Antigen delivery systems are important for inducing and modifying immune responses. A key to development of vaccines is the ability to deliver antigens to antigen-presenting cells (APCs) more efficiently and to induce subsequent activation of T cell-mediated immunity. Thus, strategies that target APCs and modulate APC functions
in vivo have significant implications for vaccine design. We have demonstrated that oligomannose-coated liposomes (OMLs), which consist of DPPC, cholesterol, Man3-DPPE at a molar ratio of 10:10:1, can induce strong cellular immunity. In this review, we discuss OMLs as novel antigen-delivery vehicles that also have a strong adjuvant effect on induction of Th1 immune responses and CTLs specific for the encased antigen. This property of OMLs is due to their ability to assist specific cellular uptake in vivo and to promote subsequent APC maturation, presentation of antigens on APCs, preferential secretion of IL-12 from APCs, and migration of APCs into lymphoid tissues from peripheral tissues. Administration of an OML-based vaccine can eliminate an established tumor, inhibit elevation of the serum level of IgE against an allergen, and prevent progression of some protozoan infections in mouse models. In addition, OMLs with an encased antigen are able to induce antigen-specific CTLs in PBMCs obtained from patients. These feasibility studies of OML-based vaccines have revealed their potential for clinical use in vaccination for diseases in which CTLs and/or Th1 cells act as effector cells.
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