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Cautious optimism or reckless hope?
Experts stress that it is far too early to call the experiment a cure. For one thing, post-transplant survival in people who are battling leukemia is far from a sure thing. And as Chun points out, an immune system with CD4 cells lacking the CCR5 receptor is still susceptible to virus that uses another receptor dubbed CXCR4. If the German transplant patient has CXCR4-using virus anywhere in his body, it can potentially reseed his immune system with HIV.
Chun, who is working on techniques for eradicating HIV in the laboratory of NIAID director Anthony Fauci, MD, has good reason to be cautious. It was not long after researcher David Ho claimed in 1996 that protease inhibitors had given us the tool to eradicate HIV that we learned of the virus’ ability to hide out for years in the immune system, meaning that antiretroviral therapy, at least as we currently know it, is a lifelong proposition for most people with HIV.
Dr. Lederman, on the other hand, takes a more optimistic view. Despite the dangers and costs associated with stem cell transplants, he says it may be worthwhile to consider the procedure in people with HIV who do not otherwise require a transplant, such as for leukemia, but in whom none of the current or experimental antiretrovirals are working and who have low CD4 counts and uncontrolled virus. “I think such an approach is entirely defensible, especially in light of this experiment that we see here,” says Lederman.
When asked if he is planning additional experiments in other patients with HIV and leukemia, Dr. Hütter says while such patients are rare, he would certainly consider it.
Dr. Lederman also believes that if Dr. Hütter’s experiment continues to look successful, it could have implications for other experimental approaches that wouldn’t require the dangers of a stem cell transplant. Dr. Lederman points to technologies like gene therapy and “RNA silencing” as promising methods for artificially knocking out the delta-32 gene responsible for producing CCR5 receptors.