REVEAL Biomarkers of Engraftment After Alternative Donor HSCT

Inclusion Criteria: General * Ability to undergo 18F FLT imaging without sedation * Patients \> 4 years of age and less than 80 years of age at highest risk for graft failure: cord blood HSCT, haplo HSCT, or lack of engraftment by day 28. * Diagnosed with a condition for which hematopoietic stem cell transplant (HSCT) is standard of care and HSCT is planned (Arm A) or occurred (Arm B) * In morphologic remission prior to HSCT * Patient or guardian able to give informed consent * Investigational therapies within past 28 days or planned on protocol are pre-approved by the PI or Site PI * Karnofsky or Lansky performance status \> 60% Arm A * A1 Cord blood recipients: Absence of donor specific antibodies to cord HLA * Haplo-identical recipients: ≥ 5/10 and \< 7/8 allele mismatch donor * A2- myeloablative Haplo-identical transplant is planned * A3- reduced intensity Haplo-identical transplant is planned (non-myeloablative is excluded) * A1- myeloablative or reduced intensity transplant is planned (non-myeloablative is excluded) * Diagnosed with a condition for which hematopoietic stem cell transplant (HSCT) is standard of care and HSCT is planned * Total bilirubin \< 2.5 mg/dL (unless documented Gilbert's syndrome) and transaminases (ALT and AST) \< 5 x the upper limit of normal * Creatinine clearance or GFR \> 60 ml/min/1.73 m2. (performed pre-HSCT) * FEV1 \> 80% pre or post-bronchiolator whichever is higher and DLCO Adj \> 70% (performed pre-HSCT if age appropriate) and Sa02 \> 94% on room air * Ejection fraction \> 50% (performed pre-HSCT) Arm B • Non-engraftment recipients of HCT with any donor source (related or unrelated): primary graft failure as defined by ANC not \> 500 for 3 consecutive days and at least 20 days after HSCT. Inclusion Criteria - Donors * 1-2 cords and \>.4/6 match to recipient for each (as per current National Marrow Donor guidelines), with a dose \>2 x 10e6 CD34 cells/kg for each cord OR \> 5/10 and \<7/8 allele mismatch related donor * Institutional guidelines met for donor suitability Exclusion Criteria: * History of psychiatric disorder which may compromise compliance with transplant protocol, or which does not allow for appropriate informed consent * Clinically significant systemic illness with manifestations of significant organ dysfunction which, in the judgment of the PI, or Co-I, would render the patient unlikely to tolerate the protocol therapy or complete the study * Presence of active malignancy from an organ system other than hematopoietic * Pregnant or lactating females * Patients who are unable or unwilling to use effective form (s) of contraception during the course of the study * Prior history of fluorothymidine allergy or intolerance * Decline enrolment on CIBMTR research protocol