Alloimmunization to transfused HOD red blood cells is not increased in mice with sickle cell disease

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.

Diversity of variant alleles encoding Kidd, Duffy, and Kell antigens in individuals with sickle cell disease using whole genome sequencing data from the NHLBI TOPMed Program

BACKGROUND

Genetic variants in the SLC14A1, ACKR1, and KEL genes, which encode Kidd, Duffy, and Kell red blood cell antigens, respectively, may result in weakened expression of antigens or a null phenotype. These variants are of particular interest to individuals with sickle cell disease (SCD), who frequently undergo chronic transfusion therapy with antigen-matched units. The goal was to describe the diversity and the frequency of variants in SLC14A1, ACKR1, and KEL genes among individuals with SCD using whole genome sequencing (WGS) data.

STUDY DESIGN AND METHODS

Two large SCD cohorts were studied: the Recipient Epidemiology and Donor Evaluation Study III (REDS-III) (n = 2634) and the Outcome Modifying Gene in SCD (OMG) (n = 640). Most of the studied individuals were of mixed origin. WGS was performed as part of the National Heart, Lung, and Blood Institute's Trans-Omics for Precision Medicine (TOPMed) program.

RESULTS

In SLC14A1, variants included four encoding a weak Jka phenotype and five null alleles (JKnull ). JKA*01N.09 was the most common JKnull . One possible JKnull mutation was novel: c.812G>T. In ACKR1, identified variants included two that predicted Fyx (FY*X) and one corresponding to the c.-67T>C GATA mutation. The c.-67T>C mutation was associated with FY*A (FY*01N.01) in four participants. FY*X was identified in 49 individuals. In KEL, identified variants included three null alleles (KEL*02N.17, KEL*02N.26, and KEL*02N.04) and one allele predicting Kmod phenotype, all in heterozygosity.

CONCLUSIONS

We described the diversity and distribution of SLC14A1, ACKR1, and KEL variants in two large SCD cohorts, comprising mostly individuals of mixed ancestry. This information may be useful for planning the transfusion support of patients with SCD.

Red blood cell alloimmunization and sickle cell disease: a narrative review on antibody induction

The high prevalence of red blood cell (RBC) alloantibodies in people with sickle cell disease (SCD) cannot be debated. Why people with SCD are so likely to form RBC alloantibodies, however, remains poorly understood. Over the past decade, a better understanding of non-ABO blood group antigen variants has emerged; RH genetic diversity and the role this diversity plays in RBC alloimmunization is discussed elsewhere. Outside of antigen variants, the immune systems of people with SCD are known to be different than those of people without SCD. Some of these differences are due to effects of free heme, whereas others are impacted by hyposplenism. Descriptive studies of differences in white blood cell (WBC) subsets, platelet counts and function, and complement activation between people with SCD and race-matched controls exist. Studies comparing the immune systems of alloimmunized people with SCD to non-alloimmunized people with SCD to race-matched controls without SCD have uncovered differences in T-cell subsets, monocytes, Fcγ receptor polymorphisms, and responses to free heme. Studies in murine models have documented the role that recipient inflammation plays in RBC alloantibody formation, with human studies reporting a similar association. Murine studies have also reported the importance of type 1 interferon (IFNα/β), known to play a pivotal role in autoimmunity, in RBC alloantibody formation. The goal of this manuscript is to review existing data on factors influencing RBC alloantibody induction in people with SCD with a focus on inflammation and other immune system considerations, from the bench to the bedside.

Effectiveness of strategies to screen for blood donors with RH variants in a mixed population

INTRODUCTION

Patients with RH variants presenting antibodies directed to RH high frequency antigens or multiple RH antibodies might, in some occasions, be better served with RH genotype-matched units, requiring screening for RH variants among blood donors. To date, strategies to identify donors with RH variants were restricted to selecting individuals of African descent based on self-reported race, what can be inaccurate in racially mixed population. Our goal was to: 1) Screen for donors with RH variants in a mixed population using self-declared race and Rh phenotype as selection criteria; and 2) Verify if including the Duffy null genotype in the screening algorithm increases its effectiveness.

