The Clinical Immunogenetics Laboratory provides the following clinical services:
- HLA typing of patients, family members, and potential related and unrelated or cord blood donors prior to allogeneic hematopoietic stem cell transplant (HSCT) under research protocols.
- Request HLA Typing at SCCA
- HLA Requisition (PDF)
- HLA Specimen Drawing and Storage Requirements (PDF)
- Chimerism Testing
- Evaluation of patient alloimmune status and antibody sensitization prior to HSCT.
- Evaluation of previous HLA typing for the SCCA Clinical Coordinator Office prior to consult appointments (includes review of CIL and outside lab typing).
- Review and advice on HLA linkage for the Unrelated Donor Program to define efficient search strategies for unrelated donor/patient workups.
- Chimerism testing of patients after HSCT (and for certain specific protocols before transplant) to determine recipient/donor origin of nucleated hematopoietic cells.
Description of HLA
HLA stands for “Human Leukocyte Antigen.” These antigens are protein molecules we inherit from our parents. Together, these molecules make up your HLA type. We currently know about more than 2500 different HLA molecules. It is very important to determine your HLA type before you have a stem cell transplant, and we can do this by taking a sample of your blood or other body tissue cells.
HLA testing will also determine the HLA type of anyone who may donate stem cells to you. It is important in stem cell transplants to see how closely the HLA type of the transplant patient matches the HLA type of the stem cell donor. The HLA “match” is the number of HLA molecules that any two people have in common for stem cell transplantation. HLA matching is usually based on 10 HLA molecules. The more molecules two people share, the better the match. When two individuals share the same HLA molecules, they are said to be a good “match.” That is, their immune systems will not see each other as “foreign” and are less likely to attack each other.
The most likely place to find an HLA match between two people is among siblings (that is, brothers and sisters who have the same mother and same father). If two siblings inherit the very same HLA molecules from both parents, they are said to be an “HLA identical match.”
You have a 25 percent (1 in 4) chance of being an HLA identical match with your sibling. Why? Because there is a basic rule in HLA inheritance: you have a 25 percent chance of inheriting the same HLA molecules as your sibling, a 25 percent chance of inheriting none of the same HLA molecules as your sibling, and a 50 percent chance of inheriting half of the same HLA molecules as your sibling.
However, two unrelated people can just happen to be a good HLA match, too. Although it is less likely, it is possible that you could have some of the same HLA molecules as someone you don’t even know.
Finding the best match
When a doctor decides that a stem cell transplant is the best treatment for a patient, the patient, all of his or her siblings, and sometimes their parents will have samples collected for HLA typing. If one of the family members is an HLA identical match, the lab will do further testing to be absolutely sure that they are the best match possible.
If none of the siblings are a good HLA match, the doctor will sometimes ask to have additional family members tested. Since your HLA type is inherited from your parents and passed on to your children, among your relatives, your parents and children have the next best chance of being closely HLA matched with you. If it happens that there are no close HLA matches within the patient’s family, an unrelated search can be initiated in order to find an unrelated volunteer donor with the same HLA molecules as the patient.
What are HLA antibodies?
HLA antibodies are proteins that may be present in the patient’s blood, which could interfere with the success of the transplant. If the stem cell donor is not an absolutely perfect match, HLA antibodies can attack the donated stem cells and may make the patient’s body reject them. The patient may also need to have transfusions of platelets during the recovery period. HLA antibodies can interfere with platelet transfusions by killing the donated platelets before they have a chance to work. That is why patients are tested for HLA antibodies before a transplant.
Some people do not develop HLA antibodies at all, while others do. It is not clearly understood why this is so, but people are most likely to develop HLA antibodies from pregnancies, prior blood or platelet transfusions, or organ transplants.
The HLA antibody level is referred to as the PRA (Panel Reactive Antibody). The PRA tells us what percentage of the general population the patient has HLA antibodies to, and can give us a good idea about how easy or difficult it will be to find a compatible platelet donor for this patient. In addition to measuring how much or how little PRA a patient has, we can also test if a patient has antibody to a particular HLA molecule. Some patients have antibody to one or two HLA molecules, while others have antibodies to many HLA molecules and therefore have a higher PRA.
HLA: Human Leukocyte Antigen, proteins we inherit from our parents, found on the surface of cells, also called histocompatibility or tissue antigens.
HLA Matching: Comparing the number of HLA molecules (antigens) two people have in common.
Haplotype: a set of HLA antigens that are inherited from each parent.
Molecular HLA typing: an HLA typing that was determined by using DNA to look at the gene that codes for the protein found on the surface of the cells.
