Plasmodium falciparum:: Immunogenicity of alum-adsorbed clinical-grade TBV25-28, a yeast-secreted malaria transmission-blocking vaccine candidate

Plasmodium falciparum: Immunogenicity of alum-adsorbed clinical-grade TBV25-28, a yeast-secreted malaria transmission-blocking vaccine candidate. Experimental Parasitology 97, 61-69. The fusion of Pfs25 and Pfs28, two major surface antigens on zygotes and ookinetes of Plasmodium falciparum, as a single recombinant protein (TBV25-28) was previously shown to elicit potent transmission-blocking antibodies in mice. Clinical-grade TBV25-28 was subsequently manufactured and its potency was evaluated in rabbits. Rabbits received three doses of either clinical-grade TBV25H or clinical-grade TBV25-28 adsorbed to alum with or without QS-21. As measured in a standard membrane-feeding assay, addition of QS-21 to the formulations appeared to enhance transmission-blocking potency of rabbit sera after two vaccinations but not after three vaccinations. Surprisingly, TBV25H elicited more potent transmission blocking antibodies than did TBV25-28, a result strikingly different from those of previous mouse experiments using research-grade TBV25-28. The apparent decrease in potency of clinical-grade TBV25-28 in rabbits appears to reflect an enhancement in potency of clinical-grade TBV25H in a new formulation rather than simply a species difference in immunogenicity of TBV25-28. (C) 2001 Academic Press.