Histocompatibility Testing

The MHC genes are mapped within a region called HLA (human leukocyte antigen system A) located on the short arm of chromosome 6. Disparity at major loci requires vigorous immunologic intervention to avoid rejection or, should engraft-ment occur, subsequent graft versus host disease (GVHD).

The class I molecules are composed of an a-chain and P2-microglobulin, are highly polymorphic, and are expressed on most nucleated cells and on platelets. The HLA class II loci are also highly polymorphic and are involved in exogenous antigen processing. The HLA class II antigens are heterodimeric cell surface molecules formed by the a- and P-chains, each of which is polymorphic. HLA terminology is designated by the World Health Organization (WHO) nomenclature committee for factors of the HLA system and is updated at regular intervals. The broadest designation is on serologic typing, and the highest resolution is based on actual DNA sequence.

Typing of HLA class II alleles can be determined using nucleotide sequence polymorphism. The following different techniques have been used for identification of class I and II polymorphism for determination of bone marrow donor and recipient selection by:

• Sequence-specific oligonucleotide probe (SSOP)

• Sequence specific primer (SSP).

Medical evaluation of bone marrow donors includes:

• Physical examination

• Complete blood count

• Biochemistry profile

• Cytomegalovirus (CMV) antibody, Epstein-Barr virus (EBV) profile, herpes antibody titers, Human T-Lymphotropic Viruses antibody (HTLV)

• Human immunodeficiency virus (HIV) profile

• Hepatitis screen.

Further evaluation is required in 2-20% of donor candidates.

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