ADAM17 Inhibitor/ Rituximab After Auto HCT for DLBCL

Inclusion Criteria: * 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 * Able to take daily aspirin (325 mg) for the duration of INCB7839 treatment and 1 week after the last dose to reduce the risk of thrombosis (not applicable if on other anti-coagulant therapy at time of study enrollment) * Females are either postmenopausal for at least 1 year, are surgically sterile for at least 3 months, or must agree to take appropriate precautions to avoid pregnancy (with at least 99% certainty) from screening through 12 months after the last dose of rituximab if of childbearing potential. (Note: Permitted methods that are at least 99% effective in preventing pregnancy should be communicated to the participants and their understanding confirmed). * Males must agree to take appropriate precautions to avoid fathering a child (with at least 99% certainty) from screening through 12 months after the last dose of rituximab. (Note: Permitted methods that are at least 99% effective in preventing pregnancy should be communicated to the participants and their understanding confirmed). * Voluntary written consent signed before performance of any study-related procedure not part of normal medical care Exclusion Criteria: * 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