Allele-specific HLA-B39 antibody reactivity in a highly-sensitized kidney transplant candidate

A 43-year-old highly sensitized female waitlisted over 16 years received a deceased donor kidney offer. Virtual crossmatch (VXM) revealed three historic donor-specific antibodies (DSA) against the potential donor. Additionally, the patient appeared to have strong current allele-specific DSA to HLA-B*39:01 based on positive reactivity by single antigen bead (SAB) testing and self-typing of B*39:08. The donor was typed B39 homozygous by real-time PCR (RT-PCR) by an outside laboratory with the allele-string including B*39:02/05/08/13. B*39:01 is the only bead representing B39 antigen group in the main SAB panel from One Lambda. Allelic differences suggested potential differential reactivity. PXM yielded a negative result. Investigation into the reactivity using alternate bead panels, surrogate flow cytometry crossmatching and high-resolution HLA typing showed the confirmed allele-specific B*39:01 antibody cross-reacts with B*39:04/05/06 and does not react with B*39:02/08/13. This case underscores the need for enhanced VXM tools and workflows integrating expanded antibody panels and high-resolution typing.