Advancements in HLA Typing Techniques and Their Impact on Transplantation Medicine.

HLA typing serves as a standard practice in hematopoietic stem cell transplantation to ensure compatibility between donors and recipients, preventing the occurrence of allograft rejection and graft-versus-host disease. Conventional laboratory methods that have been widely employed in the past few years, including sequence-specific primer PCR and sequencing-based typing (SBT), currently face the risk of becoming obsolete. This risk stems not only from the extensive diversity within HLA genes but also from the rapid advancement of next-generation sequencing and third-generation sequencing technologies. Third-generation sequencing systems like single-molecule real-time (SMRT) sequencing and Oxford Nanopore (ONT) sequencing have the capability to analyze long-read sequences that span entire intronic-exonic regions of HLA genes, effectively addressing challenges related to HLA ambiguity and the phasing of multiple short-read fragments. The growing dominance of these advanced sequencers in HLA typing is expected to solidify further through ongoing refinements, cost reduction, and error rate minimization. This review focuses on hematopoietic stem cell transplantation (HSCT) and explores prospective advancements and application of HLA DNA typing techniques. It explores how the adoption of third-generation sequencing technologies can revolutionize the field by offering improved accuracy, reduced ambiguity, and enhanced assessment of compatibility in HSCT. Embracing these cutting-edge technologies is essential to advancing the success rates and outcomes of hematopoietic stem cell transplantation. This review underscores the importance of staying at the forefront of HLA typing techniques to ensure the best possible outcomes for patients undergoing HSCT.

KIR genotype and haplotype repertoire in Kuwaiti healthy donors, hematopoietic cell transplant recipients and healthy family members.

The gene complex located on chromosome 19q13.4 encodes the Killer-cell Immunoglobulin-like Receptors (KIRs), which exhibit remarkable polymorphism in both gene content and sequences. Further, the repertoire of KIR genes varies within and between populations, creating a diverse pool of KIR genotypes. This study was carried out to characterize KIR genotypes and haplotypes among 379 Arab Kuwaiti individuals including 60 subjects from 20 trio families, 49 hematopoietic cell transplantation (HCT) recipients and 270 healthy Kuwaiti volunteer HCT donors. KIR Genotyping was performed by a combination of reverse sequence specific oligonucleotide probes (rSSO) and/or Real Time PCR. The frequencies of KIR genes in 270 healthy Kuwaiti volunteer donors were compared to previously reported frequencies in other populations. In addition, we compared the differences in KIR repertoire of patients and healthy donors to investigate the reproducibility of previously reported significant differences between patients with hematological malignancies and healthy donors. The observed frequencies in our cohort volunteer HCT donors was comparable to those reported in neighboring Arab populations. The activating genes KIR2DS1, KIR2DS5 and KIR3DS1 and the inhibitory gene KIR2DL5 were significantly more frequent in patients compared to healthy donors, however, none of the previously reported differences were reproducible in our Kuwaiti cohort. This report is the first description of KIR gene carrier frequency and haplotype characterization in a fairly large cohort of the Kuwaiti population, which may have implications in KIR based HCT donor selection strategies.

Identification of a novel HLA-DRB4 allele, HLA-DRB4*01:152 in a Kuwaiti family.

One nucleotide substitution in codon 179 of HLA-DRB4*01:03:01:01 results in a novel allele HLA-DRB4*01:152.

Identification of the novel HLA-DPA1 allele, HLA-DPA1*01:03:34 in a Kuwaiti family.

One nucleotide substitution in codon 85 of HLA-DPA1*01:03:01:04 results in a novel allele HLA-DPA1*01:03:34.

Analysis of Common Driver Mutations in Philadelphia-Negative Myeloproliferative Neoplasms.

BACKGROUND: Philadelphia-negative myeloproliferative neoplasms (MPNs) are a group of hematopoietic stem cell disorders that include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). This study examines the driver mutations among patients with MPNs in Kuwait. PATIENTS AND METHODS: This study was a retrospective review of 942 MPN cases with a driver mutation from July 2007 to June 2019 to examine their demographic, clinical, and laboratory attributes. RESULTS: The annual incidence of MPNs is 1.6 per 100,000 persons, and ET is the most common subtype. The median age of our cohort was 55 years, and the patients were predominantly male. We found that the most frequent gene mutation of MPNs in our cohort was the JAK2V617F mutation, which was present in 90% of cases, followed by the CALR exon 9, MPLW515L/K, and JAK2 exon 12 mutations. In our cohort, thrombotic events were observed in 18.7% of cases. CONCLUSION: Although Philadelphia-negative MPNs are rare hematologic malignancies, thrombosis is a relatively common initial presentation. The JAK2V617F mutation was the driver mutation in the majority of patients with MPN.

