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Abstract B186: Tumor cell-derived proteases contribute to antigen processing and enhance cross-presentation

Tumor lysates (TLs) offer a source of both undefined tumor antigens and endogenous adjuvants, called danger-associated molecular patterns (DAMPs), to induce antitumor immune responses. TLs can therefore serve clinical applications for immunotherapy, including vaccination and as a platform for the expansion for tumor-specific T-cells for use in adoptive cell therapy. TL-based approaches offer the advantage of inducing antitumor immunity without the need to identify specific tumor antigens, a major challenge limiting the clinical application of immunotherapies for solid tumors. Immunogenic cell death (ICD) in tumor cells has proven crucial for the generation of robust antitumor immune responses, suggesting that the induction of ICD may improve the efficacy of TL-based immunotherapies. Here, we examined the immunogenicity of TLs prepared from tumor cells exposed to increasing levels of heat (37°C, 42°C and 56°C), using the MC38-OVA/OT-I system. Molecular correlates of ICD were assessed during the course of heat-treatment and in TL preparations. Notably, lethal heat-treatment (56°C) induced primary necrosis with concomitant caspase activation, calreticulin exposure, HMGB1 release and HSP upregulation. All TLs promoted maturation of bone marrow-derived dendritic cells (BMDC), as evidenced by CD80 and CD86 upregulation, and elicited protective antitumor immunity in vaccinated mice. However, only TLs prepared from lethal heat-treated tumor cells promoted cross-presentation in BMDC to elicit antigen-specific T-cell activation ex vivo. Marked proteolytic activity was observed in lethal heat-treated tumor cells, which were capable of processing antigen and binding resultant peptides. Interestingly, inhibition of broad protease activity in lethal heat-treated TLs markedly reduced cross-presentation. Selective inhibition of calpains, but not caspases, cathepsins or the proteasome, reduced antigen processing by heat-killed tumor cells.Together, this demonstrates that tumor-derived proteases can contribute to antigen processing and enhance cross-presentation. Our data suggest that in addition to DAMP release, antigenic processing by proteases in dying tumor cells can influence the immunogenicity of cell death. Citation Format: Nicholas J. Shields, Katie A. Young, Christopher Jackson, Sarah L. Young. Tumor cell-derived proteases contribute to antigen processing and enhance cross-presentation [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B186.