Human plasmacytoid dendritic cells efficiently cross-present exogenous Ags to CD8+ T cells despite lower Ag uptake than myeloid dendritic cell subsets

Abstract

Abstract In human peripheral blood, 4 populations of dendritic cells (DCs) can be distinguished, plasmacytoid dendritic cells (pDCs) and CD16+, CD1c+, and BDCA-3+ myeloid DCs (mDCs), each with distinct functional characteristics. DCs have the unique capacity to cross-present exogenously encountered antigens (Ags) to CD8+ T cells. Here we studied the ability of all 4 blood DC subsets to take up, process, and present tumor Ags to T cells. Although pDCs take up less Ags than CD1c+ and BDCA3+ mDCs, pDCs induce potent Ag-specific CD4+ and CD8+ T-cell responses. We show that pDCs can preserve Ags for prolonged periods of time and on stimulation show strong induction of both MHC class I and II, which explains their efficient activation of both CD4+ and CD8+ T cells. Furthermore, pDCs cross-present soluble and cell-associated tumor Ags to cytotoxic T lymphocytes equally well as BDCA3+ mDCs. These findings, and the fact that pDCs outnumber BDCA3+ mDCs, both in peripheral blood and lymph nodes, together with their potent IFN-I production, known to activate both components of the innate and adaptive immune system, put human pDCs forward as potent activators of CD8+ T cells in antitumor responses. Our findings may therefore have important consequences for the development of antitumor immunotherapy.