Cotreatment with JQ1 and ABT-199 or palbociclib is synergistically active against primary MCL cells. (A-B) Primary MCL cells were treated with the indicated concentrations of JQ1 and the BCL2-specific inhibitor, ABT-199 or the CDK4/6 inhibitor, palbociclib at a fixed ratio for 48 hours. At the end of treatment, cells were washed with 1× phosphate-buffered saline and stained with PI. The percent of nonviable cells was determined by flow cytometry. Median dose effect and isobologram analyses were performed. CI values <1.0 indicates a synergistic interaction of the two agents in the combination. FE, fractional effect.