Targeted long-read sequencing facilitates phased diploid assembly and genotyping of the human T cell receptor alpha, delta and beta loci

T cell receptors (TCRs) recognize peptide fragments presented by the major histocompatibility complex (MHC) and are critical to T cell mediated immunity. Early studies demonstrated an enrichment of polymorphisms within TCR-encoding (TR) gene loci. However, more recent data indicate that variation in these loci are underexplored, limiting understanding of the impact of TR polymorphism on TCR function in disease, even though: (i) TCR repertoire signatures are heritable and (ii) associate with disease phenotypes. TR variant discovery and curation has been difficult using standard high-throughput methods. To address this, we expanded our published targeted long-read sequencing approach to generate highly accurate haplotype resolved assemblies of the human TR beta (TRB) and alpha/delta (TRA/D) loci, facilitating the detection and genotyping of single nucleotide polymorphisms (SNPs), insertion-deletions (indels), structural variants (SVs) and TR genes. We validate our approach using two mother-father-child trios and 5 unrelated donors representing multiple populations. Comparisons of long-read derived variants to short-read datasets revealed improved genotyping accuracy, and TR gene annotation led to the discovery of 79 previously undocumented V, D, and J alleles. This demonstrates the utility of this framework to resolve the TR loci, and ultimately our understanding of TCR function in disease.