BioVex is developing so-called oncolytic viruses, which are designed to infect and destroy tumor cells — long a promising but never-proven anti-cancer technique. The company put an unusual twist on the concept by adding a gene to a herpes simplex virus that expresses GM-CSF (granulocyte macrophage-colony stimulating factor), a molecule that stimulates a strong immune response. Ideally, this virus should infect tumor cells while leaving healthy cells alone, then hijack the tumor cells’ own internal machinery to manufacture GM-CSF, stimulating an immune response that should also be directed at the tumor cells.

That experimental drug, OncoVex GM-CSF, is currently in mid-stage human tests against skin cancer and early tests against head and neck cancer. BioVex is also developing a vaccine against genital herpes. The company had filed to go public last year, but withdrew its proposed offering last October.