Effect of Heterozygosity Loss in HLA Region before Transplantation on HLA Typing in Patients with Leukemia / 中国实验血液学杂志

ABSTRACT

<p><b>OBJECTIVE</b>To investigate the effect of loss of heterozygosity(LOH) in HLA region at initial diagnosis and remission of leukemia patient before transplantation on HLA typing.</p><p><b>METHODS</b>The HLA typing was performed in DNA extracted from peripheral blood obtained at diagnosis (Sample 1 and Sample 2) and remission (Sample 3) in one pretransplant male patient with mixedphenotype acute leukemia (MPAL). HLA typing for HLA-A, B, C, DQB1, DRB1 was performed by Sequence-based typing (SBT), Sequence-specific oligonucleotide probe hybridization (SSO) and Sequence-specific primers (SSP). To define more precisely a cutoff limit for the detection of a heterozygous DNA present in a fraction of the cells by the SBT technology, DNA mixing experiments were performed.</p><p><b>RESULTS</b>SBT results showed that Sample 1 and Sample 2 were both homozygous HLA results at five loci (lost one haplotype) although the sequencing background of Sample 1 was a little high. Except HLA-C locus was homozygous, Sample 3 was heterozygous HLA results at four loci. Based on DNA mixing experiments, a cutoff limit for the detection of heterozygous DNA was 20% by SBT technology, and a detection threshold for HLA-A, B, C, DQB1, DRB1 heterozygosity in blood samples was <75% blasts.</p><p><b>CONCLUSION</b>Because LOH may be partial, any homozygous HLA result obtained during a blast crisis, especially ≥75% blasts, would have to be confirmed by a second typing on a buccal swab or on peripheral blood from the patient in complete remission.</p>