 Shares of DBV Technologies tumbled 8.5 in premarket trading on Wednesday, the day after the company said it had received a complete response letter from the Food and Drug Administration for its experimental peanut allergy treatment. The regulator asked for a new study stemming from its concerns about the efficacy of the Viaskin Peanut patch. Given the uncertainty regarding the timeline for BLA resubmission, we are taking a conservative approach and pushing Viaskin Peanut launch out by two years, SVB Leerinks Joseph Schwartz wrote in a note to investors on Tuesday. In January the FDA approved Aiummune Therapeutics Inc.s Palforzia, the first peanut allergy treatment. It is an oral immunotherapy. DBVs stock is down 76.2 since the start of the year, compared with the SP 500 , which has gained 2.3. 