HIV (Human Immunodeficiency Virus) was first identified in the late 50s / early 60s in humans. HIV is a very unique virus as the incubation time is around 8 years and the disease resulting from a sustained infection isn’t actually what kills you. This complex and unique disease took years to develop effective treatment for, and back in the 60s, 70s, 80s, and much of the 90s, it was considered a death sentence; people would fall sick around 8 years after diagnosis, and then die within 2 years after that. Nowadays, there is a cocktail of drugs that can be used to treat HIV called HAART (highly active anti-retroviral therapy), which can allow those infected with HIV to live to within 2 years of their normal life span – an amazing feat of science. Development of drug treatment for HIV is considered one of the greatest feats of molecular medicine having had millions of pounds funnelled into it’s research, which then begs the question, why haven’t we cured it?
To tackle this question, we need to look at the pathogenesis (how the infection leads to disease) of the virus itself. HIV is an infection of a group of white blood cells that make up part of your immune system called T helper cells, which have the really important role of triggering your bodies protective responses when it encounters a dangerous pathogen. HIV can attach to and enter these cells using a couple of receptors found on the outside of the cell; CD4 is the name of the main receptor that the virus will initially grab onto, but once it had a hold on this receptor, it will also grab onto another receptor called CCR5. Once the virus has a hold on both of these receptors found on your T helper cells, only then can it can then invade the cells and cause the damage.
The CCR5 receptor, found on these important cells in your body, has a set structure depending on part of your DNA code, so if that code changes, so will the structure of that receptor. In fact, around 5% of people in the world don’t have a normal code for CCR5, and therefore don’t have the normal structure of the receptor. This means that if a HIV virus particle came across one of these cells, grabbed onto the CD4 receptor, and then tried to grab onto the CCR5 receptor, it wouldn’t be able to, and therefore it wouldn’t be able to get inside the T helper cells and cause any damage. Effectively, these 5% of people are immune to HIV.
These T helper cells are created by part of your body called your bone marrow. The cells in the bone marrow will all be the same, until each cell gets a set of instructions from your body; some of these cells will be told to become T helper cells (with its receptors that HIV uses to get inside), and will be released to protect your body from infections.
Although this all seems a bit confusing at the moment, hang in there. It’s all about to make sense.
Timothy Ray Brown was a man who suffered from a HIV infection, but also suffered from leukaemia, a cancer of the blood cells, and so he needed a bone marrow transplant. After he received his bone marrow transplant, his doctors found that it had in fact cured his HIV infection. But why did this happen?
As it turns out, the person who he received the bone marrow transplant from, was part of that 5% of the population that was immune to HIV. This meant he had the CCR5 receptor in the form where the structure was altered, and HIV particles couldn’t grab onto it and infect the T helper cells. As these cells are made in the bone marrow, once Timothy had received the bone marrow from the immune donor, it started making these T helper immune cells that were immune to HIV in Timothy’s body, meaning he was essentially cured of the HIV infection he had.
Therefore, in practice, you can actually cure HIV, but with over 3.7 million people across the world living with HIV, it would not be physically and logistically possible to give all of these people bone marrow transplants. The good news is, as mentioned earlier, that HIV diagnosis is no longer an immediate death sentence, and those living with the disease can live long, happy lives thanks to the breakthroughs in drug treatment.
Thanks for reading.
The World of Infectious Diseases 