*Purpose: To evaluate the impact of timing of T-cell mediated rejection (TCMR) occurrence in the first year after kidney transplantation (KT).

*Methods: Single center retrospective cohort study of 195 kidney transplant recipients performed between 2013-2017. Patients had at least one episode of TCMR (either clinical or subclinical) in the first year after KT. TCMR episodes in the first year were grouped into early (0-6 months) and late (6-12 months) rejections. Based on the timing of TCMR cohort was divided into three groups-early (6_month;N=59), late (12_month; N=89) or both (6m_12m; N=47). Differences in interstitial fibrosis and tubular atrophy (IFTA) scores, eGFR change along with graft failure was assessed among the 3 groups.

*Results: Study population had a mean age of 49 years, with 53% males and 28% African-Americans. 16% had PRA >20%. Baseline characteristics were similar across the groups except for slightly higher BSA and numerically higher class II PRA in the 6m_12m group. The three groups had similar renal function and chronicity scores in the 0-6m period; proportion with IFTA score >2 at 6 months among the 6m, 12m and 6_12m groups were 6 (9.5%), 6 (6.5%) and 8 (15.1%) respectively (p value=0.24) (Table). At 12m, IFTA score >2 for the 6m, 12m and 6_12m groups were 8 (12.7%),14 (26.4%) and 24 (26.1%) respectively (p value=0.1) showing worsening in the 12m and 6m_12m rejection groups. Proportion of patients developing a loss of eGFR of 10ml/min or more between 3m to 24m were lowest in the 3m only rejection group; 15(25.4%), 33(37%), 23(49%) for 6m, 12m, 6m_12m group respectively (p value=0.043). Finally, proportion of patients developing a composite outcome of graft loss and impending graft loss (defined as eGFR <20ml/min) was highest among the 6m_12m group; 5 (8.5%), 10(11%), 12 (25.5%) for 6m, 12m and 6m_12m groups respectively; p value=0.026.

*Conclusions: Rejection occurring early after transplantation and recurring or persisting at the end of 1 year had the worst chronicity and renal outcomes. Early rejection that resolves showed the best outcomes with low chronicity progression and preserved renal function. Patients without early rejection but developing rejection at 1 year demonstrated significantly worse chronicity scores suggesting that absence of early rejection does not imply immune quiescence and requires close monitoring.

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