Transforming growth factor beta (TGF-β) activity in immuno-oncology studies

Transforming growth factor beta (TGF-β) is a potent pleiotropic polypeptide cytokine, with a complex and context dependent control of its activation, signaling and effector functions. This cytokine is pivotal in the regulation of immunological responses, tumor initiation and development, stromal homeostasis and all their intricate related interactions. Last decade advances in cancer immunotherapy have reactivated the clinical interest on potential drug with TGF-β inhibition effect, combined with immunomodulating enhancer drugs. The correct quantification of the in vitro and in vivo biological activity of this cytokine is essential to understand the intrinsic underlying biological mechanisms and TGF-β role in the immune system, tumor and stromal codevelopment, modulation and interactions. There is a wide variety of available procedures to quantify TGF-β activity, which includes different methodological approximations like ELISA, Bioassays including reporter gene assays, Flow cytometry (FC), Western blotting (WB), immunochemical/fluorescence microscopy, among others. Here, we detail available methods for TGF-β biological activity analysis, together with their applicability and suitability for each experimental setting, in order to get a complete analytical perspective and more comprehensive information along the development and design of combined antitumor immunotherapies, which include the inhibition of TGF-β biological activity.