A Study to Evaluate Vimseltinib in Adults With Active Chronic Graft-Versus-Host Disease (cGVHD)

Inclusion Criteria:

1. Must be allogeneic hematopoietic stem cell transplant (HSCT) recipients withmoderate to severe cGVHD requiring systemic immune suppression. a. May have persistent active GVHD (aGVHD) and chronic GVHD (cGVHD) manifestations (overlap syndrome).

2. Participants with active cGVHD who have received and failed at least 2 prior linesof systemic therapy.

3. Stable dose of systemic corticosteroids is permitted but not required. If beingtaken, participants should be on a stable dose of corticosteroids for at least 2weeks prior to starting study drug treatment.

4. Adequate organ and bone marrow functions.

5. Participants of reproductive potential agree to follow the contraceptionrequirements.

6. Karnofsky Performance Scale (KPS) of ≥60.

Exclusion Criteria:

1. Has aGVHD without manifestations of cGVHD.

2. Prior use of colony-stimulating factor 1 receptor (CSF1R) inhibitor for cGVHD.

3. History or other evidence of severe illness, uncontrolled infection, or any otherconditions that would make the participant unsuitable for the study.

4. History of malignancy except for:

5. Underlying malignancy for which the transplant was performed

6. Malignancy treated with curative intent and with no evidence of active diseasepresent for more than 3 years prior to enrollment and felt to be at low riskfor recurrence.

7. Malabsorption syndrome or other illness that could affect oral absorption.