The Top 12 Most Impactful Papers in Clinical Transplantation in 2025: TI Editors’ Choice

The New Year is a perfect opportunity, not only for resolutions (that are unlikely to last very long), but also to reflect on the events of the past year and how they are likely to impact the future. In this piece, the editorial board of Transplant International is presenting what we think are the original articles in clinical transplantation published in 2025 that are the most likely to be game changers in our field in the near or not-so-near future. As the saying goes, "it is diaicult to make predictions, especially about the future", but despite the (very limited) risk, we are hopeful that we have not succumbed to hype in our selection, which was based on insights from members of the editorial board, but also on how well cited these papers already were. So, here are the top 12 papers, listed in Table 1, grouped by the topic they address. Selection is obviously a tricky task and for this reason, we will also mention other significant 2025 papers to provide the readers with a somewhat broader picture of what has happened in each of the selected topics (Supplementary Table 1).Xenotransplantation (1,2) Xenotransplantation has repeatedly made the headlines in recent years since the nearsimultaneous transplantation in the fall of 2021of genetically modified porcine kidneys into human brain-dead recipients, or what is called the human decedent model (13). The availability of genome-edited pigs has been the game changer in the field, allowing to significantly lower the immune barriers met in xenotransplantation (14). The first clinical transplants using this resource were performed compassionately in 2022 in patients with no access to deceased donor organs and a compromised survival prognosis in the short term. Although the heart and the kidney xenotransplant recipients did not survive more than a few months, their causes of death not being fully clear, these first 2 cases provided evidence that the early phases of immune xenorejection had been harnessed (1,2) thanks to the gene modification strategy, in particular the knocking oa of 3 carbohydrate antigen genes known to cause hyperacute rejection (α 1-3 Gal, β 1-4 Gal, CMAH). The two featured articles provide a comprehensive narrative of the clinical course of the first heart recipient (1) and the first kidney recipient (2), from transplantation to death. While these cases cannot be considered successes from the patient perspective, they will provide invaluable information on the unforeseen hurdles met and how to overcome them (15). In this regard, and despite the limitations of the decedent model (16), the in-depth analysis of the physiology, immunology and pathology of the first pig-to-human decedent kidney xenotransplant (single gene modification), using multi-omics analysis techniques (17,18), and in particular the novel patterns of immune rejection unveiled and characterized, will also contribute to the better understanding of the physiological processes that will have to be tackled by the next generation of protocols and gene-edited animals. This paragraph would not be complete without mentioning the reports a case of geneedited pig-to-human auxiliary liver transplantation in a living recipient, as a bridge to transplant (19), and lung transplantation using the decedent model (20). Although the cell therapy procedure of islet transplantation would seem to have been an easier clinical model to explore in xenotransplantation, no attempt at transplanting genetically modified porcine islets has been reported to date (21).ABO-incompatible living-donor kidney transplantation has evolved into a standard option to expand the donor pool, but it usually requires desensitization to mitigate the risk posed by preformed anti-A/B antibodies. Protocols commonly include antibody removal (immunoadsorption/antibody adsorption and/or plasma exchange) alongside immunomodulatory therapy, adding complexity, cost, and potential morbidity despite outcomes approaching those of ABO-compatible living-donor transplantation. Kidney paired exchange is an alternative, although limited O-compatible availability may lead to extended waiting times for patients bearing the O blood group. This paper reports the successful conversion of an A blood group kidney into O blood group, using α-galactosidase from Bacteroides fragilis during hypothermic machine perfusion. Three hours of machine perfusion were suaicient to remove >95% of blood group A antigens and allowed successful transplantation of the kidney in a decedent model without experiencing hyperacute rejection (3). After A-antigen regeneration, antibody-mediated lesions and complement deposition were found starting 3 days post-transplant, but single-cell sequencing confirms the elevated expression of accommodation-related genes, suggesting the potential for longer-term tolerance (3). This paper was published a few months after a previous similar report in the less common B-to-O combination, with similar outcomes (22). These two papers provide compelling proof of concept that ex vivo antigen modification can safely expand the donor pool in ABO-incompatible living kidney donation and may therefore fundamentally reshape access in kidney transplantation. This strategy could also be employed in a deceased donor setting in the most urgent cases. While the validity of this method requires confirmation in the setting of clinical live donor kidney transplantation, it could also be explored in the more challenging model of liver transplantation, in which traditional techniques of pre-transplant ABO antibody clearance can be associated with deleterious outcomes (23).The field of islet of Langerhans transplantation has seen 2 landmark clinical papers published last year. They represent a major step forward in beta-cell replacement therapies. The studies show that immune rejection and limited cell availability can be addressed. They set new benchmarks for safety, eaicacy, and translational feasibility. Importantly, they provide insights to guide the next generation of durable islet replacement