P043 Assessment of donor specific antibody by single antigen bead/ epitope analysis combined with flow cytometry cross match facillitates better patient management after kidney transplantation

Abstract

Post transplant epitope analysis of anti-donor specific antibody (DSA) using single antigen bead (SAB) assays when combined with flow cytometry cross matches (FCXM) may provide enhanced ability to direct the management of a patient’s immunosuppressive therapy. This proposal is illustrated by the following case report. A 57 year old female (HLA, A2, A31, B51, B53, DR13, DR15) received a deceased donor kidney transplant (TX) (Donor HLA, A1, B13, B37, C6, DR7, DR15, DQ2, DQ6). The patient was sensitized (cPRA 97%) from a prior kidney TX. Pre-TX DSA was detected to B*37:01, MFI = 645 with a possible epitope 156DA, the sum of which is the MFI- score (MFI-s) = 4515). T and B cell FCXMs were negative. The patient did not receive plasmapheresis (PPE) prior to TX and DSA was not detected one day after transplantation. On day 8, DSA was detected to the A*01:01 SAB (MFI = 591) with and MFI-score of 3992 to the possible epitope 163R that includes A1. The patient’s DSA increased to 2451, A*01:01, MFI-s of 14,936, on day 12 but the creatinine (Cr) decreased from 4.1 to 2.5 mg/dL over the next 14 days so treatment was withheld. On day 30 an increase in Cr from 2.3 mg/dL to 3.7 mg/dL was noted. SAB testing indicated DSA to B*37:01, as well as the A1 bead. A C3d test and a FCXM test was performed (with frozen donor cells).The DSA did not bind C3d and the FCXM was negative. Typically the FCXM would be positive with this level of DSA (14,936). In view of the negative FCXM, further epitope analysis was performed as the patient’s post transplant serum likely contained antibodies with several overlapping specificities. In this case the donor antigen A1 did not express the epitope that was broadly expressed on other beads, 163R, but rather an epitope that was restricted to A1 alleles only 163RG with an MFI-s = 2787. This explained why the FCXM was negative. PPE, IVIG and Rituxan therapy was initiated but only 5 PPE were given since the DSA was of relatively low strength. The patient’s DSA was undetecTable 10 days later and her Cr stabilized to 2.1 mg/dL. This case illustrates how post-transplant assessment of anti-HLA antibody with SAB/ epitope analysis, combined with FCXM, can provide important information on the specificity and strength of the DSA for use in the management of recipients that develop antibodies after kidney transplantation. A.J. Norin:2. Consultant; Company/Organization; ICON PLC, Stony Brook Pathologists. 3. Speaker’s Bureau; Company/Organization; Immuncor, One Lambda.