INDUCTION OF PLASMODIUM-FALCIPARUM SPOROZOITE-NEUTRALIZING ANTIBODIESUPON VACCINATION WITH RECOMBINANT PFS16 VACCINIA VIRUS AND OR RECOMBINANT PFS16 PROTEIN PRODUCED IN YEAST/

Pfs16 is a sexual stage/sporozoite-specific antigen of Plasmodium falc iparum and is a potential candidate for a sporozoite-neutralizing vacc ine. To obtain more information on the function of Pfs16 and to invest igate its role during transmission and hepatocyte invasion, immunizati on experiments were performed with both a Pfs16-specific recombinant v accinia virus and virus-like particles produced in yeast composed of t he hepatitis B surface antigen (HBsAg) and antigen Pfs16 fused to HBsA g. Upon transformation of yeast cells, harbouring a genomic copy of th e HBsAg gene, with a plasmid carrying the fusion gene Pfs16-HBsAg (Pfs 16-S) virus-like hybrid particles composed of HBsAg and Pfs16-S were f ormed of a size similar to those present in human sera after infection with the hepatitis B virus. Cells infected with recombinant Pfs16 vac cinia virus synthesized a polypeptide of approx. 16 kDa that reacted w ith a Pfs16-specific polyclonal antibody. Animals vaccinated with the yeast hybrid particles and/or recombinant vaccinia virus both produced Pfs16-specific antibodies. These antibodies showed no transmission-bl ocking activity, but they efficiently diminished or abolished in vitro invasion of sporozoites into human hepatoma cells (HepG2-A16) and pri mary human hepatocytes.