This study will be conducted to compare Axatilimab Versus Best Available Therapy in Pediatric Participants With Chronic Graft Versus Host Disease After at Least 2 Prior Lines of Systemic Therapy.

Inclusion Criteria:

• Aged ≥ 2 to < 18 years at the time of signing the informed consent.
• Active, moderate to severe cGVHD, requiring systemic immune suppression.
• Participants with refractory or recurrent cGVHD who have received at least 2 lines of systemic therapy, including corticosteroids and ruxolitinib.
• Concomitant use of systemic corticosteroids is allowed. Participants on systemic corticosteroids must be on a stable dose of corticosteroids for at least 2 weeks prior to C1D1. Topical and inhaled corticosteroid agents are allowed.
• Participants must accept to be treated with one of the following BAT options on C1D1: CNI (cyclosporine or tacrolimus), ECP, MMF, an mTOR inhibitor (everolimus or sirolimus), rituximab, imatinib, methotrexate, or ibrutinib.
• History of allo-HCT from any donor HLA type (related or unrelated donor with any degree of HLA matching) using any graft source (bone marrow, peripheral blood stem cells, or cord blood). Recipients of myeloablative, nonmyeloablative, or reduced-intensity conditioning are eligible.

Exclusion Criteria:

• Receipt of more than 1 prior allo-HCT. Prior autologous HCT is allowed.
• Evidence of relapse of hematologic disease or treatment for relapse after the allo-SCT was performed, including DLI for the treatment of molecular relapse. Note: Participants who have received a scheduled DLI as part of their transplant procedure and not for management of malignancy relapse are eligible.
• Systemic treatment with CNIs or mTOR inhibitors started within 2 weeks prior to C1D1.
• Severe renal impairment, that is, GFR < 30 mL/min/1.73 m2 as estimated using modified Schwartz formula, or end-stage renal disease on dialysis.
• 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.
• History of acute or chronic pancreatitis.
• Active, symptomatic myositis.
• Female adolescent participants who are pregnant or breastfeeding.

Other protocol-defined Inclusion/Exclusion Criteria may apply.

Incyte shares data with qualified external researchers after a research proposal is submitted. These requests are reviewed and approved by a review panel on the basis of scientific merit. All data provided is anonymized to respect the privacy of patients who have participated in the trial in line with applicable laws and regulations. The trial data availability is according to the criteria and process described on https://www.incyte.com/our-company/compliance-and-transparency

Data will be shared after the primary publication or 2 years after the study has ended for market authorized products and indications.

Data from eligible studies will be shared with qualified researchers according to the criteria and process described in the Data Sharing section of the www.incyteclinicaltrials.com website. For approved requests, the researchers will be granted access to anonymized data under the terms of a data sharing agreement.