1 Institute of Inflammation and Repair, University of Manchester, Oxford Road, M13 9PL Manchester, UK. Electronic address: Giulio.cossu@manchester.ac.uk.
3 Centre for Regenerative Medicine "Stefano Ferrari", University of Modena and Reggio Emilia, Via del Pozzo 71, 41100 Modena, Italy. Electronic address: michele.deluca@unimore.it.