What makes HIV so hard to eradicate? And how close has science brought us to a cure? Everyday Einstein explores the human immunodeficiency virus.
Can We Cure HIV?
The first person was functionally cured of HIV in 2007. Known at first only as the Berlin patient, the American man later revealed himself to be Timothy Brown. In his detailed account of his experience with HIV and with his cure, Brown describes how his latent HIV eventually led to a leukemia diagnosis. During chemotherapy treatment for leukemia, his doctor, Dr. Gero Huetter, looked for stem cell donors as part of his leukemia treatment. The goal of such transplants is to replace a patient’s blood and immune system cells, cells found in bone marrow, while the existing, compromised immune system cells are wiped out by chemotherapy. Dr. Huetter decided to look for a donor who not only shared his patient’s tissue type but also had a rare genetic mutation known as CCR5 Delta 32. The CCR5 mutation is a protein that sits on the CD4 immune system cells and essentially acts as a gatekeeper, barring HIV from entering.
The Center for Disease Control reports that the number of new HIV infections in the US was declining until 2013 when that number began to level off at around 39,000 new infections per year.
While in remission from leukemia, Brown initially refused the proposed bone marrow transplant, not wanting to be a self-described “guinea pig” for stem cell research. He changed his mind when his leukemia returned and his survival from leukemia became dependent on the donor bone marrow. After first being diagnosed with HIV in 1995, Brown received the bone marrow transplant from a donor with the HIV-resistant mutation in 2007 and stopped taking his HIV medication the same day. Three months later no HIV was found in his blood.
There have been numerous similar attempts since Timothy Brown’s story that have not had the same success. Some patients died from complications related to their cancer. Others died from complications related to the transplant. Others still simply did not show the same HIV remission or showed signs of being cured of HIV only to have the virus return months or years later. Some patients have undergone the transplant but have not stopped their antiretroviral HIV treatment drugs (and so their HIV status is not known).
Twelve years later in 2019, the second person, known as the London patient, was reported to have been “functionally cured” of the virus, meaning that he is no longer taking antiretroviral therapy and has shown no signs of HIV in his blood a year later. The British man contracted HIV in 2003 and was diagnosed with Hodgkin’s Lymphoma, a type of cancer of the blood, in 2012. Like Timothy Brown, he received chemotherapy treatment and later a bone marrow transplant from a donor with the same rare genetic mutation that resists HIV infection.
Donor transplants aren’t an option for everyone living with HIV. They are expensive and risky as evidenced by what these success stories have in common: each patient was not simply looking to experiment but needed the transplant in order to survive. An exact match between donor and recipient blood or tissue type also has to be made. Some people have few matches to start with, let alone finding a match that also has the rare, HIV-resistant mutation found in only 1% of Caucasian people of northern European origin. All of these caveats add up to a very precise set of conditions that have to be met in order for an effective cure to be reached.
Both Timothy Brown and the London patient also experienced “graft-versus-host” complications. This is when donor immune cells attack the recipient’s immune cells rather than support them. It is not clear whether or not these complications assisted in the eradication of the HIV or if the transplant alone was enough.
The Center for Disease Control reports that the number of new HIV infections in the US was declining until 2013 when that number began to level off at around 39,000 new infections per year. The lack of continued decline may be due to the fact that not everyone has adequate access to HIV prevention and treatment, and others still are not aware of their HIV status. Of the estimated 37 million people living with HIV, only 59% are undergoing antiretroviral therapy: that’s up from previous years but still leaves more than an estimated 16 million people without the drugs they need to maintain their own health as well as reduce their risk of sharing the infection with others.
HIV is no longer the pandemic that it was in the 1980s but we have lost 35 million people worldwide to the virus. Researchers continue to search for a cure that is less risky and more reliable than bone marrow transplants, including developing synthetic molecules that block HIV pathogens from infecting healthy cells. But until such a cure is accessible to everyone, the intermediate goal must be to make sure everyone living with HIV has access to the treatment they need.
Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at firstname.lastname@example.org.
HIV virus image courtesy of Shutterstock.