Introduction: An unexpected diversity in the human genome has been identified including more than 2,500 nonsynonymous single nucleotide polymorphisms (nsSNP) and up to 20 homozygous loss of function (LoF) variants per individual that result in the complete absence of a certain gene product. We specifically hypothesize, that in addition to HLA antigens, alloimmunity occurs through genome-wide genetic incompatibilities due to nsSNPs and LoF variants.

Methods: Genotyping of 50 kidney transplant D/R pairs was performed using a customized gene chip (iGeneTRAiN transplant array V1.0, Affymetrix) with over 750,000 genomic markers. We developed a bioinformatics pipeline for automated analysis if LoF and nsSNP mismatch. A LoF mismatch was defined as at least one functioning copy of a specific gene in the donor and a homozygous gene loss in the recipient. nsSNPs include all variants that result in an altered amino acid sequence.

Results: Demographic data of our cohort is summarized in table 1. We identified a median of 4 homozygous LoF mutations per D/R pair with an interquartile range (IQR) of 2 to 6. A total of 106 different LoF mismatched proteins were identified. Homozygous LoF variants are enriched for olfactory receptor, G-protein coupled receptor and transmembrane signaling receptor activity as well as protein binding pathways and include known minor histocompatibility antigens such as MICA. We further identified a median of 2,386 nsSNP with an IQR of 2,276 to 2,455. We found a total of 10,247 polymorphic proteins based on nsSNP. LoF as well as nsSNP mismatch was significantly less in transplants from living related donors compared to unrelated deceased donors (p<0.05).

Conclusion: LoF and nsSNP mismatch in D/R pairs can be identified using genome-wide genotyping. A broader analysis of imputed variants is forthcoming. Clinical relevance will be tested in a prospective cohort of 2000 D/R pairs. Based on genotype-derived LoF mismatches and polymorphic proteins, we will use peptide arrays to screen for non HLA alloantibodies.

CITATION INFORMATION: Reindl-Schwaighofer R, Kainz A, Cole B, van Setten J, Jelencsics K, Keating B, Oberbauer R. Alloimmunity Through Non-HLA Epitopes in Kidney Transplantation. Am J Transplant. 2016;16 (suppl 3).

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