DISEASE CHARACTERISTICS: Histologically proven intestinal (esophagus, stomach, small intestine, or colon) graft-versus-host disease (GVHD) exhibiting symptoms such as nausea, vomiting, anorexia, diarrhea, or abdominal pain in the absence of another explanation for these symptoms Specific contraindications to high-dose immunosuppressive therapy, such as: Recurrent malignant disorder for which an allogeneic antitumor effect is desired Aspergillus or other fungal infection Severe myopathy, hyperglycemia, bone problems, or neuropsychiatric symptoms related to corticosteroid use Thrombotic thrombocytopenic purpura or hemolytic uremic syndrome related to immunosuppressive therapy Epstein-Barr virus-related immunoproliferative disease No GVHD unresponsive to prior high-dose immunosuppressive therapy No concurrent infections involving the intestinal tract such as: Salmonella Shigella Clostridium difficile (toxin positive) Rotavirus Giardia lamblia Cytomegalovirus by shell vial culture

PATIENT CHARACTERISTICS: Age: 5 to 75 Performance status: Not specified Life expectancy: Not specified Hematopoietic: Platelet count adequate Hepatic: Not specified Renal: Not specified Other: Able to swallow oral capsules No persistent vomiting of all oral intake No multiorgan failure No sepsis syndrome, including positive bacterial or fungal cultures within 72 hours of study

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 7 days since prior anti-thymocyte globulin Chemotherapy: Concurrent cyclosporine, methotrexate, tacrolimus, mycophenolate mofetil, or prednisone allowed if plan in place to taper or discontinue Endocrine therapy: See Disease Characteristics Radiotherapy: Not specified Surgery: Not specified Other: At least 7 days since prior investigational agents At least 7 days since prior immunosuppressive agents At least 24 hours since prior drugs that suppress gastric acid secretion (e.g., H2 receptor antagonists or omeprazole) No concurrent drugs that suppress gastric acid secretion