HLA Matching Explained

Human Leukocyte Antigens (HLA) are protein molecules found on the surface of the body’s cells. They make up a person’s tissue type and play a crucial part in the way the immune system reacts to and protects against foreign cells/substances.

For anyone who requires an allogeneic (donor) stem cell transplant, a successful outcome is largely dependent on how well the HLA antigens of the donor’s stem cells match the HLA antigens of the recipient’s stem cells[1]. Without a good match, there is an increased risk that the body will not accept the donor stem cells. A close match can also reduce the likelihood of developing the potentially fatal Graft-versus-host disease (GVHD), a condition that can occur following a transplant.

There have been numerous advances in stem cell technology in recent years and it is becoming an increasingly common alternative to bone marrow transplants for several reasons. One of these is that finding such a close HLA match is not as necessary with cord blood stem cells because they are considered more adaptable.

HLA types are inherited, so siblings can sometimes be a match for each other[2]. Every sibling with the same parent has a 1 in 4 chance (25%) of being a complete or a full match. However, finding a match even within the family is still difficult and some HLA types are rarer than others. This means that cord blood transplants can be performed in cases where the donor and the recipient are partially matched, increasing the patient’s chances of finding a suitable donor.

Other advantages of cord blood stem cells include:

  • Cord blood contains a higher volume of stem cells than bone marrow.
  • A cord blood transplant is not invasive for the donor as the stem cells have already been collected at birth.
  • Cord blood stem cells are considered ‘purer’ with better regenerating properties because they are collected from the umbilical cord and cryogenically frozen.

[1] Leukaemia and Lymphoma Society: “Cord Blood Stem Cell Transplantation Facts”

 https://www.lls.org/sites/default/files/file_assets/FS2_Cord_Blood_Transplantation_6_16FINAL.pdf

[2] National Marrow Donor Program, Be The Match: “HLA Matching”

https://bethematch.org/patients-and-families/before-transplant/find-a-donor/hla-matching/

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