Inclusion Criteria:  Male and female subjects at least 18 years of age who have had allogenic hematopoietic cell transplant (HCT). Previously received at least 1 and not more than 5 lines of systemic therapy for cGVHD Receiving glucocorticoid therapy with a stable dose over the 2 weeks prior to screening; Have persistent cGVHD manifestations and systemic therapy is indicated  Exclusion Criteria:  Subject has not been on a stable dose / regimen of systemic cGVHD treatments for at least 2 weeks prior to screening. (Note: Concomitant corticosteroids, calcineurin inhibitors, sirolimus, MMF, methotrexate, rituximab, and extracorporeal photophoresis (ECP) are acceptable. Systemic investigational GVHD treatments are not permitted). Histological relapse of the underlying cancer or post-transplant lymphoproliferative disease at the time of screening. Current treatment with ibrutinib. Prior treatment with ibrutinib is allowed with a washout of at least 28 days prior to treatment.