The patent is related to commercial purification and production of the so-called adenovirus, which is a vehicle researchers use to carry healthy genes into patients in gene therapy trials. Introgen's vice president of intellectual property said the company will look for potential licensing opportunities.

"We expect that companies will have an interest in talking to us once they have picked themselves up off the floor. They know our phone number," said David Parker, vice president of intellectual property at Introgen.

One analyst said landing the patent looks good for Introgen. The adenovirus vector is used in about 25 percent of gene therapy studies, second only to the retrovirus which is used in 38 percent of trials.

The payment of licensing fees could become a major issue for companies such as Onyx Pharmaceuticals (ONXX), which has been using the vector for years and is now in the final stages of FDA clinical trials with their gene therapy for head and neck cancer. An Onyx spokeswoman said lawyers at the company had not yet reviewed the patent.

Other companies that use the adenovirus vector include Cell Genesys (CEGE) and Genzyme (GZMO).

Cell Genesys spokeswoman Jennifer Williams said the company uses four types of vectors for their gene therapy research, and the adenovirus is only third on the list in order of importance. The company's most important vector, she said, is a so-called adeno-associated virus (AAV).

Williams also said that Cell Genesys has the largest patent portfolio in the gene therapy industry.

Researchers at Schering-Plough are using the adenovirus in phase 2 trials on the treatment of ovarian cancer, but a company spokesman said Schering-Plough has its own patents on its gene therapy technique.

"There are a number of gene therapy products that have been developed using adenovirus vectors and they're all different. There are numbers of ways of altering the adenovirus to serve as your vector," said Bob Consalvo, a spokesman for Schering-Plough.

The adenovirus is popular with gene therapy researchers for several reasons, Parker said. First, it can be made in reasonably large quantities for a small amount of money. It also has shown few side effects in the approximately 500 patients Introgen has treated using the adenovirus.

The adenovirus was singled out as the cause in the first death to result from gene therapy in September 1999. However, the method used to deliver the treatment was considered very risky. Instead of delivering the gene therapy into a tumor like Introgen and most other gene therapy researchers, University of Pennsylvania investigators injected the adenovirus directly into 18-year-old Jesse Gelsinger's liver. He died four days later.

The FDA has since banned Penn's Institute for Human Gene Therapy from doing experiments on humans, and in December the agency threatened to ban the researcher in charge of the institute from further human clinical trials.

Many researchers say Gelsinger's death was tragic but an isolated incident. About 3,000 patients total have been treated to date using the adenovirus vector without the complications seen in Gelsinger's case.

"I think the fact that (there was) one questionable outcome in an academic environment that was kind of out there on the fringes is a pretty good record overall," Parker said.

Parker touted Introgen's own gene therapy method, saying the company has been held up as a "poster child" by the FDA as an example of how gene therapy should be done.

Introgen was the first company to bring a gene therapy for cancer to phase 3 clinical trials in head and neck cancer, which is the final stage of research in FDA testing. Onyx and Vical (VICL) have since also entered into phase 3 trials.

Parker wouldn't comment on preliminary phase 3 results but said he would be "very pleased if the results came back the same as in phase 2."