Characterising prognostic complement biomarkers during clinical normothermic machine perfusion for renal...

Complement activation during clinical kidney normothermic machine perfusion (NMP) is poorly defined. We examined whether perfusate complement biomarker levels measured during prolonged NMP were associated with early graft recovery. Samples and outcome data were obtained from the normothermic kidney perfusion 1 phase-1 trial of prolonged kidney NMP before transplantation (n = 36). Perfusate complement component 1s, collectin-11, complement component 2, complement component 3, complement component 3d, factor B, complement factor B activation fragment Ba, and soluble terminal complement complex/membrane attack complex (C5b-9) levels were measured at hour 1 and at the end of perfusion. Associations with functional delayed graft function and the time to 50% fall in serum creatinine levels were assessed using nonparametric testing, Kaplan-Meier analysis, and Cox models incorporating the United Kingdom donor risk index (UKDRI). Paired preperfusion and postreperfusion biopsies underwent multiplex immunofluorescence for complement component 4d, C5b-9, and intercellular adhesion molecule 1 levels. Complement component 1s, collectin-11, complement component 3d, and soluble C5b-9 levels increased during NMP, whereas complement component 2 and factor B levels decreased. Kidneys developing functional delayed graft function had higher end-perfusion soluble C5b-9 and hour-1 complement component 3 levels, both significant after false discovery rate correction. Complement profiles stratified using the time to 50% fall in serum creatinine levels, including within UKDRI score strata, and an hour-1 grouping improved Cox model fit beyond UKDRI score alone. Postreperfusion tissue C5b-9 and intercellular adhesion molecule 1 levels increased, whereas complement component levels did not. Complement activation during prolonged NMP is associated with early graft outcomes and may support biomarker level-guided assessment and future targeted intervention in clinical kidney transplantation practice.