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What: Shares of biotech Theravance (Nasdaq: THRX) have jumped today by as much as 23% on news that behemoth drugmaker GlaxoSmithKline (NYSE: GSK) is boosting its stake in the company.

So what: GlaxoSmithKline is investing roughly $213 million in the smaller company in a deal that gives it 10 million new shares through a private placement at a price of $21.29 each, a 9% premium to Friday's closing price. That brings GlaxoSmithKline's stake up to 25.8 million shares, or almost 27% of Theravance.

Now what: The two companies are currently partnering to develop Relovair, an experimental drug for lung disease and asthma. The pair has been collaborating for a decade and the investment signifies further confidence in Theravance. Relovair is seen as the follow-up successor to GlaxoSmithKline's Advair asthma drug, and Relovair has already completed phase 3 development.

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