HIV Targets Immune Cells Designated as First-line Defense Against Virus, Study Shows

A study published today in Nature confirms the "long-standing suspicion" that HIV targets the very immune cells that are engineered to attack it, a finding that could have implications for both AIDS vaccine research and structured treatment interruptions, the AP/Nando Times reports. Dr. Daniel Douek and a team of researchers from the National Institute of Allergy and Infectious Diseases examined CD4 T cells in the blood of 12 people with HIV and found that CD4+ T cells, which specifically target HIV, contained two to five times more HIV than other immune cells (Callahan, AP/Nando Times, 5/1). The investigators said that CD4+ T cells are probably more susceptible to HIV because they are "naive" to the virus when the immune system initially attacks HIV, and they "bear the brunt" of fighting the infection. After initial exposure, the cells multiply into "mature HIV-fighting cells," but they remain "very vulnerable" to HIV infection during the multiplication process (BBC News, 5/1).

Implications for Research
The confirmation that CD4+ T cells are targeted by HIV may change the approach that researchers take toward vaccine development. Most vaccine candidates seek to stimulate the CD4+ T cell response; however, according to the current study, doing so may only give the virus more "attractive targets." A different approach that would elicit both a CD4+ T cell response and a CD8 white blood cell response while also "rallying anti-HIV antibodies" may prove more effective, Douek stated, noting that NIH researchers are already pursuing this type of vaccine. The study also raised questions about the effectiveness of structured treatment interruptions, which are treatment regimens designed to boost the body's own immune response by taking HIV-positive patients off antiretroviral therapy at timed intervals. The NIAID team examined four patients who were on STIs as part of a clinical trial and found that their viral levels rose significantly when treatment was suspended. The rise in HIV then triggered a "corresponding surge" in CD4+ T cells, thereby giving the virus more targets. "That tells us that if you're going to interrupt therapy, you should interrupt it for a brief enough period of time that the virus does not rebound," Roger Pomerantz, director of the Center for Human Virology at Thomas Jefferson University, said (AP/Nando Times, 5/1).