Abstract 655: Necroptosis promotes tumor growth through IL1-alpha release and recruitment of immunosuppressive myeloid cells

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Abstract Programmed cell death (PCD) was originally limited to apoptosis, but now includes pyroptosis, ferroptosis, necroptosis, and paraptosis. Necroptosis has attracted particular interest as an approach for immunotherapy as activation of the RIPK1/RIPK3 necrosome phosphorylates MLKL to form membrane pores, leading to loss of integrity and enhanced ability to induce an antigen-specific immune response in models of vaccination. Here we sought to determine if necroptosis within tumor cells was an important regulatory of anti-tumor immunity. Deficiency in Ripk3 or Mlkl did not impact tumor incidence or growth in genetic models of mammary carcinoma or lung adenocarcinoma. Similarly, the growth of syngeneic cell lines was not altered by loss of Ripk3 or Mlkl in vitro or in vivo. We next examined the induction of apoptosis or necroptosis in syngeneic tumor models using genetic constructs with doxycycline-controlled expression. In line with published data, subcutaneous vaccination demonstrated that RIPK3-induced necroptosis promoted an antigen-specific CD8+ T cell response greater than that observed with caspase 8-induced apoptosis. Surprisingly however, when necroptosis was induced within established PyMT-B6 orthotopic mammary tumors, we observed significantly reduced survival, which correlated with higher neutrophil and macrophage recruitment, along with lower CD8+ T cell infiltration and IFN-γ expression. In vitro, necroptosis induced with either RIPK3 or MLKL greatly enhanced expression of Cxcl1 and Cxcl2, a property that could be recapitulated by transferring dead cell supernatant to live cells, suggesting the presence of an alarmin or damage-associated molecular pattern (DAMP). We therefore knocked out MyD88, which serves as a critical adapter protein to a number of surface receptors, including the TLR family, the IL1 receptor, and RAGE. The loss of MyD88 completely eliminated the ability of tumor cells to express Cxcl1 in response to supernatant from necrotic cells. Expression was not driven by release of HMGB1 or signaling through RAGE or TLRs. Instead, we found that blocking the interleukin (IL)1 receptor or IL1α, but not IL1β, prevented Cxcl1 expression. IL1α is a constitutively expressed by some tumors, suggesting a potential role for IL1α in regulating immune responses to therapies that induce necrotic-like forms of cell death. In support of this, Il1a expression was strongly predictive of progression free survival in triple-negative breast cancer. These findings suggest that IL1α has an unexplored role in regulating the tumor microenvironment. By understanding how IL1α regulates the immune response during cytotoxic therapy, our findings may explain why certain therapies are immunogenic (or not) in different cancers. Citation Format: Kay Hänggi, Aysenur Keske, Alycia Gardner, Jie Li, Olabisi Osunmakinde, Daiana Celias, Amer Beg, Brian Ruffell. Necroptosis promotes tumor growth through IL1-alpha release and recruitment of immunosuppressive myeloid cells [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 655.