Tumor Dendritic Cells (DCs) Derived from Precursors of Conventional DCs Are Dispensable for Intratumor CTL Responses

The success of adoptive CTL therapy for cancer depends on interactions between tumor-infiltrating CTLs and cancer cells as well as other cells and molecules in the tumor microenvironment. Tumor dendritic cells (DCs) comprise several subsets: CD103⁺CD11b^- DC1 and CD11b⁺CD64^- DC2, which originate from circulating precursors of conventional DCs, and CD11b⁺CD64⁺ DC3, which arise from monocytes. It remains controversial which of these subset(s) promotes intratumor CTL proliferation, expansion, and function. To address this issue, we used the Zbtb46-DTR-transgenic mouse model to selectively deplete DC1 and DC2 from tumors and lymphoid tissues. Wild-type and Zbtb46-DTR bone marrow chimeras were inoculated with B16 melanoma cells that express OVA and were treated with OT-1 CTLs. We found that depletion of DCs derived from precursors of conventional DCs in Zbtb46-DTR bone marrow chimeras abolished CTL proliferation and expansion in tumor-draining lymph nodes. By contrast, intratumor CTL accumulation, proliferation, and IFN-γ expression were unaffected by their absence. We found that adoptive cell therapy increases the frequency of monocyte-derived tumor DC3, which possess the capacity to cross-present tumor Ags and induce CTL proliferation. Our findings support the specialized roles of different DC subsets in the regulation of antitumor CTL responses.