*Purpose: Recent studies have shown that inflammation in areas of interstitial fibrosis and tubular atrophy (i-IFTA) is associated with worse kidney allograft outcomes. How i-IFTA changes following typical anti-rejection treatments, and how such changes correlate with outcomes is not known.

*Methods: i-IFTA scores have been routinely reported on kidney allograft biopsies at our institution since 5/2017, after the release of the Banff 2015 Kidney Meeting Report. We treat Banff borderline and grade I acute cellular rejection (AMR) with steroids, and in addition, patients with grade II and III rejections receive anti-thymocyte globulin. We treat antibody-mediated rejection (ABMR) with steroids, intravenous immunoglobulin with or without plasmapheresis and/or rituximab. A protocol follow-up biopsy is done 3 months later to evaluate for resolution of rejection. For patients with rejection diagnosed on a biopsy between 5/2017 and 5/2019, serial biopsies were examined to determine how i-IFTA changed following treatment.

*Results: 755 kidney transplant recipients had a total of 1163 biopsies performed. Of these patients, 152 (20.1%) had rejection on first biopsy and had at least one follow-up biopsy available. Mean age at transplant was 44.1 years, 31.6% were women, 31.6% nonwhite and 25.0% had prior transplants. 34.2% had ACR only, 48.7% had ABMR only, and 17.1% had mixed rejection. Median time from transplant to first biopsy was 4.3 years (range: 0.02 – 20.7 years). Median number of biopsies per individual kidney transplant was 2 (range 2-5). 50.6% of initial biopsies had i-IFTA score greater than 0. Mean i-IFTA was 1.2±1.3.

Among patients with initial i-IFTA score of 0, worsening of i-IFTA was observed on the last available biopsy in 34.7% (26/75); notably, rejection resolved in half of these (13/26). 71.4% (15/21) of patients with initial i-IFTA of 1 had no improvement/ worsening on last available biopsy; rejection resolved in 33.3% (5/15) of these. 40.0% (6/15) of patients with i-IFTA of 2 had no improvement/ worsening, with resolution of rejection in 66.7% (4/6). 34.2% (14/41) of those with i-IFTA of 3 had no improvement despite resolution of rejection in 28.6% (4/14).

*Conclusions: i-IFTA was present on initial biopsies in half of the cases with rejection. Our most notable finding was that i-IFTA frequently does not improve or progresses despite successful treatment of rejection in many cases. Further studies are needed to determine the impact of residual or worsening i-IFTA on patient and graft outcomes.

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