Comparison of the immunogenic properties of recombinant proteins representing the Plasmodium vivax vaccine candidate MSP1(19) expressed in distinct bacterial vectors

The 19 kDa C-terminal region of the merozoite surface protein 1 (MSP1(19)) is one of the most promising vaccine candidates against the erythrocytic fo rms of malaria. In the present study, we used three different Escherichia c oli expression vectors to generate five recombinant proteins representing t he MSP1(19) of Plasmodium vivax. These proteins were compared for reactivit y with a panel of sera from individuals naturally exposed to P. vivax and f or their immunogenicity in mice. Among the proteins studied, MSPI 19 expres sed by the vector pET (His(6)-MSP1(19)) was better recognized by the antibo dies of several individuals exposed to P. vivax. The addition of the T-cell Pan-allelic DR epitope (PADRE) did not alter the recognition of this recom binant protein by human antibodies. Although recombinant proteins were immu nogenic to mice, immunization with MSP1(19) expressed by the pET or pGEX ve ctors induced significantly higher antibody titers than a protein produced by the pMAL vector. The antibody immune response elicited by His(6)-MSP1(19 ) containing the PADRE epitope was compared using different adjuvant formul ations. After only two immunizing doses, antibody titers induced in the pre sence of the adjuvants TiterMax, MPL/TDM/CWS or alum plus CpG ODN 1826 were as high as Liters generated by complete Freund's adjuvant. We concluded th at, among the bacterial recombinant proteins, MSPI1(19) expressed by the ve ctor pET should be selected for further evaluation in pre-clinical immuniza tions against P. vivax. (C) 2001 Published by Elsevier Science Ltd.