Liposomes as carriers of antigens and adjuvants.

Liposomes have been widely used as carriers of protein or peptide antigens. Antigenic materials can be attached to the outer surface, encapsulated within the internal aqueous spaces, or reconstituted within the lipid bilayers of the liposomes. The natural tendency of liposomes to interact with macrophages has served as the primary rationale for utilizing liposomes as carriers of antigens. Liposomes also serve as carriers of a variety of adjuvants and mediators, including lipid A, muramyl dipeptide and its derivatives, interleukin-1, and interleukin-2. Research utilizing in vitro cell culture models has demonstrated that liposomes containing both appropriate antigens and major histocompatibility gene complex molecules can induce antigen-specific genetically restricted cytotoxic T lymphocytes. Liposomes induce immune reactions through classical interactions with antigen presenting cells. However, modelling experiments have also demonstrated that liposomes can even substitute for antigen presenting cells, and cell-free genetically restricted and nonrestricted presentation of antigens by liposomes to helper T lymphocytes has been demonstrated. Liposomes are successful for inducing potent immunity in vivo and they are now being employed in numerous immunization procedures and as vehicles for candidate vaccines.