Could the tide be turning for Regeneron Pharmaceuticals Inc. (NASDAQ:REGN) after a surprising shift in analyst sentiment?As investors digest the latest upgrade, what factors are driving this newfound optimism for the biotech giant?Bank of America (BofA) Securities on Wednesday upgraded Regeneron Pharmaceuticals, citing several factors, including higher sales for key products.Analyst Tazeen Ahmad upgraded Regeneron from Underperform to Buy, and raised the price forecast from $627 to$860.BofA's prior Underpe ...