody response and support the safety of transfusing D(+) RBCs in most of D(-) patients during LT surgery.