Serologic HLA typing: an HLA typing that was determined by looking at the reactivity of the HLA molecule on the surface of the cells with known antibodies.
HLA Antibodies: proteins in the patient’s blood directed against the donor’s HLA that could attack transplanted or transfused cells.
PRA: Panel Reactive Antibody: a measure of how much HLA antibody the patient has.
Crossmatch: a laboratory test that looks for patient antibodies directed against a potential donor’s cells.
Stem Cell: cells responsible for generating red blood cells, white blood cells, and platelets.
Bone Marrow: the inner spongy portion of large bones, where most stem cells reside.
Graft versus Host Disease (GVHD): an immune attack by transplanted donor cells against the patient’s body.
Host versus Graft (HVG): an immune attack by the patient’s cells (host) against the donated (transplanted) cells (graft), can lead to the patient's rejection of the transplant.
The Science Behind HLA
Human Leukocyte Antigens (HLA) are cell surface proteins involved in immune function. Document in PDF format.
Request HLA typing
We typically receive HLA typing requests from treating physicians, for example, your primary oncologist. While we can certainly discuss HLA typing with you directly, we recommend that your physician be involved to work with us.
Upon receiving your request, our Intake department will work with your local physician to determine three things:
- What is the clinical urgency? This is based on your clinical condition.
- What is your treatment plan?
- Is searching for an alternate donor being considered if there is no family match?
After determining the items above:
- We contact you to explain the HLA typing process and collect insurance and family member information.
- We contact your insurance carrier for financial clearance and communicate financial issues to you to ensure you are aware of any financial implications from HLA typing.
- If we need to discuss altering the HLA typing strategy based on any of the information collected, our Clinical Coordinator Physician will contact your local physician and/or you.
- Our Clinical Immunogenetics Laboratory (CIL) will send instructions on how to collect and send specimens for HLA typing to your local physician.
If you want to discuss HLA Typing, feel free to contact our Intake department. The Intake department hours of operation are Monday through Friday from 8:30 am to 5:00 pm (PST) and our main phone number is (800) 804-8824 or (206) 606-1024.
Tests we offer
The primary purpose of HLA testing is to identify suitable donors for patients being considered for hematopoietic cell transplantation (HCT). List of histocompatibility tests performed (PDF).
The primary purpose of HLA testing is to identify suitable donors for patients being considered for hematopoietic cell transplantation (HCT). Potential donors can be categorized as follows:
- HLA Identical Sibling (“Genotypic Match”). The ideal donor is a healthy sibling who has inherited the same HLA determinants as the patient. The HLA genes reside on chromosome 6 within the major histocompatibility complex (MHC). Five HLA genes are defined for matching purposes (A, B, C, DRB, and DQB) and are usually inherited as a block or “haplotype.” HLA-A, B, and C are referred to as Class I genes and HLA-DRB and DQB are referred to as Class II genes. Any two full siblings have a 25% chance of inheriting the same HLA genes (genotypic match) because they have inherited the same two haplotypes from their parents.
- HLA Phenotypic Match. Because some HLA alleles are common in certain populations, there may be a family member who has the same HLA alleles as the patient, despite having inherited one different haplotype. In this case, patient and the phenotypically matched donor would have the same HLA type, but may differ for other so called minor histocompatibility antigens.
- HLA Haplotype Match. A patient’s parent or child will be a haplotype match with the patient because they will share one haplotype due to inheritance. The other unshared haplotype may, due to chance, carry one or more HLA alleles in common with the patient, but usually the unshared haplotype will carry different HLA alleles.
- HLA Matched Unrelated. An unrelated donor (URD) who has the same HLA alleles as the patient at HLA-A, B, C, DRB, and DQB. If a patient cannot find a suitable family donor, an unrelated search will attempt to identify a fully matched URD for 10 out of 10 HLA alleles.
- HLA Mismatched Unrelated. An unrelated donor who is mismatched for one, two, or even three HLA alleles.
- Unrelated Umbilical Cord Blood. Frozen umblicial cord blood (UCB) units are an alternative source of hematopoietic cells. Cord blood units are typed to the allele level at HLA-DRB and to an intermediate (antigen) level at HLA-A and B but are not typed at HLA-C and DQB.
- High Resolution/Allele Level Typing/Sequencing. The gold standard for HLA typing is high resolution molecular typing at the allele level. This test determines the exact DNA sequences at the HLA-A, B, C, DRB1, and DQB1 loci. DNA is isolated from nucleated cells (peripheral blood lymphocytes or, in some cases, buccal swabs) and the DNA within the HLA region is amplified using PCR (polymerase chain reaction) methods. This amplified DNA is then sequenced and analyzed using sophisticated software to identify the HLA alleles encoded. Allele typing is reported using four or more digits preceded by an asterisk (HLA-B*4501, for example). Depending on the HLA alleles involved, there may be ambiguous combinations of alleles. If this is the case, a second amplification and sequencing assay is required to remove the ambiguity.
