Meta-analysis of tumor and T cell intrinsic mechanisms of sensitization to checkpoint inhibition
Checkpoint inhibitors (CPIs) augment adaptive immunity. Systematic pan-tumor analyses may reveal the relative importance of tumour cell intrinsic and microenvironmental features underpinning CPI sensitization. Here we collated whole-exome and transcriptomic data for >1000 CPI-treated patients across eight tumor-types, utilizing standardized bioinformatics-workflows and clinical outcome-criteria to validate multivariate predictors of CPI-sensitization. Clonal-TMB was the strongest predictor of CPI response, followed by TMB and CXCL9 expression. Subclonal-TMB, somatic copy alteration burden and HLA-evolutionary divergence failed to attain significance. Discovery analysis identified two additional determinants of CPI-response supported by prior functional evidence: 9q34.3 (TRAF2) loss and CCND1 amplification, both independently validated in >1600 CPI-treated patients. We find evidence for collateral sensitivity, likely mediated through selection for CDKN2A-loss, with 9q34.3 loss as a passenger event leading to CPI-sensitization. Finally, scRNA sequencing of clonal neoantigen-reactive CD8-TILs, combined with bulk RNAseq analysis of CPI responding tumors, identified CCR5 and CXCL13 as T cell-intrinsic mediators of CPI-sensitisation.