Vaccination with Plasmodium knowlesi AMA1 Formulated in the Novel Adjuvant Co-Vaccine HT™ Protects against Blood-Stage Challenge in Rhesus Macaques

Abstract

Plasmodium falciparum apical membrane antigen 1 (PfAMA1) is a leading blood stage vaccine candidate. Plasmodium knowlesi AMA1 (PkAMA1) was produced and purified using similar methodology as for clinical grade PfAMA1 yielding a pure, conformational intact protein. Combined with the adjuvant CoVaccine HT™, PkAMA1 was found to be highly immunogenic in rabbits and the efficacy of the PkAMA1 was subsequently tested in a rhesus macaque blood-stage challenge model. Six rhesus monkeys were vaccinated with PkAMA1 and a control group of 6 were vaccinated with PfAMA1. A total of 50 µg AMA1 was administered intramuscularly three times at 4 week intervals. One of six rhesus monkeys vaccinated with PkAMA1 was able to control parasitaemia, upon blood stage challenge with P. knowlesi H-strain. Four out of the remaining five showed a delay in parasite onset that correlated with functional antibody titres. In the PfAMA1 vaccinated control group, five out of six animals had to be treated with antimalarials 8 days after challenge; one animal did not become patent during the challenge period. Following a rest period, animals were boosted and challenged again. Four of the six rhesus monkeys vaccinated with PkAMA1 were able to control the parasitaemia, one had a delayed onset of parasitaemia and one animal was not protected, while all control animals required treatment. To confirm that the control of parasitaemia was AMA1-related, animals were allowed to recover, boosted and re-challenged with P. knowlesi Nuri strain. All control animals had to be treated with antimalarials by day 8, while five out of six PkAMA1 vaccinated animals were able to control parasitaemia. This study shows that: i) Yeast-expressed PkAMA1 can protect against blood stage challenge; ii) Functional antibody levels as measured by GIA correlated inversely with the day of onset and iii) GIA IC50 values correlated with estimated in vivo growth rates.

An Empirical Approach towards the Efficient and Optimal Production of Influenza-Neutralizing Ovine Polyclonal Antibodies Demonstrates That the Novel Adjuvant CoVaccine HT™ Is Functionally Superior to Freund's Adjuvant

“…This adjuvant offers the advantage of presenting amphipathic membrane target antigens in native formation due to the squalane-in-water formulation. It has shown efficacy in combination with a range of antigens including malarial antigens [48], influenza glycoproteins [47] and gonadatropin-releasing hormone [49]. In order to determine if CV is capable of inducing anti-HA antibody responses comparable to those generated with FA, sheep were primed with rHA either traditionally emulsified with complete FA or gently mixed with CV and boosted fortnightly with rHA in incomplete FA or CV respectively.…”

Humoral Immune Responses to a Single Allele PfAMA1 Vaccine in Healthy Malaria-Naïve Adults

“…A novel proprietary adjuvant, CoVaccine HT™, has yielded promising results in rhesus macaques and rabbits [23], [27]. Moreover, P. knowlesi AMA1 formulated with CoVaccine HT™ has induced protection against blood-stage challenge with P. knowlesi in the rhesus macaque model and the degree of protection was correlated with GIA titre [28]. It would therefore be interesting to combine DiCo AMA1 with CoVaccine HT™ in a Phase I trial.…”

Correlation between Virus Replication and Antibody Responses in Macaques following Infection with Pandemic Influenza A Virus

“…Hematology parameters were measured in EDTA-blood mixtures with a Sysmex XT-2000iV automated hematology analyzer (Sysmex Corporation of America) as previously described (31).…”