Bfl-1⁺ lymphomas are codependent on additional antiapoptotic Bcl-2 family proteins for survival. (A) SUDHL1 cells were transfected with nontargeting control (NTC) or BCL2A1 siRNA for 72 hours, or treated with 0.5 µM AZD5991, 0.5 µM venetoclax, or 0.5 µM AZD5991 plus 0.5 µM venetoclax for 8 hours followed by flow cytometric measurement of MOMP. Results are plotted as TMRE⁻ cells, normalized to untreated cells (0%). (B) Western blot analysis for Bfl-1 protein knockdown efficiency and effects on Bcl-2 family prosurvival proteins following 72 hours of BCL2A1 transfection in SUDHL1 cells. Loading control, vinculin. (C) Mcl-1 and Bcl-2 were immunoprecipitated from whole-cell lysates (WCL) in SUDHL1 and OCILY10 cell lines following 72 hours transfection with 0.5 µM nontargeting control or 0.5 µM BCL2A1 siRNA and immunoblotted for the indicated Bcl-2 family proteins. Species specific isotype controls are included in lanes 1 (mouse IgG) and 2 (rabbit IgG). (D) Lymphoma cell lines were transfected with the indicated concentrations of NTC or BCL2A1 siRNA for 72 hours followed by treatment of 6 hours with a dose titration of Mcl-1 (AZD5991), Bcl-2 (venetoclax) or Bcl-xL (compound 15) inhibitors before measuring caspase activation. **P < .01.