I didn't have Leukemia, but the treatment is basically the same. I had aplastic anemia, which basically meant that my marrow stopped working for pretty much no good reason at all.
They wipe out your old marrow with a combination of a prewar poison and horse serum, which coincidentally destroys your immune system and makes all your hair fall out. They collect the donor's stem cells with a pheresis machine (they don't actually have to go straight to the source anymore), and give it to you through your IV while you're pretty much dead and living on transfusions of red blood cells, platlets, antibiotics, saline, and electrolites, which is why you need two giant catheters.
I got about three separate infections during this process, which made the whole thing far worse than it needed to be. Then I experienced three major flare ups of GVHD, which is apparently not unusual, and thus the need for steroids, which also caused a dozen more infections. It's not a happy process but it seems to be the best we've got.
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yea, um, ****. I think you "won".