Unveiling the improved targeting migration of mesenchymal stem cells with CXC chemokine receptor 3-modification using intravital NIR-II photoacoustic imaging

Background: Therapy with genetically modified mesenchymal stem cells (MSCs) has clinical translation promise. Optimizing the targeting migratory ability of MSCs relies on accurate imaging of the distribution and extravasation kinetics of MSCs, and the corresponding imaging results could be used to predict therapeutic outcomes and guide the optimization of the treatment program. Among the different imaging modalities, second near-infrared (NIR-II) optical-resolution photoacoustic microscopy (OR-PAM) has merits, including a fine resolution, a deep penetration, a high sensitivity, and a large signal-to-background ratio. It would be an ideal candidate for precise monitoring of MSCs, although it has not been tested for this purpose so far. Results: Penetrating peptide-decorated conjugated polymer nanoparticles (TAT-CPNPs) with strong NIR-II absorbance were used to label chemokine-receptor genetically modified MSCs, which were subsequently evaluated under intravital NIR-II OR-PAM regarding their targeting migratory ability. Based on the upregulation of chemokine (C-X-C motif) ligand 10 in the inflamed ears of contact hypersensitivity mice, MSCs with overexpression of corresponding receptor, chemokine (C-X-C motif) receptor 3 (Cxcr3) were successfully generated (MSC^Cxcr3). TAT-CPNPs labeling enabled NIR-II photoacoustic imaging to discern MSC^Cxcr3 covered by 1.2 cm of chicken breast tissue. Longitudinal OR-PAM imaging revealed enhanced inflammation-targeting migration of MSC^Cxcr3 over time attributed to Cxcr3 gene modification, which was further validated by histological analysis. Conclusions: TAT-CPNPs-assisted NIR-II PA imaging is promising for monitoring distribution and extravasation kinetics of MSCs, which would greatly facilitate optimizing MSC-based therapy. Graphical Abstract: [Figure not available: see fulltext.]