Goldman Sachs analyst Paul Choi double downgraded Nektar Therapeutics to Sell from Buy with a price target of $16, down from $54. The stock closed Monday down 30c to $18.67.

Near-term catalysts are unlikely to re-rate the stock higher in the face of quality issues and a narrower focus for bempegaldesleukin, Choi tells investors in a research note. The shares over the past 18 months have underperformed as execution missteps related to suboptimal batches overshadowed original announcements of mostly positive clinical developments, says the analyst.

Even with shares down over 60% since its January 19 high, the analyst thinks uncertainty on bempeg's safety or efficacy, as well as Nektar's ability to execute on a large-scale clinical development program, will likely continue to be an overhang on shares.