Enzymatic blood group conversion of human kidneys during ex vivo normothermic machine perfusion

Prolonged normothermic perfusion of the kidney prior to transplantation: a historically controlled, phase 1 cohort study

Kidney transplantation is the preferred treatment for end-stage renal disease and is limited by donor organ availability. Normothermic Machine Perfusion (NMP) might facilitate safe transplantation of marginal organs. NKP1 is a single centre, phase 1, 36-patient, three-stage cohort study investigating the safety and feasibility of up to 24 hours of renal NMP prior to transplantation. 30-day graft survival (primary endpoint) was 100%. Secondary objectives were assessment of the effect of NMP on post-transplant clinical outcomes and ischaemia-reperfusion injury, identification of predictive biomarkers, and characterisation of the performance of the preservation system. Clinical outcomes were comparable to a matched control cohort with 12-month estimated glomerular filtration rate (eGFR) 46.3 vs 49.5 mL/min/1.73m2 (p = 0.44) despite much longer total preservation times (15.7 vs 8.9 hours controls, p < 0.0001). We saw strong correlations between biomarkers measured ex-situ and post-transplant outcomes, including graft function at one year (correlation between GST-Pi delta and 12-month eGFR, R = 0.54, p = 0.001). Renal NMP is useful for optimising logistics and as an organ assessment technique, and has potential to expand the donor pool. Trial registration number: ISRCTN13292277.

Enzymatic conversion of blood group B kidney prevents hyperacute antibody-mediated injuries in ABO-incompatible transplantation

Matching ABO blood group antigens between donors and recipients is critical to prevent hyperacute rejection in kidney transplantation. Enzymatic conversion of blood group antigens to the universal O type presents a promising strategy to overcome barriers in ABO-incompatible kidney transplantation. In this study, we employ α-galactosidase from Bacteroides fragilis to convert type B kidneys to type O during hypothermic machine perfusion. After 3 hours of perfusion with enzyme, more than 95% of blood group B antigens in the kidney endothelium are effectively removed. Subsequently, enzyme-treated kidneys are protected from antibody-mediated injuries in an ex vivo simulation of ABO-incompatible kidney transplantation. Encouraged by these results, a discarded type B kidney, following enzymatic conversion, is transplanted into a type O brain-dead recipient with high titer of anti-B antibody. The allograft survives for 63 hours without hyperacute rejection. Blood group B antigens re-express within 48 hours, with histopathological analyses indicating no evidence of antibody-mediated rejection. This enzymatic conversion approach holds the potential to broaden the practice of ABO-incompatible kidney transplantation, decrease waiting times and facilitate equitable organ allocation.

Challenges and opportunities in organ donation after circulatory death

In recent years, there has been resurgence in donation after circulatory death (DCD). Despite that, the number of organs transplanted from these donors remains low due to concerns about their function and a lack of an objective assessment at the time of donation. This overview examines the current DCD practices and the classification modifications to accommodate regional perspectives. Several risk factors underscore the reluctance to accept DCD organs, and we discuss the modern strategies to mitigate them. The advent of machine perfusion technology has revolutionized the field of DCD transplantation, leading to improved outcomes and better organ usage. With many strategies at our disposal, there is an urgent need for comparative trials to determine the optimal use of perfusion technologies for each donated organ type. Additional progress in defining therapeutic strategies to repair the damage sustained during the dying process should further improve DCD organ utilization and outcomes. However, there remains wide variability in access to DCD donation and transplantation, and organizational efforts should be doubled up with consensus on key ethical issues that still surround DCD donation in the era of machine perfusion.

Developing and Expanding Deceased Organ Donation to Its Maximum Therapeutic Potential: An Actionable Global Challenge From the 2023 Santander Summit

On November 9 and 10, 2023, the Organización Nacional de Trasplantes (ONT), under the Spanish Presidency of the Council of the European Union, convened in Santander a Global Summit entitled "Towards Global Convergence in Transplantation: Sufficiency, Transparency and Oversight." This article summarizes two distinct but related challenges elaborated at the Santander Summit by Working Group 2 that must be overcome if we are to develop and expand deceased donation worldwide and achieve the goal of self-sufficiency in organ donation and transplantation. Challenge 1: the need for a unified concept of death based on the permanent cessation of brain function. Working group 2 proposed that challenge 1 requires the global community to work toward a uniform, worldwide definition of human death, conceptually unifying circulatory and neurological criteria of death around the cessation of brain function and accepting that permanent cessation of brain function is a valid criterion to determine death. Challenge 2: reducing disparities in deceased donation and increasing organ utilization through donation after the circulatory determination of death (DCDD). Working group 2 proposed that challenge 2 requires the global community to work toward increasing organ utilization through DCDD, expanding DCDD through in situ normothermic regional perfusion, and expanding DCDD through ex situ machine organ perfusion technology. Recommendations for implementation are described.

Current Basic Research in Normothermic Machine Perfusion

BACKGROUND

Normothermic machine perfusion (NMP) is gradually being introduced into clinical transplantation to improve the quality of organs and increase utilisation. This review details current understanding of the underlying mechanistic effects of NMP in the heart, lung, liver, and kidney. It also considers recent advancements to extend the perfusion interval in these organs and the use of NMP to introduce novel therapeutic interventions, with a focus on organ modulation.

