*Purpose: We hypothesize that Subclinical Acute Rejection (SubAR) under the new Banff 2019 criteria will be more strongly associated with a 2-year composite endpoint (2Y-CCE) than previous criteria.

*Methods: SubAR and 2Y-CCE were assessed in a previously studied patient cohort. SubAR was defined as histology on a surveillance biopsy consistent with acute rejection (≥Banff borderline changes and/or antibody-mediated rejection). Transplant excellent (TX) was defined as negative histology for acute rejection. 2Y-CCE was defined as any of the following: evidence of ≥ Banff grade II IFTA at 2-year biopsy, biopsy-proven rejection on “for-cause biopsy,” or a decrease in eGFR by >10 m/min/1.73m². For logistic regression analysis, subjects were divided into three groups (because subjects had more than one biopsy in the trial) based on biopsy sample classification under 2019 and 2007 criteria: 1) subAR-only, 2) TX-only, 3) subAR and TX (mixed).

*Results: 253 unique subjects with 551 biopsy samples were assessed. Of these, 192 subjects with 444 samples had 2Y-CCE results and were eligible for analysis, 1) subAR only (2019 Banff: n=13; 2007 Banff: n=21), 2) TX only (n=141; n=106), 3) mixed (episodes of both subAR and TX) (n=38; n=65) (Figure 1). A total of 82 subjects reached 2Y-CCE under either set of criteria (n=82). 65 borderline samples were reclassified to TX by the 2019 Banff criteria (Table1). The subAR-only group was found to have a significantly higher odds ratio (OR) for developing 2Y-CCE than the TX-only group under both 2007 (OR = 19.27 (95% CI [4.25, 87.42], p =0.001)) and 2019 (OR = 19.33 (CI [2.44, 152.92], p =0.01) Banff criteria. The SubAR only group by 2019 Banff criteria had a slightly stronger association with 2Y-CCE than by 2007 criteria. There was no significant association with developing 2Y-CCE between the TX-only group and the mixed group under 2007 and 2019 Banff criteria.

*Conclusions: The subAR only group classified by 2019 Banff criteria, which brought an increase in the diagnostic threshold for borderline changes, showed slightly stronger association with developing 2Y-CCE than by 2007 Banff criteria. The subAR group classified with either criteria are significantly associated with 2Y-CCE compared to the Tx only group. Further investigation is warranted with a larger cohort and longer follow-up to evaluate the impact of the prognostic ability of the new 2019 Banff criteria.

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