RAFTsomes containing epitope-MHC-II complexes mediated CD4+ T cell activation and antigen-specific immune responses.

To develop a liposome formulation incorporating antigen-presenting cells (APCs) membrane microdomains with enriched epitope/MHC complexes to evaluate the activities of these liposomes (RAFTsomes) to activate T cells and prime immune responses. We isolated membrane microdomain structures that contained the epitope/MHC complexes from ovalbumin (OVA) primed dendritic cells (DCs), and reconstituted them on liposomes surface by detergent dialysis. The resulted RAFTsomes were purified by density gradient centrifugation. Their T cell activation functions were evaluated by IL-2 secreting and proliferation assays in vitro. In vivo immune responses and the protective effect against OVA expressing EG.7 tumor challenge were also examined. Membrane microdomains containing enriched epitope/MHC complexes can be reconstituted into liposomes with defined size and composition. The integrity and activities of these complexes after reconstitution were confirmed by in vitro T cell assays. OVA epitope loaded RAFTsomes injected in vivo resulted in high anti-OVA IgG production (predominantly IgG1). The immunized mice were protected from EG.7 tumor cell inoculation challenge. Based on these findings, we propose that RAFTsomes can be prepared with unique properties that may be used as an antigen delivery system for immunotherapeutic applications.