Unleashing Type-2 Dendritic Cells to Drive Protective Antitumor CD4+ T Cell Immunity

Differentiation of proinflammatory CD4+ conventional T cells (Tconv) is critical for productive antitumor responses yet their elicitation remains poorly understood. We comprehensively characterized myeloid cells in tumor draining lymph nodes (tdLN) of mice and identified two subsets of conventional type-2 dendritic cells (cDC2) that traffic from tumor to tdLN and present tumor-derived antigens to CD4+ Tconv, but then fail to support antitumor CD4+ Tconv differentiation. Regulatory T cell (Treg) depletion enhanced their capacity to elicit strong CD4+ Tconv responses and ensuing antitumor protection. Analogous cDC2 populations were identified in patients, and as in mice, their abundance relative to Treg predicts protective ICOS+ PD-1lo CD4+ Tconv phenotypes and survival. Further, in melanoma patients with low Treg abundance, intratumoral cDC2 density alone correlates with abundant CD4+ Tconv and with responsiveness to anti-PD-1 therapy. Together, this highlights a pathway that restrains cDC2 and whose reversal enhances CD4+ Tconv abundance and controls tumor growth. [Display omitted] •cDC2 initiate activation but not differentiation of antitumor CD4+ Tconv•Treg depletion relieves cDC2 suppression driving antitumor CD4+ Tconv differentiation•Human equivalent of mouse cDC2 are present in the tumor and draining lymph node•The balance of human cDC2/Treg in the TME dictates T cell quality and prognosis A subtype of conventional dendritic cells, cDC2, are able to prime CD4+ T cells for antitumor functions and the presence of cDC2 in human cancer samples may serve as a predictive biomarker for survival and response to immune checkpoint blockade.