*Purpose: The purpose of this study was to determine if donor-derived cell-free DNA (dd-cfDNA) can be used one-month post-transplant to predict later allograft rejection.

*Methods: Retrospective analysis of 203 subjects from a multi-center, observational study over 24 months. Dd-cfDNA levels were measured as a proportion of total cfDNA using the TRAC assay, from blood samples drawn 1-month post-transplant. Dd-cfDNA levels >0.7% are considered positive. Protocol and for cause biopsies determined rejection or no rejection status over the observation period. Subjects were grouped into 3 categories: dd-cfDNA <0.7 (group 1), dd-cfDNA level ≥0.7 and <1 (group 2), and dd-cfDNA level ≥1 (group 3). Risk of rejection and graft failure were analyzed using the logistic regression and Cox proportional hazard model.

*Results: Of 203 subjects, 136 had a 1-month dd-cfDNA <0.7 (group 1), 40 had a dd-cfDNA level => 0.7 and <1 (group 2, and 27 had a dd-cfDNA level ≥1% (fig.1). 94 (46.3%) experienced rejection at some point during the observation period and 17 (10.8%) had graft failure out to 5 years, with 17 having unknown graft status (Table 1). A higher % of dd-cfDNA in the 1^st month post-transplant trended with a significantly increased risk of rejection (p=0.04). The hazard of graft failure in group 2 (HR 2.22, 95% CI [0.81-6.10], P-value = 0.12) tended to be higher than group 1 but was not statically significant. No concordance was detected between graft failure and dd-cfDNA level (p=0.2).

*Conclusions: A significant number of kidney recipients have elevated dd-cfDNA levels one-month post-transplant. Higher levels are associated with future episodes of allograft rejection. Further investigation is needed to determine if the same association exists with graft failure.

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