HLA genotyping has witnessed a remarkable evolution, with a primary focus on the essential HLA-A, -B, -C, -DRB1, and -DQB1 loci for HSCT. These loci are crucial for understanding immune compatibility and transplant compatibility (Shaw et al. 2010). However, with the widespread dissemination and acceptance of next-generation sequencing technologies, simultaneous typing method for more HLA loci has been used for selection for the patient and suitable donor. Now, the potential donors in the the Umbilical Cord Blood Bank of Zhejiang province, China was simultaneous genotyped of 11 HLA loci.
In our previous reports, we contributed genotype data for HLA-A, -B, -C, -DRB1, -DQB1 for 3580 volunteers from Chinese Marrow Donor Program (Chen et al. 2019), and provided data on an additional 1,734 cord blood samples for the extra HLA-DRB3/4/5 loci (Wang et al. 2021). Nonetheless, there has been no published report detailing the distribution and diversity of alleles at all 11 HLA loci specifically for the Zhejiang Han population, China. To understand these HLA genetic profiles, it is particularly vital in the context of HSCT donor matching and disease-related studies, further enhancing our capacity to make informed clinical decisions for improving HSCT outcomes and protecting from disease.
In this study, we utilized the commercial AllTypeTM NGS kit for HLA genotyping. The distribution of alleles across HLA-A, -B, -C, -DRB1, -DRB3/4/5, -DQA1, -DQB1, -DPA1, and -DPB1 loci analyzed adhered to the principles of HWE. Most loci provided high-resolution results for the majority of alleles at the 4-field level. However, it’s important to note that many alleles failed to produce unique results concerning the fourth field, resulting in cases such as HLA-A*02:01:01:24, *24:02:01:01/HLA-A*02:01:01:20, 24:02:01:01, where all results were recorded at the 2-field level. Similar to our previous studies (Chen et al. 2019; Wang et al. 2021), some ambiguous combinations in typing were not discriminated by the method used. In most cases, these ambiguous combinationswere eventually resolved by following the guidelines provided for common alleles and well-documented alleles (CWD) in China (He et al. 2018). However, it’s worth noting that there were still two alleles for HLA-DRB1, one allele for HLA-DPA1, and 12 alleles for HLA-DPB1 could not be definitively discriminated using CWD and were consequently assigned to the G group.
In our further analysis, the distribution of HLA-A, -B, -C, -DRB1, -DRB3/4/5, and -DQB1 was consistent with our previous reports (Chen et al. 2019; wang et al. 2014; Wang et al. 2020; Wang et al. 2021). However, the genotyping data for HLA-DQA1, -DPA1, and -DPB1 had not been previously reported for the Zhejiang Han population. To provide a comprehensive understanding, we compared the distribution of HLA-DQA1, -DQB1, -DPA1, and -DPB1 loci among various populations (Baek et al. 2021), including East Asian ( Korean and Japan), Southeast Asian, Southwest Asian, Oceanian, Australian, North African, North American, European, and Sub-Saharan African. These comparisons revealed diverse diversity among these populations. For HLA-DQA1, DQA1*03:02(17.41%) was the most common allele in our cohort but had not been identified in Southeast Asian, Southwest Asian, Oceanian, Australian, North African, and Sub-Saharan African, and it was reported in European and North American populations but with low frequency. The second most frequent allele, HLA-DQA1*01:02(15.81%), was the most frequent allele in Oceanian (45.8%) and Sub-Saharan African (31.9%) but was rare in both North and South American. Furthermore, the third most frequent allele, DQA1*05:05(11.19%), was only reported in East Asian, such as Korea and Japan. For HLA-DQB1, DQB1*03:01 was the most frequent allele in most populations, including East Asian (South Korean, Zhejiang Han), Southeast Asian, Oceanian, and North/South America, albeit with higher distribution in North/South America. In addition, DQB1*03:03 and DQB1*06:01 were the other two common alleles in East Asian, but were infrequent or not yet found in other populations. For HLA-DPA1, the locus with the lowest polymophism in the Zhejiang Han populations displayed similar distribution in Asian and Oceanian, with DPA1*02:02 as the most frequent one around 50%. However, it was rare in other populations. Among these countries, European and North America showed extremly high DPA1*01:03 frequency, greater than 80%. The Chinese CWD principles we used only includes data for HLA-A, -B, -C, -DRB1, and -DQB1, without data for -DRB3/4/5, -DQA1, -DPA1, and -DPB1, most of the alleles can be determined according to CWD principles, with only HLA-DQA1 having an allele that cannot be confirmed and is thus assigned as the G group. However, nearly half (48.59%) of the HLA-DPB1 alleles were indistinguishable and yielded ambiguous results, which were then classified as the G group. Consequently, the results of HLA-DPB1 in our cohort were not compared with other populations. It is clear that the sequencing method needs improvement, and the scope of CWD should be expanded to enhance the determination of ambiguous alleles and reduce the number of ambiguous combinations.
In conclusion, our study represents the first comprehensive report on the characteristics of 11 HLA loci, encompassing alleles and haplotypes of HLA-A, -B, -C, -DRB1, -DRB345, -DQA1, -DQB1, -DPA1 and -DPB1 at two-field resolution level within the Zhejiang province of China. Our data highlights the diversity distribution of HLA alleles across different ethnicities while revealing a close resemblance among East Asian populations. These findings have the potential to significantly contribute to the study the associations between certain HLA molecular and distinct outcomes of infectious diseases. Furthermore, they may facilitate the search for unrelated bone marrow donors for patients, and prove invaluable for guiding clinical decision-making.