Researchers at the Shin-Yamanote Hospital, Japan transfected B16 melanoma cells with a plasmid encoding the M. tuberculosis antigen, early secretory antigenic target-6 (ESAT-6). The secreted exosomes bearing both tumor-associated antigens and the pathogenic antigen (or their epitopes) were collected. When the exosomes were injected into foot pads of mice, they significantly (p < 0.05) evoked cellular immunity against both ESAT-6, and B16 tumor cells. Intra-tumoral injection of the exosomes significantly suppressed (p < 0.001) tumor growth in syngeneic B16 tumor-bearing mice, while the exosomes derived from the non-transfected B16 cells showed no effect on tumor growth, although both exosomes should have similar tumor antigens.
Possible mechanism of the antitumor effect induced by exosomes bearing both tumor antigens and pathogenic antigens
Exosomes bearing both tumor antigens and the M. tuberculosis antigen (or their epitopes) have a high potential as a candidate for cancer vaccine to overcome the immune escape by tumor cells.