* Indexes up: Dow 0.5 pct, S&P 0.61 pct, Nasdaq 0.76 pct
By Chuck Mikolajczak
NEW YORK, Sept 24 (Reuters) - Biotech stocks are moving higher on Wednesday, bouncing back from a two-day drop, helped by gains in Gilead Sciences after trial results for the company's HIV treatment.
Gilead said its HIV tablet containing tenofovir alafenamide was found better than its approved drug, Stribild, in two mid-stage studies, sending shares up 2.5 percent to $108.06.
Of the 119 stocks that comprise the Nasdaq biotech index, only 10 were in negative territory.
The gains helped lift the biotech index 2.4 percent, putting it on track for its best day in two months. Also moving higher were Biogen Idec, up 4 percent to $345.50 and Vertex Pharmaceuticals, up 4.9 percent to $109.95.
* S&P 500 was rising 9.89 points, or 0.5 percent.
* Nasdaq Comp was gaining 34.30 points, or 0.76 percent.
* Dow industrials was adding 103.91 points, or 0.61 percent.
* Russell 2000 was adding 5.8 points, or 0.52 percent.
* S&P MidCap was adding 2.41 points, or 0.17 percent.
* S&P SmallCap was gaining 2.95 points, or 0.46 percent. (Reporting by Chuck Mikolajczak; Editing by Meredith Mazzilli)