Background: In ABO-incompatible (ABOi) transplantation, the criteria for antibody-mediated rejection (AMR) are controversial, as C4d deposition is common in ABOi. This study examined the impact of microvascular inflammation (MVI: g and ptc) within 1 year after transplantation on ABOi graft outcome.

Methods and materials: Between 2001 and Jan 2015, 227 recipients received ABOi living related kidney grafts. Among these, recipients with preformed donor-specific antibody (DSA) (n=55), and without detailed clinical/pathological findings (n=29) were excluded. The remaining 143 recipients were divided into two groups based on the presence of MVI: Group 1 (n=30), recipients with MVI score ≥ 2. Group 2 (n=113), with MVI score < 2. We compared graft survival, function and other pathological findings groups.

Results: ABOi recipients received the same regimen of tacrolimus/ mycophenolate mofetil/ methylprednisolone/ basiliximab. As a B-cell targeting therapy, recipients received splenectomy with transplantation until Dec 2004, and low-dose 200 mg/body rituximab after 2005. There was no significant difference in C4d deposition between Groups 1 and 2 (96.7% vs. 87.9%, p= 0.308). The difference in graft survival between Groups 1 and 2 was marginally significant (5-year survival rate: 89.5% vs. 96.7%, p= 0.0833), whereas graft function was significantly worse at 1 and 10 years after transplantation in Group 1 (1-year serum creatinine level: 1.58 ± 0.44 vs. 1.30 ± 0.39 mg/dL, p=0.0016; 10-year: 1.67 ± 0.38 vs. 1.20 ± 0.40 mg/dL, p=0.0182). Significantly higher rates of T-cell mediated rejection (70.0% vs. 7.96%, p=0.001) and interstitial fibrosis/ tubular atrophy (43.3% vs. 21.2%, p=0.0193) were seen in Group 1.

Conclusions; Higher MVI scores reflected worse graft function after ABOi kidney transplantation. The significance of MVI in enabling AMR diagnosis in ABOi, regardless of C4d deposition, was confirmed in this study.

CITATION INFORMATION: Ishihara H, Ishida H, Unagami K, Hirai T, Okumi M, Omoto K, Shimizu T, Tanabe K. The Significance of Microvascular Inflammation in Antibody-Mediated Rejection in ABO-Incompatible Kidney Transplantation. Am J Transplant. 2016;16 (suppl 3).

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