TopBP1 controls conventional dendritic cell development and Flt3L-driven cDC1 differentiation via PU.1 and IRF8

DNA topoisomerase II-binding protein 1 (TopBP1) plays a vital role in V(D)J recombination during B and T cell development. However, its role in the development of conventional dendritic cells (cDCs) remains unexplored. Mice with DC-specific depletion of TopBP1 (TopBP1cKO) showed accelerated tumor progression due to impaired anti-tumor immunity, characterized by cDC deficiency and pre-DC accumulation. Notably, Flt3 ligand (Flt3L)-mediated tumor immunotherapy was ineffective in TopBP1cKO tumor-bearing mice. Our study demonstrates that TopBP1 is required not only for the steady-state differentiation of total cDCs, including both cDC1 and cDC2, but also for the terminal differentiation of XCR1⁻CD24⁺ emergency progenitors (EPs; CD11c⁺cKit⁺) into XCR1⁺CD24⁺ cDC1s in response to Flt3L. Furthermore, we revealed that TopBP1 directly interacts with PU.1 and IRF8, key transcription factors (TFs) required for cDC development, triggering the expression of their downstream target genes. These findings identify TopBP1 as a crucial factor for cDC development and Flt3L-driven EP differentiation into cDC1s, revealing that the function of key TFs for cDC development is mediated via interaction with TopBP1. Our work underscores the importance of TopBP1 in promoting cDC development and the therapeutic efficacy of Flt3L-mediated tumor immunotherapy.