SUMMARY

The re-establishment of circulation during NMP leads to the upregulation of inflammatory and immune mediators, similar to an ischaemia-reperfusion injury response. The level of injury is determined by the condition of the organ, but inflammation may also be exacerbated by the passenger leucocytes that emerge from the organ during perfusion. There is evidence that damaged organs can recover and that prolonged NMP may be advantageous. In the liver, successful 7-day NMP has been achieved. The delivery of therapeutic agents to an organ can aid repair and be used to modify the organ to reduce immunogenicity or change the structure of the blood group antigens to create a universal donor blood group organ.

KEY MESSAGES

The application of NMP in organ transplantation is a growing area of research and is increasingly being used in the clinic. In the future, NMP may offer the opportunity to change practice. If organs can be preserved for days on an NMP system, transplantation may become an elective rather than an emergency procedure. The ability to introduce therapies during NMP is an effective way to treat an organ and avoid the complexity of treating the recipient.

Advancing immunosuppression in liver transplantation: A narrative review

Immunosuppression is essential to ensure recipient and graft survivals after liver transplantation (LT). However, our understanding and management of the immune system remain suboptimal. Current immunosuppressive therapy cannot selectively inhibit the graft-specific immune response and entails a significant risk of serious side effects, i.e., among others, de novo cancers, infections, cardiovascular events, renal failure, metabolic syndrome, and late graft fibrosis, with progressive loss of graft function. Pharmacological research, aimed to develop alternative immunosuppressive agents in LT, is behind other solid-organ transplantation subspecialties, and, therefore, the development of new compounds and strategies should get priority in LT. The research trajectories cover mechanisms to induce T-cell exhaustion, to inhibit co-stimulation, to mitigate non-antigen-specific inflammatory response, and, lastly, to minimize the development and action of donor-specific antibodies. Moreover, while cellular modulation techniques are complex, active research is underway to foster the action of T-regulatory cells, to induce tolerogenic dendritic cells, and to promote the function of B-regulatory cells. We herein discuss current lines of research in clinical immunosuppression, particularly focusing on possible applications in the LT setting.

Glycoengineering in antigen-specific immunotherapies

Advances in immunotherapy have revolutionized modern medical care paradigms. However, many patients respond poorly to the current FDA-approved treatment regimens that primarily target protein-based antigens or checkpoints. Current progress in developing therapeutic strategies that target disease-associated glycans has pinpointed a new class of glycoimmune checkpoints that function orthogonally to the established protein-immune checkpoints. Glycoengineering using chemical, enzymatic, and genetic methods is also increasingly recognized for its massive potential to improve biopharmaceuticals, such as tailoring therapies with antigen-targeting agents. Here, we review the recent development and applications of glycoengineering of antibodies and cells to suit therapeutic applications. We highlight living-cell glycoengineering strategies on cancer and immune cells for better therapeutic efficacy against specific antigens by leveraging the pre-existing immune machinery or instructing de novo creation of targeting agents. We also discuss glycoengineering strategies for studying basic immuno-oncology. Collectively, glycoengineering has a significant contribution to the design of antigen-specific immunotherapies.

Advances in the understanding and exploitation of carbohydrate-active enzymes

Carbohydrate-active enzymes (CAZymes) are responsible for the biosynthesis, modification and degradation of all glycans in Nature. Advances in genomic and metagenomic methodologies, in conjunction with lower cost gene synthesis, have provided access to a steady stream of new CAZymes with both well-established and novel mechanisms. At the same time, increasing access to cryo-EM has resulted in exciting new structures, particularly of transmembrane glycosyltransferases of various sorts. This improved understanding has resulted in widespread progress in applications of CAZymes across diverse fields, including therapeutics, organ transplantation, foods, and biofuels. Herein, we highlight a few of the many important advances that have recently been made in the understanding and applications of CAZymes.

Akkermansia muciniphila exoglycosidases target extended blood group antigens to generate ABO-universal blood

Matching donor and recipient blood groups based on red blood cell (RBC) surface ABO glycans and antibodies in plasma is crucial to avoid potentially fatal reactions during transfusions. Enzymatic conversion of RBC glycans to the universal group O is an attractive solution to simplify blood logistics and prevent ABO-mismatched transfusions. The gut symbiont Akkermansia muciniphila can degrade mucin O-glycans including ABO epitopes. Here we biochemically evaluated 23 Akkermansia glycosyl hydrolases and identified exoglycosidase combinations which efficiently transformed both A and B antigens and four of their carbohydrate extensions. Enzymatic removal of canonical and extended ABO antigens on RBCs significantly improved compatibility with group O plasmas, compared to conversion of A or B antigens alone. Finally, structural analyses of two B-converting enzymes identified a previously unknown putative carbohydrate-binding module. This study demonstrates the potential utility of mucin-degrading gut bacteria as valuable sources of enzymes for production of universal blood for transfusions.

Enzymatic conversion of human blood group A kidneys to universal blood group O

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.

Current Evidence and Future Perspectives to Implement Continuous and End-Ischemic Use of Normothermic and Oxygenated Hypothermic Machine Perfusion in Clinical Practice

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.