- Medium Resolution Level Typing. Medium resolution molecular typing also uses DNA and PCR methods, but does not determine an exact DNA sequence at HLA-A, B, C, DRB1, and DQB1. Instead it takes a more general approach using a panel of DNA probes to identify groups of HLA alleles. Such probes are called “sequence specific oligonucleotide probes” or SSOPs. A medium resolution result is usually expressed as a number followed by a letter code (B*45CKB, for example). The letter code is translated in the body of the report (e.g. B*45CKB = B*4501/*03/*07 means that the sample could be either a B*4501, a B*4503, or a B*4507). Medium resolution typing is faster and cheaper than sequencing, and thus is used to screen potential donors. Donors who are matched with the patient by medium resolution typing can then be tested by sequencing.
- Serological Typing/Antigen Level Typing. Serology (or microcytotoxicity) is the original HLA typing method. This method requires intact viable cells (usually lymphocytes) that express HLA antigens on their cell surface. These cells are incubated with known HLA antisera and then treated with complement to create a pattern of cytotoxicity. By interpreting this pattern, the HLA antigens present on the cells can be deduced. Serological results are not preceded by an asterisk (“B45” in our example).
- Antibody Screening (“PRA”). Another traditional test, PRA (for “Panel Reactive Antibody”) is a general measure of a patient’s antibody status regarding anti-HLA antibodies (or alloantibodies). Patient sera is tested against a panel of cells expressing a diverse set of HLA antigens. A patient who has never been pregnant and has never had a transfusion or transplant should not have any circulating alloantibodies; this patient’s serum would not react against any of the cells in the panel and would have a PRA of “0%.” Patients who have undergone multiple transfusions may have many anti-HLA antibodies in their circulation –- their sera will react with many of the cells on the standard panel and so could have a high PRA (70 – 100%).
- Crossmatch Studies. Crossmatch tests are designed to identify specific alloantibodies directed against a particular donor. These donor specific antibodies may be directed against Class I molecules (detected in T or B cell crossmatches) or against Class II molecules (detected in B cell crossmatches). In addition, the alloantibodies may be further characterized as IgG or IgM in flow cytometry crossmatches.
Samples received in CIL must be accompanied with an SCCA requisition, available here. (PDF)
A. New Patient Initial Typing (No Prior Typing):
1) Patients without prior typing, their full siblings, or other potential family donors are typed in a two step process:
a) HLA-A, B, and DRB by medium resolution. If a family member is matched, then HLA-C and DQB by medium resolution and HLA-DRB1 by high resolution.
b) If no family match is found and the clinician plans to proceed with an alternate donor search, then full typing on the patient (HLA-A, B, C, and DQB by medium resolution and HLA-DRB1 by high resolution) may be requested.
B. Recommended Testing Following Review of Previous Typing (Prior Typing done by an outside laboratory)
If HLA testing if requested for a patient with prior HLA typing, test plans are determined on a case-by-case basis following a review of the existing HLA typing results and acceptability of the existing results for the treatment plan being considered at SCCA (allo transplant, URD search, etc). Usual reasons for requesting HLA typing to be done by CIL:
- To confirm reported HLA match between patient and reportedly matched family member(s)
- To complete incomplete typing of patient (for example, only HLA-A and B typing results available) to be able to predict availability of potential unrelated donors
- To confirm patient’s reported type and HLA type family members that have not yet had HLA typing completed
- To update reported HLA typing results with molecular-based typing methods
- To resolve reported discrepancies and inconsistencies with external HLA typing results.
C. Modified Typing of Patients or Family Members
For some patients, circumstances may require modification of either the Standard Typing Plan (No Prior Typing) or the Recommended Typing Plan (Prior Typing).
Examples of circumstances include (1) expedited typing needed in cases of clinical urgency, (2) unusually large immediate family available, or (3) exceptional financial considerations present. For each patient, following the collection of family information and determination of HLA typing benefits, the CCO/Transplant Coordinator will determine if modified typing is needed. If modified typing is needed, details of typing to be completed are provided to CIL.
The Clinical Immunogenetics Laboratory offers chimerism testing of patients after HSCT (and for certain specific protocols before transplant) to determine recipient/donor origin of nucleated hematopoietic cells.