Background: Mammalian cells expressing the small hepatitis B virus surface protein (HBs) secrete highly immunogenic 20 nm lipoprotein particles. Previous studies demonstrated that the fusion of foreign sequences into certain regions of HBs leads to chimeric particles carrying epitopes for the foreign peptide, as well as for HBs. The present study investigates immunologic and biochemical properties of the fusion of the C-terminal region of the merozoite surface 1 protein of P. vivax, the most widely distributed human malaria parasite, and HBs (PvMSP1(19)-HBs).
Materials and methods: COS7 cells were transfected with a plasmid coding for PvMSP1(19)-HBs. The hybrid products were analyzed by density gradient centrifugation and electron microscopy or detected by metabolic labeling and immunoprecipitation with anti-HBs and patient-derived anti-P. vivax serum. Mice were immunized with the vector and the antibody response was checked by ELISA.
Results: The fusion PvMSP1(19)-HBs formed particles of 20-45 nm size, which were secreted from COS7 cells. The particles were immunoprecipitable with anti-HBs and serum of different P. vivax-positive individuals. Immunization of mice with the construct as a genetic vaccine showed that antibodies were raised mostly against the PvMSP1(19) domain and recognized the native protein.
Conclusion: Due to its biochemical and antigenic properties, the hybrid particle will be useful in future vaccine trials against the asexual blood stages of P. vivax as a genetic and/or a proteic subunit candidate.