Impact of recipient/donor KIR/HLA mismatches on the outcome of islet transplantatation

The killer immunoglobulin-like receptor (KIR) genes encode a family of activating and inhibitory receptors regulating the activity of NK cells and some T cell subsets by interacting with HLA class I molecules. Moreover, the KIRs have been implicated in the outcome of solid organ transplantation and most studies highlighted the impact of KIR/HLA mismatch on graft survival. However, to propose KIR/HLA matching as prognostic tool, is relevant to know copy number variation (CNV) and expression level of KIRs. Indeed, although KIRs show high variability in both gene content and expression among individuals, current KIR typing methods found out their presence/absence but failed to infer their CNV and transcriptional landscape. In light of these considerations, we aimed at developing a novel high-throughput analytical platform to investigate the effects of recipient/donor KIR/HLA pairs on the outcome of islet transplantation. The analytical platform allows qualitative (gene presence/absence) and quantitative (gene dosage and expression) evaluation of all KIRs, starting from low amounts of DNA/RNA. The platform was tested on HLA-typed cohorts of patients following transplant of pancreatic islets and kidney (as control) with 5-year follow-up. The transplant outcome was expressed as the integration of dichotomous variables of the graft function (good/bad) and survival (yes/no), according to circulating c-peptide, insulin needs as IU/kg/day, and HbA1c percentage (for islet), and of serum creatinine level and glomerular filtration rate (for kidney).Our platform demonstrated to reliably identify KIR genes at the genomic and transcriptional levels, and to distinguish among homologous ones, including the challenging 2DL5A/B genes. The system was successful to build up the genomic organization of KIR locus and obtain information on the functional status, determining CNV and expression of KIRs, and the presence of null/cytoplasmatic retained alleles. KIR-specific amplification and CNV determination achieved the highest accuracy in benchmarks, with an AUC >0.9. Finally, we exploited the platform on islet transplant patients to correlate recipient/donor KIR/HLA combinations with primary loss of function and overall graft survival. The development of accurate and efficient tools for KIR typing and expression analysis allows studies on the function of KIR-expressing cells and their impact on the outcome of islet transplantation.