Attempts to cure HIV are frustrated by the fact that the virus enters a latent, non-replicating state in certain immune cells, becoming invisible to anti-HIV meds. New research contradicts the belief that viral latency is an evolutionary accident, unessential to the HIV’s survival. Using computer modeling and other laboratory research, scientists projected that natural selection has favored strains of HIV that enter latency. HIV typically first comes into contact with mucosal tissue, which has a relatively low level of immune cells. If the virus infected and killed all of the adjacent cells, it would be less able to make its way into the body and establish a chronic infection. But if some infected cells go latent, they can get around this problem. The scientists’ research showed that HIV also has the ability to stop or start replication on its own; this shift is not caused by the infected cell.