Stem-04. fate-based conversion for in situ vaccination in glioblastoma

Abstract BACKGROUND Although immune checkpoint inhibitors have shown high benefit for other solid tumors, their efficacy is limited in GBM due in large part to the “cold” tumor microenvironment (TME) of the GBM tumor. New approaches are necessary to overcome these challenges. We propose a shift in the scientific and treatment paradigm of cancer immunotherapy, calling for tumor cells to take on a central, active role in initiating their own immunity right in the TME. METHODS Using AI, we identified cell fate determinants (CFDs) to convert GBM cells directly into induced dendritic cells (iDC) inside the TME. CFDs were delivered using a viral vector and conversion assessed by immunophenotyping, scRNA-seq, and functional assays for classical DC properties. RESULTS A four-CFD subnetwork anchored by PU.1 was sufficient to convert mouse GBM cells to iDCs (CD45+MHCII+CD80/86+MHCI+). iDCs are growth arrested, exhibit 3-fold higher phagocytic activity and upregulate the canonical antigen processing and presenting machineries by 10-40-fold, resulting in 100-fold greater efficiency at processing ovalbumin and cross-presenting SIINFEKL to naive OTI-CD8+ cytotoxic T lymphocytes (CTL). In addition, iDCs efficiently cross-present exogenous antigens to naïve CD8+ CTLs and elicit >30-fold higher activation and cytotoxicity in tumor-specific T cells compared to native GBM cells, confirming their DC-like properties. Lastly, intratumoral GBM-DC conversion in a syngeneic orthotopic GBM model resulted in significant reduction in tumor burden and increase in survival compared to controls (Log-rank, p = 0.01) with synergistic efficacy with ICIs and classical DC-based tumor vaccination. We have also successfully converted human GBM cells to iDCs with similar properties using a 2-CFD combination also anchored by PU.1. CONCLUSIONS GBM-derived iDCs acquired DC-like functions and were capable of eliciting robust intratumor immune activation, thereby overcoming many current limitations of immunotherapy in GBM. Our goal is to develop a low cost, off-the-shelf gene therapy-based fate conversion tumor immunotherapy.