Phase 2 Open Label Prospective Dose-Ranging Clinical Trial With Escalation and Expansion Cohorts to Evaluate Safety, Tolerability, Pharmacokinetics, Pharmacodynamics, Dosing, and Efficacy of RLS-0071 for the Treatment of Hospitalized Patients With Steroid-Refractory Acute Graft-versus-Host Disease

Inclusion Criteria: * Male or female adults or adolescents (\>12 years old). * Hospitalized with steroid-refractory aGvHD (grade II-IV) after allo-HSCT * Anticipated hospital length-of-stay of at least 1 week from the time of RLS-0071 initiation. * No plans to add additional GvHD treatment medications or to add, dose-adjust, or discontinue GvHD prophylactic medications during the 7-days of RLS-0071 treatment. * Neutrophil recovery following the stem-cell transplantation, defined as blood neutrophil count \>500/mL for at least 3 consecutive measurements and not supported by growth factor suppl…