LAUSR

Clinical History: A 62 year-old male with chronic glomerulonephritis underwent kidney transplant from a donation after cardiac death donor in Jan 2017. Cold ischemia time was 8 h. The recipient had no donor specific antibody detected in any pretransplant sera tested since 2012. Flow-cytometric crossmatch (FCXM) was negative with the day of transplant sample. He received induction with Thymoglobulin, methylprednisolone, mycophenolate mofetil, and tacrolimus. Post-op day (POD)#1 creatinine was 7.90 mg/dl. He experienced delayed graft function, but otherwise no complications. He was discharged on POD#7 with a creatinine of 2.82 mg/dl. On POD#8 his creatinine was 1.7 mg/dl. De novo HLA-B8 antibody (14,365 MFI) was detected on a Thymo-absorbed and heat inactivated sample from the same day. The patient began therapeutic plasma exchange (TPE) and IVIG treatments on an every other day schedule. The kidney biopsy showed no evidence of antibody-mediated rejection. The Anti-HLA-B8 levels decreased to ∼ 2,000MFI. To understand the nature of this antibody, the FCXM was repeated using the POD#8 sample and was negative (T cell channel shift = 36 and B cell = 65). Therefore TPE/IVIG was stopped after 2 cycles. An incidental cavitary lesion was identified in the mid lobe of his right lung post-transplant. Quantiferon gold test was intermediate positive, but AFB culture was negative. 15 months post transplant, he continues to have HLA-B8 antibody 1500–3000 MFI, a stable creatinine ∼ 1.2 mg/dl, no proteinuria, and protocol biopsy in March 2018 showed no evidence of rejection. Discussion: The single antigen bead (SAB) assay is a very sensitive and specific antibody assay. During the manufacturing process, HLA antigens can become denatured and unfolded. This artificial unfolding allows for unmasking of cryptic epitopes on the recombinant HLA antigens. These cryptic epitopes may cross-react with epitopes found in microorganisms or allergens and may generate antibodies that react with denatured HLA proteins. False positive SAB assay may lead to unnecessary procedures in patients, and may limit patients’ to access to organ transplantation. Therefore, it is of utmost importance to recognize these artifacts and when possible utilize different platforms of testing to confirm the presence of artifactually denatured antibodies.