Long term non-invasive imaging of embryonic stem cells using reporter genes.

Development of non-invasive and accurate methods to track cell fate after delivery will greatly expedite transition of embryonic stem (ES) cell therapy to the clinic. In this protocol, we describe the in vivo monitoring of stem cell survival, proliferation and migration using reporter genes. We established stable ES cell lines constitutively expressing double fusion (DF; enhanced green fluorescent protein and firefly luciferase) or triple fusion (TF; monomeric red fluorescent protein, firefly luciferase and herpes simplex virus thymidine kinase (HSVtk)) reporter genes using lentiviral transduction. We used fluorescence-activated cell sorting to purify these populations in vitro, bioluminescence imaging and positron emission tomography (PET) imaging to track them in vivo and fluorescence immunostaining to confirm the results ex vivo. Unlike other methods of cell tracking, such as iron particle and radionuclide labeling, reporter genes are inherited genetically and can be used to monitor cell proliferation and survival for the lifetime of transplanted cells and their progeny.