Abstract 4034: Lag3 blockade enhances the anti-tumor effect of dual GITR agonism and PD-1 blockade in a preclinical melanoma model

Abstract Immune checkpoint blockade (ICB) therapies, specifically anti PD-1 and anti CTLA-4, have resulted in tremendous success in the clinic. However, a substantial number of patients still relapse due to either inherent or acquired resistance to ICB therapies. In this scenario, activation of T cell co-stimulation pathways along with ICB emerges as a promising strategy to improve anti-tumor responses. Engagement of Glucocorticoid induced TNFR Related protein (GITR) costimulatory molecule, leads to enhanced activation of cytotoxic T cells while destabilizing suppressive T regulatory cells in the tumor microenvironment. Additionally, combining GITR agonism with PD-1 blockade improves the anti-tumor response in a murine model of advanced melanoma resistant to ICB, positioning GITR as an attractive immunotherapeutic target. In this study, we evaluated the therapeutic efficacy of combining blockade of the immune checkpoint LAG3 with GITR agonism for treating ICB-resistant advanced melanoma, using the B16 model. The combination of LAG3 blockade with GITR agonism was well tolerated, leading to better tumor control and improved survival. Our data revealed increased B cell infiltration and activation within tumors and draining lymph nodes (LNs) of treated mice. B cell depletion diminished the anti-tumor effect of the combination therapy, suggesting that B cells play an active role in controlling tumor growth. Spleens from treated mice exhibited increased lymphocytic hyperplasia, along with more and larger germinal centers. B cell receptor sequencing revealed an increased clonality and reduced entropy. Treating B cells with GITR agonism and LAG3 blockade in vitro led to increased activation and proliferation, suggesting a direct effect of these therapies on B cells. Furthermore, adding LAG3 blockade to the dual combination of GITR agonism and PD-1 blockade resulted in superior tumor control and increased B cell activity in the draining LNs. Collectively, our findings suggest that the humoral response significantly contributes to the anti-tumor responses elicited by ICB when combined with GITR agonism. This triple combination therapy (LAG3 blockade + PD1 blockade + GITR agonism) holds promise as a safe and potent therapeutic strategy to overcome ICB resistance. Further investigation into the mechanism of action by which GITR agonism leads to enhanced B cell responses when combined with ICB is warranted in order to design more effective therapies for cancer treatment. Citation Format: Rachana R. Maniyar, Yuval Elhanati, Levi Mangarin, Yacine Marouf, Ashley Ahmed, Benjamin Greenbaum, Jedd Wolchok, Taha Merghoub. Lag3 blockade enhances the anti-tumor effect of dual GITR agonism and PD-1 blockade in a preclinical melanoma model 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 4034.