Postdoctoral associate David H. Koch Institute for Integrative Cancer Research, MIT Somerville, Massachusetts, United States
Disclosure(s):
Tiffany Emmons, PhD: No financial relationships to disclose
Introduction/Rationale: Immunogenic cell death (ICD) is a process where dead cells expose damage-associated molecular patterns to stimulate the immune system. Although the ICD paradigm focuses on immunogenicity induced by cell death, we evaluated whether live but stressed/DNA-damaged tumor cells could also modulate their immunogenicity.
Methods: Murine ovarian cancer cell lines expressing ovalbumin were treated with various DNA-damaging agents, then incubated with bone-marrow derived dendritic cells (DCs) or treated with IFNγ for 24hrs, followed by incubation with OT-I CD8+ T cells. T cell activation was evaluated using flow cytometry. Tumor cell killing was imaged over the course of 3 days.
Results: Treatment of tumor cells with topoisomerase II inhibitors potently induced T cell activation and anti-tumor immunogenicity. Notably, T cell activation was only induced by the live cell fraction after toposimerase treatment, with minimal immunogenic activity conferred by the dead cell fraction. Transwell assays demonstrated that contact between tumor cells and T cells was necessary, and the requirement for DCs could be bypassed by exogenous administration of IFNγ to the tumor cells after DNA damage. IFNγ-treated DNA-damaged tumor cells increased expression of positive co-stimulatory ligands and induced Granzyme B production in T cells, indicating the presence of both Signals 2 and 3 required for T cell activation. These studies suggest that certain types of DNA damage can increase the efficacy of anti-cancer immunotherapy by coordinated stress and immune signaling that allow live tumor cells to directly activate T cells.
Conclusion: Tumor cells surviving topoisomerase II-induced DNA damage activate T cells through DC-dependent and DC-independent pathways more potently than dead cells. These findings indicate that the efficacy of chemotherapy combined with immunotherapy may be improved by using doses of DNA damaging agents that increase tumor cell stress, but do not lead to excessive tumor cell death.
