Risk factors for alloimmunization by patients with sickle cell disease

Global burden of transfusion in sickle cell disease

Sickle cell disease (SCD) is the most common hereditary hemoglobinopathy. The underlying pathophysiology of the red blood cell (RBC) leads to pan-systemic complications which manifest at an early age. While curative and disease-modifying treatments exist for SCD, a key intervention in the management and treatment of SCD is RBC transfusion, which can alleviate or prevent many complications. SCD patients often require chronic RBC transfusion therapy which can result in complications, such as iron overload, alloimmunization and infection. In low- and middle-income countries (LMICs), SCD patients lack appropriate access to healthcare such as newborn screening, health education, prophylaxis for infection, and treatments to reduce both mortality and SCD-related adverse effects. Poor access to RBCs for transfusion, coupled with donated blood not meeting safety standards set by the World Health Organization, presents a significant barrier for patients requiring chronic transfusions in LMICs. Unmet needs associated with blood collection, blood component processing and recipient matching all pose a serious problem in many LMICs, although this varies depending on geographic location, political organizations and economy. This review aims to provide an overview of the global burden of SCD, focusing on the availability of current treatments and the burden of chronic RBC transfusions in patients with SCD.

Study of the Frequency and Specificity of Red Cell Antibodies in Patients with Hemoglobinopathies

Patients with thalassemia and sickle cell disease (SCD) require blood transfusions as part of their supportive care. However, one of the most serious side effects of this treatment is the risk of red cell alloimmunization. The goal of this study was to assess the prevalence and Specificity of red cell alloimmunization in Egyptian thalassemia and sickle cell anaemia patients. This study included 200 multi transfused Egyptian patients, one hundred and forty patients with transfusion dependent thalassaemia and sixty patients with sickle cell anaemia, who were attending the Paediatric Children Hospital-Cairo University at the period from March 2019 to October 2019. Alloantibody identification was made by Diamed- ID microtyping system. In the studied groups both thalassemia and sickle patients, the prevalence of alloimmunization was 22/200 (11%) patients. The two most often alloantibodies were, antibodies against Kell antigen (37%) and against E antigen (30%). The prevalence of alloimmunization was more in females in comparison to males, but it did not reach statistical significance and patients with thalassemia major had higher alloimmunization rates than other studied groups but was not statistically significant. In the D negative patients in the research group, alloimmunization demonstrated a statistically significant difference (p = 0.01). Age, gender, age of transfusion onset and splenectomy were not contributing factors to the antibody presence in the group of patients being investigated. Before receiving blood transfusions, extended red blood cell phenotyping should be thought of as a crucial procedure for hemoglobinopathies patients who would likely have several transfusions. It is advised that haemoglobinopathies patients in Egypt be checked through phenotyping of RBC units for Kell and all Rh antigens to be phenotyped before starting transfusion in these patients which is also standard of care for these patients presently.

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.

Major histocompatibility complex (MHC) antigens polymorphism and alloimmunization study in thalassemia patients with febrile non-hemolytic transfusion reaction (FNHTR)

OBJECTIVES

HLA alloimmunization is one of the most troublesome consequence of regular transfusion which is itself a mainstay measure to provide longevity to the thalassemia patients. Febrile non-hemolytic transfusion reaction (FNHTR) is one of the most common complication which might be related to the HLA alloimmunization. Here, we studied the HLA antigenic system and alloimmunization rate in the Iranian β-thalassemia patients who suffered from FNHTR compare to the β-thalassemia patients without FNHTR.

MATERIALS & METHODS

Total of 60 β-thalassemia patients with FNHTR (case group) and 20 β-thalassemia patients without FNHTR (control group) randomly have been selected and enrolled in the study. All were tested for HLA-A and -B loci by PCR-SSP method and also for the presence of anti-lymphocyte antibodies by LIFT method. Comparisons between two groups were performed by Pearson's χ2 test.

RESULTS

Totally, a significant predominance was noted for two HLA alleles, HLA-A*24 (P = 0.029) and B*55 (P = 0.034) which have higher prevalence in control group. Although no significant association was found between the presence of anti-leukocyte antibodies and the development of FNHTR, the HLA-A*32 (P = 0.047) allele was considered as possible genetic markers in the susceptibility to the development of anti-leukocyte antibodies.

CONCLUSION

Here some evidences about the possible role of HLA polymorphism in susceptibility to FNHTR are provided. Those results indicated that HLA-A*24 and HLA-B*55 might play protective role on inducing FNHTR in β-thalassemia patients. Further studies which investigate the allele level of HLA-I alongside with specific reactivity of HLA-I antibodies might reveal more deep data about these phenomena.

Increased Prevalence of Alloimmunization in Sickle Cell Disease? Should We Restore Blood Donation in French Guiana?

Patients with sickle cell disease often undergo frequent blood transfusions. This increases their exposure to red blood cell alloantigens of donor units, thus making it more likely that they produce alloantibodies. This cross-sectional study aimed to describe the prevalence of allo-immunization in patients with sickle cell disease who were monitored at Cayenne Hospital in 2016. Of the 451 patients recruited during the study period, 238 (52.8%) were female. There were 262 (58.1%) homozygous sickle cell and 151 (33.5%) compound heterozygous sickle cell patients. The median age of the participants was 23.09 years (range, 0.5–68). We noted different red blood cell extended phenotypes: -in the Duffy system, the Fy^a- Fy^b–profile was found in 299 patients (66%);—for the Kidd system, the most represented profile was Jka+ Jkb-, with 213 patients (47%). The Jka antigen was present in 355 patients;—in the MNS system, the S-s+ profile was found in 297 patients (66%);—the Lea antigen of the Lewis system was absent in 319 patients. The most frequent Rh phenotype in our patients was D+ C- E- c+ e+ K-, representing 51% of the patients. A total of 6,834 transfused packed red blood cell units were recorded. Sixty-eight patients (23%; 95% confidence interval, 20–25%) had detectable RBC alloantibodies. In multivariate logistic regression, only the mean number of single transfusions was statistically higher for the alloimmunized patients (p < 0.04). Thirteen (19%) of the patients with alloimmunization developed a delayed hemolytic transfusion reaction, thus representing 4.4% of the total number of transfused patients. Whether differences between donors from France vs. recipients from French Guiana could explain this high prevalence of alloimmunization to be examined. In conclusion, careful transfusion strategies for patients with RBC alloantibodies should allow further reduction of the rate of alloimmunization.

