Abstract 4527: CD8 T cell-melanoma cell interactions in response and resistance to ipilimumab plus nivolumab: Biopsy analysis of SWOG S1616

Abstract Background: In the randomized S1616 trial (NCT03033576), patients with metastatic melanoma refractory to anti-PD-1-based therapy had improved progression free survival (PFS, HR = 0.63, p = 0.037) and objective response to ipilimumab plus nivolumab (ipi/nivo, RR 28%) compared to ipilimumab alone (ipi, RR = 9%). We hypothesized that reversal of resistance to PD-1 blockade with CTLA-4 blockade would result in increased CD8 T-cell infiltration in patient biopsies. Methods: Multiplex ion beam imaging (MIBI) for 32 protein markers, spanning tumor, immune, and stromal cell types, was used to evaluate the tumor microenvironment in melanoma tumor biopsies collected at baseline (N=21 samples) and one month on-treatment (N=22; N=16 paired timepoints). Tumor-immune cell dynamics were determined by comparing baseline and on-treatment biopsies within clinical groups (ipi/nivo response, N=10; ipi/nivo no-response, N=9; ipi no-response, N=8). Results: Multiplex analysis in ipi/nivo responsive patients demonstrated increased proportions of CD8 (median 1.6X increase), CD4 (2.1X), regulatory T cells (1.6X), and monocytes (1.4X), with a paralleled 8.1X decrease in melanoma cells over the course of treatment. This was confirmed by histopathologic evidence of tumor regression, necrosis, and immune infiltrate in on-treatment, responding tumor biopsies, as determined by dermatopathologists. Melanoma cells had direct, cell-membrane interactions with CD8 T cells in ipi/nivo responsive patients, both at baseline (median 26%) and on-treatment (median 86%). The shared interface between melanoma and CD8 T-cells had polarized expression of CD3, CD8, and CD45RO. There was no change in T-cell infiltration nor tumor cell content over the course of treatment in ipi/nivo non-responders nor ipi non-responders; similar proportions of melanoma cells were interacting with CD8 T-cells at baseline (median 24%) and on-treatment (27%). Conclusion: Reversal of resistance to PD-1 blockade is associated with increased frequency of CD8 T-melanoma cell interactions and pathological response, reflective of different stages of antitumor immune responses. Response to ipi/nivo in the anti-PD-1 refractory setting was further associated with increased tumor-polarized and activated CD8 T cells interacting with melanoma cells, demonstrated by the colocalized expression of immune synapse proteins at tumor-CD8-T-cell membrane interfaces. Citation Format: Katie M. Campbell, Lawrence Kuklinski, Zaid Bustami, Jessica Maxey, Egmidio Medina, Sandra Santulli-Marotto, Cynthia R. Gonzalez, Nataly Naser Aldeen, Kari Kendra, Sapna Patel, Siwen Hu-Lieskovan, James Moon, Shay Bellasea, Christine N. Spencer, Marshall A. Thompson, Michael Wu, Ari Vanderwalde, Philip O. Scumpia, Antoni Ribas. CD8 T cell-melanoma cell interactions in response and resistance to ipilimumab plus nivolumab: Biopsy analysis of SWOG S1616. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4527.