Loss of heterozygosity leading to incorrect HLA typing for platelet-transfusion refractory patient

Management of platelet-transfusion refractory (PR) patients due to anti-HLA antibodies includes the provision of HLA-matched (HLAm) platelets (PLT) or PLTs that are negative for HLA antigens corresponding to the recipient antibodies. Obtaining HLAm PLTs is predicated on accurate HLA antigen typing of the recipient and donor. Here, we present the clinical implications of a case involving loss of heterozygosity (LOH) in a patient presented for PR workup.

HLA typing was performed by three methods: (1) Real-time PCR; (2) Sequence-specific oligonucleotide (SSO) typing test; and (3) Next-Generation Sequencing (NGS). Cytogenomic SNP microarray was utilized to assess LOH.

A 30-year-old female with newly diagnosed acute myelogenous leukemia was found to be PR secondary to HLA sensitization. A peripheral blood (PB) sample, containing 93% myeloid blast cells, was sent for HLA typing for the provision of HLAm PLTs. HLA typing revealed homozygosity at the HLA-A locus but was heterozygous at the -B and -C loci. After chemotherapy, HLA typing on a new PB sample, devoid of blast cells, identified HLA-A locus heterozygosity, which was subsequently confirmed by real-time PCR and NGS. Cytogenomic SNP microarray analysis demonstrated LOH of the HLA-A locus on chromosome 6p in the pretreatment sample but not in the posttreatment sample.

In hematologic patients with high tumor burden, HLA homozygosity should be viewed with suspicion for potential LOH. Therefore, HLA testing should be repeated, preferably with a non-hematological source (e.g., buccal swab) or following successful reduction of the tumor burden.