ABO blood group compatibility restrictions present the first barrier to donor-recipient matching in kidney transplantation. Here, we present the use of two enzymes, FpGalNAc deacetylase and FpGalactosaminidase, from the bacterium Flavonifractor plautii to enzymatically convert blood group A antigens from the renal vasculature of human kidneys to ‘universal’ O-type. Using normothermic machine perfusion (NMP) and hypothermic machine perfusion (HMP) strategies, we demonstrate blood group A antigen loss of approximately 80% in as little as 2 h NMP and HMP. Furthermore, we show that treated kidneys do not bind circulating anti-A antibodies in an ex vivo model of ABO-incompatible transplantation and do not activate the classical complement pathway. This strategy presents a solution to the donor organ shortage crisis with the potential for direct clinical translation to reduce waiting times for patients with end stage renal disease.

Kidney transplantation remains the best therapeutic option for patients with end-stage kidney disease, and yet a major restriction to transplantation is the requirement for ABO blood group compatibility between donor and recipient. This requirement prevents the recipient’s pre-existing circulating antibodies from initiating antibody-mediated damage to a graft expressing incompatible antigens, which may lead, in extreme cases, to hyperacute rejection^1–3. This short report details, for the first time, the successful use of an α-galactosidase enzyme to remove type B blood group antigens from human kidneys as a strategy for overcoming the ABO barrier in kidney transplantation.

The use of high-risk renal grafts for transplantation requires the optimization of pretransplant assessment and preservation reconditioning strategies to decrease the organ discard rate and to improve short- and long-term clinical outcomes. Active oxygenation is increasingly recognized to play a central role in dynamic preservation strategies, independent of preservation temperature, to recondition mitochondria and to restore the cellular energy profile. The oxygen-related decrease in mitochondrial succinate accumulation ameliorates the harmful effects of ischemia-reperfusion injury. The differences between normothermic and hypothermic machine perfusion with regard to organ assessment, preservation, and reconditioning, as well as the logistic and economic implications, are factors to take into consideration for implementation at a local level. Therefore, these different techniques should be considered complementary to the perfusion strategy selected depending on functional intention and resource availability. This review provides an overview of the current clinical evidence of normothermic and oxygenated hypothermic machine perfusion, either as a continuous or end-ischemic preservation strategy, and future perspectives.

Normothermic machine perfusion (NMP) typically uses red blood cell (RBC)-based perfusates, with associated challenges, including free haem-driven ferroptotic tubular injury. Acellular perfusates avoid these risks. Subnormothermic machine perfusion (SMP, 32°C) may reduce metabolic demands while preserving organ viability, but the effect of perfusate type under these conditions remains unclear. In a paired experimental design, kidneys from eight deceased donors were randomized 1:1 to 6 hours of SMP with RBC-based (RBC-SMP) or acellular perfusate (SNAP), followed by 4 hours of RBC-based NMP (37°C) to simulate reperfusion. Upregulation of transcriptomic ischaemia-reperfusion injury (IRI) related pathways and downregulation of oxidative phosphorylation at 6 hours SMP and 4 hours reperfusion were similar between RBC-SMP and SNAP kidneys. No differences were observed between groups in transcriptional profiles, metabolic pathway scores, urinary tubular injury biomarker concentrations, or histology. We integrated publicly available NMP transcriptomic data for comparison, demonstrating that compared to 6 hours RBC-NMP at 37°C, both SMP groups showed equivalent pro-inflammatory pathway activation and oxidative phosphorylation depletion. Thus, we provide evidence that SNAP maintains kidneys with equivalent transcriptional and urinary tubular injury biomarker profiles to RBC-SMP. These findings support the feasibility of SNAP for clinical translation in future studies.

Normothermic machine perfusion (NMP) typically uses red blood cell (RBC)-based perfusates, which is associated with logistical challenges. Subnormothermic machine perfusion (SMP, 32°C) may reduce metabolic demands while preserving organ viability, but the effect of perfusate type under these conditions remains unclear. In a paired experimental design, kidneys from eight deceased donors were randomized 1:1 to 6 hours of SMP with RBC-based (RBC-SMP) or acellular perfusate (SNAP), followed by 4 hours of RBC-based NMP (37°C) to simulate reperfusion. Upregulation of transcriptomic ischaemia-reperfusion injury (IRI) related pathways and downregulation of oxidative phosphorylation at 6 hours SMP and 4 hours reperfusion were similar between RBC-SMP and SNAP kidneys. No differences were observed between groups in transcriptional profiles, metabolic pathway scores, urinary tubular injury biomarker concentrations, or histology. We integrated publicly available NMP transcriptomic data for comparison, demonstrating that compared to 6 hours RBC-NMP at 37°C, both SMP groups showed equivalent pro-inflammatory pathway activation and oxidative phosphorylation depletion. Thus, we provide evidence that SNAP maintains kidneys with equivalent transcriptional and urinary tubular injury biomarker profiles to RBC-SMP. These findings support the feasibility of SNAP for clinical translation in future studies.