Immune protection effect of exosomes against attack of L1210 tumor cells

We investigated the anti-tumor immunity of L1210 cell-secreted exosomes. Exosomes were purified by ultrafiltration centrifugation and sucrose gradient ultracentrifugation. Expression of H-2D and interstitial cell adhesion molecule (ICAM)-1 was investigated by solid-phase immuno-electron microscopy and expression of Hsp70 was investigated by western blotting. DBA/2 mice were immunized with a given dose of exosomes (2.5 or 5 mu g). Transmission electron microscopy revealed that L1210-derived exosomes were membrane vesicles. They were labeled by colloidal gold H-2D and ICAM-1. Western blot analysis demonstrated the presence of Hsp70 antigens in L1210 exosomes. Exosome immunization partly inhibited the growth of implanted tumor in mice. There was a significant difference between exosome groups and the control group (P<0.05). In conclusion, exosomes can be considered as a candidate therapeutic vaccine for leukemia.