Gilead Sciences (GILD, news, chart) is seeing active trading. Shares of the biotech company are down $2.50 to $50.18 after Bank of America downgraded the stock from Buy to Neutral. The firm says GILD HIV sales growth is flattening and it is beginning to look like a mature company. The cautious comments come the day before a presentation at the Thomas Weisel Partners Healthcare Conference in Boston. In the options market, volume is running double the usual. 20,000 calls have traded, compared to 8,800 puts. While some players are closing out long calls on the heels of the downgrade, others appear to be using today’s decline as an opportunity to enter bullish trades. The November 55 calls ar the most actives, with 4,300 calls traded and 58 percent trading on the offer. Another 2,500 of the January 50s have traded, with 87 percent trading offerside.