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.

Retrospective Study on Prevalence, Specificity, Sex, and Age Distribution of Alloimmunization in Two General Hospitals in Athens

Objective:

Blood transfusion is a common lifesaving treatment but it is often complicated with alloimmunization. Previously studies in Greece have concentrated on alloimmunization in multiply transfused thalassemic patients or antenatal women. However, the relative frequency of red blood cell (RBC) alloantibodies in the general patient population has not been studied so far. The aim of the present retrospective study was to estimate the prevalence and specificity of RBC alloantibodies in a large cohort of patients in two general hospitals and their association with age, sex, and the patients’ clinic of hospitalization.

Materials and Methods:

Data from 2012 to 2016 from the “Sismanogleio” and “Thriasio” general hospitals in Athens, Greece, were studied retrospectively. Statistical analysis was performed with SAS for Windows 9.4.

Results:

Six hundred twenty-six patients (626/53800, 1.16%) were alloimmunized for one or more alloantibodies. The mean age was 67.99±17.56 years. Most antibodies were found in women [62.66% (438/699) in women vs. 37.34% (261/699) in men (p=0.0007)], while the vast majority of antibodies (66.81%) were found in patients aged 61-90. The most frequent antibody was anti-Kell (26.61%), followed by anti-E (16.02%), anti-D (15.02%), anti-Jka (5.87%), and anti-M (5.72%). Anti-C (81.48%, n=27) and anti-Cw (54.17%, n=24) tended to be found more often in patients with multiple antibodies. Most alloimmunized cases were found in general surgery (42.65%) and internal medicine departments (38.66%).

Conclusion:

According to our results, the alloimmunization data in a general patient population in Greece were consistent with the majority of studies in the international literature. Whether a strategy at national level needs to be directed towards extending matching for the whole population or towards applying sensitive and compulsory indirect antiglobulin tests before any transfusions in order to efficiently prevent alloimmunization remains an issue of debate.

Chronic transfusion therapy effectiveness as primary stroke prophylaxis in sickle cell disease patients

Introduction

About 10% of sickle cell anemia patients will have ischemic stroke. Adams showed stroke incidence reduction in children receiving monthly erythrocyte transfusions by reducing transcranial Doppler (TCD) velocities. Since then, chronic transfusion is recommended as primary stroke prophylaxis. This study aims to assess the effectiveness of chronic transfusions as stroke prophylaxis.

Method

Retrospective study, reviewing medical records from 15 sickle cell anemia patients undergoing chronic transfusion. Data collected were age, sex, adverse reactions, stroke, hemoglobin, reticulocytes, ferritin, HbS and TCD values (baseline, after 12 and 24 months of treatment).

Results

The mean age was 118.67 ± 41.40 months; six patients experienced allergic reactions. No stroke was recorded. One patient had alloimmunization. There was a decrease in the HbS rate and an increase in hemoglobin values in the first 12 months. Values were maintained after 24 months, but with no improvement of data. Before treatment, the mean HbS rate was 75.18%±11.69; after 12 months, 41.63 ± 14.99 and after 24 months, 43.78 ± 10.6. Thirteen patients initiated chelation after 12 months from the beginning of chronic transfusions and ferritin decline after 24 months. Pre-transfusional TCD velocities were 204.28 ± 9.41 cm/s (right) and 198.85 ± 33.37 cm/s (left). After a 12-month treatment, these values were 158.5 ± 28.89 cm/s and 157.62 ± 34.43 cm/s, respectively, and this reduction was statistically significant (p = 0.002 right and p = 0.02 left). After 24 months, these values were 149.63 ± 26.95 cm/s (right) and 143.7 ± 32.27 cm/s (left).

Conclusion

Significant reduction of TCD velocity occurred after treatment with chronic transfusion in sickle cell anemia patients, leading to a normal or conditional test and reducing stroke risk in all but one patient.

Red Blood Cell Alloimmunization in Transfused Patients With Sickle Cell Disease in Sub-Saharan Africa; a Systematic Review and Meta-Analysis

Sickle cell disease (SCD) is the most common monogenic disorder in sub-Saharan Africa (SSA). Blood transfusion to increase the oxygen carrying capacity of blood is vital in the management of many patients with SCD. However, red blood cell (RBC) alloimmunization is a major challenge to transfusions in these patients. Commonly in SSA, pretransfusion tests only involve ABO D grouping and compatibility without RBC antibody testing. Data on the frequency of RBC alloimmunization in patients with SCD in SSA are limited. We performed a systematic review and meta-analysis on available data on alloimmunization in transfused patients with SCD to determine the published prevalence of RBC alloimmunization in SCD patients in SSA. Six databases were systematically searched to identify relevant studies, without year or language restrictions. In all, 249 articles were identified and 15 met our selection criteria. The overall proportion of alloimmunization was 7.4 (95% confidence interval: 5.1-10.0) per 100 transfused patients. Antibodies against E, D, C, and K antigens accounted for almost half of antibody specificities, and antibodies to low- and high-frequency antigens were also common and represented almost 30% (20% to low-frequency antigens and 9% to high-frequency antigens) of specificities. Heterogeneity between studies was moderate, and meta-analysis found region of Africa as the major contributor to the heterogeneity. We also observed inconsistencies across studies in reporting of factors that may influence alloimmunization. This review provides an overview of the extent of the alloimmunization problem in SSA and provides a baseline against which to compare the effect of any interventions to reduce the alloimmunization risk.

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.

Rh-Matched Transfusion through Molecular Typing for β-Thalassemia Patients Is Required and Feasible in Chinese

Background

Molecular typing for RHCE blood group alleles has been established in many countries for patients and blood donors. In the Chinese literature nearly 80% of transfused patients with alloimmunization have antibodies specific for antigens of the Rh blood group system. We investigated if it is feasible to match packed red blood cells (RBCs) for Chinese β-thalassemia patients by RHCE genotyping.

