An experimental cancer vaccine has been found to reduce tumor size by an average of 80%, researchers from the Mayo Clinic and the University of Georgia reported in Proceedings of the National Academy of Sciences. In their animal experiment, mouse models that mimic most human pancreatic and breast cancer cases had dramatic reductions in tumor size - even among those that had not responded to standard treatments.
Tumors that share the same distinct carbohydrate signature may be especially treatable with this new vaccine, say the authors. This includes various cancers such as colorectal, ovarian, breast, pancreatic and some others.
Co-senior author Geert-Jan Boons, wrote:
"This vaccine elicits a very strong immune response. It activates all three components of the immune system to reduce tumor size by an average of 80 percent."
Sugars on the surface proteins of cancerous cells are different from those in healthy cells, the authors explain. For several years, researchers have sought ways of getting the immune system to identify the differences and target the cancer cells only, leaving the healthy ones alone. However, this is not easy, because cancer cells start off in the patient's own body, and his/her immune system does not see them as foreign or pathogenic, and does not attack them.
Study co-author, Sandra Gendler, developed some unique mice for this experiment. Tumors in mice overexpress MUC1, a type of protein, on the surface of their cells. The surface of MUC1 found in tumors has a unique, shorter set of carbohydrates (this is not the case with carbohydrates on the surface of healthy cells).
"This is the first time that a vaccine has been developed that trains the immune system to distinguish and kill cancer cells based on their different sugar structures on proteins such as MUC1. We are especially excited about the fact that MUC1 was recently recognized by the National Cancer Institute as one of the three most important tumor proteins for vaccine development."
MUC1 was found to exist in over 70% of all lethal cancer, Gendler explained. In ovarian, pancreatic and breast cancers, as well as multiple myeloma, in 90% of cases MUC1 is expressed with the shorter carbohydrate.
When a cell becomes cancerous, its structure alters and MUC1 is overproduced - this promotes tumor formation. Hence, the potential for a vaccine that targets MUC1, either as a preventative (prophylactic) measure for high risk patients, or to reduce the risk of cancer recurrence. The vaccine could also be extremely helpful in cancer cases where surgery is not possible, such as pancreatic cancer, to be used together with chemotherapy.
Some cancer patients do not respond to hormonal therapy, such as aromatase inhibitors, Tamoxifen, or Herceptin. In 90% of these patients, MUC1 is overexpressed. Tripe-negative tumors are very aggressive and hard to treat.
"In the U.S. alone, there are 35,000 patients diagnosed every year whose tumors are triple-negative. So we might have a therapy for a large group of patients for which there is currently no drug therapy aside from chemotherapy."
Boons' vaccine is much simpler than other therapeutic ones, such as Provenge (for prostate cancer), because it is fully synthetic and can be manufactured in a laboratory with assembly-line precision.
The vaccine has three components:
- An adjuvant (an immune system booster)
- A component that encourages the production of T-helper cells (part of the immune system)
- A peptide linked to carbohydrate that makes the immune system target those cells that bear the MUC1 proteins
"We are beginning to have therapies that can teach our immune system to fight what is uniquely found in cancer cells. When combined with early diagnosis, the hope is that one day cancer will become a manageable disease."
Written by Christian Nordqvist