Molecular and immune predictors of response and toxicity to combined CTLA-4 and PD-1 blockade in metastatic melanoma (MM) patients (pts).

Abstract

9579 Background: Combined treatment with ipilimumab and nivolumab (Ipi/Nivo) achieves clinical responses in > 50% of mm pts. However, responses are not universal and toxicity may be limiting, thus biomarkers of response and toxicity are needed to optimize and personalize this therapy. Methods: Tumor biopsies were collected before (n = 29) and on treatment (n = 7) from mm pts (n = 40) treated with Ipi/Nivo. Whole exome sequencing (WES), gene expression profiling, TCR sequencing, and immunohistochemistry (IHC) were performed to define molecular and immune features of the tumors. Radiographic responses in patients were assessed via RECIST 1.1criteria, and patients were classified as responders (R) deriving clinical benefit (with SD, PR, CR) and non-responders (NR) not deriving clinical benefit (PD). Toxicity was also scored, with patients dichotomized into low toxicity ( < grade 2) versus high toxicity ( > grade 3) re: immune-related (IR) toxicities. Results: In this cohort, the response rate was 80%, with 53% of patients experiencing > grade 3 toxicity. There was no significant difference in baseline mutational load in responders (R) vs non-responders (NR) to Ipi/Nivo, but NR had a higher burden of copy number alterations (CNA; p = 0.013), with frequent alterations detected in PTEN, JAK2, and B2M. There were no significant differences in baseline CD8+ T cell density, expression of immune-related genes, or T cell clonality for R vs NR pts. Ipi/Nivo treatment increased intratumoral T cell clonality, but this did not correlate with response. A more diverse peripheral T cell repertoire at baseline was detected in pts who developed IR toxicity (p < 0.05). Conclusions: This data suggests that responses to Ipi/Nivo in mm may occur in the absence of high mutational load or brisk immune infiltrate at baseline. Putative mechanisms of resistance to Ipi/Nivo include high burden of CNA and alterations in PTEN, JAK2, and B2M. Together these studies identify candidate biomarkers of resistance and toxicity for Ipi/Nivo, though they need to be tested in larger cohorts and across cancer types.