Apr. 21, 2002
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New clinical trial tests prostate cancer vaccine

CHICAGO -- Apr. 21, 2002 (Cancer Digest) -- A new clinical trial will test the safety of a vaccine based on the PSA protein commonly used detect the presence or recurrence of prostate cancer.

The vaccine uses a fragment of a protein called prostate specific antigen (PSA) to stimulate the body's own immune system against prostate tumors.

The early stage trial, sponsored by the National Cancer Institute, will assess the safety and effectiveness of the vaccine created in the laboratory of Dr. David Peace, assistant professor of medicine, at the University of Illinois at Chicago.

Studies in Peace's laboratory showed that the vaccine causes subsets of the immune system's white blood cells to morph into highly specific killer white blood cells, called cytotoxic T lymphocytes, which selectively destroy tumor cells that express PSA. The white blood cells Peace used to create the vaccine were drawn from healthy individuals as well as patients with advanced prostate tumors.

"Our laboratory findings suggest that the vaccine should be effective in treating advanced prostate cancer, where the patient's immune system is severely challenged," Peace said in a prepared statement. Results of the laboratory study were presented at the Experimental Biology 2002 meeting in New Orleans on April 21.

The vaccine includes a fragment of PSA, which is produced by cells lining the tubules of the prostate gland, as well as by prostate cancer cells. It has been used for years as a clinical marker for prostate cancer to screen for and monitor the disease. In the trial, Peace will determine whether PSA can also be used therapeutically -- to help the immune system target prostate cancer cells for destruction.

The trial calls for a total of 28 patients who will receive the vaccine either by injection under the skin, along with a compound known to stimulate the immune system, or delivered intravenously, after being loaded onto dendritic cells. These are a type of white blood cell that activate the immune system by scavenging antigens, like PSA, and presenting them to T-cells, one of the body's most important defense mechanisms.

All patients will continue their regular treatments while participating in the trial.

For purposes of the study, the vaccine was designed to work in patients with a specific immune type found in about 50 percent of individuals in the United States. However, Peace's laboratory is developing similar PSA vaccines for patients with other immune types.

"The advantage of these kinds of vaccines is that they can be customized to each patient, based on his immune type. The specificity of the vaccine enables the immune system to target the tumor cells with exquisite precision, with minimal risk of damage to the body's normal tissues," Peace said.

Patients with prostate cancer are eligible to participate in the vaccine trial if, after undergoing surgery or radiotherapy to eliminate the tumor, (1) there is a high risk the tumor will recur, (2) the individual's PSA level is rising, or (3) the cancer has spread beyond the prostate gland.

Patients are considered to be at high risk for a recurrence of the cancer if their initial PSA level was greater than 10 ng/mL or their tumor grade (Gleason score) is greater than 6. Patients with metastatic prostate cancer must have their tumor under control with hormone blockade or other therapies.

According to Peace, the vaccine also holds promise as a treatment for types of breast cancers whose cells express PSA.

Patients interested in more information about the trial can contact the University of Illinois at Chicago at (312) 413-3100 or by visiting its Web site.