The TEAMMATE Trial will enroll 210 pediatric heart transplant patients from 25 centers at 6 months post-transplant and follow each patient for 2.5 years. Half of the participants will receive everolimus and low-dose tacrolimus and the other half will receive tacrolimus and mycophenolate mofetil. The trial will determine which treatment is better at reducing the cumulative risk of coronary artery vasculopathy, chronic kidney disease and biopsy proven-acute cellular rejection without an increase in graft loss due to all causes (e.g. infection, PTLD, antibody mediated rejection).

Median survival after pediatric heart transplantation (HT) is 15 years in the current era. This means that a substantial fraction of patients transplanted during childhood fail to survive to adulthood, or require heart re-transplantation, because of complications related to heart transplant. These complications include heart transplant rejection, infection, coronary artery disease, post-transplant lymphoproliferative disorder (PTLD; a form of lymphoma seen in transplant recipients), and kidney failure. Most complications stem not from the heart transplant itself, but from the drugs commonly used to suppress the immune system in order to prevent rejection. In the US, tacrolimus (TAC) and mycophenolate mofetil (MMF), have emerged over the past decade as the standard of care for pediatric heart transplant immunosuppression. While pediatric survival has improved significantly in the era of TAC and MMF, post-HT complications remain a major problem that limits median survival to 15 years. Recently, everolimus (EVL) has emerged as a potential alternative immunosuppressant that may prevent rejection, coronary artery disease and kidney failure more effectively than TAC/MMF when administered in combination with low-dose tacrolimus (LDTAC). Preliminary studies suggest that EVL, and its first-generation analog sirolimus, are well tolerated in children after HT, regardless of whether it is started in response to coronary artery disease, in response to chronic kidney disease, or empirically 4-6 months after transplant in an effort to prevent the development of these complications1. However, studies are generally limited to single-center experiences using historical controls and have inadequate statistical power to demonstrate treatment differences. This will be the first multicenter randomized clinical trial of maintenance immunosuppression in pediatric heart transplantation to systematically evaluate the safety and efficacy of EVL with LDTAC vs. TAC/MMF to prevent long-term complications which lead to death/graft loss. The major adverse transplant event (MATE) score will serve as the primary endpoint to power the trial. Because no Food & Drug Administration (FDA)-approved immunosuppressants currently exist for children after heart transplant (all prescriptions are off-label) and market incentives to support a trial are limited, the investigators have funded the trial through a Fiscal Year 2016 Peer Reviewed Medical Research Program Clinical Trial Award sponsored by the Department of Defense office of the Congressionally Directed Medical Research Programs. It is worth noting that in contrast to adults, children have a substantially longer potential life expectancy if post-transplant complications can be minimized, making the prevention of late complications an urgent priority for the pediatric heart transplant community.

Inclusion Criteria:

1. Orthotopic heart transplantation
2. Age < 21 years at time of transplant
3. Stable immunosuppression at the time of randomization with no contraindication to everolimus, tacrolimus, or mycophenolate mofetil
4. Planned follow-up at a study site for the 30 month duration of the study.
5. Subject or legal adult representative capable of providing informed consent (in general, assent will be sought for children aged 12 years or older).

Exclusion Criteria:

1. Multi-organ transplant (e.g. heart-lung or heart-liver).
2. Known hypersensitivity to everolimus, sirolimus, tacrolimus or mycophenolate mofetil (MMF), or to components of the drug products.
3. Patients on maintenance corticosteroid therapy exceeding a dose equivalent of prednisone 0.1 mg/kg/day at randomization.
4. High-risk for rejection defined as active rejection, recurrent (≥ 2 episodes of grade 2R rejection) cellular rejection, recurrent rejection (≥ 2 episodes of any grade) with hemodynamic compromise, steroid-resistant rejection or unresolved antibody-mediated rejection during the first 6 months post-heart transplant
5. Graft dysfunction (LVEF <40% or wedge pressure >22 mmHg or cardiac index <2.2 L/min/m2)
6. Stage 4 or 5 CKD (eGFR <30 ml/min/1.73 m2)
7. Moderate or severe proteinuria
8. Active infection requiring hospitalization or treatment dose medical therapy.
9. Patients with ongoing wound healing problems, clinically significant wound infection requiring continued therapy or other severe surgical complication in the opinion of the Site Principal Investigator.
10. Fasting Serum Cholesterol ≥300 mg/dL OR greater than or equal to 7.75 mmol/L, AND fasting triglycerides ≥2.5x the upper limit of normal (ULN). Note: In case one or both of these thresholds are exceeded, the patient can only be included after initiation of appropriate lipid lowering medication, and reduction of serum cholesterol and triglyceride levels to below exclusion ranges is confirmed.
11. Uncontrolled diabetes mellitus.
12. Diagnosis of post-transplant lymphoproliferative disorder (PTLD) during the first 6 months post-heart transplant.
13. History of non-adherence to medical regimens.
14. Patients who are treated with drugs that are strong inducers or inhibitors of cytochrome P450 3A4 (CYP3A4) and cannot discontinue the treatment
15. Patients who are pregnant or breast-feeding or intend to get pregnant during the study period.

The Coronary Angiography Core Laboratory readers will be blinded to treatment assignment and time point (study visit). The Adjudication Committee members will be blinded to treatment assignment.