Malaria caused by Plasmodium falciparum continues to threaten millions of people living in the tropical parts of the world. A
vaccine that confers sterile and life-long protection remains elusive despite more than 30years of effort and resources invested in solving this problem.
Antibodies to a
malaria vaccine candidate circumsporozoite
protein (CSP) can block invasion and can protect humans against
malaria. We have manufactured the
Falciparum Malaria Protein-013 (FMP013)
vaccine based on the nearly full-length P. falciparum CSP 3D7 strain sequence. We report here immunogenicity and challenge data on FMP013
antigen in C57BL/6 mice formulated with two novel adjuvants of the Army
Liposome Formulation (ALF) series and a commercially available adjuvant
Montanide ISA 720 (
Montanide) as a control. ALF is a liposomal adjuvant containing a synthetic
monophosphoryl lipid A (3D-PHAD®). In our study, FMP013 was adjuvanted with ALF alone, ALF containing
aluminum hydroxide (ALFA) or ALF containing
QS-21 (ALFQ). Adjuvants ALF and ALFA induced similar antibody titers and protection against transgenic parasite challenge that were comparable to
Montanide. ALFQ was superior to the other three adjuvants as it induced higher antibody titers with improved boosting after the third immunization, higher serum IgG2c titers, and enhanced protection. FMP013+ALFQ also augmented the numbers of splenic germinal center-derived activated B-cells and antibody secreting cells compared to
Montanide. Further, FMP013+ALFQ induced
antigen-specific IFN-γ ELISPOT activity, CD4+ T-cells and a TH1-biased
cytokine profile. These results demonstrate that soluble CSP can induce a potent and sterile protective immune response when formulated with the
QS-21 containing adjuvant ALFQ. Comparative mouse immunogenicity data presented here were used as the progression criteria for an ongoing non-human primate study and a regulatory toxicology study in preparation for a controlled human
malaria infection (
CHMI) trial.