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: CD103CD11b DC1 and CD11bCD64 DC2, which originate from circulating precursors of conventional DCs, and CD11bCD64 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.