METHODS

Brazilian donors were included if self-declared as black and phenotyped as R0r or R1r. All individuals were genotyped for RHCE exons 1, 5, 6 and 7 and for the FY*B c.-67 T > C polymorphism in order to determine the Duffy null genotype. RHD variants were searched for in cases of altered RHCE.

RESULTS

Among 2500 blood donors, 217 fulfilled the inclusion criteria and were enrolled. Fifty-three (24.4 %) had a predicted clinically relevant Rh phenotype (partial antigens or lack of high frequency antigens). Twelve donors (5.5 %) had a predicted RhCE phenotype lacking either hrB or hrS. Most cases with predicted lack of high frequency antigens (66.7 %) occurred in donors with the Duffy null genotype.

CONCLUSION

Selecting donors based on self-declared race, Rh phenotype and Duffy null genotype is feasible and effective in identifying RH variants lacking Rh high frequency antigens among racially mixed donors.

Diversity of RH and transfusion support in Brazilian sickle cell disease patients with unexplained Rh antibodies

BACKGROUND

Genetic diversity in the RH genes among sickle cell disease (SCD) patients is well described but not yet extensively explored in populations of racially diverse origin. Transfusion support is complicated in patients who develop unexpected Rh antibodies. Our goal was to describe RH variation in a large cohort of Brazilian SCD patients exhibiting unexpected Rh antibodies (antibodies against RH antigens to which the patient is phenotypically positive) and to evaluate the impact of using the patient's RH genotype to guide transfusion support.

STUDY DESIGN AND METHODS

Patients within the Recipient Epidemiology and Evaluation Donor Study (REDS)-III Brazil SCD cohort with unexpected Rh antibodies were selected for study. RHD and RHCE exons and flanking introns were sequenced by targeted next-generation sequencing.

RESULTS

Fifty-four patients with 64 unexplained Rh antibodies were studied. The majority could not be definitively classified as auto- or alloantibodies using serologic methods. The most common altered RH were RHD*DIIIa and RHD*DAR (RHD locus) and RHCE*ce48C, RHCE*ce733G, and RHCE*ceS (RHCE locus). In 53.1% of the cases (34/64), patients demonstrated only conventional alleles encoding the target antigen: five of 12 anti-D (41.7%), 10 of 12 anti-C (83.3%), 18 of 38 anti-e (47.4%), and one of one anti-E (100%).

CONCLUSION

RHD variation in this SCD cohort differs from that reported for African Americans, with increased prevalence of RHD*DAR and underrepresentation of the DAU cluster. Many unexplained Rh antibodies were found in patients with conventional RH allele(s) only. RH genotyping was useful to guide transfusion to determine which patients could potentially benefit from receiving RH genotyped donor units.

Recipient priming to one RBC alloantigen directly enhances subsequent alloimmunization in mice

Individuals that become immunized to red blood cell (RBC) alloantigens can experience an increased rate of antibody formation to additional RBC alloantigens following subsequent transfusion. Despite this, how an immune response to one RBC immunogen may impact subsequent alloimmunization to a completely different RBC alloantigen remains unknown. Our studies demonstrate that Kell blood group antigen (KEL) RBC transfusion in the presence of inflammation induced by poly (I:C) (PIC) not only enhances anti-KEL antibody production through a CD4⁺ T-cell-dependent process but also directly facilitates anti-HOD antibody formation following subsequent exposure to the disparate HOD (hen egg lysozyme, ovalbumin, fused to human blood group antigen Duffy b) antigen. PIC/KEL priming of the anti-HOD antibody response required that RBCs express both the KEL and HOD antigens (HOD × KEL RBCs), as transfusion of HOD RBCs plus KEL RBCs or HOD RBCs alone failed to impact anti-HOD antibody formation in recipients previously primed with PIC/KEL. Transfer of CD4⁺ T cells from PIC/KEL-primed recipients directly facilitated anti-HOD antibody formation following (HOD × KEL) RBC transfusion. RBC alloantigen priming was not limited to PIC/KEL enhancement of anti-HOD alloantibody formation, as HOD-reactive CD4⁺ T cells enhanced anti-glycophorin A (anti-GPA) antibody formation in the absence of inflammation following transfusion of RBCs coexpressing GPA and HOD. These results demonstrate that immune priming to one RBC alloantigen can directly enhance a humoral response to a completely different RBC alloantigen, providing a potential explanation for why alloantibody responders may exhibit increased immune responsiveness to additional RBC alloantigens following subsequent transfusion.

