CD4+ T Cells Drive Anti-Tumor Immunity Elicited by In Vivo Dendritic Cell Reprogramming

Immunotherapies have revolutionized the field of cancer treatment and rely on the activation of anti-tumor T cell responses. Downregulation of antigen presentation in tumor cells, the immunosuppressive microenvironment and dysfunction of dendritic cells limit the efficacy of current treatments. Conventional type-1 dendritic cells (cDC1s) play a crucial role in orchestrating anti-tumor T cell responses and their presence correlates with better survival in cancer patients. However, there is no efficient method to generate cDC1s for immunotherapy. In vivo cell fate reprogramming enables the conversion of cells within tissues at the disease location into another cell identity with therapeutic potential. Previously, our lab has shown that direct cell reprogramming can be used to convert fibroblasts or tumor cells into cDC1-like cells by overexpression of the transcription factors PU.1, IRF8 and BATF3, called PIB, in vitro. In this master thesis, we hypothesize that PIB mediate in vivo reprogramming of cancer cells into tumor antigen-presenting cDC1-like cells (tumor-APCs). PIB overexpression generates tumor-APCs that persist in the tumor for 9 days, acquire a CCR7- resident profile and elicit robust and durable anti-tumor immunity. CD4+ T cells are recruited and interact with reprogrammed cells in the tumor and are required for complete tumor regression. In vivo reprogrammed cells employed complementary immune mechanisms to induce tumor growth control, demonstrated by the use of single knock-outs for MHC-II, MHC-I, CD40 and XCR1. Lastly, we identified a model that escaped immunological memory and showed resistance to anti-tumor immunity elicited by in vivo reprogramming which was not mediated by downregulation of cDC1-related immune mechanisms. Ultimately, we show that in vivo reprogrammed cells remain in the tumor and drive a CD4+ T cell response by employing multifaceted immune mechanisms. This study paves the way for the generation of a gene therapy based on in vivo cDC1 reprogramming and identification of resistance mechanisms.