2891 - Loss of Tumor Intrinsic RIPK1, Antitumor Immune Responses, and the Efficacy of PD-1 Blockade

F. Teng¹, P. Wang², Y. Li¹, J. Yuan³, T. Yin^1,4, X. Shi¹, J. Xu¹, C. Liu⁵, and J. Yu⁶; ¹Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong, China, ²Shandong Cancer Hospital & Institute, Cheeloo college of medicine, Shandong University, Jinan, China, ³Department of Radiation Oncology and Shandong Provincial Key Laboratory of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China, ⁴Cancer Center, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China, ⁵Department of Radiation Oncology, Peking University First Hospital, Beijing, China, ⁶Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong, China

Purpose/Objective(s): Receptor-interacting protein 1 (RIPK1) kinase has emerged as a key upstream regulator that controls inflammatory signaling as well as the activation of multiple cell death pathways, including apoptosis and necroptosis. Despite its critical functions, the role of RIPK1 in tumor immunity and its impact on immunotherapy responses remain poorly understood. This study aimed to elucidate the influence of RIPK1 on antitumor immunity and the efficacy of immunotherapy. Materials/

Methods: Tumor growth was monitored to evaluate the antitumor efficacy of targeting intrinsic RIPK1 both with and without anti-programmed cell death protein-1 (PD-1) antibodies in MC38 and B16F10 tumor models. To determine the role of intrinsic RIPK1 in reprogramming the tumor microenvironment (TME), techniques such as flow cytometry, immunofluorescence, and T cell depletion experiments were utilized. Additionally, quantitative real-time PCR (qRT-PCR), Western blotting, flow cytometry, cycloheximide chase assays, and immunoprecipitation methods were employed to elucidate the mechanisms through which RIPK1 regulates antitumor immunity.
Results: We found that the loss of RIPK1 in tumor cells significantly reprogrammed the tumor immune microenvironment and enhanced anti-tumor immunity. This reprogramming manifests as a pronounced increase in the infiltration of CD45+ immune cells, including CD8+ T cells and dendritic cells, alongside a pivotal shift in macrophage polarization from an M2 to an M1 phenotype. Furthermore, the loss of RIPK1 exhibited enhanced responsiveness to immunotherapy evidenced by superior tumor control and a surge in the infiltration of activated CD8+ T cells. Additionally, the loss of RIPK1 has been shown to induce systemic antitumor immune responses, which manifest as abscopal effect and the establishment of immune memory, thereby rendering mice resistant to tumor rechallenge. Significantly, our research highlights the critical role of cytokine signaling in this context, particularly emphasizing the influence of CCL2 on immune cell recruitment and macrophage polarization. We further elucidated the underlying mechanisms and found that RIPK1 deficiency promotes RIPK3-MLKL-mediated necroptosis while inhibiting NF-?B-mediated pro-survival signaling and forming an immune-activated tumor microenvironment conducive to enhanced antitumor immunity.
Conclusion: RIPK1 plays a crucial role in antitumor immunity through the RIPK3-MLKL and NF-?B pathways, suggesting that targeting RIPK1 may provide a potential new therapeutic avenue in tumor immunotherapy.