Portable two-color in vivo flow cytometer for real-time detection of fluorescently-labeled circulating cells

The recent introduction of the in vivo flow cytometer for real-time, noninvasive detection and quantification of cells circulating in the vasculature of small animals has provided a powerful tool for tracking the roles of different types of cells in disease progression. We describe a portable version of the device, which provides the capability to: a) excite and detect fluorescence at two distinct colors simultaneously, and b) perform data analysis in real time. These advances improve significantly the utility of the instrument and provide a means of increasing detection specificity. As examples, we present the depletion kinetics of circulating green fluorescent protein (GFP)-labeled breast cancer cells in the vasculature of mice, and the specific detection of circulating hematopoietic stem cells labeled in vivo with two antibodies.