NEW YORK ( TheStreet) -- CHANGE IN RATINGS Aetna ( AET) upgraded at JPMorgan to Overweight from Neutral. $52 price target. Expectation of upwardly revised numbers post CVH deal closing. Affymetrix ( AFFX) downgraded to sell at TheStreet Ratings. Alexion Pharmaceuticals ( ALXN) rated new Neutral at Citi. $104 price target. Will need significant upside to offset P/E contraction. Allot Communications ( ALLT) downgraded to hold at TheStreet Ratings. American Greetings ( AM) downgraded to hold at TheStreet Ratings. DST Systems ( DST) upgraded at Sterne Agee to Buy from Hold, Sterne Agee said. $71 price target. Clear path to monetize non-core assets. Mid America Apartment Communities ( MAA) rated new Hold at KeyBanc. Shares are fairly valued given the company's balanced growth. Marathon Petroleum ( MPC) rated new Neutral at JPmorgan. $62 price target. Attractive exposure to US Mid-Continent. Melco Crown Entertainment ( MPEL) upgraded at JPMorgan to Overweight from Neutral, JPmorgan said. $20 price target. Shares are attractive at current levels.