Abstract 2276: Spatiotemporal analysis of metastatic melanoma reveals mechanisms of resistance to immune checkpoint blockade

Abstract The treatment of metastatic melanoma has been revolutionized with the introduction of immune checkpoint blockade (ICB) therapies in the last decade. Despite durable responses exhibited by a subgroup of patients, most of patients do not respond to ICB therapies and the vast majority (60%-90%) of patients experience disease progression within five years. Molecular mechanisms of primary and acquired resistance to ICB are still widely unknown, which warrants further mechanistic investigation. Towards that goal, we used a holistic approach driven by integrated genomic tools to molecularly profile 35 longitudinal tumor specimens at pre-, on-, and post-treatment time points which were derived from seven patients with metastatic melanoma who progressed on sequential ICB therapies, including three responders and four non-responders. We integrated analyses of data generated from RNA sequencing, Whole-exome Sequencing (WES), NanoString nCounter vantage 3D, Cyclic Immunofluorescence (CyCIF), NanoString Digital Spatial Profiling (DSP) and Multiplex Immunohistochemistry (mIHC) platforms to elucidate evolutionary trajectories that occurred in both the tumor and the tumor immune microenvironment (TiME) that may have orchestrated response and resistance to ICB therapies. Simultaneous analyses conducted on genomic, transcriptomic and proteomic levels identified the re-activation of the MAPK pathway as a potential mechanism of resistance to ICB therapies. Spatially-resolved, image-based immune monitoring analysis at single cell resolution revealed that response to ICB is associated with infiltration of immune cells accompanied by induced activities of myeloid, T cells and macrophages in the TiME. In summary, integrated analyses allow us not only to reveal the dynamic co-revolution of both tumor and immune cells in TiME following sequential ICB therapies but also to provide a comprehensive perspective to molecular mechanisms of response and resistance to ICB therapies. A deeper understanding and elucidation of the evolution of mechanisms of response and resistance to ICB therapies will point us to generate hypothesis-driven, potential salvage therapies to overcome resistance to ICB therapies. Citation Format: Shiyou Wei, Jinho Lee, Marilyne Labrie, Courtney Betts, Lunxu Liu, Lisa Coussens, Meenhard Herlyn, Genevieve Boland, Gordon Mills, Gao Zhang. Spatiotemporal analysis of metastatic melanoma reveals mechanisms of resistance to immune checkpoint blockade [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 2276.