Design of pH-sensitive polymer-modified liposomes for antigen delivery and their application in cancer immunotherapy

The accurate delivery of antigens into the cytosol of antigen-presenting cells, such as dendritic cells, is crucially important for the induction of cellular immunity in efficient cancer immunotherapy. To date, the cytoplasmic delivery of antigens has been achieved with various delivery systems. Among them, pH-sensitive liposomes are a promising option because of their pH-responsive membrane disruption or fusion abilities, which cause the encapsulated antigen to be transferred into the cytosol. Recently, liposomes modified with pH-sensitive polymers have been used as highly effective antigen delivery systems. The control of the pH-responsive fusion ability and the intracellular distribution of antigens, the induction of humoral or cellular immunity in vivo, the induction of protective immunity against pathogens, and the treatment of tumor-bearing mice have been achieved using these liposomes. The design and function of these pH-sensitive polymer-modified liposomes are outlined in this review.