Activation of human CD141+ and CD1c+ dendritic cells in vivo with combined TLR3 and TLR7/8 ligation

Mice reconstituted with human hematopoietic stem cells are valuable models to study aspects of the human immune system in vivo. We describe a humanized mouse model (hu mice) in which fully functional human CD141+ and CD1c+ myeloid and CD123+ plasmacytoid dendritic cells (DC) develop from human cord blood CD34+ cells in immunodeficient mice. CD141+ DC are the human equivalents of murine CD8+/CD103+ DC which are essential for the induction of tumor‐inhibitory cytotoxic T lymphocyte responses, making them attractive targets to exploit for the development of new cancer immunotherapies. We used CD34+‐engrafted NSG‐A2 mice to investigate activation of DC subsets by synthetic dsRNA or ssRNA analogs polyinosinic‐polycytidylic acid/poly I:C and Resiquimod/R848, agonists for TLR3 and TLR8, respectively, both of which are expressed by CD141+ DC. Injection of hu mice with these agonists resulted in upregulation of costimulatory molecules CD80, CD83 and CD86 by CD141+ and CD1c+ DC alike, and their combination further enhanced expression of these molecules by both subsets. When combined, poly I:C and R848 enhanced serum levels of key cytokines associated with cross‐presentation and the induction of cytotoxic T lymphocyte responses including IFN‐α, IFN‐β, IL‐12 and CXCL10. These data advocate a combination of poly I:C and R848 TLR agonists as means of activating human DC for immunotherapy. Immunodeficient mice were engrafted with human cord blood hematopoietic stem cells. Myeloid and plasmacytoid dendritic cells were identified within multiple tissues. DC activation was analyzed at time points after injection of synthetic TLR agonists. Activation markers were upregulated by myeloid DC when TLR agonists were combined. Serum cytokines were elevated in serum of mice injected with combined TLR agonists.