Imaging TCR-dependent NFAT-mediated T-cell activation with positron emission tomography in vivo

A noninvasive method for molecular imaging of T-cell activity in vivo would be of considerable value. It would aid in understanding the role of specif ic genes and signal transduction pathways in the course of normal and patho logic immune responses, and could elucidate temporal dynamics and immune re gulation at different stages of disease and following therapy. We developed and assessed a novel method for monitoring the T-cell receptor (TCR)-depen dent nuclear factor of activated T cells (NFAT)-mediated activation of T ce lls by optical fluorescence imaging (OFI) and positron emission tomography (PET). The herpes simplex virus type 1 thymidine kinase/green fluorescent p rotein [HSV1-tk/GFP (TKGFP)] dual reporter gene was used to monitor NFAT-me diated transcriptional activation in human Jurkat cells. A recombinant retr ovirus bearing the NFAT-TKGFP reporter system was constructed in which the TKGFP reporter gene was placed under control of an artificial cis-acting NF AT-specific enhancer. Transduced Jurkat cells were used to establish subcut aneous infiltrates in nude rats. We demonstrated that noninvasive OR and nu clear imaging of T-cell activation is feasible using the NFAT-TKGFP reporte r system. PET imaging with [I-124]FIAU using the NFAT-TKGFP reporter system is sufficiently sensitive to detect T-cell activation in vivo. PET images were confirmed by independent measurements of T-cell activation (e.g., CD69 ) and induction of GFP fluorescence. PET imaging of TCR-induced NFAT-depend ent transcriptional activity may be useful in the assessment of T cell resp onses, T-cell-based adoptive therapies, vaccination strategies and immunosu ppressive drugs.