Protective Immunity in Mice Immunized With P. vivax MSP1 19 -Based Formulations and Challenged With P. berghei Expressing Pv MSP1 19

The lack of continuous in vitro cultures has been an obstacle delaying pre-clinical testing of Plasmodium vivax vaccine formulations based on known antigens. In this study, we generated a model to test available formulations based on the P. vivax MSP1 19 antigen. The Plasmodium berghei strains ANKA and NK65 were modified to express Pv MSP1 19 instead of the endogenous Pb MSP1 19 . The hybrid parasites were used to challenge C57BL/6 or BALB/c mice immunized with Pv MSP1 19 -based vaccine formulations. The Pv MSP1 19 was correctly expressed in the P. berghei hybrid mutant lines as confirmed by immunofluorescence using anti- Pv MSP1 19 monoclonal antibodies and by Western blot. Replacement of the Pb MSP1 19 by the Pv MSP1 19 had no impact on asexual growth in vivo . High titers of specific antibodies to Pv MSP1 19 were not sufficient to control initial parasitemia in the immunized mice, but late parasitemia control and a balanced inflammatory process protected these mice from dying, suggesting that an established immune response to Pv MSP1 19 in this model can help immunity mounted later during infection.