Soros takes 5.17% stake in PlasmaTech By: MarketMinute.com Stock News May 05, 2015 at 14:35 PM EDT Billionaire investor George Soros acquired a 5.17% stake in PlasmaTech Biopharmaceuticals Inc. (Nasdaq: PTBI). The stock price more than doubled by leaping $$4.30 to $7.16.