Bcl6-Independent In Vivo Development of Functional Type 1 Classical Dendritic Cells Supporting Tumor Rejection

The transcriptional repressor Bcl6 has been reported as required for development of a subset of classical dendritic cell (cDCs) called cDC1, which is responsible for cross-presentation. However, mechanisms and in vivo functional analysis have been lacking. We generated a system for conditional deletion of Bcl6 in mouse cDCs. We confirmed the reported in vitro requirement for Bcl6 in cDC1 development and the general role for Bcl6 in cDC development in competitive settings. However, deletion of Bcl6 did not abrogate the in vivo development of cDC1. Instead, Bcl6 deficiency caused only a selective reduction in CD8α expression by cDC1 without affecting XCR1 or CD24 expression. Normal cDC1 development was confirmed in Bcl6^cKO mice by development of XCR1⁺ Zbtb46-GFP⁺ cDC1 by rejection of syngeneic tumors and by priming of tumor-specific CD8 T cells. In summary, Bcl6 regulates a subset of cDC1-specific markers and is required in vitro but not in vivo for cDC1 development.