Safety and Efficacy of Itacitinib in Combination With Corticosteroids for Treatment of Graft-Versus-Host Disease in Pediatric Subjects

Inclusion Criteria:

- Male and female participants: 12 to < 18 years old (Cohort 1), 6 to < 12 years old
(Cohort 2), 2 to < 6 years old (Cohort 3), Weighing > 8 kg to < 2 years old (Cohort
4), and 28 days old to weighing ≤ 8 kg (Cohort 5).

- Undergone 1 allogeneic hematopoietic stem cell transplantation (allo-HSCT) from any
donor and source for hematological malignancies or disorders. Recipients of
myeloablative and reduced-intensity conditioning regimens are eligible.

- Clinically suspected Grade II to IV aGVHD as per Mount Sinai Acute GVHD International
Consortium (MAGIC) criteria, occurring after allo-HSCT and any GVHD prophylactic
medication.

- Evidence of myeloid engraftment.

Exclusion Criteria:

- More than 1 allo-HSCT.

- Received more than 2 days of systemic corticosteroids for aGVHD before the first study
drug administration.

- Presence of GVHD overlap syndrome.

- Presence of an active uncontrolled infection.

- Known HIV infection.

- Active hepatitis B virus (HBV) or hepatitis C virus (HCV) infection that requires
treatment or at risk for HBV reactivation.

- Evidence of relapsed primary disease or have been treated for relapse after the
allo-HSCT was performed.

- Any corticosteroid therapy for indications other than GVHD at doses > 1 mg/kg once
daily of methylprednisolone (or equivalent) within 7 days of the first study drug
administration.

- Receipt of live (including attenuated) vaccines or anticipation of need for such
vaccines during the study.

- Receipt of JAK inhibitor therapy after allo-HSCT for any indication.

- Treatment with any other investigational agent, device, or procedure within 21 days
(or 5 half-lives, whichever is greater) of enrollment.