Liposome Encapsulation of Oncolytic Virus M1 To Reduce Immunogenicity and Immune Clearance in Vivo.

Oncolytic viral therapy is an attractive novel strategy for cancer therapy. As a natural alphavirus, oncolytic virus M1 is able to infect and kill various zinc finger antiviral protein (ZAP)-deficient tumor cells selectively, while leaving normal cells undamaged. However, M1 can trigger the production of neutralizing antibodies that dramatically weaken its antitumor effect. In order to attenuate immunogenicity of the therapeutic M1 virus, we encapsulated it into liposomes (referred to as M-LPO) using the thin-film hydration method. The effect of anti-M1 neutralizing antibody on M-LPO was examined in LoVo and Hep 3B cell lines. In the absence of neutralizing antibodies, treating cells with naked M1, blank liposomes (LPO), M-LPO, or a simple mixture of M1 and liposomes (LPO+M1) inhibited cell growth. In the presence of neutralizing antibodies, only M-LPO inhibited cell growth. After intravenous administration, M-LPO reduced the production of the M1-neutralizing antibody and the corresponding immune response. Analysis of the M-LPO uptake by cells was examined by confocal microscopy using M1 labeled with FITC and liposomal shells labeled with RhB. The results suggest that M1 may be released from liposomes before or after M-LPO internalization. Taken together, our results suggest that encapsulating oncolytic virus M1 in liposomes may reduce intrinsic viral immunogenicity for improved anticancer therapy.