An in vitro nanocarrier-based B cell antigen loading system; tumor growth suppression via transfusion of the antigen-loaded B cells in vivo.

B cell-based vaccines are expected to provide an alternative to DC-based vaccines. However, the efficacy of antigen uptake by B cells in vitro is relatively low, and efficient antigen-loading methods must be established before B cell-based vaccines are viable in clinical settings. We recently developed an in vitro system that efficiently loads antigens into isolated splenic B cells via liposomes decorated with hydroxyl PEG (HO-PEG-Lips). Therefore, the purpose of this study was to expand this system in order to achieve another approach to in vivo tumor growth suppression. By using HO-PEG-Lips as a carrier for model antigen OVA along with an adjuvant, α-galactosylceramide (GC), the amount of antigen loading to the B cells in vitro was increased compared with that of both free OVA and free GC. Transfusion of B cells treated with HO-PEG-Lips that encapsulated OVA and GC suppressed the growth of OVA-expressing murine thymoma (E.G7-OVA) tumors in vivo through strong induction of OVA-specific T cells. Under fluorescence microscopic observation, migration of the transfused B cells in the spleens of recipient mice were confirmed. Our results indicate that our novel antigen-loading system could become a promising approach to facilitate the development of cell-based therapeutic cancer vaccines utilizing B cells as alternative APCs.