NEW YORK (TheStreet) -- Biotech stocks were mixed on Thursday, an unusually quiet day in the realm of early-stage experimental medicines, where an FDA decision or a tentative government contract can slice in half or nearly double the market cap of a company.

The Nasdaq Biotechnology Index was in the red Thursday afternoon, down 4.9 points to 913.04.

Among the biggest losers among biotechs Thursday was

Geron

(GERN) - Get Report

, the embryonic stem-cell outfit, whose shares had ripped higher this week as the company commenced its pioneering study of a possible spinal-cord-injury cure -- the first ever human clinical trial of a therapy derived from human stem cells.

Geron hasn't commercialized a drug in its 14-year history as a public entity. The Phase 1 clinical trial of its spinal-cord drug is aimed at proving its safety, not its efficacy.

Thursday afternoon, Geron shares were losing 3.8% on elevated trading volumes. Up until today's session, the stock had posted gains of 13% for the week. The stock's 52-week high came nearly a year ago, on Oct. 19, when it touched $7.18.

One of the sharpest winners Thursday was

Inspire Pharmaceuticals

( ISPH), whose share were rising 5.6% to $6.62 on heavier-than-average volume but little in the way of real news. Elsevier Business Intelligence, a publisher of healthcare industry newsletters, cited the company's cystic fibrosis drug Denufosol in its "2011 Top Biopharma Projects to Watch" list. Elsevier released the list on Thursday.

Among other gainers,

Jazz Pharmaceuticals

(JAZZ) - Get Report

was advancing 4% to $11.40. The stock has climbed back from a steep drop earlier this week. The Food and Drug Administration told the company on Monday that it wouldn't OK its treatment for chronic muscle-pain relief unless it conducted more studies, which led to speculation that the company would forfeit development of the drug.

On the pink sheets,

Actelion

shares jumped again Thursday on takeover speculation,

Reuters

reports, with

GlaxoSmithKline

(GSK) - Get Report

as the reputed buyer. The pair are co-developing an insomnia cure called almorexant. The lightly traded shares of Actelion, known more for a treatment for pulmonary hypertension, were rising 9% to $55.85.

Speaking of biotech M&A,

Genzyme

( GENZ) issued a tactical press release Thursday trumpeting the fact that freshly analyzed five-year data on its multiple sclerosis treatment has demonstrated its efficacy, and that side effects are the same as earlier studies.

The release was clearly designed to counter the claims of its hostile takeover pursuer,

Sanofi

(SNY) - Get Report

, which has argued that Genzyme's experimental MS drug isn't as great as Genzyme has made it out to be -- and, thus, that Genzyme should be happy to accept the

$18.5 billion offer from Sanofi

.

Shares of the Cambridge, Mass., drug developer were slipping 14 cents to $72.46.

-- Written by Scott Eden in New York

>To contact the writer of this article, click here:

Scott Eden

.

>To follow the writer on Twitter, go to

http://twitter.com/ScottEden

.

>To submit a news tip, send an email to:

tips@thestreet.com

.

Disclosure: TheStreet's editorial policy prohibits staff editors and reporters from holding positions in any individual stocks.