HLA CLASS-I SEQUENCE-BASED TYPING

HLA oligogenotyping has been used successfully to characterize most phenotypically undetectable variants of class II genes. Limitations inherent to the class I system have, however, complicated the application of this and other molecular approaches to HLA class I typing. We have previously shown that HLA class II polymorphism can be analyzed by a SBT approach. Here we present a class I-SBT strategy that provides complete sequence information for the two most polymorphic exons of the HLA-A, -B, and -C alleles. HLA class I SBT is based on direct sequencing of PCR-amplified HLA-A, -B, and -C cDNAs and requires a total of six cDNA -PCR- sequencing reactions (two per locus) and 13 different oligonucleotides. Each combination of oligonucleotides per reaction results in locus-specific sequence ladders and allows identification of both alleles in heterozygotes. Application of HLA-A, HLA-B, and HLA-C SBT to 26 homozygous and 32 serologically heterozygous samples has resulted in the identification of 24 novel class I nucleotide sequences encoding 17 new major histocompatibility complex class I products. An unexpected high degree of heterogeneity was found at the HLA-C locus with 14 novel sequences. Although there was a good correlation between the serologic phenotypes and SBT results, HLA-C SBT of most HLA-C serologically homozygous samples (heterozygous for HLA-A and/or -B) revealed heterozygozity (six of eight). SBT, the first molecular typing approach that has been generalized to both class I and class II genes, may be of special interest in applications demanding high sensitivity and specificity, such as in paternity testing or in the evaluation of the effects of sequence allelism in the outcome of unrelated bone marrow transplantion.