PURPOSE: Neoadjuvant anti-PD1 (aPD1) therapies are being explored in surgically resectable head and neck squamous cell carcinoma (HNSCC). Encouraging responses have been observed but further insights into the mechanisms underlying resistance and approaches to improve responses are needed. EXPERIMENTAL DESIGN: We integrated data from syngeneic mouse oral carcinoma (MOC) models and neoadjuvant pembrolizumab HNSCC patient tumor RNA-Seq data to explore the mechanism of aPD1 resistance. Tumors and tumor draining lymph nodes (DLN) from MOC models were analyzed for antigen specific priming. CCL5 expression was enforced in an aPD1 resistant model. RESULTS: An aPD1 resistant mouse model showed poor priming in the tumor DLN due to type 1 conventional dendritic cell (cDC1) dysfunction, which correlated with exhausted and poorly responsive antigen specific T cells. Tumor microenvironment analysis also showed decreased cDC1 in aPD1 resistant tumors compared to sensitive tumors. Following neoadjuvant aPD1 therapy, pathologic responses in patients also positively correlated with baseline transcriptomic cDC1 signatures. In an aPD1 resistant model, intra-tumoral cDC1 vaccine was sufficient to restore aPD1 response by enhancing T cell infiltration and increasing antigen-specific responses with improved tumor control. Mechanistically, CCL5 expression significantly correlated with neoadjuvant aPD1 response and enforced expression of CCL5 in an aPD1 resistant model enhanced cDC1 tumor infiltration, restored antigen specific responses, and recovered sensitivity to aPD1 treatment. CONCLUSIONS: These data highlight the contribution of tumor infiltrating cDC1s in HNSCC aPD1 response, and approaches to enhance cDC1 infiltration and function that may circumvent aPD1 resistance in HNSCC patients.