By Mary Welch

Cerus Corp. and its partner, Baxter Healthcare Corp., started enrolling patients in a Phase III trial testing a system that inactivates viruses, bacteria and other pathogens that may be present in platelet concentrates for transfusion.

"We're looking at two things," said Gregory Schafer, chief financial officer for Concord, Calif.-based Cerus. "We want to see if the platelets themselves work, in other words, see if there is a limiting of clinical bleeding. The second is to see the safety of the product."

Already a pivotal trial is under way in Europe in what Cerus said marked the first human clinical trial for a pathogen-inactivation system for platelets.

The multicenter trial will evaluate the ability of the platelets, treated with the company's pathogen-inactivation system, to control clinical bleeding. Approximately 600 patients will receive either treated or untreated platelets for a specified period of time. The trial should last 18 to 24 months.

The clinical endpoint is the incidence of clinical bleeding while the patients are receiving platelet support. "This patient population has low platelet counts and they are subject to bleeding," Schafer said. "We want to see if that is corrected."

The Cerus FFP (fresh frozen plasma) pathogen-inactivation system is based on the company's proprietary light-activated psoralen compound, S-59. The compound targets and inactivates blood-borne pathogens, such as hepatitis B and C, while leaving the platelet's therapeutic properties complete.

"We have got to get a name for this thing. There's got to be something better than 'Cerus' proprietary pathogen- inactivation system,'" Schafer said with a laugh. "We're working on it."

Currently, the integrity of the blood supply is maintained by screening donors for high-risk activity and testing blood for some known blood-borne pathogens. A problem exists when new pathogens start emerging because blood centers can't detect them, which was the case with HIV, hepatitis B and hepatitis C before suitable tests were developed.

An estimated 10 million units of FFP worldwide are transfused annually and some 3.5 million units of platelets are transfused annually.

"Our system is designed for patients who are receiving organ transplants, chemotherapy and bone marrow transplants," Schafer said.

Cerus and Baxter, of Deerfield, Ill., are enrolling patients in one of three Phase III trials for fresh frozen plasma, which also is based on the S-59 blood compound. The three trials will evaluate coagulation factor function following transfusion of FFP treated with the company's pathogen-inactivation system. Patients who will be enrolled will include those with certain types of congenital clotting factor deficiencies, those requiring large volumes of FFP to treat diseases such as thrombotic thrombocytopenic purpura, and those with liver problems.

Separately, Cerus has a Phase Ib trial under way with its proprietary pH-activated anchor-linker-effector (ALE) compound, S-303, for inactivating pathogens in red blood cells.

Cerus Corp.'s stock (NASDAQ:CERS) closed Thursday at $23.25, up 75 cents per share.