Antibody-mediated immunosuppression can result from RBC antigen loss independent of Fcγ receptors in mice

BACKGROUND

Anti-RhD administration can prevent de novo anti-RhD formation following RhD+ red blood cell (RBC) exposure, termed antibody-mediated immunosuppression (AMIS). Recent studies suggest that AMIS may occur through target antigen alterations, known as antigen modulation. However, studies suggest that AMIS may occur independent of antigen modulation. In particular, AMIS to RBCs that transgenically express the fusion hen egg lysozyme-ovalbumin-Duffy (HOD) antigen have been shown to occur independent of activating Fcγ receptors (FcγRs) thought to be required for antigen modulation. Therefore, we sought to determine the mechanism behind AMIS following HOD RBC exposure.

STUDY DESIGN AND METHODS

Following transfer of HOD RBCs into wild-type or FcγR-chain knockout recipients in the presence or absence of monoclonal anti-hen egg lysozyme (HEL) antibody, individually or in combination, HOD antigen levels and anti-HOD antibody formation were examined.

RESULTS

Our results demonstrate that anti-HEL antibodies individually or in combination suppressed anti-HOD IgM, which correlated with the rate of detectable decrease in HEL on HOD RBCs. Furthermore, exposure to anti-HEL antibodies alone or in combination equally suppressed anti-HOD IgG formation. Unexpectedly, combination or individual anti-HEL antibodies induced AMIS and antigen modulation in an FcγR-independent manner. Pre-exposure of HOD RBCs to anti-HEL antibodies reduced antigen levels and suppressed anti-HOD antibody formation following HOD RBC exposure.

CONCLUSION

These results suggest that antibody-mediated antigen modulation may reflect a mechanism of AMIS that can occur independent of activating FcγRs and may provide a surrogate to identify antibodies capable of inducing AMIS against different RBC antigens.

How I safely transfuse patients with sickle-cell disease and manage delayed hemolytic transfusion reactions

Transfusions can be a life-saving treatment of patients with sickle-cell disease (SCD). However, availability of matched units can be limiting because of distinctive blood group polymorphisms in patients of African descent. Development of antibodies against the transfused red blood cells (RBCs), resulting in delayed hemolytic transfusion reactions (DHTRs), can be life-threatening and pose unique challenges for this population with regard to treatment strategies and transfusion management protocols. In cases where the transfused cells and the patient's own RBCs are destroyed, diagnosis of DHTR can be difficult because symptoms may mimic vaso-occlusive crisis, and frequently, antibodies are undetectable. Guidelines are needed for early diagnosis of DHTR because treatment may need to include temporarily withholding any new transfusions to avoid further hemolysis. Also needed are case-control studies to optimally tailor treatments based on the severity of DHTR and develop preventive transfusion strategies for patients at DHTR risk. Here, we will review gaps in knowledge and describe through case studies our recommended approach to prevent alloimmunization and to diagnose and treat symptomatic DHTRs for which complementary mechanistic studies to understand their pathogenesis are sorely needed.

