Recently it has been shown that modulation of CD40 molecules on antigen (Ag) carrying dendritic cells (DC) can bypass T cell help, resulting in priming cytotoxic T lymphocytes (CTL) specific for the Ag. In the present study we attempted to prime peptide Ag-specific CTL by a new method in which a peptide Ag in liposome (liposomal peptide), consisting of phosphatidylserine and phosphatidylcholine (3:7), was administrated subcutaneously with anti-CD40 and/or CTLA-4 monoclonal antibodies (mAb) to mice. We found that the subcutaneous administration of the liposomal peptide with both anti-CD40 and anti-CTLA-4 mAb enhanced CTL responses comparing with those induced by the liposomal peptide alone or the liposomal peptide plus each mAb. It was shown that liposomes were critical for induction of the CTL activity. Flow cytometry analysis of a peptide-bearing DC in lymph nodes (LN) and measurement of serum IL-12 indicated that anti-CD40 mAb promoted migration of DC to the LN, where DC might differentiate and acquire ability of priming CTL. These findings provide a possibility that our procedure is applicable to cancer patients.
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