Advaxis Inc., a small US biotechnology company, has announced it will test its experimental immuno-oncology drug, ADXS-PSA, in combination with a high-profile immunotherapy from Merck & Co Inc., pembrolizumab, as a treatment for patients with advanced prostate cancer, the most common cancer among men other than skin cancer. ADXS-PSA is a modified form of the Listeria bacterium fused to PSA, a protein shed by prostate tumors. This drug is specifically designed to boost lymphocytes into the tumor microenvironment, where they will recognize and eventually destroy cancer cells. Pembrolizumab is a monoclonal antibody that inhibits the PD-1 protein expressed at the surface of tumor cells, a receptor responsible for the weakening of the anti-tumoral immune response. ADXS-PSA will be tested both as a standalone treatment and in combination with pembrolizumab in a Phase I/Phase II clinical study. Using these different approaches and combining the two drugs will hopefully increase the chances of eliminating prostate cancer. "If the combination of drugs shows an added effect, the companies would likely continue their collaboration," Daniel O'Connor, chief executive officer of Advaxis said in a Reuters interview. The study is expected to begin in early 2015, and while it will probably be conducted by a contract research organization, Merck will provide the pembrolizumab to be used in the trial. PD-1 inhibitors have been the focus of intense research in the immune-oncology area, with trials revealing promising results in melanoma. However, this the first large study concerning anti-PD1 antibodies against prostate cancer. "We think this combination gives us the opportunity to do early exploration in prostate cancer and bring immuno-oncology into this space,"