A Stem Cell transplant is like spraying Round Up on your yard that kills everything, then you plant seed and wait for new growth. Likewise the chemo is a deadly, short acting drug that kills everything in the blood. Then they reinsert the pre harvested Stem Cells (the seed), that regenerates all the blood cells. The process is called rebirth, because for a short moment in time you die and are reborn. The first few days are critical as you wait to see if the Stem Cells engraft, sometimes they don't. During that time transfusions keep you alive, but without the ability to regenerate you don't last long. Emory Windship Cancer Center, had two whole floors of transplant patients, DW was resilient and recovered quickly, but there were many who had serious problems with the recovery and some who didn't make it. Despite being a very sterile environment, infections were always a threat, as the patients lose all their immunities. It took almost a year for DW to recover, during which time she had to retake all immunizations from childhood on. Her immune system will never fully recover, but with care she can survive.
The downside was the procedure was supposed to give her 5 yrs cancer free, she relapsed before the 2nd year was up. Luckily new treatments keep evolving that keep it suppressed, when one quits, a new one becomes available. When Multiple Myeloma was first discovered in 2009, she was at stage IV and given 24 months at the most. Doctors didn't realize she was the original "Ever Ready Bunny", she just keeps on going.
