HLA-testing and laboratory medicine

Histocompatibility typing page 495 Overview of HLA typing 496 Suggestions for typing for bone marrow and stem cell transplantation 497 Studies for chimerism 507 Cytogenetic terminology 508 Detection of minimal residual malignant disease (MRD) 509 Further reading 510 Histocompatibility typing HLA-matching or compatibility is the major condition for standard allogeneic transplantation. HLA-testing is generally done on peripheral blood leukocytes or lymphocytes. By definition HLA-matching implies identity at class I and II loci. Recently, most transplant centers switched from serologic testing to molecular testing, which offers a higher degree of definition for unrelated transplants. There are four possible scenarios for allogeneic transplantation. Overview of HLA typing Typing involves identifying given polymorphic proteins (known as human leukocyte antigens) expressed on most or all nucleated cells and are intimately involved in the functioning of the immune system. The proteins are separated into two classes based on their structure and function in the immune system; however, their function is beyond the scope of this review (see also Chapter 1). Class I molecules consist of a single 45-kDa polypeptide and are encoded by three loci (A, B, C) found on chromosome six in a region known as the major histocompatibility complex (MHC). Class II molecules are composed of a dimer of an alpha chain and beta chain, also encoded in the MHC region. The alpha and beta chains are encoded separately, and historically it is the beta chain that is polymorphic and can therefore be viewed by the immune system as “non-self” (Though newer research suggests that this may not be entirely the case).