COVID-19 convalescent plasma treatment of moderate and severe cases of SARS-CoV-2 infection: A multicenter interventional study.

OBJECTIVE: To study the effectiveness of COVID-19 convalescent plasma (CCP) therapy for patients with moderate and severe COVID-19 disease. METHODS: This non-randomized prospective cohort study was conducted from May 21 to June 30, 2020, at four major tertiary hospitals in Kuwait. CCP was administered to 135 patients. The control group comprised 233 patients who received standard treatment. All patients (N = 368, median age 54 [range 15-82]) had laboratory-confirmed SARS-CoV-2 infection and either moderate or severe COVID-19 disease. RESULTS: CCP treatment was associated with a higher rate of clinical improvement in patients with moderate or severe disease. Among those with moderate COVID-19 disease, time to clinical improvement was 7 days in the CCP group, versus 8 days in the control group (p = 0·006). For severe COVID-19 disease, time to clinical improvement was 7 days in the CCP group, versus 15.5 days in the control group (p = 0·003). In the adjusted analysis, patients with moderate disease treated with CCP had a significantly lower 30-day mortality rate. Compared to the control group, oxygen saturation improved within 3 days of CCP transfusion, and lymphocyte counts improved from day 7 in patients with moderate COVID-19 disease and day 11 in patients with severe disease. C-reactive protein levels declined throughout the first 14 days after CCP transfusion. None of the CCP patients developed a serious transfusion reaction. CONCLUSIONS: The data show that administration of CCP is a safe treatment option for patients with COVID-19 disease with a favorable outcome in the rate of, and time to, clinical improvement.

Philadelphia-negative myeloproliferative neoplasms among Kuwaiti Nationals.

The epidemiology, genetics, and thrombosis risk of MPNs among Arabs are largely unknown. This may be attributed to scarce epidemiological data, particularly from our region. Our study included 381 Kuwaiti nationals with Ph-negative MPNs and a confirmed driver mutation involving JAK2 (exon 12 14), CALR, or MPL. This first regional study examines the demographics, clinical parameters, and thrombosis-related attributes of the participants. This study reported a median age of 58 years, with females and males representing 54.9% and 45.1%, respectively. ET was the most frequent subtype of Ph-negative MPNs in our population, accounting for 52.0% of the cases, followed by PV, found in 34.6% of the participants, and PMF, found in 8.4% of participants. The crude annual cumulative incidence of Ph-negative MPNs in Kuwait ranged from 0.674 to 3.177 per 100,000 population across the study period. The most common driver mutation was JAK2V617F, with a frequency of 89.5%. At diagnosis, 19.2% of the patients presented with unexplained thrombosis, and almost half were of arterial origins. Males were more likely to present with arterial thrombosis than females (61.5% vs. 35.3%), whereas venous thrombotic events were more common in females than in males (47.1% vs. 17.9%; p-value = 0.025). Ph-negative MPNs in Kuwait are rare; however, thrombosis is a frequent complication, being documented in up to 19.2% of cases at presentation, more commonly at arterial sites. These findings call for thorough evaluation of patients with unexplained derangements in their hematological parameters during follow-ups.

Classification of major and minor blood group antigens in the Kuwaiti Arab population.

Ethnic differences in blood group frequencies might result in clinically important mismatches for transfusions. Arab people represent a large population for which no comprehensive database of red cell genotypes is available and Kuwaitis are no exception. For instance, the Rh blood group is the most elaborate blood group system that shows a high degree of polymorphism among different ethnic groups, there has been little classification of RH alleles in Arab people. Blood samples from 917 Kuwaiti Arab donors in the Kuwaiti Bone Marrow registry were tested with a single-nucleotide polymorphism DNA array. Blood group antigen prevalence were compared to known prevalence in European populations. Multiple subjects were found to be antigen negative for certain phenotypes that is considered rare by the American Rare Donor Program; (Fy(a-,b-) and Kell). In the minor blood group antigens, the FYA allele was predicted to be low in Kuwaitis, when compared to other published accounts. The frequencies of MNS blood antigens in the study population were not significantly different from those reported for European/Caucasian populations. The predicted frequency of the Diego blood group antigen was similar to that observed in a South Asian population. The weak D 1, 2, 3 phenotypes were not prevalent in the Kuwaiti Arab population; however, other RHD variants were detected. We provided information about blood group antigens in the Kuwaiti population that is important for guiding transfusion care. Several interesting findings demonstrated clinical importance, which could be useful in developing transfusion medicine policies and approaches.

