Carving out $400 million in annual cost savings is going over well with Sarepta Therapeutics Inc.’s investors, as the company’s stock got a 19.6% boost on July 17. Its big seller, the gene therapy Elevidys (delandistrogene moxeparvovec), continued its revenue numbers decline, so Sarepta chopped operating expenses by letting about 500 employees go in a 36% cutback and pared its development path.