T cell immunity induced by live, necrotic, and apoptotic tumor cells

The rules that govern the engagement of antitumor immunity are not yet fully understood. Ags expressed by tumor cells are prone to induce T cell tolerance unless the innate immune system is activated. It is unclear to what extent tumors engage this second signal link by the innate immune system. Apoptotic and necrotic (tumor) cells are readily recognized and phagocytosed by the cells of the innate immune system. It is unknown how this affects the tumor's immunogenicity. Using a murine melanoma (B16m) and lymphoma (L5178Y-R) model, we studied the clonal sizes and cytokine signatures of the T cells induced by these tumors in syngeneic mice when injected as live, apoptotic, and necrotic cells. Both live tumors induced a type 2 CD4 cell response characterized by the prevalent production of IL-2, IL-4, and IL-5 over IFN-gamma. Live, apoptotic, and necrotic cells induced CD4 (but no CD8) T cells of comparable frequencies and cytokine profiles. Therefore, live tumors engaged the second signal link, and apoptotic or necrotic tumor cell death did not change the magnitude or quality of the antitumor response. A subclone of L5178Y-R, L5178Y-S cells, were found to induce a high-frequency type 1 response by CD4 and CD8 cells that conveyed immune protection. The data suggest that the immunogenicity of tumors, and their characteristics to induce type 1 or type 2, CD4 or CD8 cell immunity is not primarily governed by signals associated with apoptotic or necrotic cell death, but is an intrinsic feature of the tumor itself.