A vaccine candidate that elicits humoral and cellular responses to multiple sporozoite and liver-stage antigens may be able to confer protection against Plasmodium falciparum (Pf) malaria, however, a technology for formulating and delivering such a vaccine has remained elusive. Here, we report the preclinical assessment of an optimized DNA vaccine approach that targets four Pf antigens: circumsporozoite protein (CSP), liver stage antigen 1 (LSA1), thrombospondin-related-anonymous-protein (TRAP), and cell-traversal protein for ookinetes and sporozoites (CelTOS). Synthetic DNA sequences were designed for each antigen with modifications to improve expression, and were delivered using in vivo electroporation (EP). ... More
A vaccine candidate that elicits humoral and cellular responses to multiple sporozoite and liver-stage antigens may be able to confer protection against Plasmodium falciparum (Pf) malaria, however, a technology for formulating and delivering such a vaccine has remained elusive. Here, we report the preclinical assessment of an optimized DNA vaccine approach that targets four Pf antigens: circumsporozoite protein (CSP), liver stage antigen 1 (LSA1), thrombospondin-related-anonymous-protein (TRAP), and cell-traversal protein for ookinetes and sporozoites (CelTOS). Synthetic DNA sequences were designed for each antigen with modifications to improve expression, and were delivered using in vivo electroporation (EP). Immunogenicity was evaluated in mice and non-human primates (NHPs) and assessed by ELISA, IFNγ ELISpot, and flow cytometry. In mice, DNA+EP delivery induced antigen-specific IFNγ production as measured by ELISpot and IgG seroconversion against all antigens. Sustained production of IFNγ, IL-2 and TNFα was elicited in both the CD4+ and CD8+ T cell compartments. Furthermore, hepatic CD8+ lymphocytes produced LSA1-specific IFNγ. The immune responses conferred in mice by this approach translated to the NHP model showing cellular responses by ELISPOT assay and intracellular cytokine staining. Notably, antigen-specific CD8+ Granzyme B+ T cells were observed in NHPs. Collectively, the data demonstrate that delivery of gene sequences by DNA/EP encoding malaria parasite antigens is immunogenic in animal models and can harness both the humoral and cellular arms of the immune system.
