TMIC-38. Dendritic cell dysfunction driven by hypoxia pathway activated DC tolerance as an immune evasion mechanism in adoptive cellular therapy

Abstract BACKGROUND Our adoptive cellular therapy (ACT) enhances dendritic cell (DC) and T cell infiltration into tumors, improving survival in murine brain tumor models. However, tumors employ mechanisms to restrict immune surveillance and efficacy of immunotherapy. We hypothesize that tumor-induced DC dysfunction facilitates immune evasion during ACT. This study investigates the mechanisms of DC dysfunction in ACT-escaped gliomas. METHODS T cell phenotypes were characterized using flowcytometry, and DC function was assessed through T cell activation assays. Gene set enrichment analysis (GSEA) was performed on transcriptomic data to identify enriched pathways. The impact of hypoxia and factors secreted from tumor-T cell interactions on DC tolerance was evaluated using RT-qPCR. In vivo correlations between hypoxia and DC tolerance were analyzed using GeoMx spatial transcriptomics. RESULTS ACT-escaped tumors retained adoptively transferred cytotoxic but non-exhausted T cells that failed to recognize antigen-shifted tumors. DCs from both untreated primary and ACT-escaped tumors showed impaired T cell activation and reduced expression of antigen-presentation genes. DCs from ACT-escaped tumors exhibited increased expression of tolerance-associated genes, with significant enrichment in hypoxia pathway genes. Hypoxia induced the expression of DC tolerance genes in a HIF1α-dependent manner, impairing T cell activation. Spatial transcriptomics confirmed a strong correlation between HIF1α and ARG1 in tumor-bearing brains. Increased immune infiltration in ACT-treated gliomas exacerbated hypoxia, as shown by HIF1α and CD45 co-expression, further driving DC dysfunction. Inflammatory factors secreted during tumor-T cell interactions activated hypoxia pathways and induced DC tolerance genes. CONCLUSION Hypoxia-driven DC tolerance is a key driver of immune escape under ACT.