At the International AIDS Society conference in Kuala Lumpur, Malaysia, doctors reported on the case of two patients who were HIV-positive and diagnosed with lymphoma, and who, after subsequent treatments and bone marrow transplants, miraculously showed no signs of HIV infection in their systems. While doctors and experts are cautious to not call this a "cure," they are hopeful that these cases will help researchers better understand the immune system and lead to a cure in the future. The process that these two patients underwent is extremely dangerous and expensive, making it implausible for the close to 40 million people infected with HIV around the world.

This echoes a case discussed earlier this year of the "Berlin Patient," who is deemed the first person to be "functionally cured" of HIV infection. Timothy Ray Brown has been HIV-positive for years but was diagnosed with leukemia. Doctors aiming to hit two birds with one stone found a bone marrow match for him that contained a mutation in the CCR5 receptor, a protein that is on the surface of CD4 cells that enables HIV to infect the cells and eventually destroy the immune system. This mutation, called CCR5 delta32, makes a person with two forms of the gene impervious to HIV infection. After the bone marrow transplant and getting off of his HIV medication, Brown is now living virus-free, though he still has lingering health problems from his intense cancer therapy.

HIV infects immune cells, called CD4 T cells, and places its own viral genome into the genome of the person's cells. This effectively leaves a blueprint for the virus inside of every infected cell, which is able to then produce more of the virus. This is what doctors and experts refer to when they say that HIV "hides" for years. After an initial infection, a patent loses a large majority of his or her CD4 cells, but the viral levels then go down to low levels after the initial infection. Years later, in a process that is not well-understood and varies between patients, the virus can then be reactivated and cause the death of the remaining CD4 cells, leading to the immunodefiencey disease AIDS. Parents with AIDS no longer have a functional immune system and are easily infected with opportunistic infections that healthy people's immune system fights off easily. HIV medications introduced in the mid-1990s block various processes in the virus replication and infection life cycle and can allow patients to live with undetectable levels of the virus indefinitely in almost perfect health.

In the case of the two Boston patients, there are many key differences in comparison to the Berlin Patient. The patients had taken immune system suppressive drugs before their bone marrow transplants, while maintaining their anti-HIV medication regimen. Their old bone marrow was partially destroyed by drugs before the bone marrow transplant from matching donors, a risky procedure that poses a 15 to 20 percent chance of death itself.

But the most interesting thing about the Boston cases is that the patients did not receive bone marrow from donors who had the delta 32 CCD5 mutation. The patients maintained their anti-HIV medication therapy through their entire bone marrow transplant process in order to prevent any new cells from being infected by HIV. The new bone marrow cells then overtook the old ones, essentially eliminating the original bone marrow cells in the patients. Both patients had their bone marrow transplants two or five years ago, but have only recently been taken off their HIV medications. A third patient was involved in the same type of trial, but died because of a reoccurrence of the preexisting lymphoma.

Usually, when a patient is on HIV medication, the virus is not produced by cells and the levels of the virus become undetectable in the blood. When a person goes off of anti-retroviral drugs, the virus comes roaring back more powerful than ever and mutates to become resistant to the drug previously used. One of the current Boston patients stopped taking HIV medication seven weeks ago and the other one week ago with no sign of the virus in blood or tissues. The immune cells were also tested to see if they could produce the virus by being activated in laboratory conditions. The cells from both patients were seen to not produce any virus. The patients were also tested for levels of antibodies that react with HIV, and no evidence was found in blood or tissues indicating the virus is active.

But the researchers are very cautious about calling this a cure — because the follow-up period is only a matter of weeks after ceasing HIV treatment — and say that they much prefer to call it a form of remission.

The researchers following the two patients were also cautions because the virus may just take time to reassert itself. "It could come back in a week, or in six months," said Dr. Timothy Henrich, a doctor overseeing the two patients, according to the New York Times. "Only time will tell."

Eventually, by studying these patients and the reason that they apparently no longer harbor the HIV virus, scientists and doctors will better understand how to treat patients on a mass scale to eliminate the virus.

A discussion of the Boston patients begins at 14:00 in the video below.