IMiDs enhance CTL-mediated cytotoxicity against SOCS1-expressing MM cells. (A) Specific cytotoxic T cell activity against SOCS1 gene re-expressing target MM cell lines MM.1S and U266 were evaluated by ⁵¹Cr-release assay. To re-express SOCS1 gene, target MM cell lines were incubated either alone or in combination with AzaC, TsA, lenalidomide, or pomalidomide. MM cell–specific CTLs were generated from healthy donors by restimulation with γ-irradiated MM1.S or U266 apoptotic bodies using dendritic cells. CTLs were pretreated with lenalidomide or pomalidomide for 24 hours before use as effector cells against SOCS1 gene re-expressing MM cells in ⁵¹Cr-release assay. x-axis represents ratio of effector (IMiDs-pretreated MM cell–specific CTLs) to target SOCS1 gene re-expressing MM cells. y-axis represents specific lysis (percent) of target cells by effector cells. Top panel shows lenalidomide pretreated effector CTL lytic activity against SOCS1 gene re-expressing MM1.S cells; bottom panel shows pomalidomide-pretreated effector CTL lytic activity against SOCS1 gene re-expressing MM1.S cells. One representative of 3 independent experiments is shown. (B) Proliferation of CD8T cells cultured with the combination of lenalidomide and pomalidomide with AzaC or Tsa compared with lenalidomide or pomalidomide alone was evaluated by CFSE-flow cytometric analysis. x-axis represents CFSE stained proliferating cells, y-axis represents gated CD8⁺ T cells. Data are shown as histo-gram proliferation plots using Flowjo analysis software. One representative of 3 independent experiments is shown. (C) Direct antitumor activity of lenalidomide and pomalidomide, either alone or in combination with AzaC, was shown by 3[H]thymidine incorporation assay in MM1.S and U266 cells at 96 hours of culture. Data represent mean ± standard deviation of triplicate cultures. (*) indicates statistical significance determined by Student t test, 1-tailed distribution P < .01. One representative of 3 separate experiments is shown.