A genetically modified Plasmodium berghei parasite as a surrogate for whole-sporozoite vaccination against P. vivax malaria

Two malaria parasite species, Plasmodium falciparum ( Pf ) and P. vivax ( Pv ) are responsible for most of the disease burden caused by malaria. Vaccine development against this disease has focused mainly on Pf . Whole-sporozoite (WSp) vaccination, targeting pre-erythrocytic (PE) parasite stages, is a promising strategy for immunization against malaria and several Pf WSp-based vaccine candidates are currently undergoing clinical evaluation. In contrast, no WSp candidates have been developed for Pv , mainly due to constraints in the production of Pv sporozoites in the laboratory. Recently, we developed a novel approach for WSp vaccination against Pf based on the use of transgenic rodent P. berghei ( Pb ) sporozoites expressing immunogens of this human-infective parasite. We showed that this platform can be used to deliver PE Pf antigens, eliciting both targeted humoral responses and cross-species cellular immune responses against Pf . Here we explored this WSp platform for the delivery of Pv antigens. As the Pv circumsporozoite protein (CSP) is a leading vaccine candidate antigen, we generated a transgenic Pb parasite, Pb viVac, that, in addition to its endogenous Pb CSP, expresses Pv CSP under the control of a strictly PE promoter. Immunofluorescence microscopy analyses confirmed that both the Pb CSP and the Pv CSP antigens are expressed in Pb viVac sporozoites and liver stages and that Pb viVac sporozoite infectivity of hepatic cells is similar to that of its wild-type Pb counterpart. Immunization of mice with Pb viVac sporozoites elicits the production of anti- Pv CSP antibodies that efficiently recognize and bind to Pv sporozoites. Our results warrant further development and evaluation of Pb viVac as a surrogate for WSp vaccination against Pv malaria.