<p><b>PURPOSE: </b>Currently there are no-FDA approved immunosuppressants specific to pediatric heart transplantation (HT). In recent years, everolimus (EVL) has emerged as an alternative to tacrolimus (TAC) as a primary immunosuppressant to prevent rejection that may also prevent kidney and coronary disease. However, the two regimens have never been evaluated systematically.</p><p><b>METHODS: </b>The TEAMMATE Trial (IND 127980) is designed to evaluate the safety and efficacy of EVL and low-dose (LD-TAC) compared to standard-therapy TAC and mycophenolate mofetil (MMF). The study design and rationale are reviewed in light of challenges inherent in rare disease research.</p><p><b>RESULTS: </b>The TEAMMATE trial is the first multicenter randomized clinical trial (RCT) in pediatric HT. The primary purpose is to evaluate the risk-benefit profile of the two regimens to prevent major adverse transplant events (MATE), and to support FDA approval of 1 or both regimens for pediatric HT. Children <21 years at HT will be randomized (1:1 ratio) at 6 mo. post-HT to either regimen for 30 months (Figure). Children with recurrent rejection or a GFR <60 ml/min/1.73m2 are excluded. The primary efficacy hypothesis is that compared to TAC/MMF, EVL/LD-TAC is more effective in preventing 3 MATEs: cellular rejection, CKD and CAV. The primary safety hypothesis is that EVL/LD-TAC does not have a higher cumulative burden of 6 MATE (AMR, infection, and PTLD + the 3 above). The primary endpoint is the MATE Score, a surrogate endpoint reflecting the frequency and severity of MATEs and validated against graft loss. The study will enroll 210 patients across 26 sites and is powered to demonstrate superior efficacy of EVL/LDTAC. The trial is projected to be completed in 2022.</p><p><b>CONCLUSION: </b>The TEAMMATE trial is the first RCT in pediatric HT. It is anticipated that the study will provide important information about the safety and effectiveness of EVL and TAC and provide valuable lessons into the design and conduct of future trials in pediatric HT.</p>