Participants must be 2 years of age or older, at the time of signing the informed consent.

Participants who are allogeneic hematopoietic stem cell transplantation (HSCT) recipients with active cGVHD requiring systemic immune suppression. Active cGVHD is defined as the presence of signs and symptoms of cGVHD per 2014 NIH Consensus Development Project on Criteria for Clinical trials in cGVHD.

Participants with refractory or recurrent active cGVHD despite at least 2 lines of systemic therapy.

• Refractory disease defined as meeting any of the following criteria:

  • The development of 1 or more new sites of disease while being treated for cGVHD.
  • Progression of existing sites of disease despite at least 1 month of standard or investigation therapy for cGVHD.
  • Participants who have not achieved a response within 3 months on their prior therapy for cGVHD and for whom the treating physician believes a new systemic therapy is required.

• Recurrent cGVHD is active, symptomatic disease (after an initial response to prior therapy) as defined, based on the NIH 2014 consensus criteria, by organ-specific or global assessment or for which the physician believes that a new line of systemic therapy is required.

Participants may have persistent, active acute and cGVHD manifestations (overlap syndrome), as defined by 2014 NIH Consensus Development Project on Criteria for Clinical trials in cGVHD.

Karnofsky Performance Scale of ≥60 (if aged 16 years or older); Lansky Performance Score of ≥60 (if aged <16 years)

Adequate organ and bone marrow functions evaluated during the 14 days prior to randomization.

Creatinine clearance (CrCl) ≥30 milliliter/minute based on the Cockcroft-Gault formula in adult participants and Schwartz formula in pediatric participants.

Contraceptive use by men or women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.

Concomitant use a of systemic corticosteroid is allowed but not required. Topical and inhaled corticosteroid agents are allowed. If a participant is taking corticosteroids at study randomization, they must be on a stable dose of corticosteroids for at least 2 weeks prior to Cycle 1 Day 1.

Concomitant use of CNI or mammalian target of repamycin (mTOR) inhibitors (sirolimus or everolimus) is allowed but not required.

Capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and protocol. A parent/guardian should provide consent for pediatric participants unable to provide consent themselves; in addition, where applicable pediatric participants should sign their own assent form.