*Purpose: Donor-derived cell-free DNA (dd-cfDNA) testing, which has been validated for monitoring kidney transplant (KTx) rejection, may provide an alternative to pancreas biopsy that prevents morbidity and graft loss. We determined, for the first time, dd-cfDNA levels in pancreas transplant (PTx) recipients with and without rejection.

*Methods: Patients undergoing PTx were enrolled. Dd-cfDNA levels were collected monthly through month 12 and quarterly thereafter and were assessed in context of patient creatinine, biopsy, and demographics.

*Results: n=182 dd-cfDNA samples were collected from N=78 patients up to 132 months post-PTx. Mean and median dd-cfDNA levels in all subjects were 0.60±0.9% and 0.28%, respectively. Mean and median dd-cfDNA levels of subjects without rejection or infection were 0.52±0.8% and 0.28% [N=56, n=87], and peaked at 1.03±0.7% and 0.74% within 1-month post-PTx. Mean and median dd-cfDNA levels of subjects with suspicion of rejection were 0.88±1.3% and 0.50% [N=19, n=34]. Mean and median dd-cfDNA levels of subjects at time of infection were 0.69±1.1% and 0.27% [N=43, n=89]. Figure 1 shows dd-cfDNA trends without rejection or infection, revealing an initial elevation in dd-cfDNA <3 months post-PTx (mean 0.85±1.0%, median 0.63%), followed by stabilization >3 months post-PTx (mean 0.3±0.4%, median 0.20). Figure 2 compares dd-cfDNA during rejection, infection and no known complications following stabilization >3 month post-PTx.

*Conclusions: The mean dd-cfDNA level for PTx recipients is <1.0%, consistent with the published KTx rejection threshold of >1.0%. Early levels of dd-cfDNA (>1.0% at 1 month) are transiently higher than later measurements. PTx dd-cfDNA elevation also correlates with rejection and infection. dd-cfDNA is a promising biomarker for PTx immune and infectious complications. Additional data are needed to define a true rejection threshold.

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