#3077 Activity and chronicity index as graft lost predictors in kidney transplant with antibody mediated rejection or isolated microvascular inflammation

Abstract Background and Aims Antibody mediated rejection (ABMR) is the major cause of graft lost in kidney transplant (KT) recipients. Banff classification considers active ABMR (aABMR) and chronic active ABMR (caAMBR) but does not consider isolated microvascular inflammation (iMVI). Considering histologic lesions in kidney biopsies (KB), activity (AI) and chronicity index (CI) have been developed. Only CI ≥4 has been associated to worse graft survival in ABMR, yet the prognostic value of AI and CI in iMVI is still unknown. Our aim was to evaluate chronicity and activity index as prognostic tools in ABMR and iMVI. Method Retrospective study of KT recipients (1987-2022) with KB (2013-2022) with ABMR (category 3, Banff’2019) [group 1] and iMVI [group 2]. We evaluated AI ([glomerulitis (g) + peritubular capillaritis (ptc), arteritis (v) + C4dscore] e CI ([interstitial fibrosis (ci), tubular atrophy (ct), chronic vasculopathy (cv), and 2xchronic glomerulopathy (2cg) scores)]). Our aim was to evaluate chronicity and activity index as prognostic tools in ABMR and iMVI. Results One hundred thirty-nine KT with aABMR (n=48) and caABMR (n=46) (group 1) and MVIi (n=45) (group 2). Graft loss along time of follow-up (35 [15-69] months) was higher in group 1 (41.5% vs 22.2%; p=0.02). AI was higher in group 1 (4 [3-4.5] vs. 2 [2-4]; p<0.001) and CI similar in both groups (4 [3-7] vs. 4 [4-6]; p=0.7). In the multivariate analysis CI (per unit increase) with HR 1.24 [1.09-1.42; p=0.001] and IA ≥4 in ABMR with HR 2.23 [1.08-4.58; p=0.029]. Death-censored graft survival was worse in IA. IA≥ 4 e IC ≥4 La supervivencia del injerto muerte-censurada fue peor en el grupo RH con IA≥ 4 e IC ≥4 (Fig. 1). Conclusion Our findings suggest that the activity index in ABMR and the chronicity index both in ABMR and iMVI are valuable prognostic tools.