A Study to Evaluate the Safety and Efficacy of Axatilimab in Combination With Ruxolitinib in Participants With Newly Diagnosed Chronic Graft-Versus-Host Disease

Inclusion Criteria:

• ≥ 12 years of age at the time of informed consent.

• New-onset moderate or severe cGVHD, as defined by the 2014 NIH Consensus DevelopmentProject Criteria for Clinical Trials in cGVHD, requiring systemic therapy.

• History of 1 allo-SCT (any type of stem cell donor, any conditioning regimen, andsource of hematopoietic stem cells).

• Adequate hematologic function independent of platelet transfusion and growth factorsfor at least 7 days prior to study entry: ANC ≥ 0.75 × 109/L and platelet count ≥ 20 × 109/L.

• Willingness to avoid pregnancy or fathering children.

Exclusion Criteria:

• Received more than 1 prior allo-SCT. Prior autologous HCT is allowed.

• Has overlap cGVHD, defined as simultaneous presence of features or characteristicsof aGVHD in a patient with cGVHD.

• Received previous systemic treatment for cGVHD, including systemic corticosteroidsand extracorporeal photopheresis.

• Received systemic corticosteroids within 2 weeks prior to C1D1, regardless ofindication.

• Initiated systemic treatment with CNIs or mTOR inhibitors within 2 weeks prior toC1D1.

• Prior treatment with a JAK inhibitor within 8 weeks before randomization.Participants who received a JAK inhibitor for the treatment of aGVHD are eligibleonly if they achieved a response (CR or PR) to JAK inhibitor treatment and did notdiscontinue due to toxicity.

• Evidence of relapse of the primary hematologic disease or treatment for relapseafter the allo-SCT was performed, including DLIs for the treatment of molecularrelapse.

• History of acute or chronic pancreatitis.

• History of thromboembolic events (such as deep vein thrombosis, pulmonary embolism,stroke, myocardial infarction) in the 6 months prior to study entry.

• Active symptomatic myositis.

• Severe renal impairment, that is, estimated CrCl < 30 mL/min measured or calculatedby Cockcroft-Gault equation in adults and Schwartz formula in pediatricparticipants, or end-stage renal disease on dialysis. Participants with CrCl of 30to 59 mL/min on treatment with fluconazole are not eligible.

• Impaired liver function, defined as total bilirubin > 1.5 × ULN and/or ALT and AST > 3 × ULN in participants with no evidence of liver cGVHD.

• Currently active significant cardiac disease, such as uncontrolled arrhythmias,uncontrolled hypertension, or Class 3 or 4 congestive heart failure as defined byNew York Heart Association, or a history of myocardial infarction or unstable anginawithin 6 months prior to randomization.

• Pregnant or breastfeeding.

Other protocol-defined Inclusion/Exclusion Criteria may apply.