Vitamin C With Steroids for Gastrointestinal GVHD

1. Patients 5 years of age or older at time of enrollment.
2. Patients experiencing their initial presentation of stage 2 or greater acute LGI GVHD (with or without other organ involvement) or stage 1 LGI + skin aGVHD requiring systemic therapy after allogeneic transplant for any malignant or non-malignant indication using any graft/donor source or conditioning intensity.
3. KPS ≥70%
4. Patients should not have received systemic immune suppressive therapy for treatment of active GVHD except for a maximum of 72 hours of steroid therapy (with or without ruxolitinib) prior to enrollment. Topical skin and GI corticosteroids (such as budesonide and oral beclomethasone diproprionate) are allowed.
5. Informed Consent explained to, understood by and signed by patient/guardian. Patient/guardian given copy of informed consent.

Exclusion Criteria:

1. Relapsed, progressing or persistent malignancy or evidence of minimal residual disease (MRD) requiring withdrawal of systemic immune suppression.
2. Patients with acute GVHD developing after administration of a donor lymphocyte infusion (DLI) for relapse/progression of disease.
3. Patients with uncontrolled infections will be excluded. Infections are considered controlled if appropriate therapy has been instituted and, at the time of enrollment, no signs of progression are present. Progression of infection is defined as hemodynamic instability attributable to sepsis, new symptoms, worsening physical signs or radiographic findings attributable to infection. Persisting fever without other signs or symptoms
4. Known or suspected hypersensitivity to vitamin C.
5. De novo chronic GVHD or overlap syndrome developing before or present at the time of enrollment.
6. Patients receiving other drugs for the treatment of GVHD except as noted above. GVHD prophylaxis agents (e.g., calcineurin inhibitors) may be continued at local Investigator's discretion.
7. Patients on renal replacement therapy.
8. Patients requiring continuous supplemental oxygen > 2L/min to maintain peripheral O2 saturation [SpO2] > 90%.
9. Patients with active hepatic sinusoidal obstructive syndrome (SOS) and/or clinical evidence of impaired hepatic function (ascites or encephalopathy related to liver disease.

10. Patients receiving systemic corticosteroids (CS) for any indication within 7 days before enrollment, except the following:

    1. Corticosteroids administered as premedication for supportive care (such as before transfusion of blood products or before intravenous medications to prevent infusion reactions, fever, etc.).
    2. If steroid therapy has been administered for treatment of a non-GVHD related condition and tapered to \< 0.6 mg/kg/day prednisone (0.5 mg/kg/day methylprednisolone) for 7 or more days prior to enrollment.
11. History of G6PD deficiency, sickle cell disease or hemochromatosis.
12. History of oxalate kidney stones.
13. Patients unlikely to be adherent to study specific assessments at the transplant center.