The shares of Opexa Therapeutics Inc. (NASDAQ:OPXA - 3.31) are through the proverbial roof this afternoon, sparking a run on bullish bets in the options pits. So far today, the biopharmaceutical concern has seen roughly 2,500 calls cross the tape -- about seven times the number of OPXA puts traded.

About half of the action has transpired at the March 2.50 call, which has seen nearly 1,800 contracts change hands at a volume-weighted average price (VWAP) of $0.09. Most of the calls traded on the ask side of the tape, and with just 10 contracts currently docked at the strike, we can assume the options -- which represent just 25 shares in the wake of the stock's 1-for-4 reverse split -- are being bought to open.

By purchasing the calls to open, the buyers expect OPXA to extend its rally north of $2.59 (strike plus VWAP). In fact, the farther the stock soars beyond this breakeven level, the more the buyers stand to make. However, even if OPXA surrenders today's gains, the most the traders can lose is the initial premium paid for the calls.

Elsewhere on Wall Street, the lingering shorts are likely shaking in their boots. Short interest on the stock dropped nearly 78% during the past month, but these bearish bets still represent nearly four sessions' worth of pent-up buying demand, at OPXA's average pace of trading.

At last check, OPXA is up 174% to trade near $3.31, and is on pace to end the week atop its 80-week moving average for the first time since April 2011. Earlier in the session, the equity tagged a new annual high of $5.19, after the company entered into a licensing agreement with Germany-based Merck KGaA to develop and commercialize Tcelna, Opexa's experimental multiple sclerosis treatment. The deal -- in which Opexa will receive an upfront payment of $5 million -- is valued at up to $225 million.