HIV can avoid the effects of antiretroviral therapy by hiding in long-living bone marrow cells, reawakening later to continue the cycle of infection, scientists reported on Sunday.

The virus is dormant in bone marrow cells, forming a reservoir of infection resistant to highly active antiretroviral therapy (HAART) and the immune response, wrote Dr. Kathleen Collins, of the University of Michigan, and colleagues. When these progenitor cells convert into blood cells, HIV can reactivate and continue proliferating. The virus kills the new blood cells and moves on to infect other cells, she said.

"If we're ever going to be able to find a way to get rid of the cells, the first step is to understand" where the reservoirs of latently infected cells are, Collins said.

Other reservoirs of latent HIV infection discovered previously include macrophages and memory T-cells. HAART fights active virus, while any enclave of latent virus can reactivate HIV infection if treatment is ever stopped. Finding these reservoirs and eliminating them would allow HIV/AIDS patients to stop taking the drugs once the infection was eradicated.

"I don't know how many people realize that although the drugs have reduced mortality, we still have a long way to go," Collins said. "That is mainly because we can't stop the drugs, people have to take it for a lifetime."

The study was funded in part by the National Science Foundation, the National Institutes of Health, and the University of Michigan.

The full study, "HIV-1 Infects Multipotent Progenitor Cells Causing Cell Death and Establishing Latent Cellular Reservoirs," was published in Nature Medicine (2010;doi:10.1038/nm.2109).