Methods

In this study, 481 patients with β-thalassemia were enrolled. They were genotyped for RHCE alleles by a simple PCR method with sequence-specific primers (PCR-SSP). Among these patients, 203 continuously received RBCs of the identical Rh subgroups according to the genotyping results for at least 3 months. Subsequently, their phenotypes were tested through a micro-column gel card method. For validation purposes, 400 donors were serologically typed with the same technology, of which 164 were genotyped too. Finally, the C, c, E, and e frequencies and the feasibility of the simple genotyping method were analyzed.

Results

All patients showed mixed-field agglutination in the Rh subgroup gel cards before the same Rh subgroups in blood donors were selected for blood transfusion. The results, however, lacked mixed-field agglutination in all 203 cases after transfusion with RBC concentrates selected for the patient's C, c, E, and e antigens for at least 3 months. The genotyping results of 164 donors were all consistent with the serological results. Whole coding regions of RHCE were sequenced in 7 individuals with weak c, E, or e antigens. In only one sample we observed a 1059G>A nucleotide mutation coding for a truncated RhCE polypeptide (GenBank KT957625), in the other 6 samples no sequence variant was found. Both patients and donors were predominantly CcEe and CCee, with a prevalence of 55.3% and 24.9% for patients or 49.3% and 31.3% for donors, respectively. It revealed that about 80% of Chinese could receive Rh-matched RBCs easily.

Conclusion

A simple RHCE genotyping technique is safe enough for Rh-matched transfusion of β-thalassemia patients in Chinese Han.

Frequency of Red Blood Cell Alloimmunization in Patients with Sickle Cell Disease in Palestine

Background

Transfusion of red blood cells (RBC) is an essential therapeutic tool in sickle cell disease (SCD). Repeated RBC transfusions can cause alloimmunization which causes difficulty in cross-matching and finding compatible blood for transfusions. This study aimed to investigate the frequency of RBC alloimmunization and related risk factors among Palestinian SCD patients.

Materials and Methods

A multicenter cross-sectional study on 116 previously transfused SCD patients from three centers in West Bank, Palestine. Demographic, medical data and history of transfusion were recorded. Blood samples were collected from transfused consenting SCD patients. Gel card method was used for antibody screening and identification. In all patients, autocontrol and direct antiglobulin (DAT) test were performed using polyspecific (anti-IgG + C3d) anti-human globulin (AHG) gel cards for the detection of autoantibodies.

Results

Of the SCD patients, 62 (53.4%) patients were HbSS and 54 (46.6%) patients were sickle β-thalassemia (S/β-thal). There were 53 (45.7%) females and 63 (54.3%) males. Mean age was 18.8 years (range 3-53 years). The frequency of RBC alloimmunization among SCD patients was 7.76%, with anti-K showing the highest frequency (33.3%) followed by anti-E (22.2%), anti-D (11.1%), anti-C (11.1%), and anti-c (11.1%). All reported IgG alloantibodies were directed against antigens in the Rh (66.7%) and Kell (33.3%) systems. Older ages of patients, increased number of blood units transfused, and splenectomy were the commonest risk factors for alloimmunization in our study.

Conclusions

RBC alloimmunization rate among Palestinian SCD patients is low compared to neighboring countries and countries all over the world but still warrants more attention. Phenotyping of donors/recipients' RBC for Rh antigens and K₁ (partial phenotype matching) before their first transfusion may reduce the incidence of alloimmunization.

The erythrocyte alloimmunisation in patients with sickle cell anaemia: a systematic review

Transfusion therapy is a common practice in the treatment of anaemia and can cause erythrocyte alloimmunisation. To systematise data related to erythrocyte alloimmunisation in patients with sickle cell disease (SCD), a bibliographic search was carried out in September 2017 to search for studies in four electronic databases. (i) Referring to the original work, (ii) being cohort or case-control, (iii) having been developed with individuals with SCD and (iv) having evaluated the erythrocyte alloimmunisation. Two reviewers identified the articles for inclusion in the study, extracted the predetermined data and carried out the evaluation of the methodological quality of the work. 21 studies were selected; the studies included data on 20 636 individuals (children and adults), were mostly published in the last 10 years, were developed in the United States and had high methodological quality. The occurrence of erythrocyte alloimmunisation ranged from 4·4 to 76%, and there was a higher rate of alloimmunisation against antigens of the Rh system. The risk factors for alloimmunisation were age; gender (female); red blood cell (RBC) units received; presence of ≥1 autoantibodies, TNF-α, interleukin (IL1B), human leukocyte antigens (HLA)-DRB1 gene polymorphisms; first blood transfusion (BT) after 5 years of age, transfusion episodic, multiple or during inflammatory events, acute chest syndrome (ACS) and vase-occlusive crisis (VOC); increased percentage of CD41 T memory cells; and positive direct antiglobulin test. Transfusion policies should be developed to protect the patient and his or her health based on the main factors associated with its incidence.

Genomewide association study of HLA alloimmunization in previously pregnant blood donors

BACKGROUND

Alloimmunization through blood transfusion, transplantation, or circulating fetal cells during pregnancy is a significant concern. Some exposed individuals make alloantibodies while others do not, implying variation in genetic risk factors.

STUDY DESIGN AND METHODS

We conducted a genomewide association study (GWAS) of 9,427,497 single-nucleotide polymorphisms (SNPs) to identify genetic variants for HLA alloimmunization in previously pregnant blood donors with (n = 752) and without (n = 753) HLA Class I or II alloantibodies.

RESULTS

A SNP in the neurexophilin 2 (NXPH2) gene surpassed genome-wide significance (p = 2.06 × 10-8 ), with multiple adjacent markers p < 10-6 , for women with anti-Class I alloantibodies only. Little is currently known about the function of NXPH2, although gene family members have been shown to impact immunity. SNPs in the E2F7 gene, a transcription factor related to cell cycle control and cellular proliferation, also approached genomewide significance (p = 2.5 × 10-7 ).

