Front Line Ibrutinib Without Corticosteroids for Newly Diagnosed Chronic Graft-versus-Host Disease

Background: \- Chronic Graft Versus Host Disease (cGVHD) can occur after a person has had a stem cell or bone marrow transplant. In cGVHD, the donor cells attack the recipient's body. Researchers want to see if a drug called ibrutinib can block one of the proteins that lead to the immune reaction that causes cGVHD. Objective: \- To see if ibrutinib as a first-line treatment can help people with newly diagnosed cGVHD. Eligibility: \- People age 18 and older with newly diagnosed moderate or severe cGVHD Design: * Participants will be screened with: * Medical and medicine histories * Physical exam and vital signs * Electrocardiograms (to measure heart function) * Assessment of their ability to perform daily activities * Blood and urine tests * Assessment of their general well-being. * Participants will visit the Clinical Center every 2 weeks for the first 2 months. Then they will visit every 4 weeks. * Participants will take ibrutinib by mouth once every day of every cycle. One cycle is 28 days. Treatment will last up to 2 years. Participants will keep a medicine diary. * Participants will take tests to measure lung function. They may have computed tomography scans of their chest. They will complete questionnaires about their symptoms and how cGVHD is affecting their body and quality of life. They will repeat the screening tests. * Participants may have optional blood tests and/or skin biopsies to better understand the drugs effect on the body. * Participants will be contacted by phone 30 days after treatment ends. They will also be contacted once a year for 2 years to discuss how they are feeling and if they have taken any other medicines to treat cGVHD.