Human Conventional and Plasmacytoid Dendritic Cells Can Originate from Both Lymphoid and Myeloid Progenitors in a New Humanized Mouse System.

Dendritic cells play a key role in host defense by presenting exogenous antigens to T cells. Two dendritic cell subsets, conventional dendritic cells (cDCs) and plasmacytoid dendritic cells (pDCs), express distinct repertoire of Toll-like-receptors and recognize different antigens. We previously reported that murine cDCs and pDCs differentiate via either the myeloid or the lymphoid pathway (Shigematsu et al. Immunity ). It is, however, still unclear whether human cDCs and pDCs develop from myeloid, lymphoid or both lineages. In order to analyze the in vivo differentiation of human dendritic cells, we employed the newly-developed xenotrasplant assay system which utilizes newborn NOD-scid/IL2rgnull mice (Ishikawa et al., Blood, in press). Transplantation of 104 Lin-CD34+CD38- hematopoietic stem cells into sublethally irradiated newborn NOD-scid/IL2rgnull mice resulted in generation of all hematopoietic and lymphoid components for a long-term via physiological intermediates such as common myeloid progenitors (CMP) and common lymphoid progenitors (CLP). We found that in this system, dendritic cell subcomponents such as hCD11c+hIL3Ralow cDCs and hCD11c-hIL3Rahigh pDCs, efficiently developed in recipients’ bone marrow, spleen and peripheral blood. To elucidate the origin of human mDCs and pDCs, we purified CMP or CLP from the cord blood, and transplanted these cells into sublethally irradiated newborn NOD-scid/IL2rgnull mice via facial vein. At 4-6 weeks post-transplantation, CMP gave rise only to myeloid cells such as erythroid cells, platelets and granulocytes, while CLP exclusively generated T, B and NK cells. Interestingly, in either mouse group injected with CMP or CLP, cDCs and pDCs were easily detected in the spleen and in the bone marrow. Phenotypic and RT-PCR analyses of purified CMP- or CLP-derived DCs revealed that DCs possessed similar phenotypic characteristics, and transcription profiles in TLR families, BDCA antigens and costimulation molecules, irrespective of their lineage origin. Thus, human cDCs and pDCs develop through both myeloid and lymphoid pathways as in case of mouse hematopoiesis. Further characterization of DCs of different lineage origin is currently performed by microarray analyses in order to find genes specifically expressed in each DC subset.