Monoclonal IgG4/2κ Deposition Following Eculizumab Therapy for Recurrent Atypical Hemolytic Uremic Syndrome in Kidney Transplantation

Eculizumab is an emerging therapy for atypical hemolytic uremic syndrome (aHUS). Early identification and treatment of recurrent aHUS after kidney transplantation requires a high clinical suspicion but results in improved graft function and patient outcome. We present a patient who developed recurrent aHUS after kidney transplantation that responded to eculizumab therapy. A kidney biopsy was performed to confirm resolution of thrombotic microangiopathy 8 weeks after eculizumab treatment initiation and revealed no features of thrombotic microangiopathy. Instead, the biopsy revealed monoclonal immunoglobulin G (IgG)4/2κ deposition in the glomerular tufts, vasculature, and atrophic tubular basement membranes. IgG4/2κ deposits are a rare pathologic finding following eculizumab therapy, and the long-term effect of these deposits on kidney function remains unknown.