Common, intermediate and well-documented HLA alleles in world populations: CIWD version 3.0.0.

A catalog of common, intermediate and well-documented (CIWD) HLA-A, -B, -C, -DRB1, -DRB3, -DRB4, -DRB5, -DQB1 and -DPB1 alleles has been compiled from over 8 million individuals using data from 20 unrelated hematopoietic stem cell volunteer donor registries. Individuals are divided into seven geographic/ancestral/ethnic groups and data are summarized for each group and for the total population. P (two-field) and G group assignments are divided into one of four frequency categories: common (≥1 in 10 000), intermediate (≥1 in 100 000), well-documented (≥5 occurrences) or not-CIWD. Overall 26% of alleles in IPD-IMGT/HLA version 3.31.0 at P group resolution fall into the three CIWD categories. The two-field catalog includes 18% (n = 545) common, 17% (n = 513) intermediate, and 65% (n = 1997) well-documented alleles. Full-field allele frequency data are provided but are limited in value by the variations in resolution used by the registries. A recommended CIWD list is based on the most frequent category in the total or any of the seven geographic/ancestral/ethnic groups. Data are also provided so users can compile a catalog specific to the population groups that they serve. Comparisons are made to three previous CWD reports representing more limited population groups. This catalog, CIWD version 3.0.0, is a step closer to the collection of global HLA frequencies and to a clearer view of HLA diversity in the human population as a whole.

HLA Haplotype Frequencies and Genetic Profiles of the Kuwaiti Population.

OBJECTIVE: The aim of this study was to assess the HLA haplotype frequencies and genetic profiles of the Kuwaiti population. MATERIALS AND METHODS: Whole venous blood was obtained from 595 healthy, unrelated Kuwaiti volunteers. The study population was genotyped for HLA class I (HLA-A, HLA-B, and HLA-C) and class II (HLA-DRB1 and HLA-DQB1) loci using sequence-specific oligonucleotide (SSO) probe-based hybridization and high-resolution HLA genotyping. Haplotype frequencies were estimated using an implementation of the expectation maximization algorithm that resolves both phase and allelic ambiguity. The Kuwaiti population was compared with other populations from the US National Marrow Donor Program (NMDP), by running a principal component analysis (PCA) on the relevant haplotype frequencies. RESULTS: The most common HLA class I alleles in Kuwait were HLA-A*02:01g, HLA-C*06:02g, and HLA-B*50:01g with frequencies of 16, 14, and 12%, respectively. The most common HLA class II alleles in Kuwait were HLA-DQB1*02:01g and HLA-DRB1*07:01 with frequencies of 29.7 and 16.5%, respectively. The most common Kuwaiti haplotype observed was HLA-A*02:01g∼HLA-C*06:02g∼HLA-B*50:01g∼HLA-DRB1*07:01∼HLA-DQB1*02:01g at a frequency of 2.3%. The PCA demonstrated close genetic proximity of the Kuwaiti population with Middle Eastern, Southeast Asian, and North African populations in the NMDP. CONCLUSION: Identifying the haplotype diversity in the Kuwaiti population will contribute to the selection of an HLA-match for HSCT, disease associations, pharmacogenomics, and knowledge of pop-ulation HLA diversity.

HLA Haplotypes In 250 Families: The Baylor Laboratory Results And A Perspective On A Core NGS Testing Model For The 17th International HLA And Immunogenetics Workshop.

Since their inception, the International HLA & Immunogenetics Workshops (IHIW) served as a collaborative platform for exchange of specimens, reference materials, experiences and best practices. In this report we present a subset of the results of human leukocyte antigen (HLA) haplotypes in families tested by next generation sequencing (NGS) under the 17th IHIW. We characterized 961 haplotypes in 921 subjects belonging to 250 families from 8 countries (Argentina, Austria, Egypt, Jamaica, Germany, Greece, Kuwait, and Switzerland). These samples were tested in a single core laboratory in a high throughput fashion using 6 different reagents/software platforms. Families tested included patients evaluated clinically as transplant recipients (kidney and hematopoietic cell transplant) and their respective family members. We identified 486 HLA alleles at the following loci HLA-A, -B, -C, -DRB1, -DRB3, -DRB4, -DRB5, -DQA1, -DQB1, -DPA1, -DPB1 (77, 115, 68, 69, 10, 6, 4, 44, 31, 20 and 42 alleles, respectively). We also identified nine novel alleles with polymorphisms in coding regions. This approach of testing samples from multiple laboratories across the world in different stages of technology implementation in a single core laboratory may be useful for future international workshops. Although data presented may not be reflective of allele and haplotype frequencies in the countries to which the families belong, they represent an extensive collection of 3rd and 4th field resolution level 11-locus haplotype associations of 486 alleles identified in families from 8 countries.

