This peptide CKS-17 is considered as the major immunosuppressive site of retroviral TM protein. It can suppress T effector cell function in vitro. It has been shown that CKS-17 causes an imbalance of human types 1 and 2 cytokines and inhibition of the immune responses of lymphocytes, monocytes, and macrophages. CKS-17 induced increased intracellular levels of cAMP, which plays an important role in regulation of cytokine biosynthesis.