Citi analyst Mohit Bansal upgraded Spark Therapeutics to Buy from Neutral amid today's post-earnings selloff. The analyst maintains an $85 price target for the shares.

The company's update this morning on its hemophilia A gene therapy was "incrementally positive and better than our expectations", Bansal tells investors in a research note. The analyst feels investors should not be too concerned about the immune flare in two patients as he thinks these patients could be managed with prophylactic use of steroids.

Other gene therapy players are using prophylactic steroids and it was a bit surprising that Spark did not use prophylactic steroid in the first place, the analyst writes. He views today's selloff as a buying opportunity saying the data in five of seven patients are better than his expectations. Bansal notes that Spark will employ a prophy strategy going forward.

The analyst also views the company as a potential takeover candidate. He pegs Spark's buyout valuation at $130 per share. The stock in midday trading is down 29%, or $22.49, to $55.12.