The primary goal of the dose finding phase is to determine the maximum tolerated dose (MTD) of INCB7839. Up to three dose levels will be tested (100 mg bid, 200 mg bid, and 300 mg bid). As the 300 mg bid has been proven safe in the non-transplant setting, dose escalation follows a Fast-Track Design with 1 patient enrolled per dose level unless a grade 2 or greater treatment emergent event occurs within the 1st 14 days of INCB7839. At that point, dose escalation converts to a standard 3+3 design and two additional patients are enrolled at the current dose level. If dose level 3 is completed without dose limiting toxicity (DLT) in the 1st 3 patients, an additional 3 patients will be enrolled at this level (without the staggering required by the DLT rules) prior to moving to the phase II component.