strategies. They also provide strategies that have the potential to be applied in the bioengineering of other organs.The first is a proof-of-concept article in which the authors have applied their hypoimmune platform (HIP) approach to human primary islet cells. For the first time, they demonstrated the feasibility of gene-editing dissociated human islets using CRISPR-Cas12b and lentiviral transduction, to knock out HLA class I and II genes and overexpress the CD47 transmembrane molecule, which delivers a "don't eat me" signal to cells of the innate immune system. These modified islet cells were then re-aggregated and transplanted into the forearm muscle of a patient with long-standing type 1 diabetes. In this first-in-human study, HIP allogeneic islet cells transplanted without immunosuppression (IS) were not rejected, remained functional up to 12 weeks and achieved functional glucose-responsive insulin secretion. Meanwhile, this provides a landmark proof of concept that immune evasive cells can be generated by gene modification and could overcome one of the central barriers to curative cell therapy for type 1 diabetes. By design, the functional mass of endocrine cells implanted was insuaicient to reverse diabetes, and diaiculties in upscaling the technique to a suaicient islet mass can be anticipated. It should be mentioned that, before going to the clinical setting, the authors had reported successful reversal of diabetes, using the same islet modification methodology, in a humanized mouse model transplanted with human HIP stem cell islets (24) and remarkably in an allogeneic non-human primate model (25).The second landmark paper in the islet transplantation field reported the results of transplantation of stem cell-derived islets in 14 patients with type 1 diabetes (5). This trial was led by the Vertex company and utilized a cell product baptized zimislecel, obtained by an in vitro diaerentiation protocol able to obtain large quantities of fully diaerentiated and glucose-responsive islets (26). The trial was designed as phase 1-2 to determine safety and eaicacy of the product, and the paper is an unplanned interim analysis of the first 12 patients to have received a full dose of the product and completed a 12-month follow-up. The primary eaicacy endpoint was freedom from severe hypoglycemic events until day 365 after infusion, with a glycated hemoglobin level < 7%. Remarkably, all patients met the primary endpoint and 10/12 patients were insulin-independent at 1 year. All patients who came oa insulin did so after a period of several months, suggesting that further diaerentiation may have been taking place in vivo after transplantation (5). These data demonstrate a formidable technological and clinical achievement and advance and provide the first evidence that stem cell-derived tissues can be successfully used as an organ replacement therapy. However, zimislecel administration was done similarly to islet transplantation and used an identical IS protocol; accordingly, the clinical outcomes were similar to those achieved with the landmark "Edmonton protocol" (27). While zimislecel may become a solution in the USA, where allogeneic islet transplantation is essentially unavailable (29), several issues will have to be solved before it can become a real solution for bringing a cure to all type 1 diabetic patients (21). The application of the immune evasiveness strategy described above (4) to stem cell-derived islets may become a solution to that end.Ex vivo machine perfusion has rapidly developed in the last decade, driven by the everincreasing gap between the numbers of donor organs and patients on the waiting list concomitantly with the increase in the proportion of extended criteria and marginal donors (older age, DCD, fatty livers,…). Hypothermic (HMP), hypothermic oxygenated and later, normothermic machine perfusion (NMP) have become a standard-of-care solution for the reconditioning of marginal organs (29,30). Machine perfusion also oaers the possibility of assessing physical or biological parameters in the perfusate to provide information about organ quality, and thus transplantability (31).The seminal multicenter European randomized controlled trial (RCT), comparing hypothermic kidney perfusion, using the Organ Recovery Systems machine, to cold storage enrolled >800 patients and its results were published already in 2009. The primary endpoint of the trial, i.e. occurrence of delayed graft function, was verified, thus demonstrating a significantly lower rate of delayed graft function in the perfusion group. Superior 1-year graft survival was also reported (32). Better graft survival was still observed in a 3-year follow-up paper (33). The article selected presents the longawaited 10-year data (6). Remarkably, the graft survival advantage was still present, and the long term observation revealed that this advantage was only conferred to expanded criteria donors (6). This paper provides compelling evidence to recommend HMP for all kidneys procured from expanded criteria donors, notably DCDs.Advances and utilization of machine perfusion technology have largely been driven by the kidney and liver transplantation fields. The amount of evidence gathered for thoracic organs has been less extensive and has mostly addressed lung transplantation (34,35). The rapid development of DCD heart transplantation in the past decade has provided an incentive for maximizing utilization of DCD hearts using machine perfusion technology.In contrast to kidneys and livers, NMP has been the preferred, and indeed sole, approach employed in this setting (38). Unfortunately, and perhaps for understandable reasons, no prospective randomized trial is available to compare NMP to static cold storage (SCS) in DCD hearts.The OCS NMP machine (Transmedics, Andover, MA, USA) is the only one approved for clinical use in the USA. It allows normothermic pulsatile perfusion during transportation of the heart from recovery to implantation. The selected paper is a Transmedics-led study combining data from the OPTN and OCS Heart Perfusion (OHP) registries and providing real-world data on the