Lenalidomide-induced NK cell function is mediated by CD4⁺ T cells and secretion of IL-2. (A) Healthy donor PBMCs (n = 5) were sorted for CD4, CD8, and NK cells. NK cell–mediated cytotoxicity against K562 was assessed on unsorted PBMCs, sorted NK cells, or NK cells cocultured with CD8⁺ T cells or CD4⁺ T cells. These cultures were treated without (■) or with lenalidomide (*) for 3 days. (A) Pooled data from 5 separate experiments. (B) To assess whether lenalidomide-mediated NK cell function by CD4⁺ T cells was IL-2–driven, sorted NK cells were blocked with IL-2 receptor-α antibodies, then cocultured with sorted CD4⁺ T cells and lenalidomide (). (B) Pooled data from 4 separate experiments (4 normal donors).