The role of proteasome inhibition with bortezomib in the treatment of antibody-mediated rejection after kidney-only or kidney-combined organ transplantation.

Background: We report our initial experience in using the proteasome inhibitor, bortezomib, to treat established antibody-mediated rejection (AMR) in 20 patients.

Methods: There were 16 kidney-only and 4 kidney-combined organ recipients with de novo donor-specific antibody (DSA) and histologic evidence of AMR with peritubular capillaries C4d deposition. AMR was diagnosed 19.8 months (range 1-71 months) posttransplant. Patients received intravenous corticosteroids followed by a 2-week cycle on days 1-4-8-11 of plasmapheresis and 1.3 mg/m² bortezomib; then 0.5 mg/kg intravenous immunoglobulin four times.

Results: De novo class I DSA was detected in 11 (55%) and class II DSA in 18 (90%) recipients. The absolute mean difference between peak-nadir dominant DSA was 68,171 molecules of equivalent soluble fluorochrome (P<0.0001), representing 55%±22%. Only two patients (10%) had undetectable DSA after treatment. Patient survival is 100%, and graft survival is 85% with a mean follow-up of 9.8 months (range 2-20 months). The treatment was generally well tolerated but caused fatigue, gastrointestinal complaints, fluid retention, and thrombocytopenia in a number of patients. The last follow-up estimated glomerular filtration rate was 41.9±16.8 mL/min (range 20.6-72.2 mL/min). However, only 25% returned to their baseline renal function before AMR, and many have proteinuria with urine protein/creatinine more than 0.5 in 41% and more than 1.0 in 18%.

Conclusions: The bortezomib-containing regimen demonstrated activity in AMR but seems to be most effective before the onset of significant renal dysfunction (serum creatinine <3 mg/dL) or proteinuria (<1 g/day). The best use of bortezomib to treat AMR should be evaluated in controlled trials using dosing strategies that include longer courses or retreatment schedules.