ISOTOPE: ISOform-guided prediction of epiTOPEs in cancer

Juan Luis Trincado⁰, Eduardo Eyras¹
(0) Josep Carreras Leukemia Research Institute
(1) AUSTRALIAN NATIONAL UNIVERSITY

Find me on Wed Nov 25th, 1:30-2:50pm AEDT in Remo, table 62

Abstract
Immunotherapies provide effective treatments for previously untreatable tumors, but the molecular determinants of response remain to be elucidated. Here, we describe a pipeline, ISOTOPE (ISOformguided prediction of epiTOPEs In Cancer), for the comprehensive identification of cancer-specific splicing-derived epitopes. Using RNA sequencing and mass spectrometry for MHC-I associated proteins, ISOTOPE identified neoepitopes from cancer-specific splicing event types that are potentially presented by MHC-I complexes. We found that, in general, cancer-specific splicing alterations led more frequently to the depletion of potential self-antigens compared to the generation
of neoepitopes. The potential loss of native epitopes was validated using MHC-I associated mass spectrometry from normal cells. Furthermore, analysis of two cohorts of melanoma patients with ISOTOPE identified that splicing-derived neoepitopes with higher MHC-I binding affinity associate with positive response to immune checkpoint blockade therapy. Additionally, we found a more frequent depletion of native epitopes in non-responders, suggesting a new mechanism of immune escape. Our analyses highlight the diversity of the immunogenic impacts of cancer-specific splicing alterations and the importance of studying splicing alterations to fully characterize the determinants of response to immunotherapies. ISOTOPE is available at https://github.com/comprna/ISOTOPE