Plasmodium falciparum: recombinant baculoviruses direct the expression of circumsporozoite proteins in Spodoptera frugiperda cell cultures

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Abstract
The DNA coding for the circumsporozoite protein (CPS) of Plasmodium falciparum has been cloned into the baculovirus expression vector pAcYM1 and expressed in Spodoptera frugiperda (Sf9) insect cells. Three DNA constructs have been made: the first one directs the synthesis of the complete CSP (aa 1–412), the second leads to the production of a species devoid of the anchor domain (aa 1–391) and the third one to a molecule lacking both signal and membrane anchor sequences (aa 18–391). All three recombinant CPS were produced at about 3 μg per 106 infected cells and were characterized in terms of immunoreactivity and apparent molecular weight. Analytical purification of the recombinant proteins was achieved by a combination of heat treatment, acidification, isoelectric focusing and ion exchange chromatography. The purified material, when injected into mice, generated only modest antibody responses, although antisera from immunized mice reacted with control CSP antigens carrying or not the major immunodominant repeat region.