Fluorescence-Based Mono- and Multimodal Imaging for In Vivo Tracking of Mesenchymal Stem Cells

Abstract

The advancement of stem cell therapy has offered transformative therapeutic outcomes for a wide array of diseases over the past decades. Consequently, stem cell tracking has become significant in revealing the mechanisms of action and ensuring safe and effective treatments. Fluorescence stands out as a promising choice for stem cell tracking due to its myriad advantages, including high resolution, real-time monitoring, and multi-fluorescence detection. Furthermore, combining fluorescence with other tracking modalities-such as bioluminescence imaging (BLI), positron emission tomography (PET), photoacoustic (PA), computed tomography (CT), and magnetic resonance (MR)-can address the limitations of single fluorescence detection. This review initially introduces stem cell tracking using fluorescence imaging, detailing various labeling strategies such as green fluorescence protein (GFP) tagging, fluorescence dye labeling, and nanoparticle uptake. Subsequently, we present several combinations of strategies for efficient and precise detection.

Keywords: fluorescence imaging; in vivo cell imaging; multimodal imaging; stem cell tracking.

Figure 1

Schematic illustration of strategies for stem cell tracking. Graphical illustration depicts methods for tracking stem cells after implantation. Stem cells can be mono-labeled using fluorescence through fluorescence protein transfection, dye conjugation, and nanoparticle uptake. Fluorescence imaging can be combined with various imaging strategies, such as BL imaging, PET, PA, CT, and MRI, for synergistic detection. The redline on the MR images indicate the midline of the brain. Reproduced with permission from [41,42,43].

Figure 2

Fluorescent nanoparticle-based stem cell labeling via metabolic glycoengineering-involved biorthogonal click chemistry. Schematic illustrations depict (a) the mechanism of stem cell labeling via glycoengineering-involved bioorthogonal chemistry and (b) the endocytosis of BCN-AuNPs labeled on the cell membranes. (c) In vitro confocal fluorescence images of BCN-AuNP-labeled hMSCs showing the intracellular distribution of BCN-AuNPs. The orange arrows indicate colocalized fluorescence of BCN-AuNPs and lysosome. (d) Confocal fluorescence images of BCN-AuNP-labeled hMSCs with or without the preceding Ac4Man-NAz treatment. (*) indicate difference at the p < 0.05 significance. Reproduced with permission from [49]. ACS Publications, 2021.

Figure 3

Quantum dot-based fluorescence labeling probe. (a) Synthetic scheme for preparing RGD-β-CD-QDs. (b) Schematic illustration for the mechanism of action of RGD-β-CD-QDs. (c) In vitro confocal fluorescence images of RGD-β-CD-QD-labeled hMSCs showing the intracellular retention of RGD-β-CD-QDs. (d) In vivo long-term fluorescence images for tracking the RGD-β-CD-QD-labeled hMSCs after their subcutaneous transplantation. Reproduced with permission from [101]. Wiley, 2016.

Figure 4

Fluorescence-BL bimodal stem cell labeling. (a) Schematic illustration showing the process for the fluorescence-BL dual labeling of hMSCs using luciferase-expressing reporter genes and QDs. (b) Confocal fluorescence images of dual-labeled hMSCs exhibiting their fluorescence and BL expression. (c) Long-term in vivo images of hMSCs after their transplantation into skull defects (a = fluorescence by QDs, b = BL by RFLuc, c = BL by GLuc). Reproduced with permission from [132]. Wiley, 2018.

Figure 5

Fluorescence-PA bimodal stem cell labeling. (a) A scheme for the brief explanation of ICG-integrated MIGNS-based fluorescence-PA bimodal labeling of MSCs. (b) MSC viability after MIGNs treatment. (c) Volume-rendered 3D PA images and US images of MSCs in the tumor. Additional fluorescence images of MSCs in the tumor. (d) In vivo photothermal effect and tumor growth after laser irradiation by MINGs in MSCs. (*), (**) and (***) indicate difference at the p < 0.05, p < 0.01 and p < 0.001 significance, respectively. Reproduced with permission from [41]. ACS Publications, 2022.

Figure 6

Fluorescence-MR bimodal stem cell labeling. (a) Graphical illustration depicts the MSC labeling with fluorescence-MR dual probes via glycoengineering-involved bioorthogonal chemistry and dual imaging-based in vivo tracking of labeled MSCs. (b) In vitro confocal fluorescence images of BCN-dual-NP-labeled MSCs with or without the preceding incubation of Ac4Man-NAz. (c) In vitro T2-weighted MR phantom images of BCN-dual-NP-labeled MSCs. In vivo (d) fluorescence and (e) T2-weighted MR images of brain stroke-induced mouse models after transplanting Ac4Man-NAz/BCN-dual-NP-labeled MSCs into brain tissues, visualizing their migration to lesional tissues (red asterisk = stroke-induced region, yellow asterisk = labeled MSC-transplanted site). Reproduced with permission from [43]. ACS Publications, 2019.