Abstract 583: Spatiotemporal analyses of longitudinal specimens reveal mechanisms of response and resistance to immune checkpoint blockade in metastatic melanoma

Abstract Although durable responses to immune checkpoint blockade (ICB) therapies exhibit by a subgroup of patients with metastatic melanoma, most of patients have no response or develop to acquired resistance to ICB therapies within few years. Molecular mechanisms of primary and acquired resistance to ICB therapies are still elusive, which warrants further elucidation. Here, we used a holistic approach to profile 35 longitudinal tumor specimens at pre-, on-, and post-treatment time points which were derived from 7 patients (3 responders and 4 non-responders) with metastatic melanoma who progressed on sequential ICB therapies, including anti-PD-1 and anti-CTLA-4 therapies. We integrated analyses of RNA sequencing, Whole-exome Sequencing (WES), NanoString nCounter vantage 3D, Cyclic Immunofluorescence (Cyc-IF), NanoString Digital Spatial Profiling (DSP) and Multiplex Immunohistochemistry (mIHC) data of these longitudinal tumor specimens 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 of genomic, transcriptomic and proteomic data identified the re-activation of MAPK-RAS as well as PI3K pathway upon or after ICB therapies, which may elucidate the mechanism of resistance to ICB therapies. Spatially-resolved, image-based immune monitoring analysis at single cell resolution revealed that the activation status of T cell markers and T-cell checkpoint is conversely associated with potential mechanism of resistance to ICB therapies. In summary, integrated analyses of muti-oics and spatially image-based data from longitudinal tumor specimens 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 in patients with metastatic melanoma. Citation Format: Gao Zhang, Lisa Coussens, Meenhard Herlyn, Keith T. Flaherty, Genevieve Boland, Gordon Mills. Spatiotemporal analyses of longitudinal specimens reveal mechanisms of response and resistance to immune checkpoint blockade in metastatic melanoma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 583.