In Vivo Targeting of Antigens to Human Dendritic Cells Through DC-SIGN Elicits Stimulatory Immune Responses and Inhibits Tumor Growth in Grafted Mouse Models

Multiple cancer vaccine trials have been carried out using ex vivo generated autologous dendritic cells (DCs) loaded with tumor antigen before readministration into patients. Though promising, overall immunologic potency and clinical efficacy might be improved with more efficient DC-based therapies that avoid ex vivo manipulations, but are instead based on in vivo targeting of DCs. For initial in vivo proof of concept studies, we evaluated targeting of proteins or peptides to DCs through DC-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN). Because the biology of DC-SIGN is different between mice and humans, we assess human DC-SIGN targeting in the setting of elements of a human immune system in a mouse model. Administration of anti-DC-SIGN antibodies carrying either tetanus toxoid peptides or keyhole limpet hemocyanin (KLH) to Rag2gammaC mice reconstituted with human immune cells raised stimulatory human T-cell responses to the respective antigen without additional adjuvant requirements. Furthermore, administration of anti-DC-SIGN antibody-KLH conjugate enhanced the adjuvant properties of KLH resulting in inhibition of RAJI (Human Burkitt's Lymphoma Cell Line) cell tumor growth in Nonobese Diabetic/Severe Combined Immunodeficient mice transplanted with human immune cells. Thus, mouse models reconstituted with human immune cells seem to be suitable for evaluating DC-targeted vaccines, and furthermore, targeting to DCs in situ via DC-SIGN may provide a promising vaccine platform for inducing strong immune responses against cancer and infectious disease agents.