C4d Negative Antibody Mediated Rejection(AMR) Has a Similar Prognosis as C4d Positive AMR in Desensitized Live Donor Kidney Transplant Recipients.

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INTRO:AMR is characterized by graft dysfunction, donor specific antibodies(DSA), microcirculatory inflammation, and evidence of complement activation in peritubular capillaries(C4d). Many of our positive crossmatch patients have histologic features of AMR but are C4d neg. We reviewed our live donor +XM cohort to identify whether AMR outcomes differed by C4d pos and C4d neg status. METHODS/RESULTS: We performed 58 +XM kidney transplants from 9/2004 to 12/2013. All received a minimum of two pre- and post- txp plasmapheresis with IVIG replacement (100mg/kg) and maintenance immunosuppression with tacrolimus, mycophenolate, and steroids. Induction therapy varied, and included either an IL-2 receptor blocker or Thymoglobulin® with or without intra-op rituximab, and IV methylpred with taper to pred 20 mg by post-op day 4. AMR was defined as graft dysfunction, PTCitis and +DSA testing by solid phase assay or XM. 30 +XM patients met these criteria for AMR as their first rejection episode -- 15 were C4d neg and 15 were C4d pos.(see table) Both groups were similar in terms of age, gender, sensitization history, and CDC vs flow +XM. Time to rejection was shorter in the C4d neg cohort (6 vs. 10 days, p=0.01), however, response to treatment, cellular rejections, recurrent rejections, and renal function were similar between groups. More C4d neg AMR grafts failed, but this difference was not statistically significant.Table: No Caption available.CONCLUSION: Our data suggest that desensitized patients with AMR have similar outcomes regardless of C4d staining. Patients with features of AMR and negative C4d stain should be considered for DSA testing. Diagnostic criteria of AMR may need modified to include patients with negative C4d testing.