Scientists found that the HIV virus becomes dormant and remains hidden in certain immune system cells shortly after infection, but slows when patients are given antiretroviral therapy.

While current treatments are effective at controlling HIV, some of the virus remains hidden and live in certain CD4+ T cells, specialized immune system cells that the virus uses to replicate, so that they can respond swiftly to a second exposure to the same antigen.

Experts say that because the latent virus resides in memory T cells, it persists indefinitely and even in patients on potent antiretroviral therapy, and this process of latent reservoir remains is recognized as a significant barrier to curing HIV infection.

Researchers developed a mathematical model to predict the initial frequency of resting cell infection, or how often latent cells were going to be infected based on when antiretroviral therapy was started, in patients about a year after infection.

The study, published Wednesday in the Proceedings of the National Academy of Sciences, consisted of 27 patients with acute HIV infection, which occurs soon after exposure when the virus is found in the blood plasma but still not detectible in the antibodies. Researchers said all but one of the patients studied had been infected in the past 45 days before beginning the study.

Investigators found that while some virus remains hidden in cells, the earlier patients started antiretroviral therapy, the slower latency develops.

Furthermore scientists found two types of latently infected cells, one short-lived, but another that extremely resilient, referred to as a "deep" latent infection.

"We found that latent infection decayed in some patients, but that all had a few deeply latent infected cells," researcher Dr. David Margolis, professor of medicine, microbiology and immunology, and epidemiology at the University of North Carolina School of Medicine said in a statement. "These are the cells that we must eliminate to cure infection."

"These findings reinforce and extend the concept that new approaches will be needed to eradicate HIV infection, and, in particular, highlight the need to target the extremely small but universal, long-lived latent reservoir," the authors concluded.