OvaRex was tested in Canada, prior to the current Phase III trials in the U.S. “There have been a number of patients that have received OvaRex,” said Dr. Tyrrell, “We’ve had really no adverse effects from these patients.” Dr. Tyrrell explained the procedure, “After being injected intravenously, OvaRex binds to an antigen circulating in the blood.” An antibody’s general purpose is to neutralize an antigen. After an OvaRex injection, the murine monoclonal antibody binds to the CA-125 antigen.

In a way the body is tricked. But, the body is tricked in order to help “save” itself from the harmful antigen. When the OvaRex antibody is bound to the CA-125 antigen, the new combination is identified as a harmful unit. Before then, the antigen wanders through the body, without alerting the body’s defense systems, the dendritic cells, to attack and destroy the harmful antigen. Because the body is trained to identify and zero in on a foreign protein, in this case a mouse protein, it alerts the dendritic cells. Until then, the dendritic cells “tolerate” the cancerous cells. The tolerance is what permits the cancer to spread throughout the body. OvaRex seeks to break that tolerance. The murine monoclonal antibody is designed to target and bind exclusively to free floating CA-125 antigen.

The dendritic cells refuse to tolerate the foreign protein. When the antibody binds with the free-floating antigen, the dendritic cells recognize the complex (antibody plus antigen) as being foreign and engulf the new unit. The dendritic cells break down the key proteins of this unit, presenting all parts on the cells surface. At the point, the body’s killer T-Cells are alerted to fight the internal threat to the body. Once activated, the T-Cells will replicate and create more killer T-Cells. Any tumor cells expressing the CA-125 antigen is targeted for destruction. The army of T-Cells move to attack the ovarian cancer tumor.

The principle behind OvaRex is to re-program the immune system to harness the body’s defenses to prevent the growth and spread of the ovarian cancer. Will it cure ovarian cancer? “In most cases, it will be a delay,” explained Dr. Tyrrell. “However, I think that, and everyone hopes that, often in some of these tumors, you’re making incremental progress through careful clinical trials and adding new therapy. Each thing we do that improves the outcome when you start to look at the long term benefits of these, we hope that one day we will be able to cure this disease. We think this is a step. This has the potential to be an important step at helping to stimulate immune response to achieve a better outcome. Hopefully, one day we can improve that to where it is a cure.”