ACCURATE TYPING OF HLA-A ANTIGENS AND ANALYSIS OF SEROLOGICAL DEFICIENCIES

We are reporting the results of HLA-A typing by PCR-SSOP complemented by PCR-SSP of samples obtained from the National Marrow Donor Program (NMDP). These samples were a representative group from 2486 tested in duplicate by serology. A total of 390 samples gave HLA-A discrepant re sults. Comparing the molecular typing results of 238 samples (samples with available DNA) with the serological typing results, 54 homozygote s and 184 heterozygotes produced a total of 422 assignments by molecul ar methods. We found assignment discrepancies in 147/422 (35%) in labo ratory 1 and 144/422 (34%) in laboratory 2 (a combined group of 4 NMDP laboratories; laboratory 1 is not included), The serological discrepa ncies found were of 3 categories: a) false negatives, b) incomplete ty ping (discrepancies due to the level of resolution within a cross-reac tive or CREG group) and c) false positives. Major problems were identi fied using serology for typing HLA-A antigens: a) inability to identif y all WHO-recognized specificities, more frequently in non-Caucasians or in HLA-A specificities known to be found more frequently in non-Cau casians for laboratory 1 and incorrect assignments of A19 specificitie s in laboratory 2, b) incorrect assignments in cells with poor viabili ty and c) false-positive assignments in homozygotes. We propose a poss ible strategy to type HLA-A specificities with two steps: a) a minimum of serology for typing specificities for common CREG groups: A1, A2, A3, A11, A9, A10, A28, A19, However, a given laboratory can determine the level of serological assignments needed as a first step. And b) mo lecular methods to identify splits: A23, A24, A29, A30. A31, A32, A33, A34, A36, A66, A74 and A80, The technique described is useful for lar ge-scale bone marrow donor typings for cells with poor viability, and for resolving ambiguous results including false-positive assignments o f homozygous cells.