Introduction: Early detection and treatment of rejection after simultaneous pancreas and kidney transplant (SPKTx) is imperative to optimize outcomes. To date, serial monitoring of dd-cfDNA has shown to discriminate rejection after SPKTx, but a paucity of data describes the timeline and trajectory of dd-cfDNA changes during rejection. We describe for the first time, dd-cfDNA trajectories before & after rejection diagnosis, and within a quiescent reference cohort after SPKTx.
Method: This is a prospective, single-center study of SPKTx recipients enrolled from Nov 2018 to May 2021 that underwent serial dd-cfDNA (AlloSure®) testing at 2 weeks post SPKTx, followed by monthly for year 1, then every 3 months in years 2-3, and every 6 months thereafter. Rejection episodes included biopsy proven rejection (BR) and clinically diagnosed rejection (CR). CR was defined as a constellation of sustained elevations in dd-cfDNA, rising or dnDSA, or persistent elevations of lipase or creatinine. CR was treated presumptively. Baseline dd-cfDNA was defined as the patient specific nadir result obtained prior to rejection diagnosis. Month 0 was the date of rejection diagnosis. The reference quiescent cohort was defined as not meeting criteria for CR, BR, or other injury on biopsy during study.
Results: 371 dd-cfDNA draws from 40 SPKTx recipients were analyzed. Table 1 outlines demographics (CR = 5, BR = 3, Quiescent = 32). Rejections were diagnosed at a median of 50 months (IQR 25 - 60 months) post SPKTx. Median dd-cfDNA values rose ahead of rejection diagnosis: 0.14% at -4 months, 1.6% at -2 months, and 2.4% at -1 month  [Figure 1]. At time of rejection diagnosis (month 0), median dd-cfDNA was 1.4% (IQR 0.69-3.85%). Following diagnosis and treatment, median dd-cfDNA values fell: 0.69% at 1 month, 0.56% at 2 months, and 0.19% at 3 months. Similar trajectories were observed with CR and BR analyzed separately [Figure 2]. Median change in dd-cfDNA from baseline to rejection was 1900% (IQR 466 - 2553%) [Figure 3]. In the quiescent cohort, median dd-cfDNA levels were elevated early post SPKTx (2 weeks - 2 months) but followed a downward trajectory until reaching normal levels by 3 months and then remained relatively stable out to >2 years [Figure 4].


Conclusion: Our data highlights the importance of serial dd-cfDNA monitoring in allowing for earlier identification of evolving injury and reliable assessment of rejection treatment response following SPKTx.