An evaluation of a multicenter study on HLA-DPB1 typing using solid-phase Taq-cycle sequencing chemistry.
In HLA Class II genes, polymorphism is mainly located in the second exon. Most DNA based typing methods are confined to the identification of specific sequence motifs in the second exon. In contrast, Sequencing Based Typing (SBT) elucidates the entire exon 2 sequence for typing. Comparison of the obtained exon 2 sequence with an allele sequence library results in allele assignment. We tested the applicability of SBT using a protocol for amplification followed by solid phase Taq-cycle sequencing for HLA-DPB1 typing. A panel of 32 samples were typed by SBT at five test sites which are participating in the Sequencing Based Typing component of the 12th International Histocompatibility Workshop. The panel represents the existing polymorphism at all known polymorphic positions of exon 2, both in homozygous and heterozygous combinations. In this multicenter study we focused on the reliability of analyzing heterozygous sequences for HLA typing. A multi-sequence analysis approach, Polall, was developed to evaluate sequences obtained. The assignment of homozygosity and heterozygosity was validated by cluster analysis of chromatographic data of all sequences. Sequence characteristics were examined and considered for appropriate assignment. Differences in sequence characteristics that occurred between the test sites are considered in detail. The evaluation of data of 5 test sites reveals that Taq-cycle sequencing can reliably be performed for HLA-DPB1 SBT.