Mature dendritic cells pulsed with exosomes stimulate efficient cytotoxic T-lymphocyte responses and antitumour immunity.

Exosomes (EXO) derived from dendritic cells (DC), which express major histocompatibility complex (MHC) and costimulatory molecules, have been used for antitumour vaccines. However, they are still less effective by showing only prophylatic immunity in animal models or very limited immune responses in clinical trials. In this study, we showed that ovalbumin (OVA) protein-pulsed DC (DC(OVA))-derived EXO (EXO(OVA)) displayed MHC class I-OVA I peptide (pMHC I) complexes, CD11c, CD40, CD80, CCR7, DEC205, Toll-like receptor 4 (TLR4), TLR9, MyD88 and DC-SIGN molecules, but at a lower level than DC(OVA). EXO(OVA) can be taken up by DC through LFA-1/CD54 and C-type lectin/mannose (glucosamine)-rich C-type lectin receptor (CLR) interactions. Mature DC pulsed with EXO(OVA), which were referred to as mDC(EXO), expressed a higher level of pMHC I, MHC II, and costimulatory CD40, CD54 and CD80 than DC(OVA). The mDC(EXO) could more strongly stimulate OVA-specific CD8(+) T-cell proliferation in vitro and in vivo, and more efficiently induce OVA-specific cytotoxic T-lymphocyte responses, antitumour immunity and CD8(+) T-cell memory in vivo than EXO(OVA) and DC(OVA). In addition, mDC(EXO) could also more efficiently eradicate established tumours. Therefore, mature DC pulsed with EXO may represent a new, highly effective DC-based vaccine for the induction of antitumour immunity.