Status Update: June 14, 2012 (limb transplants via stem-cell transplant)

I heard something interesting recently.  Apparently researchers are working on limb-transplants using an autologous stem-cell transplant to avoid tissue rejection.  Take it with a grain of salt, because I've seen no verification of this, but here's how it would work in theory.

Say a soldier loses his arm in combat (and the lost limb cannot be reattached), and a recently-deceased person has left their body for medical research and/or organ donations.  Transplants like this have not been done in the past because the chance that the recipients body will reject this foreign tissue is almost 100%.  Apparently they are now working on this very scenario, but with a follow-up treatment of an autologous stem-cell transplant.  The assumption in the technique described below is that the limb transplant is done first, followed by the stem-cell transplant.

As I discussed in my transplant basics page, an autologous stem-cell transplant is when the transplant recipient is their own donor.  This is the kind of transplant I had.  The recipient receives two kinds of injections for several days and these injections do 2 things: 1) Accelerate the growth of stem cells in your bone marrow, and 2) Allow the stem-cells to release from their bone-marrow mooring and make their way into your blood-stream in their immature, stem-cell state (i.e. before they become white blood cells, red blood cells and platelets, etc.).

After about a week of these injections an Aeferesis line (aka Hickman port) is installed in your chest leading into a major vein.  Two ports reside outside the chest, for withdrawal of blood and simultaneous return of it.  Kidney dialysis patients use a system like this.  During a 4-hour visit to the Red Cross, the Aeferesis line is used, in conjunction with a centrifuge, to withdraw blood, separate out the heavier stem-cells, and return the rest.  One session may be enough to collect the necessary amount for a stem-cell transplant, although in some cases two or more sessions may be needed.  The collected stem cells are refined and processed, then frozen for use during the transplant.

The next step is to expose the patient to high-dosage chemo and radiation, in order to kill off their existing immune system.  When that's complete, the stem-cell transplant takes place.  The stem-cells are thawed at the patient's bedside and reintroduced by infusion through an IV drip.  This generally takes no more than 2-3 hours.

For cancer patients, the killing off the immune system is necessary to erradicate the existing blood or auto-immune disease (like leukemia or lymphoma).  This is not why it's done for limb transplants, though.  The old immune system would see the transplanted limb as foreign tissue and send out anti-bodies to fight it, resulting in tissue rejection.  The new immune system, however, may see the already attached new limb as not foreign - since it's been there 'all along' (from the point of view of the new immune system).

I'm not sure where they are in this research, but I'll be watching to see if there are any new updates in this new technology.  It's a very interesting, idea, though, and takes stem-cell usage up to a whole new level.