In this in vitro study, we tested in SLE and RA patient samples the effect on T and B cell activation and proliferation of a novel dual Bcl-2/Bcl-XL inhibitor, AZD4320, which induces tumor regression in hematologic cancer models without dose-limiting thrombocytopenia [18], and compared this compound to venetoclax and a Mcl-1 inhibitor, S63845. The gene discussed is MCL1; the disease is systemic lupus erythematosus.