Cancer vaccines are becoming an increasingly attractive focus of study, but there are still perils and pitfalls along the way to success. Two recent studies have looked at ways to get around these, focusing on experimental cancer vaccines boosted by existing drugs.
One of the issues that cancer vaccines face is that tumors can hide from the immune system, helped by the regulatory T cells or Tregs that normally turn off the immune system once it has finished fighting infection. These white blood cells have been co-opted by cancers to protect them from the normal immune response, also cutting the effectiveness of cancer vaccines that are designed to boost the immune responses against the tumors. Researchers at the University of Pennsylvania are looking at using daclizumab (Zenapax)--a monoclonal antibody used to prevent transplant rejection--to target the Tregs and convert them into normal T cells, and to therefore restore the immune response against the cancers.
Ten women with metastatic breast cancer were treated with daclizumab and an experimental cancer vaccine developed at the university. Their Tregs converted to T cells, lasting for two months; the tumors in 6 patients stopped growing, and they survived around 30% longer than the women who had the cancer vaccine alone. The results were published in Science Translational Medicine.
"Although we tested our approach in patients with breast cancer, we know that Tregs can block the immune response against most human cancers," says senior author Robert H. Vonderheide. "Drugs like daclizumab might be useful for most cancer patients, especially those receiving other types of immune therapy."
This approach could work in other cancers, but this was a very small trial in patients with advanced disease, and more studies are needed--the team is planning a study in summer 2012 with the vaccine and another similar drug, as daclizumab is not currently available from its manufacturer.
And in another story, adding the hormonal therapy letrozole to Oncothyreon's ($ONTY) Stimuvax lung cancer vaccine improved the responses in mice. Stimuvax is in Phase III trials, and results aren't expected until 2013.