*Purpose: Anti-brush border antibody (ABBA) disease is very rare, characterized by tubulointerstitial damage caused by autoantibodies against LDL receptor-related protein 2 (LRP2) in the proximal tubular brush border. This can lead to end-stage renal failure and can recur after kidney transplant. Very few cases have been reported in the literature; all in native kidneys. We report a case of de novo ABBA in a kidney transplant recipient.

*Methods: 62 year old male with end-stage renal disease secondary to biopsy-proven focal segmental glomerulosclerosis, underwent deceased donor kidney transplant. He received thymoglobulin induction, and tacrolimus and mycophenolic acid for maintenance immunotherapy. Early post-transplant course was uncomplicated. Ten months post-transplant, he developed de novo donor-specific antibodies with elevated donor-derived cell-free DNA. Renal function was stable with serum creatinine 1.5 mg/dL and proteinuria 0.6 g. Kidney biopsy showed no signs of rejection and negative peritubular capillary C4d staining. Immunofluorescence revealed focal IgG staining along the proximal tubule brush border and basement membrane (Figure 1). Electron microscopy showed scattered electron-dense deposits within the tubular basement membrane. LRP2 staining was positive along the proximal tubule brush border and basement membrane. Blood titers for anti-LRP2 antibodies returned positive at 1:100. Patient’s native kidney biopsy was reviewed, revealing features of advanced FSGS, but staining for LRP2 antibodies was negative.

*Results: Given stable kidney function and lack of evidence of any effective treatment, no specific therapy was initiated. Repeat kidney biopsy 18 months post-transplant remained negative for any signs of rejection, but revealed mild, patchy interstitial fibrosis involving 10-15% of the cortex with similar LRP2 staining pattern. Repeat blood titers were higher at 1:500. Patient is currently 30 months after transplant: serum creatinine has increased to 1.9 mg/dL (Figure 2) and proteinuria increased to 1 gm. Patient refused repeat biopsy.

*Conclusions: We believe this to be the first case report of de novo ABBA disease in a kidney transplant recipient. The trigger for the disease remains unclear. The course appears slow but progressive.

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