B7-1 Blockade Does Not Improve Post-Transplant Nephrotic Syndrome Caused by Recurrent FSGS

Abstract

FSGS is a common glomerular disorder that has a high propensity for recurrence after kidney transplant. The pathophysiology of FSGS is unknown, but podocytes seem to be the target of one or several circulating factors that lead to cytoskeleton reorganization and proteinuria. Research on podocytes has identified B7-1 as an important factor in podocyte biology and a new therapeutic target in renal disease. Indeed, in four patients with recurrent FSGS after transplant, treatment with the B7-1 blocker abatacept was associated with proteinuria remission. Here, we prospectively treated nine patients with recurrent FSGS after transplant using either abatacept or belatacept, a B7-1 blocker with higher affinity, and did not induce proteinuria remission. Furthermore, we did not detect B7-1 expression by immunofluorescence in podocytes of biopsy specimens from these or other kidney grafts or podocytes of native kidney biopsy specimens. In conclusion, B7-1 blockade did not induce FSGS remission after transplant in our study.

Keywords: focal segmental glomerulosclerosis; podocyte; signaling; transplantation.

Figure 1.

Abatacept does not improve albuminuria in patients with FSGS recurrence after Tx. Charts showing the post–Tx serum creatinine levels (black) and albuminuria-to-creatinine ratios (red) of (A) patient 1, (B) patient 2, (C) patient 3, (D) patient 4, and (E) patient 5. The orange triangles represent abatacept infusion. The purple triangles represent rituximab infusion. The light blue rectangles represent plasmapheresis. The dark blue rectangles represent IA, whereas the yellow rectangles represent iv cyclosporin, and the green rectangles represent oral cyclosporin. The red rectangle represents hemodialysis.

Figure 2.

Belatacept does not improve albuminuria in patients with FSGS recurrence after Tx. Charts showing the post–Tx serum creatinine levels (black) and albuminuria-to-creatinine ratios (red) of (A) patient 6, (B) patient 7, (C) patient 8, and (D) patient 9. The brown triangles represent belatacept infusion. The purple triangles represent rituximab infusion. The light blue rectangles represent plasmapheresis. The yellow rectangles represent iv cyclosporin, and the green rectangles represent oral cyclosporin.

Figure 3.

B7–1 is not expressed in podocytes in patients with FSGS recurrence after Tx. (A) Coimmunostaining of nephrin (green) and B7–1 (red) on transplant biopsies performed at the time of FSGS recurrence. (B) Coimmunostaining between nephrin (green) and B7–1 (red) on transplant biopsies performed at the time of FSGS recurrence showing positive cells for B7–1 in the interstitium. (C) Western blot of B7–1 in HeLa cells transfected with plasmids containing either an empty vector or B7–1 cDNA. (D) B7–1 immunostaining in HeLa cells transfected with plasmids containing either an empty vector or B7–1 cDNA. (E) Coimmunostaining of CD20 (green) and B7–1 on human tonsils at (left panel) low or (right panel) higher magnification. (A–E) For all of these experiments, the anti-B7–1 antibody from Santa Cruz Biotechnology (SC-9091) was used. (F) B7–1 immunostaining in human tonsil using three different commercially available antibodies (AF140 from R&D Systems Europe, SC-9091 from Santa Cruz Biotechnology, and MA5–15512 from Fisher Scientific). DAPI, 4′,6-diamidino-2-phenylindole. Scale bar, 10 μm.

Figure 4.

B7–1 is not expressed in podocytes in patients with proteinuric diseases of native kidneys. Representative coimmunostaining of nephrin (green) and B7–1 (red; using anti-B7–1 antibody SC-9091 from Santa Cruz Biotechnology) in native kidney biopsies from patients with primary FSGS, secondary FSGS, diabetic nephropathy, membranous nephropathy, ANCA vasculitis, or lupus nephritis classes 3 or 4. Human tonsils served as positive controls. The arrow shows circulating B7–1-positive cells. DAPI, 4′,6-diamidino-2-phenylindole. Scale bar, 10 μm.