Juno Therapeutics Inc., of Seattle, said it launched a proposed follow-on public offering of $225 million of shares of its common stock. In addition, it expects to grant the underwriters a 30-day option to purchase up to an additional $33.75 million of shares of its common stock. Juno intends to use the net proceeds for general corporate purposes and working capital. The number of shares and share price have not yet been disclosed. The company's stock (NASDAQ:JUNO) closed Thursday at $41.62, down $3.59.