*Purpose: In adults with kidney transplantation (KT), histological findings in surveillance biopsies at 1-year post KT are independent correlate to short and long-term graft survival. Donor- specific antibodies (dnDSA) are associated with antibody- mediated rejection. Non-adherence (NOA) to treatment, is a risk factor for dnDSA. Studies in children with KT with protocol biopsy are scarce.Purpose: To evaluate prevalence of histological lesions favorable (FAV) and unfavorable (UNFAV) for graft survival in protocol biopsies of KT children 1 year after KT and identify risk variables of these lesions.

*Methods: Prospective cohort study with all recipients of a 1st KT between 06/01/2018 and 05/30/2019. According to their histological risk, lesions were grouped in “FAV” and “UNFAV”. “FAV” were: 1) minor morphological changes, with absence of inflammation and / or fibrosis and / or chronic glomerulopathy or glomerulonephritis, 2) Acute Interstitial inflammation without interstitial fibrosis or glomerular changes 3) Mild Interstitial fibrosis with absence of interstitial inflammation. “UNFAV” lesions were: 1) moderate-severe interstitial fibrosis without inflammation 2) acute or chronic active rejection mediated by antibodies or T cells 3) de novo glomerular disease 4) polyoma virus-associated nephropathy. Simultaneous to the biopsy, presence of dn-DSA was sought. TAC and / or SRL variation coefficient (VC) >25% was considered a surrogate of NOA.

*Results: 38 children were included, 76% with “FAV” (Minimal morphological changes, n= 23, mild fibrosis, n= 6) and 23% with “UNFAV” histology. One had recurrence of disease, three acute vascular rejection, (2/3 subclinical rejection; 1/3 DSA+) and four moderate fibrosis (2 had graft hydronephrosis and 2 had previous AR,1DSA+). Mean eGFR in patients with “UNFAV” was 39 ± 12.1 ml / min/ 1.73m2 vs 65.3 ± 18 ml / min / 1.73m2 in those with “FAV” (p=0.0003). Both groups had similar pre KT clinical and demographic characteristics. UNFAV patients had higher incidence of previous AR: 33% vs 0% (p=0.01) TAC or SRL VC was < 25% in 71% of patients (n = 27), those with irregular intake had CV > 25% (n=11). Children with VC> 25% had higher risk of an “UNFAV” lesion in protocol biopsy (OR: 4.8; p=0,04) and higher prevalence of DSA (18% vs 0%; p=0.02)

*Conclusions: In this cohort patients “FAV” lesions, negative dnDSA and TAC VC <25% were the most prevalent. Children with UNFAV had lower eGFR. Those with TAC or SRL VC>25% had higher risk of an “UNFAV” lesion, and higher prevalence of DSA. Follow-up of this cohort is imperative.

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