The influence of novel poxvirus-based HIV 1 vaccine candidates on antigen presentation by dendritic cells

Cytotoxic T lymphocytes (CTL) directed against the HI-viral proteins Gag and Pol have been shown to control HIV replication efficiently. In a clinical phase-I trial the immunogenicity of the vaccine NYVAC-C was analyzed. NYVAC-C, consisting of the poxviral NYVAC vector coding for an artificial polyprotein Gag/Pol/Nef (GPN) and the envelope protein, induced modest Gag- and Pol-specific CTL responses in the participants. Thus, a new generation of immunogens based on GPN was developed. Immunogen expression and therefore immunogenicity should be enhanced by introducing several modifications. Again, NYVAC was chosen as antigen delivery system. To analyze the direct presentation of intracellular antigens, dendritic cells (DC) were infected with the vaccine candidates. The immunogen derived GL9 peptide was efficiently presented on DC despite incomplete maturation. Surprisingly, the weakly expressed antigen GPN induced most extensive direct presentation, whereas high expression of the new generation immunogens did not boost direct presentation.Vaccine candidate infected cells were analyzed to induce GL9 cross presentation on DC. Although poorly expressed, GPN induced the most extensive CTL restimulation by GL9-cross presentation on DC. Antigen presentation of the new generation immunogens was induced remotely and demanded high NYVAC multiplicities. Cross presentation was mainly driven by vaccine infected HeLa cells whereas Gag-derived virus-like particles did not induce GL9 presentation. Presentation of the alternative SP9 peptide was not detectable, indicating that not every immunogen-encoded peptide can be presented on APC. Thus, for induction of Gag specific CTL responses, GPN appears to be appropriate. The immunogenicity in humans could be enhanced by more effective expression without affecting the immunogenic properties of GPN.