Johns Hopkins Researchers Create Malaria Vaccine

Researchers from the Johns Hopkins School of Public Health have fashioned a DNA-based vaccine that short-circuits the parasite's development and blocks malaria transmission. The vaccine was tailor-made from bits of nucleic acid that match a segment of the malaria parasite's own DNA.

Despite intensive mosquito-control campaigns and a range of drug treatments, malaria continues to devastate the health of 300 to 500 million people each year. The disease is caused by a parasite, Plasmodium falciparum, the sexual form of which is ingested by a mosquito when it bites an infected human. The parasite incubates in the insect's midgut until maturing into an infective form, which is reintroduced into humans when the mosquito feeds again.

The researchers injected mice with the DNA vaccine both intramuscularly and intradermally, in order to force the immune system to make antibodies that would seek out and neutralize infectivity of sexual forms. Both before immunization and four weeks after, serum samples were collected from the mice and then fed along with P. falciparum sexual forms to Anopheles mosquitoes.

Eight days after this feeding, the mosquitoes were dissected and their midguts examined for the presence of oocysts of P. falciparum. The mosquitoes that had ingested sera from immunized mice showed a 75% decrease in the rates of infection, and up to a 97% decrease in the numbers of oocysts. Although all mice developed antibody responses to the DNA vaccines, antibody levels were as much as 30 times higher with the intramuscular route than with the intradermal route.

Before human vaccine trials are contemplated, studies are in progress to demonstrate comparable antibody development in nonhuman primates immunized with the DNA vaccine.

For more information: Kathy Moore, Office of Public Affairs, Johns Hopkins School of Public Health, 615 North Wolfe Street, Room 1604B, Baltimore, MD 21205. Tel: 410-955-6878. Fax: 410-955-4775. Email: kwojciec@jhsph.edu.