GARP: A Key Target to Evaluate Tumor Immunosuppressive Microenvironment

Glycoprotein-A repetitions predominant (GARP) is the docking receptor for latent transforming growth factor (LTGF-beta) and promotes its activation. In cancer, increased GARP expression has been found in many types of cancer. GARP is expressed by regulatory T cells and platelets in the tumor microenvironment (TME) and can be also expressed by tumor cells themselves. Thus, GARP can be widely present in tumors in which it plays a major role in the production of active TGF-beta, contributing to immune evasion and cancer progression via the GARP-TGF-beta pathway. The objective of this review is to highlight GARP expression and function in cancer and to evaluate the potential of membrane GARP as a predictive and therapeutic follow-up biomarker that could be assessed, in real time, by molecular imaging. Moreover, as GARP can be secreted, a focus will also be made on soluble GARP as a circulating biomarker.