ENHANCED CTL RESPONSES MEDIATED BY PLASMID DNA IMMUNOGENS ENCODING COSTIMULATORY MOLECULES AND CYTOKINES

In the course of examining epitope-specific CTL responses to intramusc ular plasmid DNA immunization with influenza nucleoprotein (NP)-expres sing vectors, a nonimmunogenic mutant NP (NPo) was identified. The cod ing region of NPo differed from the wild-type A/PR/8/34 NP sequence (d esignated NPv) by three amino acid alterations in the carboxyl-termina l portion of the molecule remote from the H-2K(d) epitope (147-155) be ing monitored. Correction of these mutations restored the immonogenici ty of the native sequence, indicating that sequence alterations remote from the CTL epitope in question can profoundly influence its immunog enicity. In an effort to identify general, nonstructural means of enha ncing the CTL response to weak plasmid DNA immunogens, vectors were co nstructed expressing NPo in tandem with the costimulatory molecules B7 -1 or B7-2. Go-linear expression of NPo with B7-2, but not B7-1, signi ficantly increased the NP epitope-specific CTL response. In addition, coinjection of these NPo plasmids with granulocyte-macrophage CSF- and /or IL-12-expressing vectors also restored near native NP-specific CTL responses. Thus, the coexpression of certain costimulatory molecules and/or cytokines, in concert with a non-self gene delivered as an intr amuscular plasmid DNA immunogen, can significantly enhance Ag-specific CTL responses.