Removal of the circumsporozoite protein (CSP) glycosylphosphatidylinositolsignal sequence from a CSP DNA vaccine enhances induction of CSP-specific Th2 type immune responses and improves protection against malaria infection

The C terminus of the circumsporozoite protein (CSP) is anchored to the par asite cell membrane by a glycosylphosphatidylinositol (GPI) glycolipid. Thi s GPI signal sequence functions poorly in heterologous eukaryotic cells, ca using CSP retention within internal cell organelles during genetic immuniza tion. Cellular location of antigen has quantitative and qualitative effects on immune responses induced by genetic immunization. Removal of the GPI si gnal sequence had a profound effect on induction and efficacy of CSP-specif ic immune response after genetic immunization of BALB/c mice with a gene gu n. The CSP produced from the plasmid lacking the GP[ anchor signal sequence (CSP-A) was secreted and soluble, but that produced by the CSP;A plasmid w as not. The CSP-A plasmid induced a highly polarized Th2 type response, in which the CSP-specific IgG antibody titer was three- to fourfold higher, an d the protective effect was significantly greater than that induced by the CSP+A plasmid. Thus, these two physical forms of CSP induced quantitatively and qualitatively different immune responses that also differed in protect ive efficacy. Engineering plasmid constructs for proper cellular localizati on of gene products is a primary consideration for the preparation of optim ally efficacious DNA vaccines.