Cross-presentation defines the unique capacity of an antigen presenting cell to present exogenous antigen via MHC class I molecules to CD8+ T cells. Dendritic cells (DCs) are specialized cross-presenting cells and as such have a critical role in anti-tumor immunity. DCs are routinely found within the tumor microenvironment, but their capacity for endogenous or therapeutically enhanced cross-presentation is not well characterized. In this study, we examined the tumor and lymph node DC cross-presentation of a nominal marker tumor antigen, hemagglutinin (HA), expressed by the murine mesothelioma tumor AB1-HA. We found that tumors were infiltrated by predominantly CD11b+ DCs with a semi-mature phenotype that could not cross-present tumor antigen, and therefore, were unable to induce tumor-specific T-cell activation or proliferation. Although tumor-infiltrating DCs were able to take up, process and cross-present exogenous cell-bound and soluble antigens, this was significantly impaired relative to lymph node DCs. Importantly, however, systemic chemotherapy using gemcitabine reversed the defect in antigen cross-presentation of tumor DCs. These data demonstrate that DC cross-presentation within the tumor microenvironment is defective, but can be reversed by chemotherapy. These results have important implications for anti-cancer therapy, particularly regarding the use of immunotherapy in conjunction with cytotoxic chemotherapy.This article is protected by copyright. All rights reserved