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The international open-access
medical journal PLoS Medicine has recently reported encouraging results from the
first human trial of a vaccine based on MSP3, by Pierre Druilhe and colleagues from the Institut
Pasteur in Paris.(1)
Plasmodium falciparum merozoite surface protein 3 is a malaria vaccine candidate that was identified, characterised, and developed based on a unique immuno-clinical
approach. The corresponding long synthetic peptide was administered to 36
volunteers and was found to induce cellular and humoral immune responses. The
vaccine-induced antibodies were able to cooperate with effector cells. In vitro, the antibodies induced an inhibition of the P. falciparum erythrocytic growth in a monocyte-dependent manner. In vivo transfer of the volunteers' sera into P. falciparum–infected humanized SCID mice profoundly reduced or abrogated parasitaemia. These inhibitory effects were related to the antibody reactivity with the parasite native protein, which was seen in 60% of the volunteers, and remained in samples taken 12 months post-immunisation.
Thus this is the first malaria vaccine clinical trial to clearly demonstrate antiparasitic activity by vaccine-induced antibodies by both in vitro and in vivo methods. The results, showing the induction of long-lasting antibodies directed to a fully conserved polypeptide, also challenge current concepts about malaria vaccines, such as unavoidable polymorphism, low antigenicity, and poor induction of immune memory.(1)
However, additional clinical trials
are needed before the vaccine can become commercially available, if at all. Druilhe and colleagues have started a Phase II efficacy field trial of the MSP3 vaccine in malaria-exposed individuals.
But the work had its own problems! 'The implementation of the phase 2 trial could
have been done four years ago, but for reasons that are not scientific, which have been painful to me, the study still has not started,' principal investigator of the study Pierre Druilhe of the Institut
Pasteur in Paris told United Press International. 'There is too much politics
going on in the development of vaccines,' he said.(2)
Other developments may also speed up the progress of a malaria vaccine. The Gates Foundation said late last month it had given $107.6 million to the PATH Malaria Vaccine Initiative to help develop GSK`s RTS,S malaria vaccine.
The RTS,S vaccine is the most advanced in terms of clinical development.(2)
References:
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Pierre Druilhe, François Spertini, Daw Soesoe, Giampietro Corradin, Pedro Mejia, Subhash Singh, Regine Audran, Ahmed Bouzidi, Claude Oeuvray, Christian Roussilhon.
A Malaria Vaccine That Elicits in Humans Antibodies Able to Kill Plasmodium falciparum.
(See)
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Steve Mitchell.
French malaria vaccine shows promise (See)
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Ballou WR, Arevalo-Herrera
M, Carucci D et al. Update on the clinical development of candidate malaria
vaccines. Am. J. Trop. Med. Hyg., 71(2 suppl), 2004, pp. 239-247. (See)
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