The downgrade by a major analyst and the significant reduction in price target are strong indicators of a negative short-term impact on Macrogenics' stock price. Analyst ratings and price targets are closely watched by investors and can influence market perception and investor sentiment towards a stock. The drastic cut from $24 to $8 suggests a substantial change in the company's valuation or future earnings potential as seen by the analyst, which could lead to a decrease in investor confidence and a potential sell-off in the short term.