-318C/T polymorphism of the CTLA-4 gene is an independent risk factor for RBC alloimmunization among sickle cell disease patients

Cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) molecule is expressed on T-lymphocyte membrane and negatively influences the antigen-presenting process. Reduced expression of CTLA-4 due to gene polymorphisms is associated with increased risk of autoimmune disorders, whose physiopathology is similar to that of post-transfusion red blood cell (RBC) alloimmunization. Our goal was to evaluate if polymorphisms of CTLA-4 gene that affect protein expression are associated with RBC alloimmunization. This was a case-control study in which 134 sickle cell disease (SCD) patients and 253 non-SCD patients were included. All patients were genotyped for the polymorphisms 49A/G and -318C/T of CTLA-4 gene. The genotype frequency of -318C/T differed significantly between alloimmunized and nonalloimmunized SCD patients, irrespective of clinical confounders (p = .016). SCD patients heterozygous for -318T allele presented higher risk of alloantibody development (OR: 5.4, CI: 1.15-25.6). In conclusion, the polymorphism -318C/T of CTLA-4 gene is associated with RBC alloimmunization among SCD patients. This highlights the role played by CTLA-4 on post-transfusion alloantibody development.

Emerging strategies of blood group genotyping for patients with hemoglobinopathies

Red cell alloimmunization is a serious problem in chronically transfused patients. A number of high-throughput DNA assays have been developed to extend or replace traditional serologic antigen typing. DNA-based typing methods may be easily automated and multiplexed, and provide reliable information on a patient. Molecular genotyping promises to become cheaper, being not dependent on serologic immunoglobulin reagents. Patients with hemoglobinopathies could benefit from receiving extended genomic typing. This could limit post transfusional complications depending on subtle antigenic differences between donors and patients. Patient/donor compatibility extended beyond the phenotype Rh/Kell may allows improved survival of transfused units of red blood cells (RBC) and lead to reduced need for blood transfusion and leading to less iron overload and reduced risk of alloimmunization. Here we discuss the advantages and limitations of current techniques, that detect only predefined genetic variants. In contrast, target enrichment next-generation sequencing (NGS) has been used to detect both known and de novo genetic polymorphisms, including single-nucleotide polymorphisms, indels (insertions/deletions), and structural variations. NGS approaches can be used to develop an extended blood group genotyping assay system.

Red blood cell alloimmunization in patients with sickle cell disease: correlation with HLA and cytokine gene polymorphisms

BACKGROUND

The reason for the difference in susceptibility to red blood cell (RBC) alloimmunization among patients with sickle cell disease (SCD) is not clearly understood and is probably the result of multiple factors. Our hypothesis is that genetic polymorphisms are associated with RBC alloimmunization.

STUDY DESIGN AND METHODS

We investigated the possible association of susceptibility to RBC alloimmunization with polymorphisms of HLA and cytokines genes in 161 SCD patients prior exposed to RBC transfusion. Cytokine gene polymorphisms were analyzed by polymerase chain reaction (PCR) and TaqMan assays. HLA Class I genotyping was performed using PCR-specific sequence of oligonucleotides. Polymorphism frequencies were compared using the Fisher's exact test.

RESULTS

Our results revealed increased percentage of the A allele and the GA genotype of the TNFA -308G/A cytokine among alloimmunized patients when compared to nonalloimmunized patients (A allele, 16.4% vs. 6.8%, p = 0.004; GA genotype, 32.8% vs. 11.7%, p = 0.0021). In addition, the IL1B -511T allele and the IL1B -511TT and CT genotype frequencies were overrepresented among alloimmunized patients (T allele, 53.0% vs. 37.5%, p = 0.0085; CT + TT genotypes, 81.82% vs. 60.87%, p = 0.0071). In relation to HLA Class I, we found a higher frequency of HLA-DRB1*15 among patients alloimmunized to Rh antigens when compared to nonalloimmunized patients (15.63% vs. 6.98%, p = 0.044).

CONCLUSION

Brazilian SCD patients with the TNFA, IL1B, and HLA-DRB1 gene polymorphisms were at increased risk of becoming alloimmunized by RBC transfusions. These findings may contribute to the development of future therapeutic strategies for patients with SCD with higher susceptibility of alloimmunization.