17th IHIW component "Immunogenetics of Ageing" - New NGS data.

The 'Immunogenetics of Aging' project is a component introduced in the 14th International HLA and Immunogenetics Workshop (IHIW) and developed further within subsequent workshops. The aim was to determine the relevance of immunogenetic markers, focusing on HLA, cytokine genes, and some innate immunity genes, for successful aging and an increased capacity to reach the extreme limits of life-span. Within the 17th IHIW we applied Next Generation Sequencing methods to refine further HLA associations at allele level in longevity, and to extend our knowledge to additional loci such as HLA-DQA1, HLA-DPB1 and HLA-DPA1. Analysis of relatively small number of healthy elderly and young controls from four populations showed that some HLA class I and class II alleles were significantly positively associated with healthy aging. Additionally we observed statistically significant differences in HLA allele distribution when the analysis was performed separately in elderly females and males compared to sex-matched young controls. Haplotypes, probably associated with better control of viral and malignant diseases were increased in the elderly sample. These preliminary NGS data could confirm our hypotheses that survival and longevity might be associated with selection of HLA alleles and haplotypes conferring disease resistance or susceptibility. Therefore HLA alleles and haplotypes could be informative immunogenetic markers for successful ageing.

Next-generation HLA typing of 382 International Histocompatibility Working Group reference B-lymphoblastoid cell lines: Report from the 17th International HLA and Immunogenetics Workshop.

Extended molecular characterization of HLA genes in the IHWG reference B-lymphoblastoid cell lines (B-LCLs) was one of the major goals for the 17th International HLA and Immunogenetics Workshop (IHIW). Although reference B-LCLs have been examined extensively in previous workshops complete high-resolution typing was not completed for all the classical class I and class II HLA genes. To address this, we conducted a single-blind study where select panels of B-LCL genomic DNA samples were distributed to multiple laboratories for HLA genotyping by next-generation sequencing methods. Identical cell panels comprised of 24 and 346 samples were distributed and typed by at least four laboratories in order to derive accurate consensus HLA genotypes. Overall concordance rates calculated at both 2- and 4-field allele-level resolutions ranged from 90.4% to 100%. Concordance for the class I genes ranged from 91.7 to 100%, whereas concordance for class II genes was variable; the lowest observed at HLA-DRB3 (84.2%). At the maximum allele-resolution 78 B-LCLs were defined as homozygous for all 11 loci. We identified 11 novel exon polymorphisms in the entire cell panel. A comparison of the B-LCLs NGS HLA genotypes with the HLA genotypes catalogued in the IPD-IMGT/HLA Database Cell Repository, revealed an overall allele match at 68.4%. Typing discrepancies between the two datasets were mostly due to the lower-resolution historical typing methods resulting in incomplete HLA genotypes for some samples listed in the IPD-IMGT/HLA Database Cell Repository. Our approach of multiple-laboratory NGS HLA typing of the B-LCLs has provided accurate genotyping data. The data generated by the tremendous collaborative efforts of the 17th IHIW participants is useful for updating the current cell and sequence databases and will be a valuable resource for future studies.

Quality control project of NGS HLA genotyping for the 17th International HLA and Immunogenetics Workshop.

