PROJECT SUMMARY/ABSTRACT: Despite the landmark approval of anti-PD1 therapy for non-small cell lung cancer (NSCLC), the majority of patients still progress. Compensatory activation of lymphocyte activation gene 3 (LAG3), to suppress T cell activation is an established mechanism of resistance to anti-PD-1 therapy in cancer. Our recent work suggests that IL-6 is an upstream inducer of LAG3 in patients with NSCLC. We have demonstrated an association between IL-6 and STAT3 activation and decreased response in patients with NSCLC receiving anti-PD-1 therapy. However, we do not know (1) the mechanism of IL-6-induced LAG3 expression which leads to anti- PD-1 resistance, or (2) if IL-6 blockade prevents T cell dysfunction in vivo. This proposal hypothesizes that (1) increased plasma IL-6 induces LAG3 expression via STAT3 activation in peripheral CD8+ T cells leading to T cell dysfunction and decreased response to anti-PD-1 therapy in patients; and (2) LAG3-mediated T cell dysfunction can be rescued with IL-6 blockade in vivo. This proposal will significantly impact future studies regarding immunotherapy resistance in cancer. Specifically, this project will inform our understanding of a novel IL-6-induced LAG3 mediated mechanism of anti-PD-1 resistance and will serve as the pre-clinical rationale for investigating the combination of IL6/STAT3 inhibition and PD-1 blockade in an early phase clinical trial for patients with advanced NSCLC. This proposal will provide Dr. Somasundaram with the opportunity to continue work with (i) animal models (design and oversee murine models), (ii) quantify changes in tumor size, volume and number in mice, and (iii) evaluate the immune landscape in murine T cells by immunohistochemistry (IHC) and flow cytometry, and RNA sequencing (RNAseq). He will continue his current work with patient samples also. These skills will be reinforced by a team of mentors, advisors, collaborators, and core resources available at the University of North Carolina and the University of Pittsburgh. The primary mentor, Dr. Jonathan Serody, is an internationally recognized, NIH R01-funded scientist with 28 years of experience in tumor immunology, and co-mentor, Dr. Dario Vignali, is an NIH R01-funded tumor immunologist with decades of experience in murine research. Also, an advisory committee of accomplished investigators with expertise in tumor immunology, IL-6, LAG3, PD-1, and NSCLC will monitor Dr. Somasundaram’s progress with quarterly meetings ensuring the completion of Dr. Somasundaram’s short-term goal of scientific independence and long-term goal of becoming a tenure-track physician-scientist with expertise in systemic inflammation, tumor immunology, checkpoint blockade resistance, and NSCLC. The results from this proposal will form the basis for an R01 studying the translational role of IL6 induced anti-PD-1 resistance in NSCLC.