Map of life expectancy at birth from Global Education Project.

Wednesday, July 03, 2013

Cure Schmure

No doubt you have encountered the hype about a purported cure for HIV infection. That would indeed be great news, but sadly, no. Here's an example of the selective and misleading coverage this is getting.

Two men who happened to develop some form of cancer (not specified in the public story) while also being HIV+ received the treatment called "bone marrow" transplant, continued to take antiretroviral medications throughout the procedure and recovery, and now appear to be free of HIV. They seem to have turned great misfortune into good fortune, but in reality, this is a big, fat, so what?

Here's the real deal. The procedure they underwent is more properly called an allogeneic hematopoeitic stem cell transplant (HSCT). Nowadays they don't actually transplant bone marrow, but rather the cells that reside in bone marrow which are the progenitors of blood cells. Doctors do this for a few different reasons. The most common is that the person has some form of leukemia -- abnormal proliferation of white blood cells, which is a kind of cancer. In this case, if chemotherapy doesn't work, the alternative is to destroy the person's HSCs with radiation or chemicals, and replace them with cells from a donor. Other reasons are lethal abnormalities of red blood cells -- aplastic anemia, and the procedure is increasingly being done for severe sickle cell disease.

The reason this appears to cure HIV is that the virus lives in white blood cells. Replace them all, and you eliminate it. It may also lurk in other reservoirs, but if so the new immune system gets to work on a very low presence of HIV infection, and is able to wipe it out.

That's all well and good but it does not mean that everybody living with HIV should now go and get one of these procedures. Alas, the cure risks being worse than the disease, because HIV can be controlled with drugs, but allogeneic HSCT creates a risk of what is called graft vs. host disease (GVHD). The new immune system was originally somebody else's, and it is likely to recognize the recipient as foreign, whereupon it starts destroying the person's tissues and organs. This is basically incurable and causes severe symptoms and a short life. In order to prevent it, you have to take immunosuppresive drugs which means that you have -- wait for it -- immunodeficiency. Which was your problem in the first place. In spite of this, some people get GVHD anyway. (And, I should have added originally, you might die while you're waiting for your new immune system to reconstitute. In fact you have about a 25% chance of that happening. It's a desperation move, not an ordinary treatment for anything.)

So whether a feasible cure for HIV/AIDS might somehow follow from this observation is unclear, but personally I don't see it. If there is a path from here to there, it's a long one. The bad news is that lots of people will see this overhyped story and get false hope, or believe that a cure exists which is being withheld, or offered only to the wealthy. I wish the hope were real, but not yet. Keep taking your pills.

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