Apparently, there are some rare people who have the ability to cure themselves of HIV infections.

There have been two instances where people infected with HIV have had levels of the virus in their bodies drop to undetectable levels after bone marrow transplants. It appears that these individuals may have cleared functional HIV with no outside help. If this were true, it would be the first known instance of a spontaneous cure.

Analysis done with an estimated 1.5 billion cells taken from a patient known as EC2 showed no functional HIV copies in any of them, researchers noted on August 26 in Nature. However, the person still had some nonfunctional copies of the virus, although nobody can say for sure that intact virus isn’t hidden in a cell somewhere in this person’s body, the studies suggest that some people’s immune systems can get the upper hand, pretty much destroying the persistent virus.

Another patient, EC1, had just one functional copy of HIV in more than 1 billion blood cells upon analysis. The copy of HIV was stuck in what was essentially a genetic supermax prison. This genetic lockup may be pivotal to being able to naturally eliminate the virus.

Those two individuals are just part of a rare group of people called elite controllers, meaning they are able to keep very low or undetectable levels of HIV without antiretroviral drugs. These people are not symptomatic or exhibit any clear signs of damage from the virus. “It’s not even that we’re talking about a few months or a few years. It’s extremely long-term,” says Satya Dandekar, an HIV researcher at the University of California, Davis School of Medicine who was not involved in the study. That being said, 99.5 percent or more of the world’s 35 million people infected with the virus combat it with drugs to keep the virus down.