Vical Inc. has signed a licensing agreement with Merck & Co.Inc. to use Vical's Gene Therapeutics technology to developvaccines for human infectious diseases.

Dannie King, Vical's president and chief executive officer, onTuesday told BioWorld that Merck has taken licenses forspecific, undisclosed indications and has options for theremaining indications in the area of infectious disease.

The deal includes research funding, milestone payments, optionand license fees, and royalty payments on product sales. SanDiego-based Vical, which is privately held, would not disclosespecific terms.

The deal is the first for Vical's Gene Therapeutics technology,which uses DNA and/or RNA gene sequences derived from aviral genome.

In laboratory studies using mouse skeletal muscle, these genesequences produced antigens that stimulate the immunesystem more effectively than conventional killed virusvaccines or recombinant protein vaccines, said Philip Felgner,a Vical co-founder and director of gene therapeutics.

Vical's system, which it developed in collaboration with theUniversity of Wisconsin, begins by injecting into a muscle cella piece of naked DNA or RNA that encodes a protein of interest.The gene product -- in this case an antigen -- is secreted, andlymphocytes in the area are stimulated to produce cytotoxic Tcells that confer immunity.

Cytotoxic T cells don't affect mature virus particles, saidFelgner. Instead, they seek out infected host cells and killthem, thus preventing the virus from replicating itself. This isa key difference between Vical's system and conventionalvaccines, which stimulate the body to produce antibodies thatcoat mature virus particles and make them less infective,Felgner said.

For vaccines, RNA sequences are preferable because they posefewer regulatory concerns than DNA sequences, said Felgner."There's some low risk in principle that DNA sequences couldbecome incorporated into the host genome, though the risk islower with our approach than with a retrovirus approach thatsome other gene therapy companies are using," he said.

Vical is also developing the technology for genetic disorderssuch as muscular dystrophy and multiple sclerosis. In thelonger term, the company is looking at Gene Therapeutics as aform of drug delivery for recombinant proteins, whereby genescould be injected that would then produce therapeutic proteins.

Merck has signed vaccine development and/or licensing dealswith several biotechnology companies, including RepligenCorp., Medimmune Inc. and Chiron Corp.

-- Karen Bernstein BioWorld Staff

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