HLA Typing: Purpose, Genetics, Procedure, Interpretation

HLA (human leukocyte antigen) typing is a kind of genetic test. HLA typing is sometimes called HLA matching.

HLA typing looks at certain factors related to the immune system. The test can help figure out if a person can safely donate bone marrow, cord blood, or an organ to someone who needs a transplant.

This article will explain how HLA typing works. You will also learn about the HLA system and what it can tell you about your immune system.

Purpose of HLA Typing

The most common reason that HLA typing is used is to find out which people will be able to provide the safest tissue transplants (solid organ or hematopoietic stem cell transplantation).

All potential tissue recipients must have the typing done. Any person who might potentially want to donate tissue needs to have the test, including the relatives of a person who needs the transplant.

People can also volunteer to have their HLA type included in a bone marrow registry for stem cell transplantation. HLA typing can also be done on terminally ill or recently deceased people who are organ donors.

The best possible donors have HLAs that closely match the HLA patterns of the recipient. This makes it more likely that a transplant will be successful. A good match also lowers the risk of complications after transplant, such as organ rejection.

Some people also need to have a component of HLA typing performed after the transplant to see if their body is making antibodies to the transplanted tissue. This can be a sign of organ rejection and means the transplant might not be a success.

Conditions That Require Transplants

There are many health conditions that are treated with transplantation. There are different types of transplants that can be used.

• Stem cell transplants: Some types of blood cancer and genetic blood disorders are treated with stem cell transplants from bone marrow or peripheral blood. For example, sickle cell disease can be cured through stem cell transplants.
• Solid-organ transplants: A solid organ transplant might be needed if an essential organ has become severely damaged. Trauma, infection, autoimmune disease, genetic illnesses, toxins, and other causes can lead a person to need an organ transplant. For example, a person might need a kidney, liver, or lung transplant if their own organs do not work anymore. A person may die if they cannot get an organ transplant.

What Is the HLA System?

The HLA system is a group of genes that play an important role in the immune system. Together, the proteins these genes make form the major histocompatibility complex (MHC).

The proteins are attached to almost all of the cells of your body. Red blood cells are the only cells the proteins are not found on.

There are many possible variations in these attached proteins that other cells in your body can look for. These variations help your body tell which cells are yours and which do not.

The Process of HLA Typing

HLA typing looks at the HLA genes that you have inherited. It might help to think about them as colored strings.

There are a number of different HLA genes and different variations of these genes. That means there are many possible color combinations. Together, the variations make up your specific HLA type.

Antibody Testing

HLA typing also tests for antibodies that are targeted to specific HLA proteins. Antibodies are made by the immune system.

If a person already has an antibody against an HLA protein, it means that it's already primed to attack a certain color string. That also means that it may attack that protein if it is transplanted, which could cause the transplant to fail.

Generally, you should not receive a transplant from someone if you already have an antibody against one of their HLA proteins.

Lymphocyte Crossmatching

HLA typing can also include lymphocyte crossmatching. Lymphocytes are a type of immune cell. Lymphocyte crossmatching checks to see if the recipient has an antibody against a protein on the donor’s lymphocytes.

If so, that person generally should not receive a transplant from that person, as there is a high risk that the transplant won't work.

Is HLA Typing the Same as Blood Typing?

HLA is much more complicated than blood typing because there are many more HLA markers that make a person’s cells unique.

There are only 8 basic blood types. Many people can safely receive more than one type of blood, depending on their type.

To receive only blood from a person, you do not need to be an HLA match because HLA is not present on red blood cells.

However, to receive a solid organ transplant, the recipient must have a blood type that works with the donor's type (compatible). They also need to have the best HLA match possible.

For stem cell donations, a person needs a very strong HLA match. A person's blood type is not as important for stem cell donation as it is for solid organ transplants.

How Are HLA Genes Inherited?

HLA genes are located close together on your DNA. That means they are usually inherited as a group. In other words, you get a whole set of colors not just one color at a time.

Your HLA type is made up of the set of HLA genes that you inherited from your mother and the HLA genes that you inherited from your father. The HLA genes contain information about the "color of the strings" that your cells will have.

Biological parents always share half of their HLA proteins with their children. This is also called a “half match.” On the other hand, a child is always a half match with their parents. That means a child would share half of the colors on their cells with each of their parents.

