IKZF1 and plasma cell myeloma: In vitro, recombinant IL‐2 increased eosinophil levels in human myeloma cells.49 Additionally, IL‐2 therapy in patients with melanoma increases eosinophil levels.57 In one study, the beneficial effect of thalidomide was demonstrated to be dependent on IL‐2 induction of natural cytotoxicity.58 Lenalidomide releases IL‐2 from T cells via the activation of the CRBN‐CRL4 E3 ubiquitin ligase to degrade the IKZF1 and IKZF3.59 IL‐2 has an important role in the immunological activity of lenalidomide and is associated with elevated eosinophil levels.