Pfizer Inc. will work with privately held biotechnology company VLST Corp. on a potential immune therapy for cancer.

VLST said Friday it plans to start testing the drug, designated CP-870,893, as a treatment for cancer in mid-stage clinical trials. The Seattle company has conducted early-stage trials of the drug and said it recently secured $5 million in financing to help fund mid-stage studies.

Pfizer and VLST will share the rights to develop and market the drug as a “cancer vaccine,” or a therapy that is designed to stimulate the immune system to fight cancer.

Shares of New York-based Pfizer gained 6 cents to $23.90 in morning trading.