- The human immunodeficiency virus (HIV) causes acquired immune deficiency syndrome (AIDS). Combination antiretroviral therapy (ART) drugs treat HIV infection. They generally decrease the amount of HIV virus in the blood (called viral load) to very low levels. This happens only if the drugs still fight HIV and if taken every day exactly as prescribed. When not taken as directed, or if the ART drugs are not strong enough, the virus can become resistant to them, and the ART will not work to control the virus. Researchers want to know how to control HIV in people who can t lower their viral load with their current ART drugs.