Evaluation of immune responses elicited in mice against a recombinant malaria vaccine based on Plasmodium vivax Duffy binding protein

Plasmodium vivax Duffy binding protein (PvDBP) binds the Duffy blood group antigen as the obligate receptor for erythrocyte invasion. We have tested in mice the immunogenicity of recombinant P. vivax region II (PvRII), the receptor-binding domain of PvDBP, formulated with five adjuvants, namely, Montanide ISA720, AS02A, alum, QS21 and MF59. All the formulations elicited high titer antibodies, with Montanide ISA720 and AS02A yielding the highest titers followed by MF59, QS21 and alum. Sera raised against PvRII formulated with AS02A and Montanide ISA720 followed by alum were most effective at blocking PvRII binding to erythrocytes in a functional assay. Analysis of cellular immune responses indicated that all adjuvant groups induced significant interferon-γ, with alum being the highest interferon-γ inducer. These results suggest that recombinant PvRII formulated with human compatible adjuvants is immunogenic in small animal models and that Montanide ISA720, AS02A and alum perform better than MF59 and QS21 in terms of their ability to elicit high titer binding inhibitory antibodies.