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Whole Exome Predictors Immune Checkpoint Therapy Response in Renal Cell Carcinoma

ABSTRACT:

Immune checkpoint therapies, including monoclonal antibodies to programmed cell death-1 (PD-1) and cytotoxic % lymphocyte associated protein-4 (CTLA-4), yield durable clinical responses across many tumor types, including metastatic melanoma, non-small cell lung cancer (NSCLC), and renal cell carcinoma (RCC). However, predictors of response to these therapies in RCC are still unknown. Genomic characterization of large clinical cohorts of patients treated with anti-CTLA-4 and anti-PD-1 agents in melanoma and NSCLC have suggested that high mutational burden, high neoantigen burden, and high expression of certain genes in pre-treatment tumors may be associated with patient response to these therapies. In this study, we sought to investigate genomic predictors of response to anti-PD1 therapy in metastatic RCC in two independent clinical cohorts using whole exome and whole transcriptome sequencing.

PROVIDER: phs001493 | dbGaP |

SECONDARY ACCESSION(S): PRJNA420786PRJNA420785

REPOSITORIES: dbGaP

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Project description:Although immune checkpoint blockade (CPB) leads to prolonged responses in 15-40% of patients with metastatic melanoma, treatment refractory disease and progression after initial response remain major causes of mortality. While predictors of response have been reported, the common mechanisms of both primary and acquired resistance are poorly understood. To identify mechanisms of resistance and examine the evolving landscape in response to CPB, we performed whole exome sequencing (WES), immunohistochemistry (IHC), and RNA-sequencing (RNAseq) of longitudinal tumor biopsies from 17 metastatic melanoma patients treated with various CPB therapies. We found no significant changes in both mutational and neoantigen loads over time between responders and nonresponders. However, we identified abnormalities in one gene, beta-2-microglobulin (B2M), an essential component of MHC Class I antigen presentation, that were present in samples during disease progression but not regression. In total, we identified B2M aberrations in 29.4% of patients, including multiple early frameshift mutations, loss of heterozygosity (LOH) overlapping B2M, and absence of tumor-specific B2M protein expression. Additional defects in the antigen presentation and IFNγ pathways were identified but were not restricted to progressing lesions in our cohort. In two independent cohorts of 105 and 38 melanoma patients treated with ipilimumab (anti-CTLA4) and pembrolizumab (anti-PD1) respectively, we found that B2M LOH was enriched 3-fold in nonresponders (~30%) vs. responders (~10%) and associated with poorer overall survival (log-rank p=0.01, p=0.006). Loss of both copies of B2M was found only in nonresponders. We also found evidence for association of LOH overlapping IFNGR1 with poorer overall survival exclusively in the anti-PD1 cohort. Thus, B2M loss is likely a common mechanism of primary and acquired resistance to therapies targeting CTLA4 or PD-1.

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Whole Exome Predictors Immune Checkpoint Therapy Response in Renal Cell Carcinoma

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