HLA allele and haplotype diversity in Central Anatolia: a comparative analysis of donors and transplant candidates across six HLA loci (HLA-A, HLA-B, HLA-C, HLA-DRB1, HLA-DQB1, and HLA-DPB1).

Background/aim: Human leukocyte antigen (HLA) polymorphisms play a central role in immune recognition, disease susceptibility, and transplant success. The distribution of HLA alleles and haplotypes varies among ethnic and geographic populations. Despite several regional studies conducted in Türkiye, large-scale and comprehensive investigations comparing HLA profiles between healthy individuals and transplant candidates remain limited. The aim of this study was to compare the distribution of HLA profiles among donors, hematopoietic stem cell transplantation (HSCT) candidates, and solid organ transplant candidates. Materials and methods: A total of 8472 individuals were included in the study, comprising 6422 donors and 2050 transplant candidates. HLA genotyping was performed using polymerase chain reaction with sequence-specific primers and polymerase chain reaction with sequence-specific oligonucleotide probes. Allele, genotype, and haplotype frequencies were calculated using the PyPop (version 1.2.0) and GENE[RATE] software tools. Results: The most frequent alleles at the HLA-A, HLA-B, HLA-C, HLA-DRB1, HLA-DQB1, and HLA-DPB1 loci were similar across all groups, with A*02, B*35, C*07, DRB1*11, DQB1*03, and DPB1*04 observed as the predominant alleles. Several alleles were significantly overrepresented in solid organ transplant candidates compared with donors, including A*31, A*33, B*15, B*42, B*51, B*54, DRB1*04, and DRB1*12, whereas DRB1*11 was significantly underrepresented (p < 0.05). A*23 was also observed at a significantly higher frequency in kidney transplant candidates. No significant allele differences were observed between HSCT candidates and donors. Haplotype analysis revealed that the most prevalent six-locus haplotype (A:B:C:DRB1:DQB1:DPB1) was 02~35~04~11~03~04 in donors, whereas 24~35~04~11~03~04 was observed in HSCT candidates and 24~35~04~04~03~04 in solid organ transplant candidates. Conclusion: To our knowledge, this study represents the largest and most comprehensive analysis of HLA distribution in Türkiye to date and the first to report six-locus HLA haplotypes, including the HLA-DPB1 locus, in transplant candidates. The results indicate that solid organ transplant candidates exhibit significant differences in HLA allele and haplotype frequencies compared with healthy donors. These findings underscore the importance of region-specific HLA data in optimizing donor selection and potentially improving transplant outcomes.