Aldagen, a small private US firm which has programmes underway for its adult stem cell technology, twice filed plans to go public, but ended up withdrawing its plans in 2008 and 2011. It has an early-stage candidate it believes can prove successful in a stroke trial, and has just agreed to be acquired by Cytomedix, a publicly traded Gaithersburg, Maryland-based company which has regenerative therapies for wound and tissue repair.