Red blood cell alloimmunization is influenced by the delay between Toll-like receptor agonist injection and transfusion

Murine models of red blood cell transfusion show that inflammation associated with viruses or methylated DNA promotes red blood cell alloimmunization. In vaccination studies, the intensity of antigen-specific responses depends on the delay between antigen and adjuvant administration, with a short delay limiting immune responses. In mouse models of alloimmunization, the delay between the injection of Toll-like receptor agonists and transfusion is usually short. In this study, we hypothesized that the timing of Toll-like receptor 3 agonist administration affects red blood cell alloimmunization. Poly(I:C), a Toll-like receptor 3 agonist, was administered to B10BR mice at various time points before the transfusion of HEL-expressing red blood cells. For each time point, we measured the activation of splenic HEL-presenting dendritic cells, HEL-specific CD4(+) T cells and anti-HEL antibodies in serum. The phenotype of activated immune cells depended on the delay between transfusion and Toll-like receptor-dependent inflammation. The production of anti-HEL antibodies was highest when transfusion occurred 7 days after agonist injection. The proportion of HEL-presenting CD8α(+) dendritic cells producing interleukin-12 was highest in mice injected with poly(I:C) 3 days before transfusion. Although the number of early-induced HEL-specific CD4(+) T cells was similar between groups, a high proportion of these cells expressed CD134, CD40 and CD44 in mice injected with poly(I:C) 7 days before transfusion. This study clearly shows that the delay between transfusion and Toll-like receptor-induced inflammation influences the immune response to transfused red blood cells.

Protective effect of HLA-DQB1 alleles against alloimmunization in patients with sickle cell disease

BACKGROUND

Alloimmunization or the development of alloantibodies to Red Blood Cell (RBC) antigens is considered one of the major complications after RBC transfusions in patients with sickle cell disease (SCD) and can lead to both acute and delayed hemolytic reactions. It has been suggested that polymorphisms in HLA genes, may play a role in alloimmunization. We conducted a retrospective study analyzing the influence of HLA-DRB1 and DQB1 genetic diversity on RBC-alloimmunization.

STUDY DESIGN

Two-hundred four multi-transfused SCD patients with and without RBC-alloimmunization were typed at low/medium resolution by PCR-SSO, using IMGT-HLA Database. HLA-DRB1 and DQB1 allele frequencies were analyzed using logistic regression models, and global p-value was calculated using multiple logistic regression.

RESULTS

While only trends towards associations between HLA-DR diversity and alloimmunization were observed, analysis of HLA-DQ showed that HLA-DQ2 (p=0.02), -DQ3 (p=0.02) and -DQ5 (p=0.01) alleles were significantly higher in non-alloimmunized patients, likely behaving as protective alleles. In addition, multiple logistic regression analysis showed both HLA-DQ2/6 (p=0.01) and HLA-DQ5/5 (p=0.03) combinations constitute additional predictor of protective status.

CONCLUSION

Our data suggest that particular HLA-DQ alleles influence the clinical course of RBC transfusion in patients with SCD, which could pave the way towards predictive strategies.

Transfusion of older red blood cell units, cytokine burst and alloimmunization: a case-control study

Background

Experimental data have shown that the transfusion of older red blood cell units causes alloimmunization, but the clinical applicability of this statement has never been properly assessed in non-sickle cell patients. It has been hypothesized that older units have higher numbers of cytokines, increasing the risk of alloimmunization related to antigen-presenting events. The goal of this study was to evaluate the association between the transfusion of older red blood cell units subjected to bedside leukodepletion and alloimmunization.

Methods

All patients submitted to transfusions of bedside leukodepletion red blood cell units proven to have become alloimmunized in one oncologic service between 2009 and 2013 were enrolled in this study. A control group was formed by matching patients without alloimmunization in terms of number of transfusions and medical specialty. The median age of transfused units, the percentage of transfused red blood cell units >14 days of storage in relation to fresher red cell units (≤14 days of storage) and the mean age of transfused units older than 14 days were compared between the groups.

