Protective Immunity in Mice Immunized With P. vivax MSP1₁₉-Based Formulations and Challenged With P. berghei...

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 MSP1₁₉ antigen. The Plasmodium berghei strains ANKA and NK65 were modified to express PvMSP1₁₉ instead of the endogenous PbMSP1₁₉. The hybrid parasites were used to challenge C57BL/6 or BALB/c mice immunized with PvMSP1₁₉-based vaccine formulations. The PvMSP1₁₉ was correctly expressed in the P. berghei hybrid mutant lines as confirmed by immunofluorescence using anti-PvMSP1₁₉ monoclonal antibodies and by Western blot. Replacement of the PbMSP1₁₉ by the PvMSP1₁₉ had no impact on asexual growth in vivo. High titers of specific antibodies to PvMSP1₁₉ 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 PvMSP1₁₉ in this model can help immunity mounted later during infection.