A novel urine cell‐free DNA preservation solution and its application in kidney transplantation

Aim Urine cell‐free DNA (cfDNA) is a new type of liquid biopsy biomarker used in tumours and allograft injury detection but is highly susceptible to degradation by the high nuclease activity of urine. This study presents a newly developed urine cfDNA preservation solution (AlloU), efficient for examining allograft injury in kidney transplant recipients (KTx). Methods We established urine‐preserve solution called AlloU based on the response‐surface methodology, with two commercial collection reagents (Streck and K2 EDTA preservation solution) included for analysis. A total of 120 urine samples from KTx patients, including morning, nocturnal and random urine from specific storage time were subjected to investigation. The urine total cfDNA concentration was quantified by fluorometry, fragment distribution was analysed by qPCR, and donor‐derived cfDNA (ddcfDNA) was detected by next‐generation sequencing. Results Urine total cfDNA concentration and fragment size of samples preserved with AlloU and Streck did not change significantly within 5 days whereas the ddcfDNA also did not change significantly within 7 days. However, compared with EDTA, the total cfDNA concentration increased significantly on the third day. When compare with different urine types, it was found that samples preserved with AlloU showed no significant differences in total cfDNA concentration, fragment size, and ddcfDNA concentration, however, the SD for morning urine was significantly smaller in total cfDNA and ddcfDNA concentration. Conclusion To the best of our knowledge, this is the first report to verify the dynamics of urine cfDNA in KTx, especially in the analysis impact of different urine types on cfDNA detection. SUMMARY AT A GLANCE Urinary cfDNA storage tube used in KTx.