(333a) Synthetic Cell-Based Biosensors for Dynamically Imaging Immune Function in Vivo

The ability to dynamically monitor or visualize local immune states in vivo would transform our ability to understand processes such as the establishment and development of dysfunctional immune states at tumor sites and the response of these multicellular networks to potential therapeutic interventions. To date, however, we are limited to systemic measures (such as profiles of serum cytokines or circulating immune cells) or terminal assays (requiring tissue biopsy or, more commonly, sacrifice of the experimental animal). We have established a novel mammalian synthetic biology technology enabling us to engineer cells into living “biosensors” that are responsive to environmental stimuli that are exclusively extracellular, such as the cytokines that characterize specific immunological states. These cell-based biosensors detect a relevant analyte of interest and then produce an optical signal that can be imaged in whole, living animals (e.g., luminescence, near-infrared fluorescence).  This approach is fundamentally distinct from a reporter gene approach, in which one can only detect whether a given gene is expressed in the engineered cell, not whether the engineered cell is exposed to the analyte, and therefore this approach provides information not currently accessible. In work enabling this approach, we have developed a modular extracellular sensing architecture (MESA) that can be adapted to diverse applications and that facilitates optimization of performance characteristics.

We have previously shown that MESA biosensors signal in a dimerization-dependent fashion, and this mechanism was used to sense the cytokine IL-10, which plays an important role in tumor-related immune dysfunction. Here, we first describe design innovations that improve signal-to-noise ratio and robustness to facilitate translation to in vivo applications. As an initial proof of principle, we engineered tumor cells to function as biosensors, such that following adoptive transfer of engineered tumor cells to a syngeneic mouse host, the tumor monitors and reports upon its own immunological milieu. We are initially applying this technology to help understand how the immune response shifts from anti-tumor (immunostimulatory) to pro-tumor (immunosuppressive) during the course of tumor progression. MESA technology can be extended to generate cell-based therapies by coupling biosensing to the expression of therapeutically-relevant gene products or cellular functions including intracellular gene or protein circuits that perform logical evaluation of multiparametric inputs. These proof-of-principle experiments thus provide a quantitative framework for engineering cell-based devices that perform customized functions in vivo to enable both scientific inquiry and novel therapeutic strategies.