The Ubiquitin Ligase Marchf1 Controls cDC Development to Sustain CD8+ T Cell Antitumor Immunity and Response Checkpoint Blockade 2259196

Abstract Introduction Conventional dendritic cells (cDCs) are essential for sustaining CD8+ T cell-mediated tumor immunity, yet the developmental mechanisms controlling their homeostasis remain unclear. We identify the E3 ubiquitin ligase Marchf1 as a critical regulator of cDC development with direct implications for tumor immune surveillance. Methods Using mice with DC-specific Marchf1 deletion (Marchf1ΔDC) or controls (Marchf1fl/fl) in murine melanoma and colon carcinoma models, we integrated scRNA-seq, flow cytometry, and immunofluorescence analyses of the TME, draining lymph nodes and bone marrow. We further analyzed human MARCHF1 expression in PBMCs from healthy individuals or melanoma patients, and analyzed the Cancer Genome Atlas (TCGA) melanoma cohort for correlations between MARCHF1 expression and clinical outcomes. Results Marchf1 deficiency led to accelerated tumor growth despite increased MHCII and CD86 expression on the DCs. The TME was characterized by a reduced immune infiltration, with selective loss of intratumoral cDC1s and impaired CD8+ T cell proliferation and cytokine production. Mechanistically, Marchf1 ablation induced premature MHCII upregulation in the bone marrow pre-cDCs, activating an apoptotic checkpoint that impaired cDC differentiation, confirmed by a competitive bone marrow chimeras. Remaining cDC1s retained cross-presentation, indicating numerical rather than functional insufficiency. Systemic Flt3L administration restored pre-cDC and cDC1 homeostasis, rescuing CD8+ T cell—mediated tumor control. In human melanoma, high MARCHF1 expression correlated with improved survival and checkpoint blockade responses, while circulating cDC1s from patients displayed selective MARCHF1 downregulation. Consistently, Marchf1ΔDC mice failed to respond to anti—PD-1/CTLA-4 therapy. Conclusion These findings identify Marchf1 as a developmental checkpoint linking cDC ontogeny to antitumor immunity and highlight MARCHF1 as a biomarker and therapeutic target to enhance DC-mediated cancer immunotherapy. Funding Source n/a. Topic Categories Classical and Non-Classical Antigen Presenting Cells (APC)