February 4, 2010

Scientists who successfully developed an experimental vaccine using non-infectious virus-like particles (VLP) intend exploring whether they will work against the Western and Eastern equine encephalitis virus.

The researchers' vaccine protected macaques and mice against the chikungunya virus, a mosquito-borne pathogen that has infected millions of people in Africa and Asia and causes debilitating pain.

Scientists at the National Institute of Allergy and Infectious Diseases (NIAID) in the US developed the vaccine because there is no vaccine or treatment for chikungunya virus infection.

"Increases in global travel and trade, and possibly climate change, may be contributing to the spread of disease-carrying mosquitoes into new areas," said NIAID Director Anthony Fauci.

"Finding safe and effective human vaccines for chikungunya virus and other insect-borne pathogens is an important global health priority."

Gary Nabel, director of NIAID's Vaccine Research Centre, said: "This virus-like particle vaccine provides a promising way to protect against an emerging infectious disease threat.

"This same approach could possibly extend to viruses related to chikungunya that cause fatal diseases such as encephalitis."

Nabel says his group plans to seek approval for clinical trials to further evaluate the safety and efficacy of the vaccine in humans.

There are two VLP vaccines for other diseases approved by the US Food and Drug Administration: one for hepatitis B and one for human papillomavirus.

This study marks the first time that scientists have used VLPs in a vaccine to protect against chikungunya virus, which is in the genus Alphavirus. The group plans to determine whether VLPs will work against other alphaviruses, such as Western and Eastern equine encephalitis virus found in the United States, and o'nyong-nyong virus found in Africa.

To develop the chikungunya vaccine, scientists identified the proteins that give rise to chikungunya VLPs.

The VLPs mimic actual virus particles but cannot cause infection, so they can be used safely as a vaccine to elicit immune responses. The researchers immunised rhesus macaques with the VLPs, waited 15 weeks before exposing the animals to chikungunya virus, and observed that the vaccine provided complete protection from infection.

When the group found that antibodies were responsible for immune protection, they transferred antibody-containing serum from the vaccinated macaques to mice with deficient immune systems. The mice then were exposed to a lethal dose of chikungunya virus, but the immune serum protected them from infection.

Investigators from Purdue University, the University of Texas Medical Branch at Galveston, and Bioqual, Inc, in Rockville, Maryland, collaborated with NIAID scientists on this study.

Details about the new vaccine have been published in the online version of Nature Medicine.