GlaxoSmithKline raised the stakes behind its anticipated launch of the investigational cervical cancer vaccine Cervarix Jan. 18, announcing the initiation of the first head-to-head trial comparing it to Merck's Gardasil . The study will evaluate differences between the two vaccines in inducing strong and sustained immune responses to the human papilloma virus in women.

The primary endpoint of the study will be immune response to HPV types 16 and 18 - the types that cause more than 70 percent of cervical cancers - in women 18 to 26 years old. Secondary objectives include evaluating immune responses to HPV 16 and 18 in women 27 to 35 years old.

GSK is betting that the head-to-head trial will demonstrate that treatment with Cervarix provides a more robust immune response to the two types of HPV because the vaccine is formulated with a proprietary adjuvant system, AS04, compared to Gardasil, which is formulated with aluminum hydroxide adjuvant alone.

The company pointed to data published in Vaccine in August that showed Cervarix induced higher antibody levels and more robust immune memory response compared to the same HPV vaccines conventionally formulated with aluminum hydroxide adjuvant alone.

"What we're looking at is the formulation types and how it makes a difference," GSK told "The Pink Sheet" DAILY. "We think this will translate into a clinical benefit."

The outcome of the study could be critical to GSK, which would enter the market after Merck has already established a strong brand position. In addition, GSK would benefit from establishing an efficacy benefit for Cervarix over Gardasil in HPV types 16 and 18 because Gardasil already has a positioning advantage over Cervarix: it is approved to protect against HPV types 6 and 11, which cause about 90 percent of genital warts cases, in addition to types 16 and 18.

Merck's Gardasil launched in June, with the company reporting $70 million in sales of the product in its first full quarter on the market (¹ Also see "Merck’s Gardasil Records $70 Mil. In Sales In Q3" - Pink Sheet, 20 October, 2006.).

Responding to the move by GSK, Merck said, "We are not surprised by this announcement as later entrants into markets have done comparative studies versus the market leaders."

"Beyond the 100% efficacy of HPV 16 and 18 related cervical precancer and noninvasive cervical cancer, Gardasil uniquely offers the broadest protection against HPV disease," the company added, pointing to the protection it provides against four types of HPV. "GSK's vaccine targets only HPV 16 and 18," the company added.

In addition, Merck said that immunogenicity data is not a substitute for efficacy data, and noted that the results of the head-to-head trial will, therefore, "not provide an equivalent to efficacy in prevention of disease."

The head-to-head trial is a randomized, observer-blind, multi-center study that will enroll 1,042 patients in the U.S. Patients will be vaccinated with Cervarix or Gardasil, and each arm of the trial will be stratified by age (18-26, 27-35 and 36-45).

Enrollment will begin in the next several weeks and is expected to take three to six months, the company said. Results are anticipated about 12 months after patient enrollment is complete, with extended follow up continuing for approximately 17 months after the last study visit.

GSK pushed back the filing timeline for submitting a BLA for Cervarix to FDA until April last year. The company had previously anticipated filing in December (² Also see "Cervarix Filing Delay Will Not Impact The HPV Vaccine’s Market Potential – GSK" - Pink Sheet, 26 October, 2006.).

GSK told "The Pink Sheet" DAILY that it plans to submit data that may be "compelling" enough to warrant a priority review by FDA.

-Jessica Merrill (j.merrill@elsevier.com)

GSK Wagers On Cervarix In Head-To-Head Trial Against Gardasil

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