Inclusion Criteria:  Part A and Part B  Must have a confirmed diagnosis of steroid dependent or refractory classic cGVHD defined at any time post-hematopoietic cell transplantation (HCT) as: a) refractory disease - progressive cGVHD manifestations requiring prednisolone at greater than or equal to (>=) 1 milligram per kilogram per day (mg/kg/day) for at least 1 week or persist without improvement despite continued treatment with glucocorticoid (prednisolone at >= 0.5 mg/kg/day or 1 mg/kg every other day) for at least 4 weeks; b) dependent disease: persistent cGVHD manifestations requiring glucocorticoid >= prednisolone 0.25 mg/kg/day or >=0.5mg/kg every other day for at least 8 weeks Part A Treated at least 2 or more therapies for cGVHD (including glucocorticoids) Participants whose identified last line of conventional salvage treatment is second-fourth line of therapy Index date (initiation date of the identified last-line of conventional salvage therapy) at least 28 weeks before the study initiation date Part B Treated at least 3 lines therapies for cGVHD (including glucocorticoids) Participants who are treated with ibrutinib in their second-fourth line of therapy  Exclusion Criteria:  Part A and Part B  Known or suspected active acute GVHD Received an investigational drug (including investigational vaccines) or used an invasive investigational medical device within 28 days Part A Treated with an investigational agent for their identified last-line of conventional salvage therapy Pregnant, breastfeeding during last-line of conventional salvage therapy Part B Pregnant, breast-feeding, or of childbearing potential without a negative serum or urine pregnancy test within 7 days of enrollment. Male or female participants of childbearing potential unwilling to use effective contraceptive precautions throughout the trial