Targeting Janus tyrosine kinase 3 （JAK3） with an inhibitor induces secretion of TGF-β by CD4＋ T cells

Regulatory T cells （Tregs） are critical for the peripheral maintenance of the autoreactive T cells in autoimmune disorders such as type 1 diabetes （TID）. Pharmacological inhibition of Janus tyrosine kinase 3 （JAK3） has been proposed as a basis for new treatment modalities against autoimmunity and allogeneic responses. Targeting JAK3 with an inhibitor has previously been shown to exhibit protective action against the development of T 1D in non-obese diabetic （NOD） mice. As the mechanism of such preventative action has been unknown, we hypothesized that JAK3 inhibition induces generation of Tregs. Here, we show that the JAK3 inhibitor 4-（4＇-hydroxyphenyl）-amino-6,7-dimethoxyquinazoline （WHI-P131） suppresses proliferation of short-term cultured NOD CD4＋ T cells through induction of apoptosis, while promoting survival of a particular population of long-term cultured cells. It was found that the surviving cells were not of the CD4＋CD25＋FoxP3＋ phenotype. They secreted decreased amounts of IL-IO, IL-4 and interferon （IFN）-y compared to the cells not exposed to the optimal concentrations of JAK3 inhibitor. However, an elevated transforming growth factor （TGF）-β secretion was detected in their supernatants. In vivo treatment of prediabetic NOD mice with WHI-P131 did not affect the frequency and number of splenic and pancreatic lymph node CD4＋FoxP3＋ Tregs, while generating an elevated numbers of CD4＋FoxP3- TGF-β-secreting T cells. In conclusion, our data suggest an induction of TGF-β-secreting CD4＋ T cells as the underlying mechanism for antidiabetogenic effects obtained by the treatment with a JAK3 inhibitor. To our knowledge, this is the first report of the JAK3 inhibitor activity in the context of the murine Tregs.

Targeting the JAK/STAT pathway in solid tumors

Aberrant activation of signal transducer and activator of transcription(STAT)proteins is associated with the development and progression of solid tumors.However,as transcription factors,these proteins are difficult to target directly.In this review,we summarize the role of targeting Janus kinases(JAKs),upstream activators of STATs,as a strategy for decreasing STAT activation in solid tumors.Preclinical studies in solid tumor cell line models show that JAK inhibitors decrease STAT activation,cell proliferation,and cell survival;in in vivo models,they also inhibit tumor growth.JAK inhibitors,particularly the JAK1/2 inhibitor ruxolitinib,sensitize cell lines and murine models to chemotherapy,immunotherapy,and oncolytic viral therapy.Ten JAK inhibitors have been or are actively being tested in clinical trials as monotherapy or in combination with other agents in patients with solid tumors;two of these inhibitors are already Food and Drug Administration(FDA)approved for the treatment of myeloproliferative disorders and rheumatoid arthritis,making them attractive agents for use in patients with solid tumors as they are known to be well-tolerated.Four JAK inhibitors(two of which are FDA approved for other indications)have exhibited promising anti-cancer effects in preclinical studies;however,clinical studies specifically assessing their activity against the JAK/STAT pathway in solid tumors have not yet been conducted.In summary,JAK inhibition is a viable option for targeting the JAK/STAT pathway in solid tumors and merits further testing in clinical trials.