Early Signals of the Transition From Immune Quiescence to Activation in the Liver Allograft Microenvironment and in the Circulation

Inclusion Criteria:

1. Participant and parent or guardian must be able to understand and provide informed assent and consent, respectively
2. Recipient of a living or deceased donor Liver transplant (LTx) at \<7 years of age
3. \> 3 years but \<7 years after LTx at the time of study enrollment
4. Stable liver tests defined as baseline serum alanine aminotransferase (ALT) level \< 30 IU/l and gamma-glutamyl transferase (GGT) level \< 50 IU/l (based on the average of the 3 most recent values prior to screening; all must be within 1 year of screening; 2 must be within 6 months of screening)
5. No Acute rejection (AR) or chronic rejection within 12 months of enrollment
6. Tacrolimus monotherapy for \> 6 months with baseline 12-hour trough levels \<8 ng/mL (based on the average of 3 values prior to screening; all must be within 1 year of screening; 2 must be within 6 months of screening)
7. Participants of childbearing potential must have a negative pregnancy test upon study entry

Exclusion Criteria:

1. Liver transplant (LTx) for autoimmune disease, including autoimmune hepatitis or primary sclerosing cholangitis
2. LTx for hepatitis B or hepatitis C
3. Recipient of any other organ transplant or liver re-transplant, except for patients who have a repeat LTx within 30 days of first LTx who are eligible for enrollment
4. \>=50 percent dose increase in tacrolimus within 12 months of enrollment
5. Discontinued a second Immunosuppression (IS) agent within 12 months of enrollment
6. Systemic illness requiring chronic or recurrent use of IS for which there is a risk of reactivation if tacrolimus is reduced
7. Use of medication to treat systemic conditions which in the judgement of the investigator could influence results of the study
8. Active or chronic infection requiring treatment
9. Inability or unwillingness to comply with the study protocol
10. Use of investigational drug within 4 weeks (or 5 half-lives of investigational drug, whichever is longer) of enrollment
11. Has any condition that, in the opinion of the investigator, will interfere with safe participation in the trial