Abstract: We propose to acquire an Orion HT multiplex fluorescent imaging system (Rarecyte inc.) to support research at Brigham and Women’s Hospital (BWH) and neighboring institutions. Immunofluorescence (IF) is a standard tool for microscopy research and is used routinely to identify cell types and study their organization and function in tissues. However, the overlapping emission spectra of common fluorophores means that standard IF is limited to a few colors, which is a major limitation for studying cell interactions in complex tissues and disease states. Many cell types can only be identified using combinations of several markers, and to understand their interactions it is often necessary to visualize multiple markers simultaneously. Thus, multiplex immunolabeling methods are essential. One approach is to perform multiple labeling cycles, and various methods have been developed to achieve this. However, these cyclical methods are slow and labor-intensive, and specimens can become degraded after multiple cycles. The Orion instrument was developed to solve these problems, and to achieve highly multiplex imaging in a single scan. Antibodies are conjugated to a palette of up to 20 fluorophores, excitation is produced by seven high-power lasers, and fluorescence is measured through a series of tunable narrow bandpass filters. Following staining, multiple fluorescence images are captured automatically, and individual labels are computationally separated using the company’s SpectralEdge algorithm. The instrument can scan an entire slide at subcellular resolution, which is especially important when studying large complex structures such as brain or tumors, whose spatial heterogeneity is not adequately captured by smaller fields of view. The Orion can also capture a H&E image on the same section, meaning that multiplex molecular data can be correlated with existing H&E datasets from clinical pathology. The reliability of the color separation has been extensively validated, and this novel technology holds great promise for a wide range of applications. The PI, Sandro Santagata, has previously collaborated with Rarecyte to develop the Orion technology, with support from a NIH SIBR grant. He also collaborates closely with Peter Sorger at Harvard Medical school, a current advisor to Rarecyte. Our users will benefit greatly from their expertise and connections to the company, and from a growing list of validated antibodies and computational tools that have been developed to support the Orion platform. The requested instrument will be installed in a shared core facility at BWH, where it will support a large community of NIH-funded researchers studying cancer, autoimmunity, inflammation, neurodegeneration and many other disorders.