Why it's so hard to cure HIV/AIDS

This animation, created in collaboration with TED Ed, provides an introduction on HIV and AIDS and antiretroviral therapy, and provides a brief explanation of why HIV has been so difficult to cure.

Check out the animation on the TED Ed site.

HIV 101

Approximately 35 million people in the world  are currently infected with HIV/AIDS, including over 3 million children. Each year, an additional 2 million people are newly infected with the virus.  In the United States, over 1 million people are HIV-infected, and it is estimated that one in six are not aware that they are carrying HIV.

HIV infection can occur when an HIV virus reaches the mucosal membranes or the bloodstream of an individual. The virus is able to recognize and infect certain types of immune cells, particularly targeting cells known as helper T cells, or CD4+ T cells.  Helper T cells play a crucial role in defending the body against bacterial and fungal infections.

During the first stage of HIV infection, called the acute infection stage, large amounts of virus are produced in helper T cells, destroying many of these cells in the process.

People often report having flu-like symptoms, such as fever, sore throat, and body aches, in addition to a skin rash during this early stage of infection.  Eventually, levels of the virus and helper T cells stabilize, and the infected individual experiences fewer symptoms.

Within a few months after the initial infection, viral loads are generally low and can remain at low levels for years, even without treatment.

Over time, however, the amount of virus increases, and the levels of helper T cells decrease. When the T cell count drops low enough, individuals are much more prone to opportunistic infection. This stage of HIV infection is known as AIDS.

Helper T cells play a critical role in our immune systems, helping us fend off infections from bacteria and fungi.  They are also the host cell for HIV, and the loss of these important cells can lead to AIDS.

The small green dot to the left of the T cell is a HIV particle, shown to scale.

Antiretroviral therapy and the search for a cure

Management of HIV/AIDS is achieved using combinations of antiretroviral drugs. There are numerous classes of drugs that target different aspects of the HIV life cycle, and therapy always involves taking two or more classes of drugs in combination.

The most commonly prescribed drugs include those that prevent the viral genome from being copied and incorporated into the cell’s DNA. Other drugs prevent the virus from maturing, or block viral fusion, causing HIV to be unable to infect new cells in the body.

Antiretroviral therapy is highly effective at managing the levels of HIV. Continued use has been shown to keep HIV-infected individuals from ever progressing to AIDS, and can lower the viral count to nearly undetectable levels. With antiretroviral therapy, most people can expect to live long and healthy lives.

Unfortunately, antiretroviral therapy is not a cure for HIV. This is due to HIV’s ability to hide its instructions inside of cells where drugs cannot reach it.

During the HIV life cycle, HIV incorporates itself into its host cell’s DNA. Antiretroviral therapies can stop new viruses that might be produced from infecting new cells, but can’t eliminate the viral DNA from the host cell’s genome.

Most host cells will be killed by infection or will eventually die of old age, but a very small number of cells appear to live for a very long time in the body. Every so often, the viral DNA can get turned on, and the cell starts to produce new virus. This is why medication adherence is critical. Stopping medication, even for a short time, might result in new cells being infected with HIV.

Researchers are working hard to find a true cure for HIV that could completely eradicate the virus from an infected person.  Current directions include finding a means to activate cells that are harboring viral DNA, forcing them “out into the open” where they can then be targeted by antiretroviral drugs.  Researchers are also looking into ways of using genetic tools to delete viral DNA from the cell’s DNA.

Some antiretroviral drugs block HIV from entering new cells.