18-P

Abstract

Aim We identified a mutation in the B∗15:01:01:01 allele during a routine new patient kidney workup, resulting in a non-expressed allele. Methods HLA-A, -B, -C, -DRB1, -DQB1 and -DRB345 loci were typed by polymerase chain reaction with sequence-specific oligonucleotide probes on Luminex Platform (rPCR-SSOP) (One Lambda, Canoga Park, CA). Confirmatory typing was performed by a combination of sequencing based typing (SBT) using SBT engine software and Gendx SBT Excellerator Kits (Netherlands), and complement-dependant cytotoxicity methods to confirm absence of B62 molecules on the cell surface. Results During a routine kidney recipient workup, a patient was typed as B∗15 (62) and B∗40 (60) by rPCR-SSOP with an ambiguous assignment, B∗46 and B∗40 (60). SBT was used to resolve the ambiguity and revealed that the typing is similar to B∗15:01:01:01 and B∗40:01:01 with a mutation in exon 4, codon 204, nucleotide position 683. Using gSSP primer, we further confirmed the mutation belongs to B∗15:01:01:01, changing codon TGG (Tryptophan) to TAG (stop codon). An Exon 4 premature stop codon can result in a non-expressed allele. A new sample was sent to an independent laboratory for serological typing, and was confirmed as B62 “blank”. To properly list this patient on UNET, the patient’s B62 was removed. Conclusions Low-intermediate resolution HLA typing is routinely used for renal patients, but non-expressed alleles are often not being ruled out. Null alleles have important implications in donor selections of 0 antigen mismatched transplant and in defining an allo antibody appearing to be against self null allele. Characterization of a variant allele with mutations affecting antigen expression is very important in renal transplant HLA typing.