Stem cells are a critical part of the human immune system. The sit beneath white cells and T-cells and usually reside in the bone marrow.

In certain types of cancers like leukemia and bone marrow cancer, the damaged stem cells must be cleaned out by chemotherapy and radiation and re[laced by healthy stem cells. Those stem cells establish themselves and go to work.

This is very tricky as small genetic variations can cause disaster. An identical twin would be the best match. Then statistics and probability take over.  Sometimes related donors but only 1 out of 4 times.

I'm donating for my older brother. He's pretty sick with an aggressive form of bone marrow cancer.    

The way this works is that you are given an injection of a drug that makes the stem cells all frolic and gets  them moving around. You take three injections over three days. Down side is that it makes you feel like you have the flu with sore joints and all over aches. 

On the fourth and fifth days they connect you to a machine and collect the stem cells for transplantation.

It's not very exciting. All I want to do is sleep. And take Tylenol. I feel like crap but it'll pass quickly after we stop taking that drug.

I just hope it works.