CD40L expressed from the canarypox vector, ALVAC, can boost immunogenicity of HIV-1 canarypox vaccine in mice and enhance the in vitro expansion of viral specific CD8⁺ T cell memory responses from HIV-1-infected and HIV-1-uninfected individuals

Human immunodeficiency virus type 1 (HIV-1) canarypox vaccines are safe but poorly immunogenic. CD40 ligand (CD40L), a member of the tumor necrosis factor superfamily (TNFSF), is a pivotal costimulatory molecule for immune responses. To explore whether CD40L can be used as an adjuvant for HIV-1 canarypox vaccine, we constructed recombinant canarypox viruses expressing CD40L. Co-immunization of mice with CD40L expressing canarypox and the canarypox vaccine expressing HIV-1 proteins, vCP1452, augmented HIV-1 specific cytotoxic T lymphocyte (CTL) responses in terms of frequency, polyfunctionality and interleukin (IL)-7 receptor α chain (IL-7Rα, CD127) expression. In addition, CD40L expressed from canarypox virus could significantly augment CD4⁺ T cell responses against HIV-1 in mice. CD40L expressed from canarypox virus matured human monocyte-derived dendritic cells (MDDCs) in a tumor necrosis factor-α (TNF-α) independent manner, which underwent less apoptosis, and could expand ex vivo Epstein-Barr virus (EBV)-specific CTL responses from healthy human individuals and ex vivo HIV-1-specific CTL responses from HIV-1-infected individuals in the presence or absence of CD4⁺ T cells. Taken together, our results suggest that CD40L incorporation into poxvirus vectors could be used as a strategy to enhance their immunogenicity.