**5. Conclusions**

The present study shows the potentiality of polymeric micelles as powerful rAAV controlled delivery systems to counteract the specific contribution of major OA-associated inflammatory cytokines in chondrocyte cultures. Here, we provide concrete evidence that encapsulation of an rAAV vector carrying a *sox9* sequence in such systems promotes significant SOX9 expression levels capable of increasing the deposition of major ECM components (type-II collagen, proteoglycans) and the cell survival processes in human OA chondrocytes while reversing their downregulation afforded by OA cytokines. While this work evidence the utility of such micellar systems to tackle the OA phenotype in chondrocytes in a 2D environment, work is currently ongoing to broaden this investigation at longer time points and to support the present findings when cells are embedded in their own pericellular matrix using an experimental model of osteochondral defect in situ [22,23] where the chondrocytes may also be influenced by interplay with subchondral bone cells that have key roles in OA development and progression. Overall, such observations show the effectiveness of polymeric micelles as rAAV controlled delivery systems in an inflammatory environment, making them attractive tools for the treatment for chronic inflammatory diseases like OA.

**Author Contributions:** Conceptualization, A.R.-R. and M.C.; methodology, A.R.-R. and M.C.; software, J.U. and A.R.-R.; validation, A.R.-R. and M.C.; formal analysis, J.U., A.R.-R. and M.C.; investigation, J.U., A.R.-R. and M.C.; resources, A.R.-R. and M.C.; data curation, J.U. and A.R.-R.; writing—original draft preparation, A.R.-R. and M.C. writing—review and editing, A.R.-R. and M.C.; visualization, A.R.-R. and M.C.; supervision, A.R.-R. and M.C.; project administration, A.R.-R. and M.C.; funding acquisition, A.R.-R. and M.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the DEUTSCHE FORSCHUNGSGEMEINSCHAFT (DFG RE 328/2-1 to A.R.R., M.C.).

**Acknowledgments:** The authors acknowledge R.J. Samulski (The Gene Therapy Center, University of North Carolina, Chapel Hill, NC, USA), X. Xiao (The Gene Therapy Center, University of Pittsburgh, Pittsburgh, PA, USA), and E.F. Terwilliger (Division of Experimental Medicine, Harvard Institutes of Medicine and Beth Israel Deaconess Medical Center, Boston, MA, USA) for providing the genomic AAV-2 plasmid clones, the pXX2 and pXX6 plasmids, and the 293 cell line. The authors also thank G. Scherer (Institute for Human Genetics and Anthropology, Albert-Ludwig University, Freiburg, Germany) for providing the human *sox9* cDNA. A.R.R. thanks the InTalent program from UDC-Inditex for the research grant.

**Conflicts of Interest:** The authors declare no conflict of interest.
