*Purpose: Treatment of acute kidney transplant rejection in children is often guided by creatinine-based estimates of GFR (eGFR) that may lack sensitivity to determine the adequacy of therapy. The purpose of this study was to analyze our center’s practice of performing follow-up biopsies to assess for resolution of acute rejection.

*Methods: We performed a retrospective cohort study of all biopsy-proven subclinical and clinical T cell-mediated acute rejection (TCMR) episodes at our center between January 2009 and December 2014. We analyzed the first subclinical or clinical TCMR episode in each patient that had at least one follow-up biopsy performed within three months of diagnosis. Treatment of rejection included standard courses of intravenous pulse steroids with a 4-6-week oral taper with the addition of anti-thymocyte globulin in severe or steroid-resistant rejection. The primary endpoint was biopsy-proven resolution of TCMR, defined by follow-up Banff injury scores of < i1t1 and v=0. The secondary endpoint was a composite outcome of acute rejection, graft loss, or death by five years. We compared continuous and categorical variables between subgroups with resolved versus persistent TCMR using standard approaches. We used Kaplan-Meier methods to compare time-to-event data between those with resolved versus persistent TCMR.

*Results: We identified 27 pediatric kidney transplant recipients with at least one follow-up biopsy within three months of diagnosis of subclinical (n=9) or clinical (n=18) TCMR. The cohort was 44% black race, 48% female sex, and 85% deceased donor recipients. Overall, 17/27 (63%) of children had eventual resolution of TCMR on serial follow-up biopsies. However, only 10/27 (37%) had resolution of TCMR on the initial follow-up biopsy within 4-6 weeks of standard treatment. We found no clinical or demographic characteristics that were associated with the response to treatment, including the type of rejection (subclinical/clinical) or improvement in eGFR. The persistent TCMR group had a trend for a higher incidence of the composite endpoint (50% versus 24%; P=0.06, Figure).

*Conclusions: Serial follow-up biopsies frequently detected unresolved subclinical and clinical TCMR that may be associated with inferior long-term outcomes in pediatric kidney recipients. Larger studies are warranted to compare biopsy-guided to eGFR-guided treatment regimens for TCMR in children.

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