Biotechnology company ReNeuron Group Plc said its experimental stem cell therapy helped some patients improve motor functions in their arms in a mid-stage study after being disabled by stroke. Shares of the company jumped 22 percent to 3.45 pence per share in morning trade on Monday on the London Stock Exchange. ReNueron's trial adds to a small but growing number of studies being conducted by a few publicly listed companies around the world that are testing stem cell therapies in various indications. Stem cell therapy development has been stalled in the past by stricter regulations in United States, and concerns...