U.S. stocks held onto big gains at midday as new 'Brexit' polls suggested the U.K. could remain in the European Union. The outcome of the referendum is announced on Friday. Walmart (WMT) - Get Report climbed on reports it is in talks to sell its Chinese e-commerce business to JD.com (JD) - Get Report . The move would likely be part of a strategic partnering that would give Walmart a better shot at competing in the region's retail industry. Federal-Mogul (FDML) jumped after billionaire Carl Icahn increased his bid to buy a minority stake to $8 dollars a share. Icahn previously offered $7 in February. CVS Health (CVS) - Get Report was downgraded to EQUAL WEIGHT at Morgan Stanley. Analysts said the company is facing increased competition in the pharmacy benefit management market.