IL-21 induces the transcription of many genes,496 including suppressors of cytokine signaling, Socs1, and Socs3, which downregulate the JAK–STAT pathway and inhibit IL-2 signaling.497,498 IL-21 activates Stat3,499,500 and Stat1.501 This latter leads to IFNγ production.502 IL-21 showed some benefit when used as monotherapy in the clinic but will probably need to be combined with other modalities.503 IL-21 is a B-cell growth factor that can potentially promote the growth of lymphomas.504 Therefore, its use as a soluble factor entails some risks. The gene discussed is IL21; the disease is lymphoma.