Siblings who have the same parents are most likely to be an identical HLA match. These siblings have a 1 in 4 chance of being a perfect HLA match. That means they have perfectly matching colored strings.

There is also about a 1 in 2 chance that siblings will share half of the HLA markers and be a half-match.

Since siblings only have a 1 in 4 chance of being HLA identical, it's not uncommon for people to not have anyone in their family that is a close match.

For a solid organ transplant that can be given by living donors, it can be worth getting HLA typing for other members of the family, such as uncles and aunts. This increases the chances of finding a good match.

Stem cell donations require a higher percentage of HLA matches, which means that it is less likely that a suitable match will be found by testing more family members.

Ethnicity

Groups of HLA “colors” are common in certain ethnic groups. Even if someone in your family isn’t a good match, it's likely that someone from a shared genetic heritage will be a match for you.

Still, it's harder for some people to find a good HLA match than others. For example, bone marrow registries have fewer potential donors of African American descent. That means it's less likely that people of this ethnic background will be able to find a good HLA match from a non-relative.

How Is the Test Done?

For the HLA typing test, you’ll need to give a tissue sample. Usually, the sample is taken with a swab that goes on the inside of your cheek or from a blood sample drawn from a vein in your arm.

You don't need to do any preparation for the test. Once your sample is taken, it's sent to a special lab to be looked at.

Since HLA typing is not a common test, you may want to check with your insurance carrier before you have it done to find out how much of the cost they will cover.

Interpreting Results

The results from HLA typing are not likely to mean much to you on their own. It can be hard to make sense of them because the HLA proteins have very technical names.

However, your healthcare provider may talk to you about how your HLA type compares to that of a potential donor.

For example, if your sibling needs a stem cell transplant, the test can tell you if the two of you are identically HLA matched. This information will help determine if you could donate stems cells to them.

How Many HLA Matches Do You Need?

Ideally, the donor and recipient would be perfectly HLA matched. However, this is not always possible. It depends on the specific type of transplant and on other medical circumstances.

Stem cell transplantation is often more challenging than solid organ transplantation in terms of the importance of a good HLA match.

In both procedures, there is a risk that the cells of transplant recipients may attack the donated tissue.

However, in a stem cell transplant, there is also a chance that some of the donated cells may attack the cells of the transplant recipient. This is known as graft-versus-host disease.

For this reason, people receiving stem cell donations usually need to have a higher percentage of matches than people receiving a solid organ.

For example, 10 years after a kidney transplant, you are more likely to still have a functioning kidney if you received a kidney with a full HLA match than if you received only a half HLA match.

Different healthcare providers and medical institutions may have different guidelines about the number of HLA matches needed to go ahead with a transplant. But in certain situations, you might still be able to have a transplant with a smaller number of matches.

Your healthcare provider will work with you to find the best treatment option if you haven’t yet found a good transplant match.

In some cases, you may want to go ahead with a transplant that isn’t a very good match. In other cases, you may want to receive other treatments while you wait for a better match to potentially become available. It’s challenging to wait, but sometimes that is the best option.

HLA Typing and Tissue Registries

Information about your HLA type is included in databases that link potential donors to recipients.

For example, the United Network of Organ Sharing determines who gets organs from deceased donors in the United States. It uses information about donors’ and recipients’ HLA types to calculate the best matches for these organs. It is one of many factors that determine who receives them.

Similarly, people are encouraged to volunteer to have HLA typing done and have that information added to a registry of potential bone marrow donors.

The information on donors is stored in a database. If an HLA match to a person needing bone marrow is found, that person is contacted to see if they can donate.

Summary

HLA (human leukocyte antigen) typing is used to figure out who will be a good match for a person who needs a transplant.

People who need stem cells or solid organs for a transplant do better when they "match up" in certain ways with donors. One way is their HLA type, which looks at genes and proteins in the immune system.

HLA typing can also be used after a transplant has been done to check if the person's body is rejecting the organ. This can be a sign that the transplant has failed.

A Word From Verywell

If you are learning about HLA typing because you or a loved one needs a transplant, you might feel overwhelmed by all the information. It's important to ask your healthcare provider questions to make sure that you understand how the testing works.

HLA typing is an important step for people who need transplants. Finding a good match gives them the best chance of a successful transplant.