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 results. Comparing the molecular typing results of 238 samples (samples with available DNA) with the serological typing results, 54 homozygotes and 184 heterozygotes produced a total of 422 assignments by molecular methods. We found assignment discrepancies in 147/422 (35%) in laboratory 1 and 144/422 (34%) in laboratory 2 (a combined group of 4 NMDP laboratories; laboratory 1 is not included). The serological discrepancies found were of 3 categories: a) false negatives, b) incomplete typing (discrepancies due to the level of resolution within a cross-reactive or CREG group) and c) false positives. Major problems were identified using serology for typing HLA-A antigens: a) inability to identify all WHO-recognized specificities, more frequently in non-Caucasians or in HLA-A specificities known to be found more frequently in non-Caucasians for laboratory 1 and incorrect assignments of A19 specificities in laboratory 2, b) incorrect assignments in cells with poor viability and c) false-positive assignments in homozygotes. We propose a possible 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) molecular methods to identify splits: A23, A24, A29, A30, A31, A32, A33, A34, A36, A66, A74 and A80. The technique described is useful for large-scale bone marrow donor typings for cells with poor viability, and for resolving ambiguous results including false-positive assignments of homozygous cells.