Sirolimus Prophylaxis for aGVHD in TME SCID

Study Design: SCID infants receiving an unconditioned haploidentical transplant will be started on Sirolimus (0.05 mg/kg/day) day -5 for Acute Graft-Versus-Host Disease (aGVHD) prophylaxis. Sirolimus levels will be monitored with goal sirolimus trough level of 5-8 ng/mL. Patients will be monitored for signs of aGVHD as defined by UCSF SOP CL 221.06 through day +100. Sirolimus will be tapered once T-regulatory cell to CD4 effector cell ratio is \> or = 9%. Setting: Inpatient BMT Unit Benioff Children's Hospital at UCSF Medical Center Study Subjects: 15 infants with diagnosis of maternally engrafted T cells SCID by CA Newborn screen receiving unconditioned haploidentical HSCT Main Outcome Measures: Incidence of aGVHD (dermatitis, hepatitis, enteritis) as defined by SOP CL 221.06 by Day +100. Hypothesis 1. Patients placed on sirolimus prophylaxis will have lower incidence of aGVHD compared to historical controls. Hypothesis 2. Lower doses of sirolimus milligram per kilogram will be required to maintain goal troughs of 5-8 ng/mL.