Abstract 2024: Deep and durable responses to ALK-targeted therapy require CD8+ T cells
Authors: Reis Greg , Phelabaum Stevie , Navarro Andre , Kleczko Emily , Heasley Lynn , Nemenoff Raphael , Schenk Erin L. 
Published: March 2024

Abstract
Despite major advances in therapies for lung cancer, it remains the leading cause of cancer related deaths in the United States. Tyrosine kinase inhibitors (TKI) designed to inhibit oncogenic anaplastic lymphoma kinase (ALK) fusions have transformed the treatment of patients with ALK+ NSCLC and many survive for several years on TKIs. While most patients experience a decrease in tumor burden on initial alectinib therapy, for many, tumor shrinkage is incomplete and persistent, residual disease remains. Critically, the degree of tumor shrinkage and amount of residual disease that persists despite TKI associates with overall survival. Multiple cancer-cell intrinsic mechanisms of persistence despite TKI therapy have been reported, but they do not fully account for the heterogeneity of this initial tumor response, suggesting other determinants are present beyond inhibiting the primary oncogene. However, extrinsic mediators of persistent disease, such as immune cells within the tumor microenvironment (TME), have not been rigorously studied in ALK+ NSCLC as they are considered immunologically “cold” tumors. Using EA-1 and EA-2, two distinct murine ALK+ adenocarcinoma cells lines derived from immunocompetent C57BL/6J mice, we have demonstrated that ALK+ NSCLC response to alectinib requires the adaptive immune system. C57BL/6J mice bearing orthotopic EA-1 tumors experience tumor shrinkage but have persistent, residual disease on CT imaging; those bearing EA-2 tumors have no residual disease. In this model system, when alectinib treatment stops, no EA-2 tumors recur but all animals bearing EA-1 tumors experience tumor outgrowth. TME interrogations by multispectral tissue imaging demonstrated more CD8+ T cells in the EA-2 TME compared to EA-1 and no difference in CD4+ T cells. Flow cytometry revealed a significant increase in activated CD8+ T cells and CD86+ CD103+ dendritic cells within the TME of EA-2 tumors compared to EA-1. When implanted into nude mice, EA-1 and EA-2 both experience initial disease shrinkage on alectinib, but EA-2 tumors now exhibit residual disease on imaging. Notably for both cell lines, tumor outgrowth occurs in the nude mice despite continued TKI therapy. Using knock out animal models, we established that CD8+ T cells, but not CD4+ T cells, were required for response to alectinib. In animals lacking CD8+ T cells, EA-2 tumors shrink with alectinib therapy but are not eliminated as in the wild type controls. Notably, despite continued alectinib therapy, tumors grew out in the CD8+ knock out animals. In the EA-2 model, CD4+ T cells we not required for response to alectinib, and CD4+ knock out animals did not experience tumor outgrowth when alectinib was held. Taken together, these data suggest that the adaptive immune system, specifically CD8+ T cells, are required for a deep and durable response to molecularly targeted therapy for ALK+ NSCLC.
Citation Format: Greg Reis, Stevie Phelabaum, Andre Navarro, Emily Kleczko, Lynn Heasley, Raphael Nemenoff, Erin L. Schenk. Deep and durable responses to ALK-targeted therapy require CD8+ T cells [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(6_Suppl):Abstract nr 2024.