Allo-SCT patients above 18 years of age with acute steroid-resistant GI-related GVHD grade III-IV.

The diagnosis of GVHD will be made on clinical grounds (in line with the major associations' recommendations) - the appearance of characteristic mucoid diarrhea within 100 days after Allo-SCT, with or without associated skin/liver involvement. In cases of atypical presentation - we will recommend biopsy or endoscopy for diagnosis. Patients suspected to have Clostridium difficille associated diarrhea will be tested for toxin (CDT).

Steroid-resistant GI-related GVHD will be defined as lack of improvement (same stage) or worsening of GI symptoms after 7 days of steroid therapy (≥ 2 ml/kg of IV methylprednisolone).

Consenting allo- SCT patients with acute steroid-resistant GI-related GVHD grade III-IV will receive autologous FMT by nasogastric tube. Standardized stool suspension will be given once a day for two consecutive days.In order to prevent aspiration, patients will be kept in a 45ᵒ upright position for four hours. Participants will fast the night before and be treated with proton pump inhibitors prior to each FMT.

In cases where complete response was not obtained within 7 days after autologous FMT, patients may be eligible for another trail of autologous FMT or to switch to other pharmacological interventions. Stool samples will be collected before and after the intervention for microbial analyses.

Development of SAEs related to autologous FMT within 7 days after the intervention. SAEs include mortality, bacteremia, and radiological-proven aspiration pneumonia requiring mechanical ventilation.

Patients will be evaluated 90 days following FMT for symptoms severity and response. Response is defined as:

1. Complete response - resolution of all GI symptoms
2. Partial response - decrease of severity of GI-related GVHD by at least one stage or ability to taper steroids to <0.5 mg/kg
3. No response - progression of symptoms or no change in GI symptoms