Role of mTOR Inhibitors in Pediatric Liver Transplant Recipients: A Systematic Review

Immunosuppressive medications play a crucial role in determining both organ and patient survival following liver transplantation (LT). Typically, immunosuppressive protocols for pediatric LT patients rely on calcineurin inhibitors (CNIs). While inhibitors of mammalian target of rapamycin (mTOR) have demonstrated beneficial outcomes in adult recipients of liver allografts, such as improved renal function post-LT, their application in pediatric liver transplant recipients is a subject of debate due to uncertain efficacy and potential adverse effects.

This review evaluates the potential roles of mTOR inhibitors in the context of pediatric LT patients.

This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol for conduct and reporting. Databases until 31 August 2023 were searched using specific terms and keywords. All clinical studies focusing on mTOR inhibitors in pediatric LT were included.

Out of 888 identified articles, 30 studies, involving 386 children who had undergone liver transplantation and received mTOR-inhibitor-based immunosuppressive regimens, met the inclusion criteria. The beneficial impacts of switching from a CNI to an mTOR inhibitor or adding an mTOR inhibitor to CNI-reduced immunosuppression in LT pediatric patients with impaired kidney function are controversial, and high-powered clinical studies are need. It appears that enhancing immunosuppression by adding an mTOR inhibitor to CNI is helpful for pediatric LT recipients who are experiencing refractory acute rejection or chronic rejection. mTOR-inhibitor-containing regimens failed to reduce the occurrence of post-transplant lymphoproliferative disorders (PTLD) among children with LT that may be due to concomitant high CNI concentration among studied patients. The effectiveness of mTOR inhibitors in treating PTLD remains uncertain; however, in patients with PTLD who are at high risk of rejection, mTOR inhibitors may be administered. Conversion to or the addition of mTOR inhibitors to maintenance immunosuppression seems to be suitable for pediatric patients who received a transplant due to hepatic malignancies such as hepatoblastoma or hepatocellular carcinoma or for those with post-transplant primary or recurrent malignancies. Switching to an mTOR inhibitor may improve some CNI-related adverse effects such as gingival hyperplasia, neurotoxicity, nephropathy, hypertrophic cardiomyopathy, or thrombotic microangiopathy.

Although the exact role of mTOR inhibitors among pediatric patients who have received a liver transplant needs further study, two algorithms are presented in this review to guide conversion from CNIs to mTOR inhibitors or the addition of mTOR inhibitor to a CNI-minimization immunosuppressive regimen for pediatric patients who may benefit from this class of drugs. This review mainly consisted of retrospective studies with inadequate sample sizes and lacked a control group, which represents the main limitation of this study.