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University of Minnesota
April 22, 2013
Dr. John Wagner, who directs the University of Minnesota's Pediatric Blood and Marrow Transplant Program.
Umbilical cord blood is potential lifesaver for a young patient
Six tablespoons of blood may turn a young person with both AIDS and leukemia into a healthy long-term survivor.
The blood, from an umbilical cord, holds the best hope for wiping out both diseases. A transplant like this is risky; however, it was attempted once before with bone marrow, in Berlin several years ago, and it worked.
On Tuesday (April 23) doctors at the University of Minnesota Amplatz Children's Hospital infused the cord blood into a boy who has traveled a long distance for this new treatment. The blood contains potent stem cells that will not only destroy the leukemia but also form a new immune system.
What makes this a momentous event is that these stem cells also carry a genetic variant that confers resistance to HIV. If the transplant is successful, the boy will never need HIV treatment again.
"Cord blood banks around the world store blood collected from the placenta shortly after the birth of a child," says Dr. John Wagner, director of the University's Pediatric Blood and Marrow Transplant Program and a recognized pioneer in cord blood transplantation. "With the discovery that one percent of whites of northern European descent carry a variant form of a protein important for HIV infection of immune cells, cord blood banks are only now starting to test their inventory for this variant."
The mutation that protects against HIV works because the virus requires two footholds to get inside its target, namely immune cells called T cells. Some T cells have a protein called CD4 sticking up from their outer surfaces like an antenna. The virus grabs onto it, but it can't get inside the cell unless it can also grab a second surface protein called CCR5. HIV-resistant T cells have a mutant form of CCR5 that HIV can't grasp, and this mutation, known as CCR5d32, is what protects those who carry it.
The common form of the protein allows HIV to infect cells, but the variant form prevents infection (see sidebar).
"It was only a matter of time that we would be able to perform such a treatment for HIV," says Dr. Michael Verneris, the University physician caring for this patient. "But with fewer than 200 units tested for the HIV-resistant variant, we were very lucky to find a suitably matched cord blood unit for this patient."
"The hope today is that we will prove that HIV can be cured and that cord blood is the best way to move this forward, based on the fact that it is banked and tissue matching is less restrictive," says Wagner. "There are patients with HIV and leukemia out there today who are waiting for such a breakthrough. But for those with HIV alone, a success in this patient would compel the scientific community to find potentially safer strategies, such as genetically inducing the variant in the patients' own marrow stem cells."
A more immediate need, Wagner says, is support to increase this line of research and spur cord blood banks to type all blood units for the HIV resistance variant.
Why cord blood?
The patient came to the University because Wagner and his colleagues have performed more cord blood transplants than any other center in the world, mostly in adults and children with leukemia. Recent data have demonstrated that the highest leukemia-free survival rates are in those transplanted with mismatched cord blood because of its potent anti-leukemia effect.
Crucially, cells from cord blood are less likely to cause graft-versus-host disease, a severe condition that happens when the transplanted immune cells "reject" the new host's body. Why cord blood cells are less reactive than adult marrow is incompletely understood, but evidence suggests the cord blood cells are immunologically immature.
It's lucky that a close match is not required, because it would be virtually impossible to find blood stem cells that both were matched to the patient and carried the HIV resistance variant, Wagner says.
Rest of the team
Dr. Michael Verneris is an associate professor of pediatrics and a leukemia therapy expert. Dr. Timothy Schacker is a professor of medicine and director of the Infectious Disease Clinic.
Care for a special patient
The patient arrived at the University several weeks ago for tests. In the week before the transplant, he underwent a regimen of chemotherapy and radiation to kill his existing bone marrow and immune system.
The cord blood will be transfused into a large central vein that empties into the heart. As they circulate, the cells will find their way into the bone marrow and produce a functional immune system in about three weeks, Verneris says. During this time the patient will be closely monitored for infection.
Also, "We'll test the patient frequently to monitor the viral load—that is, the amount of virus in the blood," says University physician Dr. Timothy Schacker. "When it is undetectable in both the blood and the tissues, we will remove the patient from HIV drugs. This is really the ultimate test of a cure. We anticipate that this will happen in the next weeks to months."