P41.14
Background: Improvement of HIV vaccine immunogenicity requires deeper understanding of antigen processing in dendritic cells (DC). To date, although antigen-targeting to DC has been explored as a novel strategy of HIV vaccine design, few studies have investigated the intracellular antigen processing and its influence on vaccine immunogenicity when different DC surface receptors are engaged. In this study, we conduct parallel experiments to determine the immunogenicity and possible underlying mechanism of DC-targeting HIV vaccines via the native ligands of PD-1 and CTLA-4, respectively.
Methods: A panel of DNA fusion vaccines was constructed including soluble PD-1 (sPD1)-p24, soluble CTLA-4 (sCTLA-4)-p24, deletion mutant sΔPD1-p24, sΔCTLA4-p24 and p24 alone. BALB/c mice were immunized with each of these DNA vaccines at 100μg dose via intramuscular in vivo electroporation following a prime/2-boost regimen with 3-week intervals. Post vaccination, immunogenicity profiles were analyzed using ELISA and ELIspot. Confocal microscopy was used to investigate p24 antigen trafficking to MHC-I or -II compartments in DC based on several endosomal markers.
Results: DC-targeting HIV vaccines were significantly more potent than corresponding deletion mutant controls. sPD1-p24 is superior to CTLA4-p24 with following distinct immune responses: (1) significantly enhanced IgG2a (Th1) antibody responses, (2) ∼3.5-fold greater p24-specific CD8+ T cell responses besides a 2-fold increase in CD4+ T cells by IFN-γ ELISpots. Mechanistically, while p24 delivered by sPD1-p24 and sCTLA4-p24 routed to Lamp-1 endosomes for MHC-II presentation to CD4+ T cells, sPD1-p24 also routed to Rab14 endosomes for MHC-I cross-presentation to CD8+ T cell.
Conclusions: PD-1 and CTLA-4 lead to distinct immunogenicity outcomes when used in our DC-targeting vaccines. Our findings provide evidence that the intracellular antigen processing in DC influences vaccine immunogenicity when different DC surface receptors are engaged.
