P081 ST14 protease resistant peptides, from glioblastoma multiforme mutant proteins, represent higher binding affinities as potential HLA class I epitopes

Abstract

Aim We previously identified a set of the most frequently mutated cytoskeleton- and extracellular matrix-related proteins (CECMPs) in numerous cancer datasets. Mutations in the cytoskeleton and extracellular matrix can induce resistance or sensitivity to proteolysis. We aim to elucidate the effects of protease cleavage on exposing new epitopes for potential HLA Class I binding. Methods Here, we use a bioinformatics approach to assess the impact of amino acid (AA) substitutions on the sensitivity of CECMPs to the ST14 protease (matriptase), a transmembrane serine protease previously implicated in cancer development. Furthermore, to assess tumor specimen immunogenicity, we identified T-cell receptor (TCR) V(D) J recombinations in GBM exome files and mapped overlaps in patient survival between 1) protease sensitivity, 2) HLA Class I binding affinities of new epitopes, and 3) V(D) J recombination reads. Results Results indicated that AA substitutions in the glioblastoma multiforme CECMPs are skewed toward increased resistance to the ST14 protease, in comparison to the wild-type peptide sequence. Furthermore, the protease resistant AA substitutions represent relatively high binding affinities to HLA class I proteins, when assessing the binding specificities using HLA class I alleles matched to the source of the mutant AA. In contrast, the protease sensitive AA substitutions create epitopes that represent lower binding affinities with HLA class I. Moreover, samples representing AA substitutions that increased protease sensitivity also represented reduced overall and disease-free survival periods for patients with glioblastoma. Although the presence of TCR V(D) J recombinations alone did not represent any significant survival differences, the overlap between ST14-protease sensitive mutant barcodes and the TCR V(D) J recombination read positive barcodes represented significantly reduced survival. Conclusions These results may provide indications of the value of the overlap of protease sensitive and resistant, mutant peptides and immune activity as a biomarker for prognosis in Glioblastoma multiforme further elucidating on the role of histocompatibility in cancer development and prognosis.