An immunologist who swapped a career in medical research for finance 10 years ago will begin trading on Dec. 1 via his own hedge fund.Ting Jia’s Octagon Investments fund is set to launch with as much as $300 million of day-one capital, a source said. Jia has hired Goldman Sachs and J.P. Morgan to clear trades. He plans to focus on the stocks of healthcare companies in the U.S., Europe and Asia.Jia began laying the groundwork for the fund...