CONCLUSION

Further work to extend the GWAS approach and to characterize variants in NXPH2 and E2F7 in the context of alloantibody formation is warranted.

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.

Prevalence and risk factors for red blood cell alloimmunization in 175 children with sickle cell disease in a French university hospital reference centre

Patients with sickle cell disease (SCD) show a high prevalence of red blood cell (RBC) alloimmunization, but few studies have focused on children. We aimed to study the prevalence and risk factors of RBC alloimmunization in SCD children. We retrospectively analysed the medical and transfusion files for 245 SCD children hospitalized in our centre in 2014 and included 175 patients who had received at least one RBC unit in their lifetime. The main clinical and immuno-haematological characteristics of alloimmunized and non-alloimmunized patients were compared. The prevalence of alloimmunization was 13·7% [95% confidence interval (CI) (8·6-18·6)], and 7·4% [95% CI (3·5-11·3)] after excluding the probable irregular natural antibodies (anti-M, anti-Le^a , anti-Le^b , anti-Le^x ). Main risk factors for alloimmunization were increased number of RBC units received (median of 65 vs. 10 units per patient; P = 0·01) and the presence of one or more red cell autoantibodies (46·2% vs. 4·7%; P < 0·0001). The alloimmunization rate was higher for episodically transfused than chronically transfused patients (1·43 vs. 0·24/100 units received; P < 0·001). The presence of red cell autoantibodies appears to be a major risk factor for alloimmunization in SCD children and could justify specific transfusion guidelines.

Alloimmunization in Patients with Sickle Cell Disease and Thalassemia: Experience of a Single Centre in Oman

Background

Blood transfusion is an integral part of the supportive care for patients with sickle cell disease (SCD) and thalassaemia. The hazard of red cell alloimmunization, however, is one of the main complications of this therapy.

Objectives

The aim of this study was to evaluate the prevalence of red cell alloimmunization in Omani patients with sickle cell anaemia and thalassemia.

Methods

This study included 262 patients whose historical transfusion records were available. One hundred and twenty-nine patients with thalassaemia who were attending the day care unit for regular transfusions, and 133 SCD patients admitted at our hospital were included in this study. The Diamed® gel system was used for the screening and identification of atypical antibodies.

Results

The rate of alloimmunization in SCD patients was 31.6% (n=42, 95%CI, 24.87–40.66), whereas in patients with thalassaemia it was 20% (n=26; 95%CI, 13.9–27.6). Antibodies to E, e, C, c, D, K, S, Fyª, Kpª, Jkª and C^w were observed; 85% of the patients were also immunised with Rh and Kell antigens. Considering the two groups together, 8 developed nonspecific antibodies and 12 developed more than one antibody.

Conclusions

Red cell transfusions were associated with a significant risk of alloimmunization. It is, therefore, imperative to perform an initial extended red cell phenotyping for both donors and recipients, and carefully select ABO, Rh and Kell matched donors. The higher incidence of alloimmunization in SCD patients is related to the inherent SCD-specific inflammatory state.

Early occurrence of red blood cell alloimmunization in patients with sickle cell disease

Red blood cell (RBC) alloimmunization is a major complication of transfusion therapy in sickle cell disease (SCD). Identification of high-risk patients is hampered by lack of studies that take the cumulative transfusion exposure into account. In this retrospective cohort study among previously non-transfused SCD patients in the Netherlands, we aimed to elucidate the association between the cumulative transfusion exposure, first alloimmunization and independent risk factors. A total of 245 patients received 11 952 RBC units. Alloimmunization occurred in 43 patients (18%), half of them formed their first alloantibody before the 8th unit. In patients with exposure to non-extended matched transfusions (ABO and RhD) the cumulative alloimmunization risk increased up to 35% after 60 transfused units. This was significantly higher compared to a general transfused population (HR 6.6, CI 4.2-10.6). Receiving the first transfusion after the age of 5 was an independent risk factor for alloimmunization (HR 2.3, CI 1.0-5.1). Incidental, episodic transfusions in comparison to chronic scheme transfusions (HR 2.3, CI 0.9-6.0), and exposure to non-extended matched units in comparison to extended matching (HR 2.0, CI 0.9-4.6) seemed to confer a higher alloimmunization risk. The majority of first alloantibodies are formed after minor transfusion exposure, substantiating suggestions of a responder phenotype in SCD and stressing the need for risk factor identification. In this study, older age at first transfusion, episodic transfusions and non-extended matched transfusions appeared to be risk factors for alloimmunization. Am. J. Hematol. 91:763-769, 2016. © 2016 Wiley Periodicals, Inc.

Clinically relevant RHD-CE genotypes in patients with sickle cell disease and in African Brazilian donors

BACKGROUND

As a consequence of the homology and opposite orientation of RHD and RHCE, numerous gene rearrangements have occurred in Africans and resulted in altered RH alleles that predict partial antigens, contributing to the high rate of Rh alloimmunisation among patients with sickle cell disease (SCD). In this study, we characterised variant RH alleles encoding partial antigens and/or lacking high prevalence antigens in patients with SCD and in African Brazilian donors, in order to support antigen-matched blood for transfusion.

MATERIAL AND METHODS

RH genotypes were determined in 168 DNA samples from SCD patients and 280 DNA samples from African Brazilian donors. Laboratory developed tests, RHD BeadChip(TM), RHCE BeadChip(TM), cloning and sequencing were used to determine RHD-CE genotypes among patients and African Brazilian blood donors.

RESULTS

The distributions of RHD and RHCE alleles in donors and patients were similar. We found RHCE variant alleles inherited with altered RHD alleles in 25 out of 168 patients (15%) and in 22 out of 280 (7.8%) African Brazilian donors. The RHD and RHCE allele combinations found in the population studied were: RHD*DAR with RHCE*ceAR; RHD*weak D type 4.2.2 with RHCE*ceAR, RHD*weak D type 4.0 with RHCE*ceVS.01 and RHCE*ceVS.02; RHD*DIIIa with RHCE*ceVS.02. Thirteen patients and six donors had RHD-CE genotypes with homozygous or compound heterozygous alleles predicting partial antigens and/or lacking high prevalence antigens. Eleven patients were alloimmunised to Rh antigens. For six patients with RHD-CE genotypes predicting partial antigens, no donors with similar genotypes were found.