largest cohort (854 patients in 56 US centers) of NMPpreserved heart transplants ever reported (7). The large numbers (> 3000 subjects, including OPTN data) and a rigorous methodology have allowed meaningful comparisons of DCD versus DBD cohorts, and NMP versus SCS strategies. The most striking result is the similar 1-year patient survival data in SCS-preserved DBD hearts and NMP-preserved DCD hearts (>90%), observed in spite of 2-3 times longer travelling distances and times. It is remarkable that >25% of hearts transplanted in the USA over the study period were preserved with NMP and <4% of procured NMP hearts were finally rejected (7). In summary the study convincingly shows that NMP allows the recovery of hearts with longer shipping distances and from extended-criteria donors. This is likely to lead to the rapid normalization, in the USA and beyond, of NMP for the preservation of DCD and other marginal donor hearts.Transplant oncology (8) Hepatocellular carcinoma (HCC) is the third most important indication for liver transplantation after alcohol-associated cirrhosis and metabolic dysfunctionassociated steatohepatitis (37). Recently, Immune checkpoint inhibitors (ICIs) have revolutionized the management of HCC and become standard-of-care as part of the treatment of advanced HCC (38). This has allowed not only prolonged patient survival, but also tumour downstaging, bringing patients within Milan or other liver transplantability criteria. Unfortunately, the mechanism of action of ICIs, which essentially boosts the adaptive immune system against the tumour, has resulted in the early experience in a high risk of acute rejection episodes in ICI-treated patients receiving a liver transplant (38,39). A consensus has evolved to suggest that ICIs were a powerful neoadjuvant therapy for downstaging or bridging purposes, but that the optimal "washout" period (free interval between end of ICI treatment and liver transplantation) was to be determined (40).The selected paper is a multi-center retrospective study of 119 liver transplant patients treated with ICIs before liver transplantation in 29 transplant centers worldwide (8). The authors analyzed the relationship between the washout period and several outcome measures, including occurrence and type of rejection, tumour recurrence and survival. They reported a 20% rejection rate, occurring early after transplantation, with a linear reverse relationship between rejection risk and washout period between 3 and 50 days. Beyond 50 days an increased rejection risk was no longer observed. Importantly, with a median follow-up of 18 months, patients with a longer washout period did not present a higher risk for HCC recurrence. There is a caveat with the fact that 9 diaerent ICIs were used in these 119 patients, making it diaicult to determine, due to low numbers, whether the 50-day cut-oa was applicable equally to each of these molecules. Nonetheless, this is the first study to provide convincing evidence about the optimal washout period to observe and the uselessness of waiting times >50 days before performing liver transplantation ICI-treated HCC patients.The field of liver transplantation oncology is not limited to HCC, as unresectable colorectal liver metastases are increasingly becoming a valid indication for liver transplantation in selected cases. The ARTx-Onc study (41) provides a US perspective and favourable outcome results that slightly diaer from those of the recent European Transmet RCT (42).BK polyomavirus nephropathy is a significant challenge for the transplant nephrologist that can have a serious impact on kidney graft function and compromise graft survival in the most serious cases. The standard IS regimen associating tacrolimus, mycophenolate (MMF) and steroids is the primary risk factor for BK viral replication, with a high risk of developing BK nephropathy. The primary strategy in the management of BK virus infection is reduction of the IS at the risk of triggering graft rejection. Due to their antireplicative properties, mTOR inhibitors, well established IS drugs, have demonstrated potent in vitro antiviral activity, including against BK polyomavirus. Accordingly, RCTs exploring the eaicacy of everolimus-based versus MMF-based IS regimens in kidney transplantation have also looked at the occurrence of BK infection and nephropathy. It was found that subjects receiving everolimus had experienced a lower rate of BK infection at 12 months, but none of these studies consistently monitored BK DNA levels (43,44). Therefore, the real role of a switch from MMF to everolimus remains undetermined and prompted the authors of this paper to launch a RCT comparing the eaicacy of reducing MMF dosage versus switching from MMF to everolimus, alongside in kidney transplant recipients with BK their the authors found that BK virus clearance was achieved significantly more and more rapidly in patients with MMF dosage reduction to those to of kidney function at the end of follow-up were identical in These data challenge the that a switch to mTOR inhibitors will lead to clearance of BK the it for BK in kidney transplant recipients and cannot be as a management strategy for BK of HLA has been utilized as an for years as a strategy to antibody and rejection for most organ A role for the innate immune system in the of graft rejection has been in recent years The to be are cell and the signal In the selected the authors have the impact of in the gene signal on the risk of rejection They first determined that only 2 were present in of the human In two of patients subjects, they found that were associated with an increased risk of rejection, graft and survival. in and graft were not only but also For the most acute survival was and graft survival was at years In a they were able to show that to CD47 in These results may impact on strategies and on the of innate and not only of with the of only 2 to and the high impact on kidney the of and could be an and strategy to as a of kidney pathology the has been the consensus system that the and of kidney graft rejection. 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