Plasmodium falciparum: immunogenicity of circumsporozoite protein constructs produced in Escherichia coli

The immunogenicity of Plasmodium falciparum recombinant circumsporozoite protein constructs R16tet32, R32tet32, and R48tet32 in mice was examined by measuring antibody responses by enzyme linked immunosorbent assay, immunofluorescence, circumsporozoite precipitation, and inhibition of sporozoite invasion. All three constructs were found to be immunogenic when administered alone, but antibody responses were greater for the larger constructs, R32tet32 and R48tet32. Increased dose, boosting, and the use of adjuvants further augmented antibody responses. R32tet32 was found to be the most immunogenic of the three constructs, and high levels of protective antibodies were found to persist for at least 44 weeks when the construct was given with alum. Clinical trials with alum adjuvanted R32tet32 have now begun.