The development of DC-targeted vaccines aims to increase immunogenicity of proteins through improved delivery of the antigens to specific antigen-presenting cells playing a key role in inducing and regulating immune memory. CD40 signaling is essential for T cell-dependent humoral responses and targeting vaccine antigen to CD40 expressing APC seems therefore an attractive option to promote anti-HIV antibody development.
To determine the impact of DC targeting on immune responses, we analyzed cellular changes at immunization site. Twelve cynomolgus macaques were immunized with homologous prime-boost strategy by HIVgp140 protein fused with anti-CD40 targeting module or with IgG4 irrelevant control. Cellular trafficking was analyzed in injection site and draining lymph node by in vivo imaging after boost. Impact on immune responses was also evaluated over time.
Combination of in vivo imaging techniques (near infrared imaging, probe-based confocal laser endomicroscopy and two-photon microscopy) allowed the identification of the lymph nodes of interest that had drained the HIVgp140 protein. A significantly higher number of vaccine-targeted APC migrated in draining LN of NHPs immunized by anti-CD40.Env-gp140 (mean of 184 cells/mm²) compared to control animals (mean of 69 cells/mm²). Moreover, the magnitude of HIV-Env specific IFN-γ T cell response was correlated to the number of vaccine-targeted cells observed in vivo within the LN. HIV-Env specific T cell responses in anti-CD40 vaccinated animals was superior to the control group at the peak of response, 2 weeks post boost (1028 and 450 SFC/106 PBMC, respectively; mean of 6 animals). Specific antibody titers against Clade C Env proteins were also greater in anti-CD40 group (1700 and 202 EC50, respectively) than in controls (840.8 and 77.5 EC50, respectively) at 5 weeks post boost. Magnitude of the cellular response after a second boost was correlated to the durability of the response measured 30 weeks after immunization.
Altogether these results exhibited that CD40 targeting influences the early immune events within the draining LN then leading to stronger T and B cells responses. We also demonstrate that CD40 targeting in presence of adjuvant significantly improves vaccine immunogenicity without requiring priming with different type of vector or targeting strategy. The safety and efficacy of the CD40-targeted vaccine justify further development for future human clinical trials.