P169 Is it really homozygous? Identifying 6P loss in the HLA typing

Abstract

Aim A peripheral blood sample for HLA typing was received in the lab for a prospective HCT patient. As with all HCT patients, SeCore™ Sequence-Based Typing and One Lambda LABType™ SSOP were performed. Sequence analysis performed using uTYPE results were A∗02:01, A∗02:01; B∗08:01, B∗08:01, C∗07:01, C∗07:01; DQB1∗03:02, DQB1∗03:02, DRB1∗04:04, 04:04. DPB1 at first glance was determined to be DPB1∗04:01, DPB1∗04:01. However, on closer inspection, the Z38 GSSP primer typed as DPB1∗10:01, and the Z39 GSSP primer typed as DPB1∗04:01. The LABType SSOP typing was A∗02, A∗03; B∗08, 08; C∗07, 07; DPB1∗04:01, 04:01; DQB1∗03, 03; and DRB1∗04:04, 04:04. The heterozygous A locus typing gave a clear indication that our sequencing had not picked up the complete typing. The B and C and DPB1 locus typings appeared homozygous, but there were a few false positive and high negative beads present, indicating the possible presence of B∗27, C∗02 and DPB1∗10:01. The DQB1 and DRB1 were concordant with the homozygous sequencing results, with no cut off adjustments necessary to obtain the typings. Methods SeCore™ Sequence-Based Typing and One Lambda LABType™ SSOP were performed. High Resolution typing was performed using LABType SSOP. Results Reexamining to the sequencing data, and inserting B∗27:05 for the B locus and C∗02:02 for the C locus into the allele comparator on uTYPE, very small double peaks could be seen at all of the points of mismatch for the B∗08:01, 27:05 typing, and C∗02:02, 07:01 typing. At this point, cytogenetics analysis performed on this patient, and if 6p loss had been detected. The laboratory confirmed that the patient’s leukemia cells exhibited partial 6p loss. Buccal swab sample was requested by the HLA lab to perform HLA typing. The buccal swab typing was A∗02:01p, 03:01; B∗08:01, 27:05p; C∗02:02p, 07:01p; DPB1∗04:01, 10:01; DRB1∗04:04, 04:04; DQB1∗03:02, 03:02. Conclusions This example confirms the necessity of performing two typing methods. It also demonstrates the key benefit of communication from the Cytogenetics Laboratory whenever 6p loss is detected in prospective HCT patients. In this case, DNA from a buccal swab was absolutely required for assurance of an accurate typing due to the homozygous DRB1 and DQB1 present in the patient.