To confirm the mechanism of exosomes as tumor vaccines inducing immunity response, dendritic cells (DCs) were induced from human peripheral blood mononuclear cells, while exosomes were isolated from DC loaded tumor antigen. The effect of exosomes on priming T cell proliferation was analysed under conditions with or without DCs, or DCs at different mature stages. The function of exosomes in immunity was detected through block test after blocking some molecules (CD11a, CD11b, CD11c, CD54, MFG-E8 and CD83). The effect of DCs on embedded exosomes was observed by confocal microscopy, the effect of blocking surface molecules on exosomes on DC-embedding exosomes was assayed by flow cytometry. The results indicated that both exosomes derived from imDC (imDex) and exosomes derived from mDC (mDex) could not prime T cells without DC or with imDC. The exosomes derived from mDC induced with different cytokines (LPS, TNF-alpha, CpG, CD40L) were no significant difference in concentrations but were different in effect. The immunity function of exosomes depended on CD11a, CD11b, CD11c, CD54, MFG-E8 and CD83 molecules, the effect of priming T cells is reduced when these molecules were blocked. Confocal microscopy and FACS assay showed that blocking CD11a and CD54 could inhibit exosome-targeted DC and DC-embedded exosomes. It is concluded that the exosomes target DCs through their surface molecules, therefore results in immune response of T cells.