Washington Editor

Positive interim immunogenicity data have further boosted the profile of StaphVAX, Nabi Biopharmaceuticals Inc.'s Staphylococcus aureus polysaccharide conjugate vaccine.

Already in Phase III to confirm that it can prevent S. aureus infections in end-stage renal disease patients, the latest data support its use in additional patient populations at risk for those infections. The product is designed to prevent the most prevalent strains of S. aureus bacterial infections, and the Phase IIb immunogenicity study included 120 cardiovascular surgery patients.

"The study showed what we thought it would," said Henrik Rasmussen, Nabi's senior vice president of clinical, medical and regulatory affairs. "It was very gratifying to get an even better immune response than in [end-stage renal disease] patients."

While the risk of S. aureus among the Phase III dialysis patients is recognizable, the company noted that there are many other patient populations at risk for contracting those infections, such as patients undergoing cardiothoracic or orthopedic surgery, in particular when it involves implantation of prosthetic devices.

Specific findings from the immunogenicity study pointed to substantial increases in antibody levels among patients who received the vaccine by the seventh day, and a week later, the company said those levels were well above the estimated protective antibody levels measured in immunecompromised end-stage renal disease patients. On the 14th day, 93 percent of the cardiovascular patients had antibody levels above the estimated protective levels compared to response rates of 80 percent to 85 percent in end-stage renal disease patients. Also, the vaccine was well tolerated, with no serious adverse events attributed to it.

The two-part, six-month, U.S.-based trial was double-blinded through the first six weeks following vaccination, which occurred prior to the cardiovascular procedures in order to assess antibody levels during the period of greatest S. aureus infection risk. While the cardiovascular patients were healthier than the Phase III end-stage renal disease patients, who Rasmussen said represent worst-case scenarios, 25 percent partially were immunocompromised due to diabetes.

The second phase of the study, an unblinded six-month period, remains ongoing.

Rasmussen told BioWorld Today that the company would include the additional data in an eventual biologics license application with the FDA to support a broader label, as well as in a supplemental marketing authorization application in Europe. Its overseas filing was accepted in January for review, and a decision could come 12 months to 18 months after acceptance.

Nabi, of Boca Raton, Fla., is awaiting results of its second Phase III study of StaphVAX in end-stage renal disease patients before filing with the FDA. Enrollment was completed in August, meaning the trial's one-year follow-up period is up next month. Rasmussen said the data likely would be released by the end of this quarter, with a U.S. regulatory submission by the end of the year. Its European filing was based on data from the first Phase III trial.

The company owns full global rights to the product, and Rasmussen said its marketing plans do not include partnerships in the U.S. and Europe. Elsewhere in the world, Nabi has yet to decide whether to seek marketing alliances. The company estimated there to be 12 million U.S. patients who are at risk of annually contracting those infections, and Rasmussen, who attributed two-thirds of hospital-based infections to Gram-positive bacteria, such as S. aureus, S. epidermidis and enterococcus, noted Nabi's strategy to build the industry's broadest and deepest Gram-positive bacterial infections franchise.

Nabi plans to present full immunogenicity data at an upcoming scientific meeting and in a publication.

Beyond StaphVAX, its other products in development include Altastaph (S. aureus immune globulin intravenous [human]), a Phase II antibody for the prevention and treatment of S. aureus infections. The company is planning to move it into Phase III by the end of the year, a timeline also planned for NicVAX (nicotine conjugate vaccine), a Phase II product to treat nicotine addiction. Also in development is Civacir (hepatitis C immune globulin [human]), an antibody for preventing hepatitis C virus re-infection in liver transplant patients.

Rasmussen was most excited about the company's hospital-based infection programs, which also include vaccines for S. epidermidis and enterococcus, "not only because they're becoming more prevalent, but also because they're becoming more difficult to treat" due to antibiotic resistance. Of course, the vaccine approach is designed to avoid that.

Additionally, the company has three products on the market: PhosLo (calcium acetate), Nabi-HB (hepatitis B immune globulin [human]) and Aloprim (allopurinol sodium [for injection]).

On Tuesday, Nabi's shares (NASDAQ:NABI) lost 31 cents to close at $14.49.

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