Renal C4D Deposition Is a Marker of Hematopoietic Stem Cell Transplant (SCT)-Associated Thrombotic Microangiopathy (TMA)

Abstract

C4d is a marker of classical complement activation by tissue specific antibodies (abs) or endothelial damage. Currently, peritubular capillary (PTC) C4d deposition aids in the diagnosis (dx) of ab mediated kidney transplant rejection (AMR). An uncontrolled case series reported PTC and glomerular C4d staining in patients with SCT-TMA (Mii et al, Path Int 2011). Expanding on these findings, we hypothesized that renal tissue from patients with SCT-TMA would more frequently show C4d deposition compared to controls. Retrospective analysis of all renal biopsy and autopsy specimens from pediatric patients undergoing SCT at our institution. Using histological criteria alone, patients were divided into TMA and non-TMA (control) groups. C4d staining was performed by immunohistochemistry on formalin-fixed, paraffin-embedded tissue and was evaluated on arterioles, PTCs, glomeruli, and tubular basement membranes. Specifically, rabbit anti-human C4d polyclonal ab was applied to sections and C4d was independently graded (diffuse: 50-100%; focal: 5-50%; rare: 1-5%; negative: 0%) by two pathologists, blinded to each subject's underlying dx. 20 total specimens were identified (19 subjects). Of these, 8 specimens (7 subjects) had histologic evidence of TMA (5 biopsy, 3 autopsy). 1 TMA subject had both a biopsy and autopsy with similar findings, therefore only the autopsy findings are included. The 12 SCT recipient autopsies without TMA served as controls. Diffuse and focal arteriolar C4d staining was far more common in TMA specimens compared to controls (71.4% versus 8.3%, p = 0.01). PTC C4d staining was present in just under half of TMA samples and was absent in controls (p = 0.04). Glomerular C4d staining was similar in both groups and tubular basement membrane staining was rare.TableC4d Deposition in TMAHistology proven TMA (n = 7)Control (n = 12)p-value∗from Fisher’s exact test for categorical variables and Wilcoxon Rank sum for continuous variables; data expressed as n (%) or median (25th-75th percentile) [range].Pathology Results Arteriolar C4d+5/7 (71.4%)1/12 (8.3%)0.01 PTC C4d+3/7 (42.9%)0/12 (0%)0.04 Glomerular capillary C4d+4/7 (57.1%)10/12 (83.3%)0.30 Tubular basement membrane C4d+2/7 (28.6%)0/12 (0%)0.12Clinical Results Age (years)3.6 (1.7-4.5) [0.6-4.9]3.2 (1.4-17.1) [0.9-28.1]0.55 Gender (male)3/7 (42.9%)8/12 (66.7%)0.38 Specimen day post-SCT237 (43 - 631) [19 - 2281]172 (78 - 253) [9 - 887]0.50 Malignancy5/7 (71.4%)2/12 (16.7%)0.03 Immunodeficiency1/7 (14.3%)9/12 (75.0%)0.03 Bone marrow failure1/7 (14.3%)1/12 (8.3%)0.03 Allogeneic2/7 (28.6%)11/12 (91.7%)0.01 Autologous5/7 (71.4%)1/12 (8.3%)0.01 GVHD in those at risk (allogeneic)1/2 (50%)3/11 (27.3%)1.00 Viral infection4/7 (57.1%)4/12 (33.3%)0.38 Dialysis6/7 (85.7%)5/12 (41.7%)0.15∗ from Fisher’s exact test for categorical variables and Wilcoxon Rank sum for continuous variables; data expressed as n (%) or median (25th-75th percentile) [range]. Open table in a new tab This is the first report of arteriolar C4d deposition in SCT-TMA, implicating localized complement fixation due to as yet unidentified abs or ab-independent direct endothelial damage in the pathogenesis of TMA. PTC C4d staining was found only in TMA, while glomerular staining was non-specific as it was similar in both groups. Although the preferential arteriolar C4d staining is incompletely understood, it may identify a renal site of injury, explaining the dramatic hypertension often seen in TMA. Future research should assess if patients with SCT-TMA and renal C4d deposition will benefit from therapies currently used to treat kidney transplant AMR.