Inclusion Criteria:  HCT recipients over 12 years of age within the first 7 days of initial treatment of high-risk aGVHD, defined as:  Newly diagnosed Minnesota high-risk aGVHD -OR- Newly diagnosed Minnesota standard risk aGVHD with plasma amphiregulin ≥ 33 pg/ml tested at the UMN Cytokine Reference Lab. For amphiregulin lab ordering information, see Fairview Lab Guide: http://labguide.fairview.org/showtest.asp?testid=6766&format=long -OR-  Newly diagnosed Minnesota standard risk aGVHD Ann Arbor 3 biomarkers tested by Viracor. For ordering information, see: https://www.viracor-eurofins.com/test-menu/403572p-agvhd-symptomatic- onset-algorithm/  Renal: Serum creatinine ≤2.5x upper limit of normal (ULN) Cardiac: Left ventricular ejection fraction (LVEF) ≥ 35% Voluntary written consent (adult or parent/guardian with minor assent for 12 through 17-year-olds).  Exclusion Criteria:  Progressive malignancy Uncontrolled bacterial, fungal, parasitic, or viral infection at initiation of protocol treatment Unwilling or unable to stop supplemental sex hormone therapy (estrogen, progesterone, and/or testosterone preparations) Unwilling or unable to stop GnRH antagonists, aromatase inhibitors, or anti-androgens History of a hormone responsive malignancy Current thromboembolic disease requiring full-dose anticoagulation - patients receiving pharmacologic prophylaxis for thromboembolic disease will be eligible Active or recent (within prior 3 months) thrombus, irrespective of anticoagulation status Pregnancy Women or men of childbearing potential unwilling to take adequate precautions to avoid unintended pregnancy from the start of protocol treatment through 30 days after the last treatment