After a long game of hide and go seek, researchers may have found out where the HIV virus likes to hide when it starts losing the battle. During an active HIV infection, HIV likes to reside in T-helper cells (also called CD4+ cells), macrophages and dendritic cells. These cells eventually die off resulting in the weakened immune system that is called AIDS. In recent years, medicine has become very proficient at killing off most of the active HIV that is found circulating in peoples blood by the use of anti-retrovirals (called HAART therapy). The problem with HIV though is that the virus can go into hiding somewhere in the body so when the patient stops taking their medication, it returns to re-infect the cells of the immune system. This hide and seek routine prevents us from killing off the virus for good. If we could find out where these hiding places were, we may be able to kick the virus out in the open so we can continue our battle against it. But where are these hiding places? Using a technique that is similar to a thermal camera but for molecules, researchers may have identified where a close cousin of HIV hides in monkeys.
To start the search for HIVs hiding places researchers turned to its cousin, the SIV virus. SIV is thought to be the virus that HIV originated from. SIV infects monkeys (SIV means simian immunodeficiency virus) and is often used in research to mimic HIV. In order to find where the SIV virus was hiding in the infected monkeys, the researchers turned to a technique called a PET scan that is often used in cancer research to identify where tumors hide. PET stands for positron emissions tomography and it can help us identify structures within the body when they are highlighted by radioactive molecules. The researchers attached a radioactive marker to a newly discovered antibody that binds the SIV virus tightly (at the gp120 protein) and injected monkeys with the antibodies. The monkeys had been treated with anti-retrovirals to force the virus into hiding before injection with the antibody. The antibodies in the monkey’s blood attached to the cells infected with the hiding virus and when the researchers put the monkeys into the scanner the areas where the virus was hiding lit up (see below).
So where did the virus end up hiding? The virus appeared to be hiding in a variety of locations around the body including: the nose, lung, gut, genitals, and lymph nodes in the armpit and groin. They think it could be hiding in the brain too but the antibody was unable to reach that area. What is common to all these places of hiding? The researchers found that in each site, the virus was hiding in patches of immune cells called lymphoid tissues. These tissues act as surveillance sites for the immune system, alerting the immune systems central hubs to infections. It then makes sense that SIV, and maybe HIV, would hide here until the assault by drugs is over. The researchers hope that if they can now verify that these hiding places are in humans infected with HIV then they may be able to flush the remaining HIV out of hiding. Once this happens, the HIV virus will be vulnerable to the drugs and perhaps we will be able to rid these people of the virus.
The researchers admit they have a long way to go before they know how to flush the virus out of HIV patients. They also admit that it won’t be able to identify viruses that are completely dormant (hidden in a person’s DNA) but hope that this discovery will bring them closer to defeating this terrible disease. HIV is running out of places to hid, and with some great new research (1, 2, 3) we may soon see the downfall of a formidable foe.