Shares of Virgin Galactic Holdings Inc. SPCE, +0.17% are off 17% in premarket trading Thursday after Credit Suisse analyst Robert Spingarn downgraded the stock to neutral from outperform. "While SPCE remains a compelling story from the perspectives of near-term catalysts toward first revenue flight, its leading market position, strong incremental margin potential, and the scarcity value of the investment opportunity (all points outlined in our initiation), we find ourselves no longer able to recommend SPCE shares after a ~185% [year-to-date] run (through Feb. 25) and commensurate expansion in the stock's multiple," he wrote. He sees limited opportunity for upside to his estimates given the "relatively more limited scalability of the business model." He upped his price target to $25 from $15 in conjunction with the downgrade. Virgin Galactic shares are up 293% over the past three months, as the S&P 500 SPX, -1.11% has lost about 1%.