DISCUSSION

Knowledge of the distribution and prevalence of RH alleles in patients with SCD and donors of African origin may be important for implementing a programme for RH genotype matching in SCD patients with RH variant alleles and clinically significant Rh antibodies.

Incidence of alloimunization in sickle cell disease: experience of a center in São Paulo

OBJECTIVE

To identify the incidence of alloimmunization in sickle cell disease patients, as well as autoantibodies and the phenotypic profile of these patients for the following erythrocyte antigen groups: Rh, Kell, Kidd, Duffy and MNS.

METHODS

fifty-seven patients were evaluated during follow-up at the Anemia Outpatient Clinic of Irmandade da Santa Casa de São Paulo, where a search for irregular antibodies and phenotyping was carried out.

RESULTS

Patients' median alloimmunization age in sickle cell disease was 25 years, and irregular antibodies were found in 22.6% of them. Anti-Kell antibody was the most frequent (7.5%) followed by anti-C (5.7%).

CONCLUSION

The prevalence of alloimmunization and of patients with autoantibodies among individuals with sickle cell disease followed at the Anemia Outpatient Clinic of Irmandade da Santa Casa de Misericórdia de São de Paulo was determined. The risk of alloimmunization was higher in patients who received more than 3 red blood cell units in the past 2 years. The most prevalent alloantibodies were anti-Kell and anti-C.

Phenotyping Rh/Kell and risk of alloimmunization in haematological patients

BACKGROUND

One of the biggest concerns in transfusion medicine is to avoid red blood cell alloimmunization. We evaluated the rate of alloimmunization in two groups of chronically transfused patients (A - not phenotyped and B - phenotyped for Rh/K antigens before the first transfusion) with primary haematological disorders and its distribution among the main haematological diseases, in order to adopt an efficient transfusional strategy.

STUDY DESIGN AND METHODS

As methodology, we used the SIBAS and SAM databases for the retrospective study of all patients with primary haematological disorder between January 2011 and April 2013.

RESULTS

A statistical difference in the rate of alloimmunization comparing groups A and B was found (P <0·0001). We also observed that alloimmunization was not homogeneously distributed in all primary haematological diseases.

CONCLUSIONS

The Rh/K phenotype should be performed on all patients diagnosed with bone marrow failure, plasma cell dyscrasia and myelodysplastic syndrome in order to avoid alloimmunization. In patients with acute leukaemia and lymphoma it seems not necessary to perform it. In patients with haemoglobinopathy and myeloproliferative disorders, a larger group of patients is needed to decide its efficacy.

Pattern and prevelence of alloimmunization in multiply transfused patients with sickle cell disease in Nigeria

BACKGROUND AND STUDY OBJECTIVES

Blood transfusion is central in the prevention and treatment of certain chronic complications of sickle cell disease. It is indispensible in correcting anaemias as well as in the practice of exchange blood transfusion. These gains are largely limited by formation of allo-antibodies. Several studies demonstrated varying frequencies of allo-immunization in various patient groups. The effect of the racial differences between the donor and recipient pool, which has been subsumed in this study, has continuously created a confounding effect on the results of previous studies.

AIM

This study was aimed at determining the pattern and frequency of allo-immunization in multiply transfused sickle cell patients, in a racially matched donor and recipient population.

PATIENTS AND METHODS

This was a cross-sectional case-controlled study involving 80 Nigerian sickle cell disease patients who had received three or more units of packed red cells in the within 4 weeks of the study and 40 controls (who were SCD that had not been transfused in their life time). Antibody screening and identification was done using the Diamed microtyping system.

RESULTS

Frequency of allo-immunization was determined to be 18.7 % (15/80) among the previously transfused and 5 % (15/120) in all sickle cell disease patients. Auto-antibodies were detected in 1.25 % of the study group and 2.5 % of the control, and all reacted with the Kell and Lutheran blood group antigens. The pattern of allo-antibodies found showed; 46.7 % Rhesus, 40 % Kell, while Lutheran and Duffy 13.3 %, each.

CONCLUSION

Sickle cell disease patients are particularly susceptible to development of allo-antibodies despite racial similarities between the donor and recipient population. The most common allo-antibodies are Rhesus, Kell and Lutheran and Duffy respectively in order of decreasing frequency. Development of auto-antibodies seems to be independent of blood transfusion in sickle cell disease with possibly different pathogenetic mechanism. Policy on extended red cell phenotyping for common antigens will reduce allo-immunization among multiply transfused patients.

Red cell allo- and autoimmunisation in transfused sickle cell and cancer patients in Kenyatta National Hospital, Nairobi, Kenya

Background

Currently, no data are available on the prevalence of red blood cell (RBC) antibody formation amongst Kenyan patients with multiple transfusion needs, such as patients with sickle cell disease (SCD) or haematological malignancies (HM) and solid (SM) malignancies.

Objectives

We determined the prevalence and specificities of RBC alloantibodies and autoantibodies in two patient groups with recurrent transfusion demands at Kenyatta National Hospital, Nairobi, Kenya.

Method

Between February and August 2014, 300 samples from SCD, HM and SM patients were collected and screened for alloantibodies. Samples from 51 healthy blood donors were screened for irregular antibodies and phenotyped.

Results

Amongst the 228 patients with viable samples (SCD, n = 137; HM, n = 48; SM, n = 43), the median transfusion frequency was two to three events per group, 38 (16.7%) were RBC immunised and 32 (14.0%) had a positive direct antiglobulin test. We identified specific alloantibodies in six patients (2.6%). Four of these six were SCD patients (2.9%) who had specific RBC alloantibodies (anti-C^w, anti-M, anti-Co^b, anti-S); amongst HM patients one had anti-K and one had anti-Le^a. RBC autoantibody prevalence was 3.1% (7/228). Amongst the healthy blood donors, the R_or, ccD.ee and R₂r, ccD.Ee phenotypes accounted for 82% of the Rhesus phenotypes and all were Kell negative.

