Vaccine Mediated Immunity To Malaria
Malaria infects millions of people every year, and despite recent advances in controlling disease spread, it remains a global health concern. Decades of research into both naturally acquired and vaccine mediated immunity have given a broad range of correlates of protection. RTS,S, the only licensed anti-malarial vaccine, has implicated antibodies against the circumsporozoite protein (CSP) as a key correlate. Not to be discounted, CD8+ T cells targeting liver-stage (LS) antigens were associated with protection in attenuated sporozoite vaccination. Clearly there is no panacea for malarial immunity, and a broad range of responses against multiple antigens is crucial. In this work we develop novel synthetic DNA vaccines targeting antigens in multiple Plasmodium pre-erythrocytic life cycle stages, and evaluate the immunity elicited by each in the context of murine models of malaria. To further evaluate protection mediated by Liver stage antigens, we focused on the exported pre-erythrocytic proteins EXP1, PFN, EXP2, ICP, TMP21, and UIS3. SynDNA antigen cocktails were tested with and without the molecular adjuvant plasmid IL-33. Immunized animals developed robust T cell responses including induction of antigen-specific liver-localized CD8+ T cells, which were enhanced by the co-delivery of plasmid IL-33. In total, 100% of mice in adjuvanted groups and 71%–88% in non-adjuvanted groups were protected from disease following Plasmodium yoelii challenge. To further evaluate protection mediated by sporozoite antigens, five synDNA vaccines encoding variations of CSP were designed and studied: 3D7, GPI1, ΔGPI, TM, and DD2. ΔGPI generated the most robust immunity, and was the most efficacious in an IV sporozoite challenge. We then compared the immunity generated by ΔGPI vs synDNA mimics for two leading malaria vaccine candidates (RTS,S and R21). They demonstrated similar anti-CSP antibody responses, however ΔGPI induced a more focused T cell response. In an infectious mosquito challenge all three of these constructs generated potent inhibition of liver stage infection, with ΔGPI appearing to also provide the best sterilizing immunity from blood stage parasitemia. Together these studies demonstrated that synDNA vaccines encoding malaria immunogens can provide substantial protection from disease, and highlighted the importance of targeting the pre-erythrocytic life cycle stages to combat malaria.