A Study to Assess the Safety and Pharmacokinetics of GDC-8264 in Combination With Standard of Care in Participants With Acute Graft-Versus-Host Disease (aGVHD)

The primary purpose of the study is to assess the safety and pharmacokinetics (PK) of GDC-8264 in participants with acute graft-versus-host disease (aGVHD).

Inclusion Criteria:Diagnosis of post-allogeneic hematopoietic stem cell transplantation (HSCT) aGVHD at screeningEvidence of engraftment post-transplantDiagnosis of high-risk aGVHD, per refined Minnesota high-risk aGVHD criteria during screeningInitiation of treatment with systemic corticosteroids for aGVHD at a dose of prednisone ≥2 milligrams per kilograms per day (mg/kg/day) by orally (PO) or methylprednisolone ≥2 mg/kg/day intravenously (or equivalent) in divided doses at diagnosis and up to 3 days prior to or on the same day as initiation of GDC-8264 (Day 1), with no taper planned prior to Day 3Exclusion Criteria:Evidence of relapsed, progressing, or persistent malignancy, or treatment for relapse after transplant, or requirement for rapid immune suppression withdrawal as pre-emergent treatment of early malignancy relapsePrior receipt of more than one allogeneic HSCTPrior systemic treatment for aGVHD, except for the standard of care corticosteroid treatment initiated as part of this trialDiagnosis of chronic GVHD or overlap syndromeUncontrolled active infection (i.e., progressive symptoms related to infection despite treatment, or persistently positive blood cultures despite treatment, or any other evidence of severe sepsis)Severe organ dysfunction (e.g., acute liver failure, renal failure requiring dialysis, ventilator support, or vasopressor therapy)Initiation or planned use of a marketed small molecule (excluding corticosteroids) or biologic therapy as treatment for aGVHD from the start of screening through the treatment period