Histocompatability

Histocompatibility testing involves the identification of HLA antigens/alleles (tissue typing), HLA antibody screening and identification, and flow cytometry based crossmatching. The vast majority of histocompatibility testing is performed in the setting of solid organ and hematopoietic stem cell transplantation.

HLA antigens/alleles are identified by molecular testing methods. The results of this testing contribute to the selection of a suitable (compatible) donor for a patient in need of a transplant. HLA matching at the allele (high resolution) level is especially critical to the success of hematopoietic stem cell transplants and is needed to reduce the risk of graft vs. host disease. Alternative uses of HLA antigen/allele identification include disease association (eg. HLA-B27 in ankylosing spondylitis and HLA-DQB2 or HLA DQB8 in celiac disease) and pharmacogenomics (eg. risk factor for untoward drug reaction with Abacavir in HIV patients who are positive for HLA-B*57:01).

HLA class I and II antibodies may develop in patients with a history of previous transplantation, pregnancy, or blood transfusions and complicate the search for a compatible donor. Screening and identification of HLA antibodies is performed using Luminex single antigen (LSA) beads and facilitates virtual crossmatching where HLA antibodies identified in the patient are compared to mismatched HLA antigens in the donor to determine if a potential incompatibility (antibody antigen interaction) exists and thus help select a compatible donor. HLA antibody identification performed post-transplant aids in the detection of donor specific antibodies (DSA) that are a risk factor for antibody mediated rejection. HLA class I antibody screening and identification is also useful in platelet refractory patients where HLA antibodies may be responsible for destroying donor platelets. Knowledge of the antibody specificity in this setting may facilitate the selection of compatible donor platelets.
           
Flow cytometry crossmatching utilizes recipient serum mixed with donor T and B lymphocytes and is performed in the setting of solid organ transplantation to reduce the risk of hyperacute rejection caused by preformed donor specific HLA antibodies in the recipient directed against donor HLA antigens. This test is performed prior to transplantation in all kidney and pancreas transplant patients and upon physician request in heart and lung transplant patients when the recipient has HLA antibodies (sensitized) and there is significant concern for hyperacute rejection.
           
The Histocompatibility Laboratory has three ASHI approved Pathologist Directors and include Dr. Jennings, Dr. Lower, and Dr. Lutz, who rotate responsibilities for case review and sign out.

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