Modern regenerative medicine has now advanced to the point where we can harvest stem cells from a stem cell donor. After collection from a donor, doctors isolate these cells and allow them to proliferate, before injecting them in another’s body. These stem cells can then fight off disease, heal tissue, and restore healthy states of being. For obvious reasons, this means many patients with terminal diseases are eager to find a stem cell donor.
The question is, how? What should a patient look for in a stem cell donor? What is the process like to identify potential donors? Where do the cells come from? What are the risks and benefits?
For people who are asking these questions either on their own behalf or for the sake of a loved one, information is key. The following will attempt to answer all of them, including what “typing” involves, what doctors look for when finding a donor and who is most likely to provide viable stem cells (hint: it’s always family). Lastly, this post will address what happens if physicians find a match, as well as what the patient’s options are if they do not.
Questions To Ask When Looking For A Stem Cell Donor
In this article:
- What Physicians Look for in a Stem Cell Donor Match
- Finding a Family Member Match
- Finding an Unrelated Stem Cell Donor
- Where Do Donor Stem Cells Come From?
- What Are the Risks and Benefits of Allogeneic Stem Cells?
What Physicians Look for in a Stem Cell Donor Match
Before a patient can utilize allogeneic stem cells – those that come from other people – their physicians must ensure the donor cells will provide the needed healing effects. If the donor cells are not a match for the host cells (the recipient’s body), the body will reject the allogeneic transplant. Allogeneic is a scientific term that means “from another person.” Even more seriously, the donor cells may attack the patient. Therefore, it is imperative that doctors determine the best possible donor through looking for a combination of traits.
In order to constitute a match, donor and patient must have compatible HLA typing. HLA stands for “human leukocyte antigens,” which are a type of protein marker that designates which cells belong to the body and which do not. They’re like a fingerprint on the surface of cells telling the body that these cells belong, whereas cells that do not have similar HLA markers do not.
If, therefore, the patient and potential donor do not have the required HLA compatibility, the transplant will not take. This is true for all types of donation, whether it’s a stem cell from bone marrow, adipose tissue, umbilical cord blood, or anything else.
Finding a Family Member Match
Luckily, about one-third of people in the United States have siblings who can become donors. That means they are a close enough match that they can donate blood cells, bone marrow or another tissue type.
To find a family member, physicians first perform a DNA test. This involves a simple cheek swab or blood sample. Doctors then send this off to a DNA lab, where it is tested to determine whether the sibling’s DNA is an HLA match. Note that this does not mean an exact match, because no two people have the exact same HLA markers – with the exception of identical twins. Doctors are simply looking for a close enough match that there exists a reasonable chance of compatibility between donor tissue and host.
Doctors will test HLA matches various testing sites in the DNA of the donor and patient. At least a dozen testing sites exist, including HLA-A, B, C and G, as well as DQB1, DRB1, DQA1, DPA1, DPB1, DRB3, DRB4 and DRB5. Most hospitals do not test all of them, but rather choose a certain amount. Dana Farber Boston Children’s Cancer and Blood Disorders Center, for instance, tests six. If five out of six HLA markers line up, that’s a match.
Full siblings are the most likely match because they share genetic material from the same two people, their parents. Other family members share genetic material from only one family member, or from family members further away. (For instance, a parent and child only share one genetic link, whereas siblings share two.)
However, although it is less likely, other members of the family may also be a match. Most physicians will test all immediate family to broaden the patient’s options of finding a match. If more than one match exists, they will use the available information to find the best prospect.
Finding an Unrelated Stem Cell Donor
Many times, unfortunately, no family match exists. If this is the case, physicians can widen the scope of their search to people unrelated by bloodline. There are several places doctors can check for a match:
- National stem cell donation registries: These are lists of people who are willing to donate stem cells or have already done so. Doctors can search these lists to find someone who might pose a match, then ask them to undergo further testing to determine if the match exists.
- International registries: If no match is found inside the country, physicians may find a better prospect abroad.
- Cord blood banks: These are banks of frozen cord blood, which parents have donated from their newborn babies’ umbilical cords. Because umbilical blood is so rich in stem cells, it is an excellent resource for those who need new stem cells. However, the same matching challenges do exist with cord blood, as with any other donation.
Typically, it’s not beneficial to test less closely related family members and friends, as they are unlikely to provide a match. However, as the charity Anthony Nolan points out, friends and family can help by joining registries.
Where Do Donor Stem Cells Come From?
So, where in the body do donor cells come from?
In short, many places. Donors may give blood, from which physicians will harvest hematopoietic stem cells – a type of stem cell capable of turning into all types of blood cells, including white blood cells and other specialty types. Physicians have to give donors growth factor shots to cause the blood to increase its stem cell production.
This is not necessary in the case of umbilical cord blood, which is already rich in stem cells. However, the main problem with cord blood is that there isn’t enough of it to truly benefit a full-sized adult and the cells present within it are difficult to expand outside the body (ex vivo). That’s why, as the American Cancer Society explains, cord blood is typically used for children or smaller adults.
Donors may also give marrow, which is taken from inside their bones.
What Are the Risks and Benefits of Allogeneic Stem Cells?
The main benefit of allogeneic transplants is that they come from a healthy, noninfected, non-cancerous individual. Their stem cells are free of problems, so they can create a thriving colony of new stem cells, which can in turn repair and regenerate damaged organs and other tissues. This neatly combats the problem of autologous (self-derived) stem cells in cancer patients, where their own stem cells are likely to reintroduce cancer.
The main risk is graft-versus-host disease, in which the donated cells initiate an immune response against the host. This attack can cause rashes, diarrhea, liver trouble or death. A physician can provide more information about possible risks.
Are you thinking of becoming a stem cell donor? Watch the process with this video from Héma-Québec.
While no procedure is risk-free, especially in cases involving fatal illnesses, stem cell transplants show great promise. For anyone who is suffering from a terminal disease, it is worth asking a physician whether your condition could potentially be resolved by a stem cell transplant.
Do you have more questions about looking for a stem cell donor? Share your thoughts in the comments below.