Re-Designing Cancer Immunotherapy to Enhance Anti-Tumor Immunity

Immunotherapy has transformed the field of oncology. However, clinical challenges of toxicity and low response rate offer opportunities to develop novel, rational strategies to integrate into current clinical oncology treatment. To address these challenges, we designed a novel local mesenchymal stromal cell (MSC) based immunotherapy to study the immune tumor microenvironment (TME), and optimized radiotherapy delivery with cGAMP and systemic α-PD-L1 immunotherapies. Using MSC, we delivered various forms of anti-CD3 and/or co-signals to explore their contribution to re-activate T cells inside the TME. Combined α-CD3 and CD40L rather than CD80 leads to superior anti-tumor efficacy compared to either alone. Mechanistically, TCR activation of pre-existing CD8+ T cells synergizes with CD40L activation of DCs inside the TME to control tumor growth. We found exogenous TCR signals can better re-activate TIL, but distal tumor control required T cells from the draining lymph node. This study supplies further evidence that TCR signaling for T cell re-activation in the TME is defective but can be rescued by proper exogenous signals, indicating the importance of the local tumor microenvironment on anti-cancer immunity. To approach the problem from another angle, we chose to optimize delivery of radiotherapy for enhanced immune stimulation. Treating radiotherapy like a vaccination in situ, we tested the hypothesis that spacing radiation doses by 10 days would allow for enhanced anti-tumor immunity. This new ablative radiation dosing scheme "personalized ultra-fractionated stereotactic adaptive radiotherapy" (PULSAR) was tested in combination with α-PD-L1 therapy and cGAMP treatment in immune activated and resistant syngeneic immunocompetent mouse models of cancer. We report that both radiation and immunotherapy sequencing as well as radiotherapy fraction spacing affects the combination treatment response. Better tumor control was achieved by giving α-PD-L1 therapy during or after radiation. Spacing fractions 10 days apart (PULSAR) achieved better tumor control when combined with α-PD-L1 and cGAMP immunotherapies than traditional single day spacing. These results illustrate that radiotherapy dosing and scheduling impacts tumor control in combination with two different immunotherapies. These pre-clinical investigations demonstrate that modifying the tumor microenvironment toward immune stimulation by local delivery of exogenous TCR signaling and radiation can lead to novel effective immunotherapy.