December 6 , 2002

Immune system control of HIV may not protect against second infection

Although antiviral therapy during the earliest stages of infection can enable HIV-infected individuals eventually to control the virus with their immune systems alone, that control may not protect against infection with another strain of HIV. In the Nov. 28 issue of Nature, an MGH-based research team reports on a study participant who, having maintained successful immune control of HIV for almost a year, became infected with another strain of the virus. Moreover, the patient's immune system has not effectively controlled the second viral strain.

"We were surprised and disappointed when we saw this person's viral levels rise," says Bruce Walker, MD, director of the Partners AIDS Research Center at the MGH. "Clearly this indicates that vaccine development is going to be a greater challenge than we had anticipated."

Walker's team has previously reported that starting patients on antiviral therapy within the first weeks to months after infection can allow the immune system to fight back against HIV. By preventing the destruction by HIV of T helper cells, which are the "generals" of the immune system, this strategy allows the production of the immune system's "infantry," which are T killer cells specifically targeted against the virus. The patient in the current study had achieved stable viral control and was able to discontinue treatment for seven months until his viral level began to rise again. Walker's team ran a series of tests and found evidence that he had been infected with a different strain of HIV. The patient did have an unprotected sexual encounter several months before the increase in his viral level.

"It's clear that a preventive vaccine is going to have to target the many strains of HIV that are out there to be successful," Walker says. He does note that the patient's ability to generate some new responses against the distinctive parts of the new virus indicates that it may be possible to strengthen the immune system in chronically infected patients. He also stresses the importance of safer sexual practices for all those infected with HIV.

Other MGH authors of the Nature report are co-first authors Marcus Altfeld, MD, and Todd Allen, PhD; Xu G. Yu, MD; Mary Johnston; Deepak Agrawal, MD; Ben Davis, MD; Paul Lee; Erica Maier; Jason Harlow; Philip Goulder, MD, PhD; Christian Brander, PhD; and Eric Rosenberg, MD, all of the Partners/MGH AIDS Research Center.