IRIS: Discovery of cancer immunotherapy targets arising from pre-mRNA alternative splicing

Alternative splicing (AS) is prevalent in cancer, generating an extensive but largely unexplored repertoire of novel immunotherapy targets. We describe Isoform peptides from RNA splicing for Immunotherapy target Screening (IRIS), a computational platform capable of discovering AS-derived tumor antigens (TAs) for T cell recep-tor (TCR) and chimeric antigen receptor T cell (CAR-T) therapies. IRIS leverages large-scale tumor and normal transcriptome data and incorporates multiple screen-ing approaches to discover AS-derived TAs with tumor-associated or tumor-specific expression. In a proof-of-concept analysis integrating transcriptomics and immuno-peptidomics data, we showed that hundreds of IRIS-predicted TCR targets are pre-sented by human leukocyte antigen (HLA) molecules. We applied IRIS to RNA-seq data of neuroendocrine prostate cancer (NEPC). From 2,939 NEPC-associated AS events, IRIS predicted 1,651 epitopes from 808 events as potential TCR targets for two common HLA types (A*02:01 and A*03:01). A more stringent screening test pri-oritized 48 epitopes from 20 events with neoantigen-like NEPC-specific expression. Predicted epitopes are often encoded by microexons of & LE;30 nucleotides. To validate the immunogenicity and T cell recognition of IRIS-predicted TCR epitopes, we performed in vitro T cell priming in combination with single-cell TCR sequencing. Seven TCRs transduced into human peripheral blood mononuclear cells (PBMCs) showed high activity against individual IRIS-predicted epitopes, providing strong evidence of isolated TCRs reactive to AS-derived peptides. One selected TCR showed efficient cytotoxicity against target cells expressing the target peptide. Our study illustrates the contribution of AS to the TA repertoire of cancer cells and demon-strates the utility of IRIS for discovering AS-derived TAs and expanding cancer immunotherapies.

Automated summary

This study describes a computational platform called IRIS that can discover tumor antigens derived from alternative splicing, providing potential targets for TCR and CAR-T immunotherapies. Through the analysis of transcriptomics and immuno-peptidomics data, the study demonstrates that the predicted targets by IRIS can bind with HLA molecules. The study illustrates the contribution of alternative splicing to the repertoire of tumor antigens and demonstrates the utility of IRIS in discovering AS-derived antigens and expanding cancer immunotherapies.