Allele Level Sequencing of Killer Cell Immunoglobulin-Like Receptor Genes Using Oxford Nanopore Long Read Sequencing

The human Killer cell Immunoglobulin-like Receptor (KIR) genes, found on chromosome 19, encode for cell surface protein receptors that, through interaction with their ligand, modulate the action of Natural Killer (NK) cells and some subsets of T lymphocytes. KIR genes exhibit extensive variation through variable gene content, copy number, and allele polymorphism. The combination of KIR genes and their ligands is implicated in various clinical settings including haematopoietic stem cell and solid organ transplant, and infectious disease progression. KIR gene content has been used in the selection of optimal stem cell donors with haplotype variations in recipient and donor giving differential clinical outcomes. With the introduction of massively parallel clonal next generation sequencing and single molecule long read third generation sequencing, allele level determination of KIR genotypes has become feasible. We describe a method for amplicon-based long read sequencing on the Oxford Nanopore Technologies platform that provides largely unambiguous allele level typing of KIR genes. The method was validated using DNA extracted from 48 10th International Histocompatibility Workshop (IHWS) cell lines with previously published allele level KIR genotypes and 176 Western Australian samples previously tested for the presence or absence of KIR genes. Our long-read sequencing method was able to accurately determine KIR alleles with an overall concordance of 97%-99% with the published data. Importantly, phasing ambiguity caused by the inability to phase heterozygous base positions over long stretches of gene sequence was resolved in several samples. Thus, our long read PCR sequencing strategy can be used to determine KIR genotypes at allele resolution level.