Antigenics posted promising early results Tuesday of its experimental herpes vaccine.

The investigational drug, called AG-707, is being used to treat herpes simplex virus-2, which causes genital herpes. Around 60 million Americans are afflicted with the disease, the company said, making the drug a potential blockbuster if it works.

AG-707 is based on what the company calls "heat shock proteins" that help the immune system recognize diseased cells. The jab combines this active ingredient with the company's experimental immune response-boosting adjuvant QS-21.

In the phase 1 study, the researchers were able to boost the response of two immune cells, CD4+ and CD8+ T cells, to herpes antigens in most patients.

"I believe these data represent the first finding of their kind in genital herpes treatments--showing a vaccine, AG-707, elicits both CD4+ and CD8+ T-cell responses in humans," Dr. David Koelle, lead investigator and a professor of medicine at University of Washington in Seattle, said in a statement.

The Salt Lake City, Utah-based company's stock surged over 20 percent on the announcement Tuesday. During recent trading Wednesday it rose 1 percent to hit 92 cents a share.