Accelerated humoral renal allograft rejection due to HLA-C14 mediated allosensitization to HLA-Bw6

Objectives To investigate immunological mechanisms underlying accelerated antibody-mediated rejection (AMR) of a living-related renal allograft in a patient with no detectable antibodies to donor human leukocyte antigens (HLA) in pre-transplant sera. Methods Pre- and post-transplant HLA antibody specificities were determined by single-antigen bead assay, and crossmatching was performed by flow cytometry- and complement-dependent cytotoxicity-based methods. Intermediate- and high-resolution HLA typing were performed by molecular methods. Results Pre-transplant patient serum reacted weakly against Bw6-positive beads; cytotoxicity and flow crossmatches were negative. The patient was mismatched for the donor antigens B62 and C10 (Bw6-positive). Following transplantation, strong antibody responses against B62, C10, and all Bw6-positive beads were detected. This reactivity was initially masked by complement interference, but became apparent at 1:20 dilution. High-resolution typing suggested that the anti-C16 antibody reactivity detected was an allele-specific response to donor C^∗16:01 (Bw6-positive) but not recipient C^∗16:02 (Bw6-negative). Alloimmunization likely occurred during pregnancy, during which HLA-C14 (Bw6-positive) was the only mismatched paternal HLA Class I allele. Conclusions Sensitization to HLA-Bw6 via exposure to paternal HLA-C14 during pregnancy likely predisposed this patient to AMR. The case demonstrates the immunogenicity of HLA-C14-associated Bw6 epitopes in vivo and the clinical significance of low-level antibodies to HLA-Bw6.