A portable two-color in vivo flow cytometer for detection of circulating cells

In vivo flow cytometers (IVFC's) are a powerful new tool for monitoring changes in circulating cell populations without the need to draw a blood sample, and a portable version has been developed to simultaneously detect fluorescently-labeled cells at two distinct wavelengths in the vasculature of small animals. The instrument identifies cells as they cross a laser beam focused across a blood vessel in the ear, and new components have been developed to increase the utility of the instrument in the detection of rare cell populations. The system has been used to investigate circulating cell populations in mice with breast cancer and to show differences in the circulation kinetics of white blood cell populations labeled with antibody-conjugated fluorescent markers. For the cancer studies, we followed dynamic changes in the numbers of circulating fluorescent cells within a small number of mice prior to and following orthotopic implantation of GFP-expressing breast cancer cells. We detected changes in the number of circulating fluorescent cells excited at 473 nm, but these changes may be only partially attributed to viable breast cancer cells. Future, more extensive studies will focus on characterizing the identity of all the cell populations that led to the detected changes. In summary, this study demonstrates that the new IVFC system can be used to non-invasively investigate changes in populations of fluorescently-labeled and autofluorescent cells in vivo.