HLA Allele and Haplotype Frequencies Among Registered Unrelated Donors in the Western Region of Saudi Arabia

The Saudi stem cell donor registry (SSCDR) has successfully recruited over 92,000 unrelated potential stem cell donors through nationwide campaigns. The Western region of Saudi Arabia is characterized by its unique ethnic diversity, shaped by centuries of immigration and pilgrimage. This study aimed to determine the distribution of HLA alleles and haplotypes among donors from this region. A total of 1112 donors registered with SSCDR were included, all recruited during campaigns conducted in the Western region between 2019 and 2021. Participants provided ancestry information to confirm their city of origin. High-resolution HLA typing for loci A, B, C, DRB1 and DQB1 was performed using sequence-based typing (SBT). Allele and haplotype frequencies were estimated for each subgroup using Arlequin 3.5 software. Distinct haplotype patterns were observed across cities. The most common haplotypes in the 1112 potential stem cell donors in the Western Region of Saudi Arabia were HLA-A*02:01∼C*07:02∼B*07:02∼DRB1*15:01∼DQB1*06:02 and HLA-A*02:01∼C*06:02∼B*50:01∼DRB1*07:01∼DQB1*02:01 in Jeddah; A*23:01∼C*06:02∼B*50:01∼DRB1*07:01∼DQB1*02:01 in Al-Madinah; HLA-A*26:01∼C*07:02∼B*08:01∼DRB1*03:01∼DQB1*02:01, HLA-A*30:01∼C*06:02∼B*13:02∼DRB1*07:01∼DQB1*02:01 and HLA-A*02:01∼C*06:02∼B*50:01∼DRB1*07:01∼DQB1*02:01 in Makkah; HLA-A*02:01∼C*15:02∼B*51:01∼DRB1*13:01∼DQB1*06:03 and HLA-A*02:01∼C*07:02∼B*07:02∼DRB1*15:01∼DQB1*06:02 in Al-Baha; and HLA-A*31:01∼C*15:02∼B*51:01∼DRB1*13:01∼DQB1*06:03 in Taif. HLA data are available in the Allele Frequencies Net Database (AFND: 3854, 3855, 3856, 3857 and 3858) under the population name 'Saudi Western Region'. In western Saudi Arabia, HLA allele and haplotype distributions demonstrate marked city-specific variation. Our research identifies DR7-, DR13- and DR15-based haplotypes as the most prevalent across the region. These findings are critical for optimizing unrelated donor searches for patients lacking compatible familial matches. Understanding these local frequencies allows for more targeted recruitment and better matching probabilities in stem cell registries.