Everybody's bone marrow has a certain type.  It's kind of like blood-typing.  Bone marrow cells have certain proteins or "antigens" on the surface of the cells.  They call these proteins Human Leukocyte Antigens (HLA).  There are six HLAs that are important when you match someone's bone marrow.  Each person receives three from their mom and three from their dad.  That is why they look at sisters and brothers first to see if anyone matches.  Since the mom can send any three of her six and the dad can send any three of his six to any given kid, it is not often that a single sibling will match his brother or sister 6 for 6.  The chances are 25%.  Since I have two brothers and one sister, I had a 58% chance that one would match.  The math is 1 - (3/4) to the nth power (where n is the number of syblings).  Unfortunately, none of mine matched.  That is why I am at the National Marrow Donor Program.  Here they have matched me to 13 potential 6/6 HLA matches.  Further studies on their blood will have to be done to see if they are indeed 6/6.  There are actually 10 antigens in all and a 10/10 match would be best, but the 6/6 is the most important.  Why is it important you ask?  Well, the HLAs are what tells the body that they belong to you.  When your immune system runs into cells that doesn't match its HLAs, it attacks and kills them.  When it runs into cells that match the immune system's HLAs, it leaves them alone.  If you transplant non-matching bone marrow into a person, when that immune system takes over and starts looking around, it will see an entire body worth of non-matching HLA and it will basically attack and kill the entire body.  This is called graph vs. host disease (GVHD).  The better the match the less GVHD a person will have.  An identical twin sister or brother provides a perfect match, a sibling provides the next best and then a stranger who has your HLA typing.  Cousins, aunts, uncles, etc. have about the same chance of matching you as the general public and that is why they are not tested, but highly encouraged to get on the National Marrow Donor Program register.  You may not be able to help the person you want to help, but there is someone out there who you could save their life.  The only exception to other relatives being tested is kids.  Since you passed 3 of 6 already to your kids, they have about a 5% chance of matching your bone marrow if your wife/husband just happened to have and pass the other 3 that you already have.  They are going to test my wife first and see if she has three of my six antigens.  If she does, then they will test my children. Was that confusing enough?  Bottom line:  You need a good match or your new immune system will reject your body and kill it.  However, a little GVHD isn't bad though.  They have found that controllable forms of GVHD actually produce a "graph vs. leukemia effect".  Since the leukemia you have running around in your body matched your HLA perfectly (otherwise your body would have killed it), a little GVHD can cause the new immune system to kill the left over leukemia cells before they get a chance to grow back.  The way they control GVHD is with steroids.  They will adjust the steroids to try and get a controllable form of GVHD.  Eventually they can taper off the steroids as your new immune system and body start to recognize each other (if you had a good enough HLA match to begin with). That is it in a nut shell.  As I learn more about what I'm about to go through, I'll pass it along.  In the meantime, please consider becoming a bone marrow donor.  I can't imagine a better gift a person could give another human being that a chance to be cured from diseases like leukemia.  All it takes is a simple blood test and you are on the register.  Click here to learn more about being a donor.

Getting the Right Bone Marrow for the Right Person