A Stem Cell Cure for HIV?
The “Berlin Patient” Is Still HIV-Free Three Years After Stem Cell Treatment
Recently, doctors announced that the “Berlin Patient” may be the first person ever to achieve a functional cure of HIV. This has big implications for the medical world and the future of stem cell research.
There are approximately 33.3 million people in the world today living with HIV/AIDS. Now, 30 years into the epidemic, we are capable of preventing and treating infection, but until today not a single person has been cured. Neither a sterilizing cure with every particle of HIV eradicated from the body nor even a functional cure with near-complete immune system control of the virus without requiring daily, potentially toxic HIV antiretroviral treatment have been found.
Until now. Timothy Ray Brown, known only as the “Berlin Patient” prior to his interview in the German magazine STERN in December 2010, is a 44-year-old who has been living with HIV since 1995. He may be the first to have outwitted the retrovirus. His disease was well controlled through years of taking antiretroviral drug therapy until 2006 when he developed acute myeloid leukemia, or AML—a potentially fatal cancer of the immune system. Mr. Brown became the first person ever to receive a unique stem cell transplant with cells specifically chosen because they are resistant to the most commonly transmitted form of HIV infection. As part of that treatment he also was subjected to highly toxic chemotherapy, total body irradiation, and immunosuppressive drug treatment, all repeated when his AML relapsed seven months later.
AML is a life-threatening blood cancer where stem cell transplantation and its attendant risk of fatal complications is warranted in certain settings. Hematopoietic stem cells are blood-forming stem cells, which grow and divide to produce red blood cells, white blood cells, and platelets. They are found primarily in the bone marrow but also in the peripheral blood (arteries and veins). Chemotherapy used to treat AML destroys these cells in the process of treating the cancer. Stem cell transplantation is the transfusion of stem cells from the peripheral blood of another person/donor (allogeneic) or one’s self (autologous) in order to replace the eradicated cells and rebuild the damaged blood and immune system. It is a very risky procedure and many patients die while waiting for their blood and immune systems to recover.
Although 75 percent of patients requiring allogeneic stem cell transplant will find at least one appropriate donor, the ideal donor is typically a sister or brother of the patient who has inherited similar markers on the surface of their cells. These molecules alert the immune system to the presence of anything foreign in the body so blood and marrow stem cells from one person will be rejected when transplanted into another person if they don’t closely “match” each other.
HIV infects and destroys the cells of the human immune system. In order to get into these cells it must use an access site, or co-receptor, located on the cell’s surface. The most common type of co-receptor is called CCR-5. But if the access site is blocked, HIV cannot enter and infect the cell and transmission doesn’t occur. Recent research has shown that approximately 3 percent of Northern Europeans have inherited from their parents two defective proteins that make up CCR-5, called the CCR5-delta32 base pair deletion. Because they lack the co-receptors where HIV particles access their cells, these individuals are resistant to transmission of the most common form of HIV infection, though they can still become infected with rarer strains.
So the “Berlin Patient” is the extremely rare patient with coincident HIV and AML, who uniquely received HIV-resistant stem cells through two stem cell transplantations from an unrelated stranger with the CCR5-delta32 base pair deletion. In what appears to be an impossible dream to others with the disease, it has been three and a half years since Mr. Brown took his last HIV medication and yet there has been no sign of the infection in his blood, liver, colon, or brain. Perhaps most importantly his immune system has recovered to that of an uninfected individual and has been replaced by that of his donor.
Has the “Berlin Patient” been “cured” of HIV? It’s impossible to say definitively. Although doctors can’t find HIV anywhere they’ve looked, their tools are not able to measure single cells hiding and waiting to multiply and no one knows what timeframe of negative testing will satisfy “has it been long enough.” But it’s fair to say that for this one highly unusual patient. Brown’s case is exceptionally rare, and the team that developed the treatment expects to find only approximately one person each year in all of Germany who meets all of these criteria who could be eligible for it. But though this is just one very specialized case, it is still a step in the right direction. Stem cell transplantation with rarely found HIV-resistant stem cells may one day lead to the elusive “functional cure,” where antiretroviral drugs and their toxicities are no longer necessary.
Dr. Leslie Serchuck is a pediatric infectious disease HIV/AIDS specialist with a master’s degree in psychology and a master’s degree in bioethics from the University of Pennsylvania.
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