Results

Alloimmunized and control groups were homogeneous regarding the most relevant clinical variables (age, gender, type of oncological disease) and inflammatory background (C-reactive protein and Karnofsky scale). The median age of transfused red blood cell units, the ratio of older units transfused compared to fresher units and the mean age of transfused units older than 14 days did not differ between alloimmunized and control patients (17 vs. 17; 68/32 vs. 63.2/36.8 and 21.8 ± 7.0 vs. 21.04 ± 7.9; respectively).

Conclusion

The transfusion of older red blood cell units subjected to bedside leukodepletion is not a key risk factor for alloimmunization. Strategies of providing fresh red cell units aiming to avoid alloimmunization are thus not justified.

Alloimmunization in sickle cell disease: changing antibody specificities and association with chronic pain and decreased survival

BACKGROUND

Alloimmunization remains a significant complication of transfusion and has been associated with multiple factors, including inflammation, an important pathophysiologic mechanism in sickle cell disease (SCD). We explored whether alloimmunization is associated with disease severity in SCD.

STUDY DESIGN AND METHODS

Adult SCD patients were enrolled in a study of outcome-modifying genes in SCD. Historical records of patients with SCD at two participating institutions were reviewed for data on antigen phenotype and alloimmunization. Differences in demographic, clinical, and laboratory findings; end-organ damage; and overall disease severity were then compared between alloimmunized and nonalloimmunized patients.

RESULTS

Of 319 patients, 87 (27%) were alloimmunized. Alloantibody specificities differed from those previously described, especially due to the significantly higher frequency of anti-S. Although alloimmunization was not associated with frequency of vasoocclusive episodes, a higher percentage of alloimmunized patients had chronic pain, as defined by daily use of short-acting narcotics (p = 0.006), long-acting narcotics (p = 0.013), or both (p = 0.03). Additionally, alloimmunized patients had poorer survival (hazard ratio, 1.92; p = 0.01) and were more likely to have avascular necrosis (p = 0.024), end-organ damage (p = 0.049), and red blood cell autoantibodies (p < 0.001), even after controlling for the effects of age, sex, and hemoglobin diagnosis. Alloimmunization was not associated with other SCD-related complications, such as acute chest syndrome or stroke.

CONCLUSION

Alloimmunization in SCD may be associated with chronic pain, risk of end-organ damage, and shorter survival. These novel findings suggest new directions for the investigation of immune response-mediated pathways common to alloimmunization and chronic pain.

Factors Influencing RBC Alloimmunization: Lessons Learned from Murine Models

Red blood cell (RBC) alloimmunization may occur following transfusion or pregnancy/delivery. Although observational human studies have described the immunogenicity of RBC antigens and the clinical significance of RBC alloantibodies, studies of factors influencing RBC alloimmunization in humans are inherently limited by the large number of independent variables involved. This manuscript reviews data generated in murine models that utilize transgenic donor mice, which express RBC-specific model or authentic human blood group antigens. Transfusion of RBCs from such donors into nontransgenic but otherwise genetically identical recipient mice allows for the investigation of individual donor or recipient-specific variables that may impact RBC alloimmunization. Potential donor-related variables include methods of blood product collection, processing and storage, donor-specific characteristics, RBC antigen-specific factors, and others. Potential recipient-related variables include genetic factors (MHC/HLA type and polymorphisms of immunoregulatory genes), immune activation status, phenotype of regulatory immune cell subsets, immune cell functional characteristics, prior antigen exposures, and others. Although murine models are not perfect surrogates for human biology, these models generate phenomenological and mechanistic hypotheses of RBC alloimmunization and lay the groundwork for follow-up human studies. Long-term goals include improving transfusion safety and minimizing the morbidity/mortality associated with RBC alloimmunization.

