Cytokines are key modulators of immunity. Most cytokines use the Janus kinase 
and signal transducers and activators of transcription (JAK-STAT) pathway to 
promote gene transcriptional regulation, but their signals must be attenuated by 
multiple mechanisms. These include the suppressors of cytokine signaling (SOCS) 
family of proteins, which represent a main negative regulation mechanism for the 
JAK-STAT pathway. Cytokine-inducible Src homology 2 (SH2)-containing protein 
(CIS), SOCS1, and SOCS3 proteins regulate cytokine signals that control the 
polarization of CD4+ T cells and the maturation of CD8+ T cells. SOCS proteins 
also regulate innate immune cells and are involved in tumorigenesis. This review 
summarizes recent progress on CIS, SOCS1, and SOCS3 in T cells and tumor 
immunity.