Finding a Match – Knowing the Difference between Related and Non-related Stem Cells

Stem cells have been used in transplant medicine with much success for the last 40 years. Since 1988, stem cells from umbilical cord blood have played a critical role in that success. Growing numbers of expectant parents are donating children’s cord blood or enrolling in family banking, based on the profound potential in cord blood stem cells.

In the event those stem cells are needed for allogeneic transplant, a successful outcome is largely dependent on finding a compatible match from a donor who can be related, like a sibling, or of no relation at all. When a patient is in need the determination of who the donor will be is based on tissue matching. Understanding the basics of tissue matching is key to making an informed decision about what to do with your baby’s cord blood.

What is HLA Matching
Your immune system uses human leukocyte antigen (HLA) markers to recognize which cells belong to your body and which do not. HLA markers are used to match patients and donors for stem cell transplants. A blood test known as “tissue typing” is used to find suitable matches.

Finding the Best Match
The best possible HLA match occurs when the donor and recipient have a six out of six match (6:6) match, because the recipient’s body is much more likely to accept the transplant. 1 A close match between recipient and donor reduces the risk that the patient’s cells will attack the donor’s cells, and vice versa, after the transplant.

The chance of finding a match is dependent on what your transplant physician will accept as a match, for the given clinical situation. When using cord blood, 6:6 is best, 5:6 is good, 4:6 acceptable and 3:6 is unlikely, but possible. In general, a 4:6 match is only used when there’s no better alternative.

Related Matches
Because these HLA markers are inherited, passed down from parents to child, a sibling is the first place to look for a match. In those cases where a child can use his/her own stem cells for treatment, it is a perfect HLA match and the risk of rejection is eliminated.

By storing cord blood from each child at a family bank, parents can increase the chance of finding the best source for a match. The likelihood that a baby’s cord blood will be a match for siblings ranges from 25 to 75 percent, depending upon the acceptable match criteria determined by a doctor. One reason why transplants from family members are about twice as successful as those received from a non-related donor 2  is because of the lower possibility that the transplant will be rejected.

You can hear directly from ViaCord families who have shared their personal stories of triumph when using related matches for transplant on our website.mismatched3_iStock_000004611901XSmall

Non-related Matches
If you don’t have access to a suitably related match, your physician will search the national donor registry. The national donor registry plays a crucial role in saving thousands of lives each year. When accessing the public registry, your best chance of finding a suitable donor is likely from someone of a similar racial or ethnic background, because HLA types are inherited.

You may have read or heard the estimate that patients have about a 90 percent chance of finding a cord blood donor from a public bank. As compelling as that number sounds, one should not conclude that access to the best match is guaranteed. Unfortunately, it’s just not that simple as reality paints a much different, more complex picture for many families in need.

The estimate relies on two material assumptions:

  1. the use of the least optimal match (4:6) not the best (6:6); and
  2. the patient is Caucasian

In fact it would take a fivefold increase over the currently available cord blood inventory to locate a perfect 6 out of 6 match for most Caucasians. 3 Because the best non-related matches occur among people who have similar ethnic backgrounds, multiracial families, a fast-growing segment of the nation’s population, have even greater difficulty in finding a suitable donor when the need arises.

You’re Officially in the Know
When it comes to knowing the difference between related and non-related stem cells, these three points are key:

  1. Related donors are generally the preferred donor source for allogeneic transplantation
  2. There is an important distinction to be made between the best possible match and the least optimal one.
  3. The public banking system is a valuable resource, but there is no guarantee that your family will be able to find a match, let alone the best match.

A successful stem cell transplant outcome is dependent upon many factors – including disease type, response to prior therapy, patient age, and more – but most importantly the availability of the best possible donor.

As you consider whether you will save your newborn’s cord blood with a family bank, make sure to speak with your OB/GYN about your options for storing cord blood.

Other posts you might like:

1. Be The Match, National Marrow Donor Program HLA Matching; Finding the Best Donor or Cord Blood Unit http://www.marrow.org/PATIENT/Donor_Select_Tx_Process/The_Search_Process/HLA_Matching_Finding_the_Best_/index.html
2. Gluckman, et al., New England Journal of Medicine 1997, pp. 373-381
3. Beatty et al, Human Immunology 2000, Probability of Finding HLA-mismatched Related or Unrelated Marrow or Cord Blood Donors, pgs 834-840

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