Cord blood transplant 101

I'm sure Bonnie and Michael have been navigating the learning curve for umbilical cord blood transplants. Here are some things I learned:

- There have been about 4000 cord blood transplants in this country, the majority of which have been for children. Umbilical cord blood is collected from the umbilical cord at the time of delivery and is a rich source of hematopoietic stem cells - the cells that give rise to all of the cells in the blood as well as the immune system. A number of different blood banks around the country and the world have now established large banks of frozen cord bloods that can be used to perform stem cell transplants. There is an increasing body of positive data, initally in children, and more recently in adults.
- Adults were not early candidates for cord blood transplants because the total number of stem cells in a single cord blood collection is low (about 10-fold lower than a typical stem cell collection in an adult). Children, with smaller body weights, were better candidates for the initial studies as they did not need as many stem cells to repopulate their smaller bone marrows. The fact that Bonnie is a relatively petite adult is in her favor here.
- In the last few years, transplant centers have "pooled" the stem cells from two different umbilical cords in order to get the volume of stem cells required for heavier adults, with positive results. Pooling cord blood presents more risk of graft v. host disease but may improve engraftment. (See below to understand these concepts better).

The advantages of umbilical cord transplants are:

- an easier match. For umbilical cord blood transplants only 4 of 6 HLA markers need to match, v. 6 of 6 for unrelated bone marrow transplants from the national registry.
- less risk of graft v. host disease. This is a common and potentially serious complication of bone marrow transplants, where the newly developing immune cells "the graft" attack the patient's body as foreign "the host". Most commonly the immune cells attack the skin, the gut, and the liver and require that the patient be treated with additional immune suppressant drugs to alleviate the symptoms. This is less prevalent with cord blood transplants, as the immune cells are more "immunologically naive," meaning that they haven't been exposed to all of the immune stimuli that an adult immune system has seen and, therefore, are less reactive.
- much less risk from CMV. CMV is a common virus that most people carry (like chicken pox). While CMV doesn't cause any problems in healthy adults it can cause serious infections in patients undergoing transplants (given that their immune systems are weakened) if either the patient or the donor carry CMV (ie. are CMV+). Bonnie is CMV-negative (a nice piece of good luck for her) and the CMV virus is much less prevalent in cord blood.

The downside to umbilical cord transplants is:

- slower "engraftment". This is the process where the new stem cells grow and mature into the patient's new immune system (the old immune system is ablated by the chemotherapy and radiation given prior to the bone marrow transplant). With cord blood transplants, this process takes longer, which means the patient has a compromised immune system for a longer time, making them more susceptible to infections during the first 100 days following the transplant.

Overall, the positive news for me is that there is increasingly positive data that suggests that the results of cord blood transplants in adults (even those performed with less than perfect matches) are now comparable to the results from the more common fully matched unrelated bone marrow transplants.

Here is a good reference within the National Marrow Donor Program, for those who are ready for "Umbilical Cord Transplants: 202":

NMDP Patient Fact Sheet: Umbilical Cord Transplants