Additional Study Information: Patients who will be receiving immune effector cell (IEC) therapy for the treatment of their cancer (leukemia) are being asked to participate in this study. IEC can produce a harmful side effect called Cytokine Release Syndrome (CRS). CRS involves a release of a large amount of proteins into the bloodstream. This may cause changes in blood pressure and heartbeat, flu-like symptoms (nausea, fever, and chills), and/or affect lung/liver/kidney function. It may also cause certain brain-related symptoms, such as dizziness, weakness, confusion, difficulty speaking, and/or decreased brain function (possible paralysis and/or coma). This study is being done to see if the study drug, itacitinib, is effective at preventing CRS. Itacitinib is an investigational drug that is being studied by Incyte Corporation for use in the treatment of CRS. Participants will receive the study drug in addition to their normal treatment.