Tendons display poor intrinsic healing properties and are difficult to treat[1]. Prior in vitro studies[2] have shown that, by targeting the Activin A receptor with magnetic nanoparticles (MNPs), it is possible to remotely induce the tenogenic differentiation of human adipose stem cells (hASCs). In this study, we investigated the tenogenic regenerative potential of remotely-activated MNPs-labelled hASCs in an in vivo rat model. We consider the potential for magnetic controlled nanoparticle mediated tendon repair strategies. hASCs were labelled with 250 nm MNPs functionalized with anti-Activin Receptor IIA antibody. Using a rapid curing fibrin gel as delivery method, the MNPs-labelled cells were delivered into a Ø2 mm rat patellar tendon defect. The receptor was then remotely stimulated by exposing the rats to a variable magnetic gradient (1.28T), using a customised magnetic box. The stimulation was performed 1 hour/day, 3 days/week up to 8 weeks. Tenogenesis, iron deposition and collagen alignment were assessed by histological staining and IHC. Inflammation mediators levels were assessed by ELISA and IHC. The presence of human cells in tendons after 4 and 8 weeks was assessed by FISH analysis. Histological staining showed a more organised collagen arrangement in animals treated with MNPs-labelled cells compared to the controls. IHC showed positive expression of tenomodulin and scleraxis in the experimental groups. Immunostaining for CD45 and CD163 did not detect leukocytes locally, which is consistent with the non-significant levels of the inflammatory cytokines analysis performed on plasma. While no iron deposition was detected in the main organs or in plasma, the FISH analysis showed the presence of human donor cells in rat tendons even after 8 weeks from surgery. Our approach demonstrates in vivo proof of concept for remote control stem cell tendon repair which could ultimately provide injectable solutions for future treatment. We are grateful for ERC Advanced Grant support ERC No.789119, ERC CoG MagTendon No.772817 and FCT grant 2020.01157.CEECIND.
