Phase I, open-label study to assess the safety, feasibility, pharmacokinetics, and preliminary efficacy of CART123 cells given in combination with ruxolitinib in patients with relapsed or refractory acute myeloid leukemia (AML). All subjects will receive a single infusion of CART123 cells following ruxolitinib administration and lymphodepletion. Ruxolitinib dosing will begin at initiation of lymphodepleting chemotherapy (Day -6 1d) and continue for up to 14 days post CART123 administration.