The purpose of this study is to develop and validate endpoint measures that can accurately determine whether patients are responding to treatment for chronic Graft-versus-Host Disease (GVHD). Hopefully, this will also lead to being better able to predict which patients will respond to what therapies.

Inclusion Criteria:

• Age 7 years or older
• Prior first allogeneic stem cell transplant, with any graft source, donor type, and GVHD prophylaxis.
• Diagnosis of chronic GVHD according to the criteria of the diagnosis and scoring group of the NIH consensus conference (Patient must have at least one diagnostic manifestation of chronic GVHD or one distinctive manifestation with pathological confirmation of the diagnosis. Concurrent acute GVHD manifestations will be allowed as long as at least one classic chronic manifestation is present.)
• Initiation of a new systemic treatment for chronic GVHD in the past 4 weeks or anticipated within the next 4 weeks. Systemic treatment is defined as any medication or intervention that has intended systemic effects, including extracorporeal photopheresis, regardless of prior lines of therapy or prior treatment with the agent(s). If a patient is restarting a treatment to which they were previously exposed, they must have been off of it for at least 4 weeks before restarting.
• No evidence of persistent or progressive malignancy at the time of enrollment
• Evaluation at the transplant center at the time of study enrollment, and agreement to be re-evaluated at the transplant center up to four subsequent times: at 3 months, 6 months, and 18 months after enrollment and once if another treatment is added for chronic GVHD.
• Signed, informed consent

Exclusion Criteria:

• Inability to comply with study procedures
• Complete resolution of chronic GVHD at the time of enrollment (patient must have some measurable chronic GVHD activity)

Patients starting initial or subsequent therapy for chronic Graft vs Host Disease.