Steroid-Responsive Acute Rejection Should Not Be the End Point for Immunosuppressive Trials

Evolution of the Definition of Rejection in Kidney Transplantation and Its Use as an Endpoint in Clinical Trials

This article outlines the evolving definition of rejection following kidney transplantation. The viewpoints and evidence presented were included in documentation prepared for a Broad Scientific Advice request to the European Medicines Agency (EMA), relating to clinical trial endpoints in kidney transplantation. This request was initiated by the European Society for Organ Transplantation (ESOT) in 2016 and finalized following discussions between the EMA and ESOT in 2020. In ESOT’s opinion, the use of “biopsy-proven acute rejection” as an endpoint for clinical trials in kidney transplantation is no longer accurate, although it is still the approved histopathological endpoint. The spectrum of rejection is now divided into the phenotypes of borderline changes, T cell-mediated rejection, and antibody-mediated rejection, with the latter two phenotypes having further subclassifications. Rejection is also described in relation to graft (dys)function, diagnosed because of protocol (surveillance) or indication (for-cause) biopsies. The ongoing use of outdated terminology has become a potential barrier to clinical research in kidney transplantation. This article presents these perspectives and issues, and provides a foundation on which subsequent articles within this Special Issue of Transplant International build.

Early Corticosteroid Cessation vs Long-term Corticosteroid Therapy in Kidney Transplant Recipients: Long-term Outcomes of a Randomized Clinical Trial

Importance

The complications of corticosteroids make the inclusion of these drugs in immunosuppressive protocols for kidney transplant patients undesirable. However, cessation of corticosteroids is associated with a higher risk of short-term rejection, and the long-term outcomes of patients withdrawn from corticosteroids remain uncertain.

Objective

To compare long-term kidney transplant outcomes of patients randomized to continue or withdraw corticosteroids.

Design, Setting, and Participants

This prospective multicenter randomized double-blind placebo-controlled trial was conducted between November 1999 and December 2002 with linkage to a mandatory national registry with validated outcome ascertainment until June 8, 2018. The study included 28 kidney transplant centers in the United States, including 386 low- to moderate-immune risk adult recipients of a living or deceased donor kidney transplant without delayed graft function or short-term rejection in the first week after transplant. Analyses were intention to treat. Analysis began September 2018 and ended June 2019.

Interventions

Patients were randomized to receive tacrolimus and mycophenolate mofetil with or without corticosteroids 7 days after transplant.

Main Outcomes and Measures

Kidney allograft failure from any cause including death and allograft failure censored for patient death defined by the requirement for long-term dialysis or repeat transplant.

Results

Of 385 patients, 191 were assigned to withdraw from corticosteroids (mean [SD] age, 46.5 [12.1] years), and 194 patients were assigned to continued corticosteroids (mean [SD] age, 46.3 [12.6] years). The median (interquartile range) follow-up time was 15.8 (12.0-16.3) years after transplant. The adjusted hazard ratios of allograft failure from any cause including death was 0.83 (95% CI, 0.62-1.10; P = .19) and for allograft failure censored for patient death was 0.78 (95% CI, 0.52-1.19; P = .25) and did not differ between the patients assigned to withdraw from corticosteroids vs assigned to continued corticosteroids. Results were consistent in a per-protocol analysis among 223 patients who continued the trial-assigned treatment of corticosteroid withdrawal (n = 114) or corticosteroids (n = 109) through at least 5 years after transplant. The outcomes of trial participants in either treatment group did not differ from similarly treated contemporary registry patients who met trial eligibility criteria and were treated with the same immunosuppressive drugs.

Conclusions and Relevance

Long-term corticosteroids may not be necessary as part of a calcineurin-based multiple drug immunosuppressive regimen in low- to moderate-immune risk kidney transplant recipients.

Discovery of a Potent, Orally Bioavailable PI4KIIIβ Inhibitor (UCB9608) Able To Significantly Prolong Allogeneic Organ Engraftment in Vivo

The primary target of a novel series of immunosuppressive 7-piperazin-1-ylthiazolo[5,4- d]pyrimidin-5-amines was identified as the lipid kinase, PI4KIIIβ. Evaluation of the series highlighted their poor solubility and unwanted off-target activities. A medicinal chemistry strategy was put in place to optimize physicochemical properties within the series, while maintaining potency and improving selectivity over other lipid kinases. Compound 22 was initially identified and profiled in vivo, before further modifications led to the discovery of 44 (UCB9608), a vastly more soluble, selective compound with improved metabolic stability and excellent pharmacokinetic profile. A co-crystal structure of 44 with PI4KIIIβ was solved, confirming the binding mode of this class of inhibitor. The much-improved in vivo profile of 44 positions it as an ideal tool compound to further establish the link between PI4KIIIβ inhibition and prolonged allogeneic organ engraftment, and suppression of immune responses in vivo.

Clinical Evaluation of Modified Release and Immediate Release Tacrolimus Formulations

The science of drug delivery has evolved considerably and has led to the development of multiple sustained release formulations. Each of these formulations can present particular challenges in terms of clinical evaluation and necessitate careful study to identify their optimal use in practice. Tacrolimus is an immunosuppressive agent that is widely used in organ transplant recipients. However, it is poorly soluble, has an unpredictable pharmacokinetic profile subject to important genetic polymorphisms and drug-drug interactions, and has a narrow therapeutic index. For these reasons, it represents an agent that could benefit from modified release formulations to overcome these limitations. The objective of this review is to discuss the clinical evaluation of immediate and modified release tacrolimus formulations in renal transplant recipients. Clinical trials from early development of immediate release tacrolimus to formulation-specific post-marketing trials of modified release tacrolimus formulations are reviewed with an emphasis on key elements relating to trial design end endpoint assessment. Particular elements that can be addressed with formulation alterations, such as pharmacokinetics, pharmacogenomics, and toxicity and corresponding clinical evaluations are discussed. In addition, current knowledge gaps in the clinical evaluation of immediate and modified release tacrolimus formulations are discussed to highlight potential avenues for the future development of different tacrolimus formulations with outcomes relevant to the regulators, the transplant community, and to transplant recipients. This review shows that new formulations may alter tacrolimus bioavailability, alleviate certain adverse events while potentially enhancing patient convenience.