Kinetic Analysis of Immune Cells in Blood and Chronic Graft-Versus-Host Disease-Affected Tissues After Allogeneic Hematopoietic Cell Transplantation

Inclusion Criteria: * \* BOTH COHORTS: * Documented written informed consent of the participant and/or parent/guardian. * Assent from pediatric participants will be documented per institutional policies and practice. * Patients who have received allogeneic hematopoietic cell transplant (HCT) regardless of donor type, condition regimen, or GVHD prophylaxis. * Age: ≥ 18 years or ≥ 7 years if 30 kg and above * Willingness to: * Provide blood sample(s), stool, saliva, and buccal mucosa, * If applicable: Permit medical record/ clinical laboratory result review * COHORT 1: * Patients who have received allogeneic hematopoietic cell transplant (HCT) regardless of donor type, condition regimen, or GVHD prophylaxis. * COHORT 2: * Patients diagnosed with cGVHD at any time-point after allogeneic HCT regardless of donor type, condition regimen, or GVHD prophylaxis. Exclusion Criteria: * \* Women of childbearing potential: Pregnant/nursing * Individuals with impaired decision-making capacity * An employee who is under the direct/ indirect supervision of the PI/ a co-investigator/ the study manager * A direct study team member