Patient description: A 17 year old boy complains of vomiting, non-bloody diarrhea, abdominal pain, fever, chills and loss of appetite for the past 3 days. He ate a salad at a restaurant prior to his diarrhea onset. Physical exam was remarkable for pallor, jaundice, and diffuse abdominal tenderness. Lab results were as follows: Hemoglobin: 9.7 g/dL Platelet: 110,000 /cu.mm Creatinine: 3.6 mg/dL blood urea nitrogen (BUN): 73 mg/dL direct bilirubin: 2.4 mg/dL lactate dehydrogenase (LDH): 881 IU/L (normal: 110-265 IU/L) Peripheral blood smear showed a moderate number of schistocytes and helmet cells. Shiga-like toxin-producing E. coli (STEC) stx1/stx2 were found in stools. He has no other underlying disease and he is not on any medications.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Diffuse Large B Cell Non-Hodgkin Lymphoma Patients 18 years or older who have undergone an autologous HCT for the treatment of DLBCL and are in a complete remission (CR), partial remission (PR) or have stable disease (SD) at the day 28 post-transplant reassessment Karnofsky Score of ≥ 70% (appendix II) Able to start the protocol therapy (1st dose of rituximab) between day 28-75 post-transplant Adequate organ function defined as Hematologic: platelets ≥ 50,000 x 109/L; ANC ≥ 1000 x 109/L unsupported by G-CSF or GM-CSF for 3 days Renal: creatinine < 1.5 mg/dl or glomerular filtration rate > 50 ml/min Hepatic: Alanine transaminase (ALT, SGPT) and aspartate aminotransferase (SGOT, AST) < 3 x upper limit of institutional normal and total bilirubin < 3.0 mg/dl (if total bilirubin is ≥ 3.0 patient is eligible if direct bilirubin is within normal limits) Pulmonary: clinically no evidence of pulmonary disease Cardiac: no symptoms of uncontrolled cardiac disease If post-transplant consolidation radiation therapy is given, the patient must be at least 14 days between last radiation treatment and 1st dose of rituximab  Pregnant or lactating Studies to evaluate the potential for embryo toxicity and teratogenicity have not been performed for INCB7839. Until additional information is available, women of childbearing potential should use appropriate precautions to avoid becoming pregnant. Rituximab is Pregnancy Category C: There are no adequate and well-controlled studies of rituximab in pregnant women. Females of childbearing potential must have a negative urine or serum pregnancy test within 14 days of study treatment start Recent venous thrombosis within 4 weeks prior to study enrollment. Patients at high risk for thrombotic events due to inherited risk factors (i.e. factor V Leiden) or DVT/PE in the past 12 months should be on secondary prophylaxis with anti-coagulant therapy (i.e. warfarin or low molecular weight heparin) prior to enrollment Active uncontrolled infection Active CNS disease Previous severe or life-threatening allergic reaction with rituximab or known allergy to the compounds found in INCB7839 Any gastrointestinal condition causing malabsorption or obstruction (eg, celiac sprue, gastric bypass surgery, strictures, adhesions, history of small bowel resection, blind loop syndrome) Unwilling or unable to swallow tablets BID Serologic or clinical evidence of current active hepatitis B or C infection, defined as elevated levels of Hep B antigen or Hep C antibody (unless active infection is ruled out by nucleic acid tests) Known HIV infection