P142 Class I variation outside the antigen recognition domain is limited in an argentine registry population

Aim The aim of this study was to use next generation DNA sequencing (NGS) to characterize full length HLA class I gene diversity in 1472 volunteers for the unrelated donor registry in Argentina. Methods DNA was prepared from blood. HLA-A, -B, -C alleles were amplified with primers annealing in the 5′ and 3′ UTRs. The sequences of exons and introns were determined by NGS with an Illumina Miseq using an in-house protocol and Conexio Assign software analysis. Analysis used the IPD-IMGT/HLA database from October 2016. Results Volunteers were recruited from 20 of the 23 provinces of Argentina and from its federal capital. The majority (80%) came from the central region of the country. Of the 2944 alleles identified at each locus, the majority have been designated as common (e.g., 92% HLA-A alleles) (Mack et al. Tissue Antigens 2013) and approximately 1% were not found in the IPD-IMGT/HLA database. A total of 79 different allele sequences were identified at the HLA-A locus with similar numbers at HLA-B and -C. The majority of the HLA proteins can be distinguished by sequencing only the antigen recognition domain (ARD)-encoding exons. For example, 94% of the HLA-A alleles could have been detected solely based on the sequence of the ARD-encoding exons. The remaining alleles differed only outside of these exons by either silent variation occurring mainly in introns (6%) or by nonsynonymous variation ( Conclusions NGS has allowed us to evaluate the frequency and characteristics of class I DNA sequence variation outside of the ARD-encoding exons. The additional variation detected is predominantly in noncoding regions. While NGS offers a strategy to achieve single genotype resolution, the amount of additional information gained related to HLA matching for transplantation is minimal.