Conclusion

The numbers of transfusions and the rates of RBC alloantibodies are low and the most important RBC alloantibody-inducing blood group antigens are relatively homogeneously distributed in this population. A general change in the Kenyatta National Hospital pre-transfusion test regimen is thus not necessary. The current transfusion practice should be reconsidered if transfusion frequencies increase in the future.

Predictors of Red Cell Alloimmunization in Kurdish Multi Transfused Patients with Hemoglobinopathies in Iraq

Hemoglobinopathies are significant health problems in Iraq, including its Northern Kurdistan region. One of the essential components of management of these disorders is regular lifelong blood transfusions. The latter is associated with several complications including red cell alloimmunization. No study has looked at the frequency of alloimmunization and its associations in the country. To address the latter issue, 401 multi transfused patients [311 with β-thalassemia (β-thal) syndrome and 90 with sickle cell disease], registered at a large thalassemia care center in Iraqi Kurdistan had their records reviewed, and their sera tested for atypical antibodies using screening and extended red cell panels. Red cell alloimmunization was detected in 18 patients (4.5%) with a total of 20 alloantibodies, while no autoantibodies were detected. The most frequent alloantibody was anti-E, followed by anti-D, anti-K, anti-C(w), anti-C, anti-c and anti-Le(a). Ethnicity was an important predictor of alloimmunization, while age at start of transfusion (>2 vs. ≤2 years) (p = 0.005), Rhesus D (RhD) negative status (p = 0.0017) and history of previous transfusion reactions (p = 0.007) showed a statistically significant higher rate of alloimmunization. However, patients' age, gender, number of units transfused, underlying diagnosis and splenectomy were not significantly associated with alloimmunization. Based on our observations, measures to reduce alloimmunization rates may include extended matching for Rhesus and Kell antigens and early initiation of blood transfusions.

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.

[Anti-erythrocyte and anti-HLA immunization in hemoglobinopathies]

AIM

Evaluate the anti-erythrocyte and anti-HLA immunization rates in hemoglobinopathies.

PATIENTS AND METHODS

Cross-sectional study (October 2009-March 2010) on 83 patients followed for hemoglobinopathies. The irregular antibodies research is realized by two techniques: indirect Coombs and enzymatic technique on gel cards. The search for anti-HLA class I antibodies is done by complement dependent lymphocytotoxicity.

RESULTS

The mean age was 30 years (14-64 years), the sex ratio M/F is 0.84. Our series included 42 cases of sickle cell disease (29 homozygous sickle cell anemia and 13 sickle-thalassemia) and 41 cases of thalassemia syndromes (26 major and 15 intermediate). The anti-erythrocyte alloimmunization rate is 10.84% without difference between thalassemia syndromes and sickle cell disease. The autoimmunization rate (22.89%) is higher in thalassemia syndromes (41.46%) than in the sickle cell disease (7.14%) (P<0.001). The anti-HLA immunization rate is 31.6% without difference between thalassemia syndromes and sickle cell disease. The young age, transfusion at a young age and the total number of transfusions are the factors that increase the risk of anti-erythrocyte autoimmunization. No clinicobiological parameter does influence the anti-erythrocyte and anti-HLA alloimmunization. There is no significant association between anti-erythrocyte and anti-HLA immunization.

CONCLUSION

The erythrocyte and anti-HLA anti-immunization rates are high in our series. Preventive strategy is needed to ensure optimal blood safety.

Molecular matching for Rh and K reduces red blood cell alloimmunisation in patients with myelodysplastic syndrome

BACKGROUND

Matching for Rh and K antigens has been used in an attempt to reduce antibody formation in patients receiving chronic transfusions but an extended phenotype matching including Fy(a) and Jk(a) antigens has also been recommended. The aim of this study was to identify an efficient transfusion protocol of genotype matching for patients with myelodysplastic syndrome (MDS) or chronic myelomonocytic leukaemia. We also examined a possible association of HLA class II alleles with red blood cell (RBC) alloimmunisation.

MATERIALS AND METHODS

We evaluated 43 patients with MDS undergoing transfusion therapy with and without antibody formation. We investigated antigen-matched RBC units for ABO, D, C, c, E, e, K, Fy(a), Fy(b), Jk(a), Jk(b), S, s, Do(a), Do(b) and Di(a) on the patients' samples and on the donor units serologically matched for them based on their ABO, Rh and K phenotypes and presence of antibodies. We also determined the frequencies of HLA-DRB1 alleles in the alloimmunised and non-alloimmunised patients.

RESULTS

Seventeen of the 43 patients had discrepancies or mismatches for multiple antigens between their genotype-predicted profile and the antigen profile of the units of blood serologically matched for them. We verified that 36.8% of patients had more than one RBC alloantibody and 10.5% of patients had autoantibodies. Although we were able to find a better match for the patients in our extended genotyped/phenotyped units, we verified that matching for Rh and K would be sufficient for most of the patients. We also observed an over-representation of the HLA-DRB1*13 allele in the non-alloimmunised group of patients with MDS.

DISCUSSION

In our population molecular matching for C, c, E, e, K was able to reduce RBC alloimmunisation in MDS patients. An association of HLA-DRB1*13 and protection from RBC alloimmunisation should be confirmed.

Flexible automated platform for blood group genotyping on DNA microarrays

The poor suitability of standard hemagglutination-based assay techniques for large-scale automated screening of red blood cell antigens severely limits the ability of blood banks to supply extensively phenotype-matched blood. With better understanding of the molecular basis of blood antigens, it is now possible to predict blood group phenotype by identifying single-nucleotide polymorphisms in genomic DNA. Development of DNA-typing assays for antigen screening in blood donation qualification laboratories promises to enable blood banks to provide optimally matched donations. We have designed an automated genotyping system using 96-well DNA microarrays for blood donation screening and a first panel of eight single-nucleotide polymorphisms to identify 16 alleles in four blood group systems (KEL, KIDD, DUFFY, and MNS). Our aim was to evaluate this system on 960 blood donor samples with known phenotype. Study data revealed a high concordance rate (99.92%; 95% CI, 99.77%-99.97%) between predicted and serologic phenotypes. These findings demonstrate that our assay using a simple protocol allows accurate, relatively low-cost phenotype prediction at the DNA level. This system could easily be configured with other blood group markers for identification of donors with rare blood types or blood units for IH panels or antigens from other systems.

