Abstract A021: A cancer immunotherapy modality based on dendritic cell reprogramming <i>in vivo</i>

Abstract Cancer immunotherapy leads to long-term survival, yet generalized success has been hampered by insufficient antigen presentation and exclusion of immunogenic cells from the tumor microenvironment (TME). A growing body of evidence indicates that intratumoral conventional type 1 dendritic cells (cDC1) are required to mount effective Tcell-mediated antitumor immunity and associate with better response to immune checkpoint blockade (ICB) therapy. However, approaches to generate cDC1s at clinical scale for immunotherapy have met limited success. We have previously demonstrated that overexpression of the transcription factors PU.1, IRF8 and BATF3 (PIB) drives cell fate reprogramming of cancer cells into functional antigen-presenting cDC1-like cells. Here, we investigated whether in vivo reprogramming of cancer cells into immunogenic antigen-presenting cDC1s can elicit systemic and durable antitumor immunity and explored the potential of in vivo delivery of PIB as a novel cancer immunotherapy modality. In vivo cDC1 reprogramming and antitumor efficacy were assessed upon subcutaneous implantation of in vitro transduced cancer cells in xenografts and ICB-resistant cDC1-dependent mouse syngeneic models. The impact of in vivo reprogramming in the TME was assessed using flow cytometry, single-cell transcriptomics, immunohistochemistry and microscopy. Tumor spheroids generated with human cancer cells in combination with cancer-associated fibroblasts or anti-inflammatory cytokines were used to investigate the impact of immunosuppressive microenvironment in cDC1 reprogramming. To select the optimal platform for in vivo delivery of PIB, we benchmarked PIB-encoding replication-deficient adenoviral (AdV), adeno-associated viral (AAV) and lentiviral (LV) vectors using mouse and human cancer cell lines and patient-derived cancer spheroids. Intratumoral delivery of PIB was performed in B16 syngeneic model to confirm in vivo efficacy induced by the gene therapy product.In vivo reprogramming to cDC1s drove complete responses (CR) in YUMM1.7 (100% CR), BRAFV600ECOX2KO (50% CR) and B2905 (80% CR) models and synergized with ICBs leading to 40% CR in B16 model, expansion of tumor-reactive T-cells and abscopal effect. Reprogrammed cancer cells recruited lymphocytes, promoted formation of tertiary lymphoid-like structures and expansion of polyclonal cytotoxic T cells. PIB-transduced human cancer cells acquired cDC1 and antigen-presentation markers in vivo with similar efficiency and kinetics as in vitro independently of immunosuppressive cells and cytokines. AdV was selected as the most efficient vector for in vivo delivery of PIB. Intra-tumoral injection of PIB-encoding AdV allowed in situ phenotypic reprogramming, enhanced infiltration of cytotoxic T cells and drove 50% CR, abscopal effect, long-term immune memory and protection against local and metastatic re-challenge. These findings provide preclinical proof-of-concept for an off-the-shelf, personalized cancer immunotherapy based on in situ cDC1 reprogramming, paving the way for first-in-human trials. Citation Format: Ervin Ascic, Fritiof Åkerström, Malavika Sreekumar Nair, André Rosa, Ilia Kurochkin, Olga Zimmermannova, Xavier Catena, Nadezhda Rotankova, Charlotte Veser, Michal Rudnik, Tommaso Ballocci, Tiffany Schärer, Xiaoli Huang, Maria de Rosa Torres, Emilie Renaud, Marta Velasco Santiago, Özcan Met, David Askmyr, Malin Lindstedt, Lennart Greiff, Laure-Anne Ligeon, Irina Agarkova, Inge Marie Svane, Cristiana Pires, Fábio Fiúza Rosa, Carlos-Filipe Pereira. A cancer immunotherapy modality based on dendritic cell reprogramming in vivo [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr A021.