GENE VACCINATION WITH NAKED PLASMID DNA - MECHANISM OF CTL PRIMING

The injection of naked plasmid DNA directly into the muscle cells of m ice has been shown to induce potent humoral and cellular immune respon ses. The generation of a cytotoxic T lymphocyte (CTL) response after p lasmid DNA injection may involve the presentation of the expressed ant igen in the context of the injected myocytes' endogenous major histoco mpatibility (MHC)-encoded class I molecules or may use the MHC molecul es of bone marrow-derived antigen presenting cells (APC) which are cap able of providing co-stimulation as well. To resolve which cell type p rovides the specific restricting element for this method of vaccinatio n we generated parent-->F1 bone marrow chimeras in which H-2(oxd) reci pient mice received bone marrow that expressed only H-2(b) or H-2(d) M HC molecules. These mice were injected intramuscularly with naked plas mid DNA that encoded the nucleoprotein from the A/PR/8/34 influenza st rain, which as a single antigen has epitopes for both H-2D(b) and H-2K (d). The resulting CTL responses were restricted to the MHC haplotype of the bone marrow alone and not to the second haplotype expressed by the recipient's myocytes. The role of somatic tissues that express pro tein from injected plasmids may be to serve as a reservoir for that an tigen which is then transferred to the APC. Consequently, our data sho w that the mechanism of priming in this novel method for vaccination u ses the MHC from bone marrow-derived APC, which are efficient at provi ding all of the necessary signals for priming the T cell.