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.