To measure serum cell-free DNA (cf-DNA) and donor-derived cell-free DNA (ddcf-DNA) in simultaneous pancreas-kidney transplantation recipients by the next generation sequencing technology and evaluate the relationship between ddcf-DNA and early acute rejection (AR).

A total of 20 recipients who underwent simultaneous pancreas-kidney transplantation in the Department of Organ Transplantation, the Second Affiliated Hospital of Guangzhou Medical University from June 2019 to June 2021 were enrolled. According to whether there was AR after operation, the 20 recipients were divided into two groups: control group (10 cases) and AR group (10 cases). Three recipients in the control group were selected as the observation group by the random number table. The serum levels of ddcf-DNA were measured before transplantation, 2 h after recanalization of blood vessel of transplanted pancreas, and 1, 3, 7, 14, 30, and 60 d after transplantation. The levels of serum ddcf-DNA in the other 7 recipients in the control group were measured before and 14 and 30 d after transplantation. Meanwhile, the testing time points of serum ddcf-DNA in AR group were as follows: before operation, during rejection and after reversal of rejection. The measurement data of normal distribution between the two groups were compared by group t test. Fisher′s exact probability method was used for counting data comparison. P<0.05 means the difference was statistically significant.

The length of ddcf-DNA fragment was 110-350 bp. The length of cf-DNA fragment from the recipients was 100-420 bp. Three recipients in the observation group were marked as cases 1, 2 and 3, respectively. The content of ddcf-DNA of the 3 recipients before operation were 0.49%, 0.55% and 0.32%, respectively. The content of ddcf-DNA increased sharply to 12.05%, 10.64% and 11.05% 2 h after recanalization, and reached its peak after blood flow restored. At the first day after transplantation, the level of ddcf-DNA showed a significant downward trend, and reached a stable state about 30 d after transplantation. The content of ddcf-DNA was (0.71%±0.09%) in the control group and (0.66±0.10)% in the AR group. There was no significant difference between the two groups (t=1.126, P>0.05). The time of diagnosis of rejection in AR group was (17±4) d after transplantation, and the content of serum ddcf-DNA was (5.4±2.0)% when AR was confirmed; while the content of serum ddcf-DNA in the control group was (1.70±0.48)% 2 weeks after transplantation, and the difference was statistically significant (t=-5.59, P<0.05). The rejection was reversed and the recipients condition were stable at (27 ± 4) d after transplantation in the AR group, at which time the content of ddcf-DNA was (0.93 ± 0.32)%. The content of ddcf-DNA in the control group was (0.87±0.25)% on the 30th day after transplantation, and the difference was not statistically significant between the 2 groups (t=-0.497, P>0.05).

The serum ddcf-DNA in simultaneous pancreas-kidney transplantation recipients increased significantly when AR occurred. When AR was reversed, the content of ddcf-DNA showed a significant downward trend.