Completely ridding a patient of HIV is extremely difficult. The virus hides within human DNA in such a way as to become "untouchable". ART (anti-retroviral therapy) helps control the virus in the bloodstream. However, as soon as ART stops, HIV usually replicates rapidly.
The two patients had been HIV-positive for over thirty years. They had both developed Hodgkin's lymphoma, a blood cancer that requires a bone marrow transplant if chemotherapy and other treatments failed. Blood cells are made in the bone marrow - experts believe the bone marrow is a major HIV reservoir.
After undergoing the bone marrow transplants, one man has had no detectable HIV in his blood for four years, and the other for two years.
Lead researcher, Dr. Timothy Henrich warned against using the C-word (cure), saying it is still early days.
In an interview with the BBC, Henrich said:
"We have not demonstrated cure, we're going to need longer follow-up. What we can say is if the virus does stay away for a year or even two years after we stopped the treatment, that the chances of the virus rebounding are going to be extremely low."
Last year, Kuritzkes and Henrich announced that HIV was easily detected in the blood lymphocytes of the two patients before their transplants, but within eight months post- transplant the virus had become undetectable. At the time the patients were still on ART.
The two patients came off ART earlier this year. They are regularly monitored and have no detectable HIV virus. Henrich said "We demonstrated at least a 1,000 to 10,000 fold reduction in the size of the HIV reservoir in the peripheral blood of these two patients. But the virus could still be present in other tissues such as the brain or gastrointestinal track."
If the virus were to rebound, it would mean that the brain, GI tract, lymph nodes or some other sites are important reservoirs of infectious virus "(and) new approaches to measuring the reservoir at relevant sites will be needed".
Bone marrow transplant not the answer to HIV infectionBone-marrow transplant as a way of curing people infected with HIV is unlikely to ever become standard clinical practice.
In this case, the two patients had blood cancer; the transplants were performed to treat the cancer, not the HIV infection.
Most HIV-positive people do not have blood cancer. Bone marrow transplants are costly and risky - patients face a 20% risk of death. Before undergoing a transplant, the patient's immune system needs to be weakened to minimize the risk of rejection.
A third patient, who also had lymphoma and was HIV-positive and had received the same transplant as the two Boston subjects, died from cancer.
With ART, a person with HIV can enjoy the same life expectancy as other people.
Doctors "cured" baby born with HIV infectionIn March this year, doctors from Johns Hopkins Children's Center, the University of Mississippi Medical Center and the University of Massachusetts Medical School announced that an HIV-positive baby who was administered ART within 30 hours of being born had been "cured".
Deborah Persaud, M.D., explained that it is very uncommon to treat a baby for HIV-infection so soon after birth. She added that this was the first case of a functional cure in an HIV-positive infant. The medical team believes that the prompt administration of antiretroviral therapy led to the newborn's cure.
Dr. Persaud said "Prompt antiviral therapy in newborns that begins within days of exposure may help infants clear the virus and achieve long-term remission without lifelong treatment by preventing such viral hideouts from forming in the first place."
First apparent HIV-infection cure probably occurred in Germany, 2010In December 2010, researchers from Charite - University Medicine Berlin, Germany, wrote in the journal Blood than an acute myeloid leukemia patient, Timothy Brown, who was also HIV-positive had been cured of HIV infection after receiving a bone marrow transplant.
The scientists wrote "Our results strongly suggest that cure of HIV has been achieved in this patient."
In 2007 Timothy Brown stopped receiving ART, had his own immune system effectively wiped out with high-dose chemotherapy and radiation therapy, and received a bone marrow transplant.
In this case, the donor had a very rare gene mutation - CCR5-delta32 - which protected him from HIV infection, meaning that Brown acquired that protection. In July 2012, scientists in California found traces of HIV in his tissue. However, Brown says that any virus that remains in his body is completely inactive ("dead") and cannot replicate.
Written by Christian Nordqvist