Abstract 141: Interrogating subclonal mechanisms of immune evasion and immunotherapy resistance in melanoma

Abstract

Abstract Immune checkpoint blockade (ICB) therapies are the current first-line melanoma treatments within the clinic; however, their specific mechanisms for combatting tumor progression remain unclear and determinants for efficacious and durable responses within patients remain unknown. Intratumor heterogeneity (ITH) provides cancers with significant adaptability, leading to metastatic progression and resistance to treatment, but its complexity often complicates its study. To understand how ITH contributes to ICB response, we derived 24 clonal sublines from single cells of an ICB-sensitive and genetically and phenotypically heterogenous mouse model of melanoma. Genomic and transcriptomic analyses uncovered the diversity of these sublines and their plasticity while in vivo studies demonstrated a wide range of responses to ICB therapy including resistant, partially sensitive, and fully responsive. Distinct responses to anti-CTLA-4 monotherapy compared to combination (anti-CTLA-4 plus anti-PD-L1) therapy were also observed, and further exploration of untreated tumors revealed correlations between highly inflamed and differentiated phenotypes with response to anti-CTLA-4. To better understand changes in plasticity and immune profile throughout the course of treatment, tumors were harvested from the parental cell line prior to treatment and at several timepoints after treatment with anti-CTLA-4 monotherapy. These samples are undergoing high throughput spatial transcriptomics analysis to map the melanoma phenotypes characterized in the clonal sublines with changes in the immune compartment. Furthermore, blood samples were collected to investigate inflammatory profiles of cytokines and chemokines to describe the evolution of the tumor microenvironment throughout the course of immunotherapy. Further studies will allow us to identify predictive and prognostic biomarkers of resistance and relapse upon ICB therapy, respectively. Overall, the 24 clonal sublines serve as a valuable tool to model tumor dynamics associated with ICB efficacy and understand the complex role melanoma plasticity plays in immune evasion mechanisms. Citation Format: Isabella Church, Charli Gruen, Antonella Sassano, Julio Valencia, Emily Wu, Howard Yang, Gabe Needle, Cari Smith, Sung Chin, Jessica Ebersole, Christina Marcelus, Anyen Fon, Huaitian Liu, Chi-Ping Day, Howard Young, Maxwell Lee, Glenn Merlino, Eva Pérez-Guijarro. Interrogating subclonal mechanisms of immune evasion and immunotherapy resistance in melanoma [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 141.