Strain C57BL/6 Mouse Mesenchymal Stem Cells with RFP

Enhanced In Vivo Delivery of Stem Cells using Microporous Annealed Particle Scaffolds

Stem cell therapies, especially using mesenchymal stem cells (MSCs), hold promise for disease treatment by repairing tissue and modulating the immune system. Yet, delivery challenges such as insufficient cell retention and environment integration remain. Koh et al. employs microporous annealed particle (MAP) scaffolds to address these issues.

Results showed that cells spread and migrated more rapidly in MAP scaffolds, with increased void volume leading to higher proliferation rates. RFP-MSCs in MAP scaffolds showed a 17-fold expansion over two weeks, compared to a 2.3-fold increase in nonporous gels (Fig. 1B). This enhanced proliferation was confirmed by lower cell-free regions in MAP scaffolds (Fig. 1C). Based on these in vitro results and the robust cell ingrowth in acellular MAP scaffolds in vivo, they hypothesized that MAP scaffolds would improve MSC retention in vivo compared to PBS or nonporous scaffolds. RFP-MSCs were injected subcutaneously into immunocompetent mice, and fluorescence intensity was measured over two weeks (Fig. 1D, E). At one week, RFP intensity was highest in MAP scaffolds (Fig. 1F), with significantly larger cell areas (Fig. 1G). The half-life of MSCs was 6.13 days for MAP scaffolds, 2.35 days for nonporous gels, and 1.91 days for PBS. These results indicate that microporous scaffolds enhance cell proliferation and survival in vivo, likely due to improved transport and cell connectivity.

Fig. 1. Controlled microporosity generated by MAP scaffolds facilitates the highest proliferation in vitro and retention in vivo (Koh J, Griffin D R, et al., 2019).

The Presence of CXCR4 is Essential for MSC Homing to the Fracture Site

The development of delayed bone union progresses into non-union which creates severe dysfunction that complicates treatment approaches. BMSCs show promise for enhancing fracture healing but scientists have yet to determine the best time to administer injections. Wang's team investigates the optimal BMSC injection times for enhancing fracture healing in a murine model by studying how different time points affect BMSC migration and bone repair processes.

To assess MSC homing at the femur fracture site, they injected RFP-transfected BMSCs (RFP-BMSCs) into mice on days 1, 7, and 14 post-fracture. In fluorescence imaging analysis, following a day-1 injection, RFP signal intensity was greater on days 7 and 14 when RFP-BMSCs were injected in the absence of AMD3100, although signal intensity was similar in both groups on day 28. A similar pattern of RFP signal intensity was seen after BMSC injection on day 14, although the overall signal intensity was higher following day 7 injection between with and without AMD3100 (Fig. 2). At day 42 post-fracture, signal intensity did not differ between BMSC injections on days 1, 7, and 14. Therefore, a higher RFP signal intensity was maintained following RFP-BMSC injection on day 7 post-fracture.

Fig. 2. Representative photographs of fluorescence imaging and semiquantitative analysis (Wang X, Wang C, et al., 2018).