Introduction: During the process of transplantation, detrimental events such as ischemia inflict harm to, and change the cell phenotype of organs, which increases the susceptibility to an early innate immune attack post-reperfusion. Here, we present data on a detailed systematic characterization of this early response post-reperfusion and its possible impact on outcome after kidney transplantation.

Method: Sixty-three consecutive kidney transplant recipients were included. Twenty-six (41%) and 37 (59%) patients received kidneys from living (LD) and deceased donors (DD), respectively. Fifteen DD-kidneys (41%) were preserved with hypothermic machine perfusion (DDmp) and 22 (59%) were preserved in cold storage (DDcs). Four venous EDTA blood samples were collected intra-operatively at baseline (pre-reperfusion from the external iliac vein) and at 1-, 10- and 30-minutes post-reperfusion from the proximal portion of the transplant vein. Samples were handled according to a meticulous and standardized routine including immediate and sustained cooling with subsequent storage of plasma samples at -80 °C. Biomarkers for the complement, coagulation and contact cascade systems were measured. Clinical outcome data for a total of 24 months were collected. Non-parametric analysis of variances on aligned rank transformed data and receiver operating characteristics (ROC) analyses were used.

Results: Patient and graft survival did not differ between DD and LD by 24 months. There were no differences in donor age/BMI between LD and DD recipients. The median kidney-donor-risk-index did not differ between DDcs and DDmp (1.56 vs 1.5). Median cold ischemic times in DDcs and DDmp were 11.4 and 13 hours, respectively. Overall, 6 patients (9.5%, all DD-recipients) experienced delayed graft function (DGF). Thromboinflammation, defined as co-activation of complement (sC5b-9), coagulation (FXIa, thrombin) and contact (FXIIa, KK) cascade systems, was detected instantly post-reperfusion in DD-kidneys (predominantly in DDcs), while being largely absent in LD-kidneys. Analyzing the slopes for serum-creatinine and eGFR between 3 to 24 months post-transplant, the release of sC5b-9 at 30 min post-reperfusion correlated with a higher serum-creatinine and lower GFR slope in DDcs, but not in LD and DDmp. Thrombin, sC5b-9, FXIa and FXIIa were predictive for DGF, de novo DSA and rejection.

Conclusion: Instant post-reperfusion thromboinflammation (IPRT) occurs in DD-kidneys exposed to ischemia, while being largely absent in LD-kidneys. This early innate immune response may be associated with impaired mid-term graft function, even in the current population with a low burden of ischemia. Furthermore, markers of IPRT were predictive for outcome measures such as DGF and rejection. Lastly, hypothermic machine perfusion seems to reduce IPRT.