Liposome-Mediated Cytoplasmic Delivery of Proteins: An Effective Means of Accessing the MHC Class I-Restricted Antigen Presentation Pathway

Abstract

Different types of liposomes have been employed to deliver soluble antigen for processing and presentation in the major histocompatibility complex class I-restricted pathway. Anionic pH-sensitive liposomes as well as cationic liposomes efficiently sensitize antigen-presenting cells for recognition by the class I-restricted cytotoxic T lymphocytes (CTL). Cytoplasmic delivery of liposome-entrapped antigen from an endocytic compartment allows the exogenous antigen to gain access to the class I presentation pathway. Cytoplasmic delivery, however, is probably not the only mechanism by which liposomes induce the class I-restricted CTL priming in vivo. Macrophages play a central role in the processing of the liposome-encapsulated antigens. The processed antigen fragments are probably released by the macrophages and taken up by the nearby dendritic cells for antigen presentation. Collaboration between the two types of immune cells with the help of the appropriate costimulatory factors is the central theme for this hypothesis. In this case, the host immune system utilizes the similar mechanism for other membranous, particulate antigens to process and present the liposomal antigens.