Vaccine 24 (2006) 2497–2505 Enhancement of functional antibody responses to AMA1-C1/Alhydrogel ® ,a Plasmodium falciparum malaria vaccine, with CpG oligodeoxynucleotide Gregory E.D. Mullen a,∗,1 , Birgitte K. Giersing a,1 , Olubunmi Ajose-Popoola a , Heather L. Davis b , Cheryl Kothe a , Hong Zhou a , Joan Aebig a , Gelu Dobrescu a , Allan Saul a , Carole A. Long a a Malaria Vaccine Development Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 5640 Fishers Lane, Rockville, MD 20852, USA b Coley Pharmaceutical Group, Ottawa, ON, Canada Received 8 August 2005; received in revised form 15 November 2005; accepted 14 December 2005 Available online 4 January 2006 Abstract Apical membrane antigen 1 (AMA1) has been shown to be a promising malaria vaccine candidate. The multiallelic AMA1-C1 vaccine currently in Phase 1 trials in the US and Mali contains an equal mixture of the ectodomain portion of recombinant AMA1 from the FVO and 3D7 clones of Plasmodium falciparum, formulated on Alhydrogel. It is hoped that inclusion of a human-optimized CpG oligodeoxynucleotide (ODN) (CPG 7909) with our existing AMA1-C1/Alhydrogel vaccine will lead to a higher concentration of functional AMA1-C1 antibodies. Preclinical studies were performed in mice, rats and guinea pigs to assess the safety, immunogenicity and functionality of the immune response to AMA1-C1 with Alhydrogel + CPG 7909 compared to antigen with Alhydrogel alone. Day 42 mean anti-AMA1 ELISA titer values derived from individual animals were compared between Alhydrogel and Alhydrogel + CPG 7909 groups at each antigen dose for each species. Sera from Alhydrogel + CPG 7909 groups displayed significantly higher antibody titers (P < 0.025) than their comparable Alhydrogel alone group. Mouse IgG isotype analysis showed that AMA1-C1/Alhydrogel induced a predominately Th2 type response while AMA1-C1/Alhydrogel + CPG 7909 gave a mixed Th1/Th2 type response. When tested for functional activity by in vitro inhibition of parasite invasion, IgG isolated from serum pools of AMA1-C1/Alhydrogel + CPG 7909 animals was more effective against both FVO and 3D7 parasites than an equal concentration of IgG from animals receiving vaccines adjuvanted with Alhydrogel alone. These promising preclinical results have recently led to the start of a Phase 1 trial in the US. © 2005 Elsevier Ltd. All rights reserved. Keywords: AMA1; CPG; Malaria vaccine 1. Introduction Plasmodium falciparum’s lifecycle is comprised of multi- ple stages, including an asexual blood stage within its human host. This stage of parasite development is responsible for the pathological and clinical manifestations of disease, resulting ∗ Corresponding author. Tel.: +1 301 435 2936; fax: +1 301 480 1962. E-mail address: gmullen@niaid.nih.gov (G.E.D. Mullen). 1 These authors contributed equally. from repeated cycles of invasion, parasite growth and release from erythrocytes. Apical membrane antigen 1 (AMA1) is expressed on the surface of the infectious form of the blood stage parasite, known as the merozoite, and is a leading blood stage malaria vaccine candidate. Vaccination with recombi- nant AMA1 has been shown to induce protection against homologous parasite challenge in both rodent and mon- key models of malaria infection [1–4]. We have previously reported that recombinant 62-kDa AMA1 antigen, based on the ectodomain amino acid sequence of the Plasmodium 0264-410X/$ – see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.vaccine.2005.12.034