Credit Suisse analyst Alethia Young upgraded Biogen (BIIB) to Outperform from Neutral and raised her price target for the shares to $385 from $321. The stock closed yesterday up $1.07 to $327.02.

The analyst this morning also downgraded Gilead Sciences (GILD) to Neutral from Outperform. A "significant turnaround" is underway for Biogen's business, Young tells investors in a research note. With 2017's hires, the company now has a "top notch management back in place" to execute commercially and clinically, the analyst adds.

If aducanumab is successful in Phase 3, Young's model puts Biogen shares at $455, versus $250-$280 per share if only giving credit to the base business alone without pipeline.