– The HLA system affects stem cell donation by influencing the compatibility and outcome of the transplant.

– HLA stands for human leukocyte antigen, and it is a group of proteins that are expressed on the surface of most cells in the body. The immune system uses these proteins to recognize which cells belong to the body and which ones are foreign.

– HLA typing is a genetic test that compares the HLA types of the donor and the recipient, to find the best match and reduce the risk of rejection. HLA typing is usually done for both solid organ transplants, such as kidney, liver, heart, or lung transplants, and stem cell transplants, such as bone marrow or cord blood transplants. However, the degree of matching required may vary depending on the type of transplant.

– Stem cell transplants usually require a higher degree of matching than solid organ transplants, because the stem cells can cause a severe immune reaction called graft-versus-host disease if they are not compatible with the recipient.

– GVHD is a condition where the donor's immune cells attack the recipient's tissues, causing inflammation and damage. A close match between the donor's and the recipient's HLA types is essential for a successful transplant outcome. HLA matching promotes the growth and development of new healthy blood cell and reduces the risk of GVHD and other complications. The more HLA types they have in common, the better the match.

– HLA matching is usually based on six HLA types:

• HLA-A.

• HLA-B.

• HLA-C.

• HLA-DR

• HLA-DQ

• HLA-DP.

– However, some transplants may require more detailed HLA typing, such as high-resolution typing or allele-level typing, which can identify more specific variants of the HLA types.

– The HLA system is highly diverse, and there are many different variants of the HLA types in the population. This diversity helps the immune system to fight against a wide range of pathogens and foreign substances, but it also makes it harder to find a matching donor for a stem cell transplant.

– Some HLA types are more common than others, and some HLA types are more common in certain racial and ethnic groups. Therefore, some patients may face a greater challenge in finding a matching donor, especially if they belong to a minority group or have a rare HLA type.

How does HLA system affect blood transfusion?

– The HLA system affects blood transfusion by influencing the compatibility and outcome of the transfusion.

– HLA typing is especially important for platelet transfusions, as platelets express HLA class I molecules and can induce the production of HLA antibodies in the recipient. HLA antibodies can cause platelet refractoriness, which is the failure of platelet transfusions to increase the platelet count or stop bleeding.

– HLA antibodies can also cause transfusion-related acute lung injury (TRALI), which is a serious and potentially fatal complication of blood transfusion that involves respiratory distress and lung damage. Therefore, HLA-matched or HLA-compatible platelets are preferred for patients who need repeated or long-term platelet transfusions, such as those with hematological malignancies, aplastic anemia, or bone marrow failure.

– HLA typing is less critical for red blood cell (RBC) transfusions, as RBCs do not express HLA molecules and are mainly matched by the ABO and Rh blood group systems.

– However, some patients may develop HLA antibodies after exposure to HLA antigens from other sources, such as pregnancy, organ transplantation, or previous blood transfusions. These HLA antibodies can cause hemolytic transfusion reactions, which are rare but serious complications of blood transfusion that involve the destruction of the transfused RBCs by the recipient's immune system.

– Therefore, HLA-matched or HLA-compatible RBCs may be required for patients who have HLA antibodies or who are at risk of developing them, such as those with sickle cell disease, thalassemia, or autoimmune hemolytic anemia.

Can I change my HLA type? Can I have more than 1 types of HLA?

– No, you cannot change your HLA type.

– Your HLA type is determined by the genes you inherit from your parents, and it remains the same throughout your life. You can have more than one type of HLA, depending on how many different alleles you have for each gene. For example, you can have two different types of HLA-A, two different types of HLA-B, and two different types of HLA-DR, making a total of six types of HLA.

How is HLA typing done for organ transplantation?

HLA typing for organ transplantation is a genetic test that compares the HLA types of the donor and the recipient, to find the best match and reduce the risk of rejection. HLA typing is done by taking a blood sample from both the donor and the recipient, and analyzing the DNA for the presence of certain HLA alleles. The more HLA alleles they have in common, the better the match.

– HLA typing is usually done for both solid organ transplants, such as kidney, liver, heart, or lung transplants, and stem cell transplants, such as bone marrow or cord blood transplants. However, the degree of matching required may vary depending on the type of transplant. For example, stem cell transplants usually require a higher degree of matching than solid organ transplants, because the stem cells can cause a severe immune reaction called graft-versus-host disease (GVHD) if they are not compatible with the recipient.