(Last updated 3/26/2015; last reviewed 9/23/2014)
Once a person is infected with HIV, the virus begins to attack and destroy the CD4 cells of the immune system. CD4 cells are a type of white blood cell that play a major role in protecting the body from infection. HIV uses the machinery of the CD4 cells to multiply (make copies of itself) and spread throughout the body. This process is called the HIV life cycle.
Without treatment, HIV infection gradually destroys the immune system and advances to AIDS. HIV medicines protect the immune system by blocking HIV at different stages of the HIV life cycle.
HIV medicines are grouped into different drug classes according to how they fight HIV. Each class of drugs attacks HIV at a different stage of the HIV life cycle.
Standard HIV treatment (also called antiretroviral therapy or ART) involves taking a combination of HIV medicines from at least two different HIV drug classes every day. Because HIV medicines in different drug classes block HIV at different stages of the HIV life cycle, ART is highly effective at preventing HIV from multiplying. Having less HIV in the body protects the immune system and prevents HIV from advancing to AIDS. ART also reduces the risk of HIV drug resistance.
Drug resistance is when HIV is no longer suppressed by HIV medicines that previously prevented the virus from multiplying.
Drug resistance can develop as HIV multiplies in the body. When HIV multiplies, the virus sometimes mutates (changes form) and makes variations of itself. Variations of HIV that develop while a person is taking HIV medicines can lead to new, drug-resistant strains of HIV. The drug-resistant HIV no longer responds to the HIV medicines that used to effectively suppress a person’s strain of HIV. In other words, the person’s HIV continues to multiply.
Once drug-resistant HIV develops, it remains in the body. Drug resistance limits the number of HIV medicines available to include in an HIV regimen.
Because ART prevents HIV from multiplying at different stages of the HIV life cycle, the virus has fewer chances to mutate and produce new, drug-resistant HIV.
ART can’t cure HIV, but by blocking HIV at different stages of the HIV life cycle, ART protects the immune system. A healthier immune system helps people with HIV live longer, healthier lives. HIV medicines also reduce the risk of sexual transmission of HIV.
To understand the HIV life cycle, it helps to first imagine what HIV looks like.
Now follow HIV as it attacks a CD4 cell. The image below shows each stage of the HIV life cycle.