A Study of Photobiomodulation (PBM) Therapy in People With Oral Graft-Versus-Host Disease (GVHD) After Stem Cell Transplant

Inclusion Criteria: * Allo-HCT recipients * Age ≥ 4 years-old * Oral cGvHD with NIH-modified OMRS score ≥ 3 who have failed ≥ 1 line of therapy, including topical corticosteroids.. * No change in systemic immunosuppressive therapy (type or intensity level) within 2 weeks prior to enrollment. * If a patient is currently using another oral topical treatment for mouth lesions/symptoms, patient must be stable on this treatment for ≥2 weeks prior to study enrollment. Patient may continue same topical dose/frequency during the study period. Exclusion Criteria: * Presence of an active uncontrolled infection. Subjects with a controlled infection receiving definitive therapy for 48 hours prior to enrollment are eligible. * Personal history of mucosal head and neck cancer in the past 5 years. * Pregnant or breastfeeding. * The subject or guardian is unable to give informed consent or unable to comply with the treatment protocol including appropriate supportive care, follow-up, and research tests. * Any serious medical or psychiatric illness that could, in the Investigator's opinion, potentially interfere with the completion of treatment according to this protocol.