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

Abstract

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.