Multimodal Imaging of Neural Progenitor Cell Fate in Rodents

Abstract

For clinical application of stem cell-based therapies, noninvasive detection of applied stem cells is of high importance. We report on the feasibility of detecting implanted neural progenitor cells (NPCs) noninvasively and follow their fate and functional status by sequential multimodal molecular imaging and reporter gene technology. We investigated C17.2 cells stably expressing herpes simplex virus type 1-thymidine kinase (HSV-1-tk) and green fluorescent protein (gfp) (C17.2-tkIRESgfp = C17.2-TIG) or HSV-1-tk, gfp, and firefly luciferase (luc) (C17.2-lucIREStkgfp = C17.2-LITG) and determined the detection sensitivity of positron emission tomography (PET) and bioluminescence imaging (BLI) for these cells in culture and in vivo in subcutaneous and intracranial glioma models. In addition, PET and BLI were used to further investigate and follow the fate of implanted C17.2-LITG cells in an intracranial glioma model. We show that both imaging modalities are sensitive in detecting reporter gene expressing NPCs; however, PET, by the use of 9-[4-[(18)F]fluoro-3-hydroxymethyl)butyl]guanine ([(18)F]FHBG), detects NPCs only at sites of disrupted blood-brain barrier. Furthermore, both imaging modalities can be used to detect stem cell fate and migration and indicate excessive proliferation and aberrant migration. In conclusion, multimodal imaging can be used for longitudinal noninvasive monitoring of grafted NPCs in rodents.

Opportunities and Challenges: Stem Cell‐Based Therapy for the Treatment of Ischemic Stroke

“…BLI had higher sensitivity for detecting Luc-expressing cells, especially if BBB was intact. 18F-FHBG-PET was useful for monitoring TKexpressing cells in conditions in which BBB was disrupted, while MRI after gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) administration can be used for evaluating the BBB integrity [118]. It is clear that developing safer, more effective, and accurate imaging modalities is crucial to advance our understanding of stem cell-based therapy.…”

“…HSV-tk-modified stem cells were tracked in the rodent brain, human ESCs, and C17.2 NSCs [117,118]. It was important to note that 18F-FHBG could not be used to detect labeled cells in the normal brain because its substrate could not cross intact BBB [118]. Nonetheless, this method was a promising candidate for tracking stem cells in injured brain, in which BBB was compromised in the acute phase.…”

“…The herpes simplex virus type 1-derived thymidine kinase (HSV1-tk), which could exclusively phosphorylate substrates composed of acycloguanosines, was routinely used to label stem cells. HSV-tk-modified stem cells were tracked in the rodent brain, human ESCs, and C17.2 NSCs [117,118]. It was important to note that 18F-FHBG could not be used to detect labeled cells in the normal brain because its substrate could not cross intact BBB [118].…”

Cell Tracking Technologies for Acute Ischemic Brain Injury

“…105 Sequential imaging in particular may enable the detection of aberrant cell migration and/or proliferation. 106,107 Despite their advantages (cheap, high-throughput), optical/ bioluminescent imaging systems are not suitable for translation into large animal models or the clinic, as they are severely limited by the low penetration of light through tissue of substantial thickness. Since they are not hampered by tissue depth, PET, SPECT, and MRI have significant potential for use in the clinic, and studies specifically investigating the translation of these modalities (radiotracer dose expansion 108 , for example) are underway.…”

Multimodal Molecular Imaging In Vivo

“…Reporter gene imaging as well as probe imaging was reported to be available for other multimodal molecular imaging. Kim et al used tri-fusion gene for PET, fluorescence and bioluminescence imaging in order to track lymphocytes [46], and Waerzeggers et al adopted a similar strategy to trace the fate of neural progenitor cells in rodents [47].…”