Immunologic characterization suggests reduced alloimmunization in a murine model of thalassemia intermedia

BACKGROUND

Transfusion therapy remains a mainstay of treatment for patients with thalassemia major and to a lesser extent for the less anemic patients with thalassemia intermedia. We have previously reported a role for regulatory T cells (Tregs) in the control of antibody responses in wild-type C57BL/6 (WT) mice exposed to allogeneic red blood cell transfusions. As an initial step to study and characterize immune regulation in thalassemias, we performed an immunologic cell-type characterization of C57BL/6 Hbb(th-1)/Hbb(th-1) mouse model of thalassemia intermedia (Thal) in steady state as well as after transfusions with allogeneic blood.

STUDY DESIGN AND METHODS

The myeloid and lymphocyte compartments including Tregs and T helper (Th) responses were analyzed in transfusion naive Thal and WT mouse spleens. The effect of allogeneic transfusions on Treg and global T helper responses was also measured.

RESULTS

We found elevated levels and activity of splenic Tregs in Thal mice with lower Th type 1/Th type 2 ratios before as well as after transfusion. Furthermore, pretransfused Thal mice had altered ratios of the splenic myeloid compartment with increased proportion of macrophages but lower frequency of conventional dendritic cells. Surprisingly, transfusions resulted in lower alloimmunization levels in Thal compared to WT mice.

CONCLUSION

These data suggest that this experimental model of thalassemia intermedia has an intrinsic alteration in splenic immunoregulation with an increased resistance to alloimmunization, raising the possibility that studying this animal model may help to identify potential immunoregulatory networks to inhibit alloimmunization.

Red blood cell alloimmunization is influenced by recipient inflammatory state at time of transfusion in patients with sickle cell disease

Sickle cell disease (SCD) patients are at increased risk of red blood cell (RBC) alloimmunization. Recipient inflammatory state at time of transfusion has been shown to regulate alloimmunization in murine models, but evidence is lacking in SCD patients. We retrospectively studied a cohort of alloimmunized SCD patients to determine the influence of pro-inflammatory SCD-related complications at time of transfusion on alloimmunization. For each transfusion, the presence of pro-inflammatory state, degree of RBC antigen matching, unit age, storage solution and alloantibody detection date were ascertained. Transfusion-associated pro-inflammatory events were compared between transfusions resulting and not resulting in new alloantibodies. Univariate analysis and multivariate logistic regression were performed. Fifty-two patients received 3166 pre-storage leuco-reduced transfusions of which 128 resulted in alloantibodies. Transfusions during inflammatory events were associated with increased alloantibody risk on univariate and multivariate analysis; acute chest syndrome and vaso-occlusive crisis showed strongest associations with alloimmunization. Increased antigen matching demonstrated a protective effect on alloimmunization (univariate and multivariate analysis). Although an association was seen between citrate-phosphate-dextrose (adenine) stored units and alloimmunization on univariate analysis, no effect was found on multivariate analysis. Identifying recipient pro-inflammatory states at time of transfusion that promote alloimmunization can impact RBC unit selection decisions for SCD patients at risk for alloimmunization.

Challenges of alloimmunization in patients with haemoglobinopathies

Red blood cell (RBC) transfusions can be life-sustaining in chronic inherited anaemias, such as thalassaemia, and the indications for blood transfusions in patients with sickle cell disease continue to expand. Complications of transfusions, such as allosensitization, can create significant medical challenges in the management of patients with haemoglobinopathies. This review summarizes key findings from the medical literature related to alloimmunization in haemoglobinopathies and examines potential measures to mitigate these risks. Areas where future studies are needed are also addressed.

Red blood cell alloimmunization in sickle cell disease: pathophysiology, risk factors, and transfusion management

Red blood cell transfusions have reduced morbidity and mortality for patients with sickle cell disease. Transfusions can lead to erythrocyte alloimmunization, however, with serious complications for the patient including life-threatening delayed hemolytic transfusion reactions and difficulty in finding compatible units, which can cause transfusion delays. In this review, we discuss the risk factors associated with alloimmunization with emphasis on possible mechanisms that can trigger delayed hemolytic transfusion reactions in sickle cell disease, and we describe the challenges in transfusion management of these patients, including opportunities and emerging approaches for minimizing this life-threatening complication.