Red blood cell and leukocyte alloimmunization in patients awaiting kidney transplantation

Objective

To determine the rates of red blood cell and leukocyte alloimmunization in patients with chronic kidney disease awaiting kidney transplantation.

Methods

In this cross-sectional and prospective study, the serum of 393 chronic kidney disease patients on a transplant waiting list in Ceará, Northeastern Brazil were tested for red cell and leukocyte antibodies. In addition, demographic, clinical and laboratory data were collected.

Results

The average age in the sample of 393 patients was 34.1 ± 14 years. Slightly more than half (208; 52.9%) were male. The average numbers of transfusions and gestations were 3.1 ± 3.3 and 1.6 ± 6, respectively. One third (33.6%) were alloimmunized: 78% with leukocyte antibodies, 9.1% with red cell antibodies and 12.9% with both. Red cell antibodies were detected in 29 cases (7.4%), 17 of whom were women, who had received more transfusions than the males (p-value < 0.0001). The most frequently detected red cell antibodies belonged to the Rh (24.1%) and Kell (13.8%) blood group systems. Leukocyte antibodies were detected in 30.5% of cases, 83 of whom were women, who had received more transfusions than the males (p-value < 0.0001) and were more reactive to panel reactive antibodies (p-value < 0.0001). The mean alloreactivity to panel reactive antibodies was 47.7 ± 31.2%.

Conclusion

Chronic kidney disease patients on the transplant waiting list in Ceará, Brazil, display high rates of red cell (7.4%) and leukocyte (30.5%) alloimmunization. In this sample, alloimmunization was significantly associated with the number of transfusions and gender.

Detection of alloimmunization to ensure safer transfusion practice

BACKGROUND

Serological safety is an integral part of overall safety for blood banks. Emphasis is on the use of routinue Red Blood Cell (RBC) antibody screen test, at set time intervals, to reduce risks related to alloantibodies. Also emphasis is on importance of issuing antigen negative blood to alloantibody positive patients. Effect of using leucodepleted blood on the rate of alloimmunization is highlighted. The concept of provision of phenotypically matched blood is suggested.

MATERIALS AND METHODS

Antibody screen test is important to select appropriate blood for transfusion. Repeat antibody screen testing, except if time interval between the earlier and subsequent transfusion was less than 72 hours, followed by antibody identification, if required, was performed in patients being treated with repeat multiple blood transfusions. Between February 2008 and June 2009, repeat samples of 306 multi-transfused patients were analyzed. Search for irregular antibodies and reading of results was conducted using RBC panels (three-cell panel of Column Agglutination Technology (CAT) and two cell panel of the Solid Phase Red Cell Adherence Technology (SPRCAT). Specificities of antibodies were investigated using appropriate panels, 11 cell panel of CAT and 16 cell panel of SPRCA. These technologies, detecting agglutination in columns and reactions in solid phase, evaluate the attachment of irregular incomplete antibody to antigen in the first phase of immunological reaction more directly and hence improve the reading of agglutination. Three to four log leuco reduced red blood cells were transfused to patients in the study using blood collection bags with integral filters.

RESULTS

Alloimmunization rate of 4.24% was detected from 306 multiply transfused patients tested and followed up. The Transfusion therapy may become significantly complicated.

CONCLUSION

Red cell antibody screening and identification and subsequent issue of antigen negative blood have a significant role in improving blood safety. Centers that have incorporated antibody screen test and identification have ensured safe transfusion. Identified patients should be flagged in a database and information shared. Such patients can be given carry-on cards and educated about the names of the identified antibodies. Full red cell phenotyping of individuals, patients and donors, can be feasibility.

Frequency of red cell alloimmunization in patients with sickle cell anemia in an Egyptian referral hospital

INTRODUCTION

Sickle cell anemia (SCA) is an important public health issue in Tanta, Egypt. Erythrocyte transfusions may reduce the morbidity of SCA, however, they are associated with numerous risks. Among other risk categories, alloimmunization to red cell antigens may result from transfusions. The objective of this study was to explore the frequency of red cell alloantibodies among SCA patients who received regular transfusions.

MATERIALS AND METHODS

A total of 42 patients with SCA were included in this study. This work planned to study the presence of alloantibodies to different red cell antigens in multi-transfused SCA patients using the ID card micro-typing system. Clinical and laboratory data were collected and analyzed to find out the frequency, pattern and factors influencing red cell alloimmunization secondary to multiple blood transfusion in these patients.

RESULTS

Of a total of 42 SCA patients included in the study, 21.4% of patients developed alloantibodies. The most common alloantibodies were anti-K, anti-E and anti-C. The rate of incidence of these alloantibodies was 7.1%, 4.8% and 4.8%, respectively. There was significant association between alloantibody and the rate of transfused blood. The mean age of patients with and without alloimmunization was 12.0 and 6.2 years.

CONCLUSIONS

Alloimmunization to minor erythrocyte antigens of variable clinical significance is a frequent finding in transfused SCA patients. Regular screening for red cell alloantibodies would provide better management of these patients.

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.

Risk factors for alloimmunization in patients with sickle cell anemia

OBJECTIVE

To determine erythrocyte phenotyping in blood donors and patients with sickle cell anemia (SS) treated at Hemocentro of Alagoas and describe the frequency and factors associated with erythrocyte alloimmunization.

METHODS

Cross-sectional study with 102 SS patients and 100 blood donors. The following tests were performed: erythrocyte phenotyping, Direct and Indirect antiglobulin test, and detection of irregular antibodies by panel of phenotyped red blood cells. Data were compared by Mann-Whitney, chi-square or Fisher's exact tests. Factors associated with alloimmunization were studied by univariate and multiple logistic regression analysis.

