Stem cell-based regenerative medicine holds great promise for clinic practices. The stem cells after transplantation experience a very different microenvironment from in vitro and their viability in vivo is critical to the therapeutic effect.

The fate of these stem cells including the distribution, viability, and cell clearance by the immune system has not been fully understood. Thus, a non-invasive in vivo imaging technique that can monitor the fate of transplanted stem cells is urgently needed to understand the role of stem cell in regenerative medicine and to speed up the clinical translation of stem cell-based therapeutics.

Recently, Prof. WANG Qiangbin’s group at Suzhou Institute of Nano-Tech and Nano-Bionics of Chinese Academy of Sciences developed a dual-labeling strategy to in situ visualize the fate of transplanted stem cells in vivo by combining the exogeneous near-infrared fluorescence imaging (NIRFI) of Ag₂S quantum dots (emitting at 1200 nm) and endogenous bioluminescence imaging (BLI) of red-emitting firefly luciferase (RfLuc, emitting at 613 nm), due to the deep tissue penetration and high spatiotemporal resolutin of NIRFI and the characteristic nature of living stem cells to express RfLuc.

For the first time, the researchers successfully traced the dynamic translocation of mouse mesenchymal stem cells (mMSCs) in vivo, differentiated the living cells and dead cell components in situ, and clarified the regenerative mechanism of living mMSCs involved in the healing of the acute liver failure by using the RfLuc/Ag₂S QDs dual-label method.

The distinct features of the dual-imaging method encourged a broad range of further applications, such as in vivo stem cell intervention, imaging-guided cell therapeutics. These findings could inspire future stem cell research, biomedicine studies, and people's fundamental understanding on the in vivo biological activities.

The study was published in Small. It was supported by the National Key Research and Development Program, the National Natural Science Foundation of China, and the Natural Science Foundation of Jiangsu Province.

Figure: Schematic illustration of the dual-labeling strategy for in vivo tracking the fate of transplanted stem cells by combining the exogenous Tat-Ag₂S QDs and endogenous RfLuc (Image by WANG Qiangbin and CHEN Guangcun)