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-alpha, IFN-beta, 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.