GP2 is an immunotherapy being developed by researchers at the University of Texas MD Anderson Cancer Center to treat breast cancer.

How GP2 works

GP2 is a cancer vaccine. Cancer vaccines aim to stimulate the immune system to detect the cancer cells so that the body’s natural defenses can remove the tumor.

The immune system can “remember” and identify infections or abnormal cells through antigens or disease-associated substances that are not normally found in the body. Cancer vaccines act to activate the immune system with tumor-associated antigens (TAAs), giving the immune system a boost.

GP2 is a so-called peptide vaccine; it contains peptides (small parts of a protein) derived from HER2, a protein associated with breast cancer. GP2 can be used by the immune system to stimulate certain immune cells called T-cells so they recognize cells expressing HER2. When these activated T-cells come in contact with a tumor cell expressing HER2, they attack and kill it.

GP2 is currently administered along with the adjuvant Leukine (sargramostim), which acts to boost the number of immune cells in the body including the antigen presenting cells.

GP2 in clinical trials

GP2 has been investigated in a Phase 1 clinical trial (NCT03014076), carried out in the U.S. During the trial, 30 breast cancer patients were treated with GP2 and Leukine, in combination with standard of care Herceptin (trastuzumab).

The results were published in the scientific journals Cancer and Annals of Surgical Oncology, and suggest that GP2 and Leukine vaccine is safe in breast cancer patients, and does not cause dose-limiting toxicities. The trial also confirmed that the vaccine could elicit an immune response, which was strongest in patients without a pre-existing immunity to HER2.

These positive results prompted the initiation of a Phase 2 trial (NCT00524277), which is ongoing at sites in the U.S, Germany, and Greece but no longer recruiting participants. Patients will be given either GP2 plus Leukine, AE37 (another cancer vaccine) plus Leukine, or Leukine alone. It is estimated that the trial will be completed by December 2017.

The results of the initial analysis from 190 women with breast cancer were presented at the American Society of Clinical Oncology (ASCO) 2014 Breast Cancer Symposium. They suggested that treatment with GP2 plus Leukine along with Herceptin standard of care could reduce the chance of the cancer recurring. Disease-free survival (DFS) among the patients who completed the trial (182 of 190 patients) was 94 percent in those given the vaccine, compared to 85 percent in those who only received Herceptin. These results were also published in the journal Oncotarget.

Researchers believe the promising results seen so far in the Phase 2 trial justify moving the GP2 investigation to Phase 3 clinical trials.


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