RESULTS

The most frequent antigens found in patients and blood donors were: c, e, M, s, JK(a). Significant differences were observed between the frequency of the phenotype of patients and donors in regard to antigens s, FY(a) and JK(b). Of 79 transfused patients, 10 presented positive Indirect Coombs. Thirteen alloantibodies were found, 7 of the Rh system, 2 of Kell and 4 were not identified. Factors associated with alloimmunization were the period of time between the last transfusion and the date of the test and more than 10 red blood cell transfusions. Patients who received more than 10 transfusions were 16.39 (95% CI: 2.23-120.59) times more likely to be alloimmunized than patients with fewer transfusions.

CONCLUSION

The prevalence of alloimmunization in SS patients was 12.7%, with 70% of antibodies belonging to the Rh and Kell systems. This study shows the importance of performing erythrocyte phenotyping in blood donors and receptors to decrease the risk of alloimmunization.

Relevance of RH variants in transfusion of sickle cell patients

Transfusion remains the main treatment of sickle cell disease patients. Red cell alloimmunization is frequent because of the antigen disparities between patients of African descent and donors of European ancestry. Alloimmunization is associated with severe hemolytic transfusion reaction, autoantibody formation, and difficulties in the management of transfusion compatibility. Beside common antigens, a number of different RH variant antigens found in individuals of African descent can be involved in alloimmunization. If some variants, such as Hr(S) negative antigens, are known to prone significant alloantibodies and delayed hemolytic transfusion reactions, it is not clear whether all the described variants represent a clinical risk for sickle cell disease patients. The knowledge of the clinical relevance of RH variants is a real issue. An abundance of molecular tools are developed to detect variants, but they do not distinguish those likely to prone immunization from those that are unlikely to prone immunization and delayed hemolytic transfusion reactions. A strategy of prevention, which generally requires rare red blood cells, cannot be implemented without this fundamental information. In this review, we discuss the relevance of RH variants in sickle cell disease, based on the published data and on our experience in transfusion of these patients.

[Frequency of red blood cell alloimmunization in polytransfused patients at the university teaching hospital of Point G, Bamako, Mali]

This prospective study conducted within 9 months period aimed to determine the frequency of red cell alloimmunization among polytransfused patients of the medical Hematology and oncology ward, and the unit of hemodialysis of the Nephrology ward at the Point-G hospital. Irregular red blood cell antibody screening and identification were performed by gel-filtration method using indirect antiglobulin test and enzymatic treated cells. We did not use saline medium. A total of 78 patients were included in this study. The mean age of the patients was 36.78±14.73 years (range: 11 and 77 years). The sex ratio was of 1.11 in favour of the women. The mean blood units transfused were 12.21±9.99 units (range: 4 and 45 units). The Rhesus phenotypes Dccee, DccEe and DCcee were most predominant, with the respective frequencies of 67.9, 15.4 and 10.3%. Kell antigen was found at a frequency of 1.28%. The total rate of red cell alloimmunization was 10.3%. There was no significant difference between the two wards. All the screened agglutinins were warm antibodies belonging to the Rhesus system: anti-E (7.7%), anti-C (1.3%) and anti-D (1.3%). Only Anti-E was present among hematologic patients. We did not find a significant link between the sex, the age, the number of blood units transfused and the positivity of the antibody screening. We conclude that the frequency of post-transfusional alloimmunization is high among polytransfused patients in Mali. A systematic antibody screening among these patients and the selection of red cells with known Rhesus/Kell phenotypes would allow an optimal blood transfusion safety.

Red cell alloimmunization in multitransfused patients and multiparous women

PURPOSE

To determine the incidence of alloimmunization against red cell antigens and the thermal amplitude and specificity of antibodies in multitransfused patients and multiparous women.

METHODS

Antibody screening was performed in 30 nontransfused orthopedic surgery cases (control), 504 multitransfused patients and 325 multiparous women. Antibody screening at 4°C, 22°C and 37°C was carried out in a saline phase, by indirect antiglobulin technique (IAT), using papain cystein, low ionic strength solution (LISS) and polyethylene glycol (PEG).

RESULTS

In multitransfused patients IgM antibodies were more frequently detected at 4°C and the IgG antibody incidence was 7.1% by enzyme method, 7.7% IAT, 9.4% LISS, 10.2% using PEG & 10.2% multiparous women. Bad obstetric history cases had significantly higher incidence of alloimmunization. The antibody specificity of antibodies was mainly in Lewis, Rh, Kidd and MN systems.

CONCLUSION

Antibody screening before transfusion, at set time intervals after transfusion and during antenatal period is recommended.

Inflammation enhances consumption and presentation of transfused RBC antigens by dendritic cells

Factors regulating which patients become alloimmunized to red blood cell (RBC) antigens are poorly understood. Using a murine model of transfusion, we recently reported that viral-like inflammation with polyinosinic polycytidylic acid [poly (I:C)] significantly enhances RBC alloimmunization. Herein, we tested the hypothesis that poly (I:C) exerts this effect, at least in part, at the level of antigen-presenting cells (APCs). Using a novel in vivo method, we report that in the noninflamed state, most transfused RBCs were consumed by splenic macrophages, with only trace consumption by splenic dendritic cells (DCs). To a lesser extent, RBCs were also consumed by APCs in the liver. However, unlike soluble antigens, no RBCs were consumed by APCs in the lymph nodes. Inflammation with poly (I:C) induced significant consumption of transfused RBCs by splenic DCs, with a concomitant increase in costimulatory molecule expression. Moreover, this resulted in increased proliferation of CD4(+) T cells specific for the mHEL RBC alloantigen. Finally, splenectomy abrogated the enhancing effects of poly (I:C) on RBC alloimmunization. Together, these data provide additional insight into the nature of transfused RBCs as an immunogen and provide a mechanism by which viral-like inflammation enhances alloimmunization to transfused RBCs.