CyCLoPs: A approach for detecting immune responses with in vivo labeling of cytokine activity

Many studies have centered on delineating cytokine-producing cells, aiming for a comprehensive grasp of upstream signals and critical transcription factors linked to cytokine production. However, it is largely unknown which cell types respond to cytokines. Herein, we developed a reporter system, Cytokine-Cellular-Locating-Platforms (CyCLoPs), that transforms the cytokine and its receptor engagement into a genetically tractable signal. In vitro, CyCLoPs exhibited remarkable specificity, a high signal-to-background ratio, and broad applicability to probe interactions between cytokines and their receptors. In vivo, the IL-17A-CyCLoPs reporter mouse enabled the detection of IL-17A-responsive cells in the ilea, primarily located at the villi rather than the crypt, following colonization by a commensal bacterium. In addition, the IFN-γ-CyCLoPs mouse facilitated the identification of IFN-γ-exposed CD8+ T cells in tumors with reduced effector function. These CD8+ T cells were marked by various cell-surface proteins, such as CD36, CD38, and Leptin receptor, of which expression was dependent on IFN-γ. Thus, our developed CyCLoPs enable visualizing cytokine-induced responses at a single-cell resolution, paving the ways to investigate how cytokines produce distinct immunological outcomes in health and disease.