The 17th International HLA and Immunogenetics Workshop (IHIW) organizers conducted a Pilot Study (PS) in which 13 laboratories (15 groups) participated to assess the performance of the various sequencing library preparation protocols, NGS platforms and software in use prior to the workshop. The organizers sent 50 cell lines to each of the 15 groups, scored the 15 independently generated sets of NGS HLA genotyping data, and generated "consensus" HLA genotypes for each of the 50 cell lines. Proficiency Testing (PT) was subsequently organized using four sets of 24 cell lines, selected from 48 of 50 PS cell lines, to validate the quality of NGS HLA typing data from the 34 participating IHIW laboratories. Completion of the PT program with a minimum score of 95% concordance at the HLA-A, HLA-B, HLA-C, HLA-DRB1 and HLA-DQB1 loci satisfied the requirements to submit NGS HLA typing data for the 17th IHIW projects. Together, these PS and PT efforts constituted the 17th IHIW Quality Control project. Overall PT concordance rates for HLA-A, HLA-B, HLA-C, HLA-DPA1, HLA-DPB1, HLA-DQA1, HLA-DQB1, HLA-DRB1, HLA-DRB3, HLA-DRB4 and HLA-DRB5 were 98.1%, 97.0% and 98.1%, 99.0%, 98.6%, 98.8%, 97.6%, 96.0%, 99.1%, 90.0% and 91.7%, respectively. Across all loci, the majority of the discordance was due to allele dropout. The high cost of NGS HLA genotyping per experiment likely prevented the retyping of initially failed HLA loci. Despite the high HLA genotype concordance rates of the software, there remains room for improvement in the assembly of more accurate consensus DNA sequences by NGS HLA genotyping software.

Next-generation sequencing characterization of HLA in multi-generation families of Kuwaiti descent.

The frequency of HLA genes in one population may not accurately represent frequencies in other populations. In this study, we characterized extended human leukocyte antigen (HLA) haplotypes in several families of Kuwaiti descent by high-resolution typing using next-generation technology. A total 81 members (including patients and related donors) from 21 families were enrolled. No haplotypes were shared among multiple families. Of 77 haplotypes identified, 23 were not listed in the HaploStats database. Two haplotypes were most common in African Americans, six in Asian Pacific Islanders, three in Caucasians, three in Hispanics, and three in Native Americans. The remaining identified haplotypes were not among the most common 200 HLA haplotypes in any of the five major populations. This cohort had 202 (19%) unique alleles, including 20 rare alleles, 16 very rare alleles, and 2 novel ones. Furthermore, no frequency data were available for 30% (23/77) of the observed haplotypes, and 6% (3/49) of B ∼ C blocks identified were not available in the HaploStats database. Kuwaiti individuals carry unique HLA haplotypes that are not shared by the majority of individuals historically reported to the US National Marrow Donor Program registry.

Kuwait bone marrow transplantation activities.

Kuwait is located in the Arabian Gulf and has a population of 3.5million. The stem cell transplantation program started in 2000. Autologous peripheral blood stem cell transplantation started first, as it was easier technically to establish. In 2011, the allogeneic program started with focus on acute leukemia and hemoglobinopathies. The success of both programs required teamwork and support of health planners. The Kuwait National Bone Marrow Registry was established in 2012. The issue of donor availability and drug shortage remain the two main obstacles for expanding the bone marrow transplantation program.

JAK2V617F allele burden in patients with myeloproliferative neoplasms.

Myeloproliferative neoplasms (MPNs) are clonal malignant diseases that represent a group of conditions including polycythemia vera (PV), essential thrombocythemia (ET), and myelofibrosis (MF). The JAK2-V617F mutation is prevalent in almost all patients with MPNs and has become a valuable biomarker for diagnosis of MPNs. A different allele burden in these entities has long been noticed. The aim of our study was to assess the JAK2 allele burden in our JAK2V617F positive cases and its association with phenotype if any and to select a simple, sensitive assay for use in our clinical molecular diagnostic laboratory. Methodologies reported in this literature include amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) and real-time quantitative polymerase chain reaction (RQ-PCR). We analyzed 174 cases by RQ-PCR for the quantification of JAK2V617F were initially screened by ARMS-PCR. We found that V617F allele burden in the entire population of patients was 73 % ranging from 0.97 to 95 %. The median V617F allele burden in PV patients was 40 %, MF was 95 %, and ET was 25 %. ARMS-PCR and RQ-PCR were proven to be sensitive since ARMS-PCR is a qualitative method; it can be used to screen JAK2V617F mutation and RQ-PCR was used to quantify the V617F cells. Our study suggests that JAK2V617F positivity is associated with MPNs, and its allele burden is an excellent diagnostic marker for disease subtypes, prognosis, disease phenotype and complication, and evolution. The data indicates that ARMS-PCR is simple and can be easily performed for the primary screening of JAK2V617F mutation, and RQ-PCR is sensitive enough to detect low mutant allele levels (>10 %), specific enough not to produce false positive results, and can be performed for the JAK2V617F allele burden quantification.

Haploidentical hematopoietic stem-cell transplantation in adults.

