Medical scientists say a new idea may soon lead to an effective malaria vaccine. A study by investigators at the Walter Reed Army Institute of Research shows how a cocktail of proteins required by only a few strains of Plasmodium falciparum, a parasite, to invade blood cells, may produce antibodies protective of multiple strains of malaria, a continuously evolving infectious disease.
Previous efforts to develop an effective malaria vaccine for the world stalled as earlier candidate vaccines using the protein-based vaccine proved effective against only one strain of the parasite, and thus ineffective against multiple strains of the disease. Now, investigator Sheetij Dutta and her colleagues say a combination of AMA1 proteins from only a few strains of the parasite may successfully produce a vaccine protective against multiple strains of evolving malarial disease.
And the work is urgent, too. Some 3.3 billion people — half the world’s population — faces a risk of malaria, according to the U.S. Centers for Disease Control and Prevention. With Africans hardest hit, 219 million people contracted malaria in 2010, as 600,000 died of the disease, according to the World Health Organization. Since 2000, the World Health Organization and its partners have implemented prevention and control measures leading to a 25 percent global drop in malaria deaths.
Still, a single infectious disease threatens half the world at the moment, with thousands of deaths every day.
In a paper published Friday, the investigators celebrate the vaccine candidacy of “Apical Membrane Antigen-1,” whose antibodies inhibit the invasion of merozoites — parasites — into red blood cells, which correlated with a lowered rate of malarial infection in nonhuman primates. With the knowledge that similar vaccines have shown an immune response directed at the parasite, investigators say the new cocktail just might work.
“[A] cocktail of AMA1 proteins from three different parasite strains was better than one or two, and one they call Quadvax, which contained AMA1 proteins derived from four different strains, led to an antibody response that was broader than the sum of strain-specific antibodies elicited by the four individual strains,” the investigators wrote. Moreover, antibodies produced in response to Quadvax inhibited a range of parasites from ensconcing themselves within the host, including many strains different from those in the Quadvax mix.
“In various tests, such antibodies inhibited the growth of 26 different strains of parasite, suggesting to investigators that “the combination of four AMA1 variants in Quadvax may be sufficient to overcome global AMA1 diversity, they wrote.
Next, the investigators say they plan to test the vaccine candidate in non-human primate models, and in human blood in the laboratory.
Source: Dutta S, Dlugosz LS, Drew DR, Ge X, Abacar D, Rovira YI, Moch KJ. Overcoming Antigenic Diversity By Enhancing The Immunogenicity Of Conserved Epitopes On The Malaria Vaccine Candidate Apical Membrane Antigen-1. PLOS Pathogens. 2013.