Haploidentical hematopoietic stem-cell transplantation is an alternative transplant strategy for patients without an HLA-matched donor. Still, only half of patients who might benefit from transplantation are able to find an HLA-matched related or unrelated donor. Haploidentical donor is readily available for many patients in need of immediate stem-cell transplantation. Historical experience with haploidentical stem-cell transplantation has been characterised by a high rejection rate, graft-versus-host disease, and transplant-related mortality. Important advances have been made in this field during the last 20 years. Many drawbacks of haploidentical transplants such as graft failure and significant GVHD have been overcome due to the development of new extensive T cell depletion methods with mega dose stem-cell administration. However, prolonged immune deficiency and an increased relapse rate remain unresolved problems of T cell depletion. New approaches such as partial ex vivo or in vivo alloreactive T cell depletion and posttransplant cell therapy will allow to improve immune reconstitution in haploidentical transplants. Results of unmanipulated stem-cell transplantation with using ATG and combined immunosuppression in mismatched/haploidentical transplant setting are promising. This paper focuses on recent advances in haploidentical hematopoietic stem-cell transplantation for hematologic malignancies.

Frequencies of non-Hodgkin's lymphoma subtypes in Kuwait: comparisons between different ethnic groups.

There is a wide variation in the prevalence of various subtypes of non-Hodgkin's lymphoma worldwide. The aim of this study was to determine the relative frequency of different subtypes of non-Hodgkin's lymphoma in Kuwait based on the Revised European-American Lymphoma (REAL) classification. From 1998 to 2006, 738 subjects were included that were registered with non-Hodgkin's lymphoma in the population-based cancer registry at the Kuwait Cancer Control Center. Expert pathologists reviewed histological slides from all subjects. We performed detailed immunohistochemical studies and classified subjects based on the REAL classification. The prevalence of different types of non-Hodgkin's lymphoma was determined based on age, sex, site of disease, and ethnicity. Ethnicity groups comprised Kuwaiti Arabs, non Kuwaiti Arabs, Asians, and others. The prevalence of B- and T-cell lymphomas was 81.8% and 14.2%, respectively. The most common age group was 41-60 years old. The three most common subtypes in Kuwaiti Arabs were diffuse large B-cell lymphoma (46.5%), follicular lymphoma (15.5%), and mycosis fungoides (9.3%). In non-Kuwaiti Arabs, the most common subtypes were diffuse large B-cell lymphoma (48%), B-cell small lymphocytic lymphoma/chronic lymphocytic leukemia (15.8%), and follicular lymphoma (12.7%). Overall, non-Kuwaiti Arabs exhibited the highest prevalence (59%), and 54% of all cases had extranodal presentation. Compared to the Western world, Kuwait had a lower prevalence of follicular lymphoma, a higher prevalence of diffuse large B-cell lymphoma and extranodal presentation, and a high frequency of mycosis fungoides. Compared to other parts of Asia, Kuwait had a lower frequency of peripheral T-cell lymphomas.

Red blood cell alloimmunization among sickle cell Kuwaiti Arab patients who received red blood cell transfusion.

BACKGROUND: Sickle cell disease (SCD) is common in the Arabian Gulf region. Most cases require a red blood cell (RBC) transfusion, increasing the potential for RBC alloantibody development. The incidence of RBC alloimmunization among Kuwaiti Arab SCD patients is not yet known. This study retrospectively assessed the effect of using two different matching protocols on the incidence of alloimmunization among multiply transfused Kuwaiti Arab SCD patients. STUDY DESIGN AND METHODS: A total of 233 Kuwaiti Arab SCD patients were divided into two groups: Group 1 (n = 110) received RBC transfusion through standard ABO- and D-matched nonleukoreduced blood; Group 2 (n = 123) received RBCs matched for ABO, Rh, and K1 poststorage-leukoreduced blood. Multivariate analysis was performed on the factors associated with RBC alloimmunization and antibody specificity. RESULTS: Sixty-five percent of patients in Group 1 developed clinically significant RBC alloantibody with an increased prevalence in females; in patients in Group 2, 23.6% developed RBC alloantibodies (p = 0.01). In Group 1, 72 patients (65.5%) had alloantibodies directed against Rh and Kell systems (p = 0.01). Multivariate analysis further confirmed the results, showing that blood transfusion type and sex have significant effects on the rate of alloimmunizations. CONCLUSION: This study confirms the importance of selecting RBCs matched for Rh and Kell to reduce the risk of alloimmunizations among Kuwaiti Arab SCD patients.