Jan. 30, 2002
     Prostate Cancer

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Prostate cancer vaccine shown safe

DURHAM, N.C. -- Jan. 30, 2002 (Cancer Digest) -- A small early phase clinical trial of a prostate cancer vaccine has shown no adverse side effects, as well as signs that the the first of its kind vaccine is able to boost a patient's immune system to fight prostate cancer.

The results the 13-patient trial, led by Dr. Johannes Vieweg of Duke University Medical Center, are published in the Feb. 2002 issue of the Journal of Clinical Investigations.

"This is the first study that has data on the safety and immunological efficacy of this type of cancer vaccine," said Vieweg in a press release. "And while this work was done in prostate cancer patients, we believe this method may prove to work in most cancers, not just prostate cancer."

The vaccine is made from a type of immune system cell called dendritic cells, which lock onto "foreign" or abnormal cells, such as those infected by virus or cancerous cells, and flags them for destruction by other immune system cells called T cells. The vaccine using these cells was developed at Duke University Medical Center

The vaccine created in the Duke study introduces genetic information from a prostate cancer patient's own dendritic cells taken from prostate-specific antigen (PSA). This antigen is secreted by the prostate gland and is elevated in some forms of prostate cancer. In the laboratory, researchers coax the dendritic cells to display, or present the PSA protein for recognition by T cells. The dendritic cells are then injected back under the patient's skin and activate the T cells to attack those cells including tumors, which display the PSA.

In the trial, 13 men with metastatic prostate cancer were given three increasing doses of the vaccine to determine the highest dose tolerated by patients without adverse effects. The researchers also performed immunological tests to ensure that T cells were functioning and able to kill tumor cells, in addition to tests to determine whether the T cell levels rose.

In all 13 participants, the researchers detected activation of PSA-specific T cell responses, suggesting the vaccine was successful in boosting the immune system and turning T cell attention to the cancer.

"Patients responded well to the vaccine because we are using materials from their own body to create a vaccine that is designed just for them," said Vieweg.

Vieweg and his colleagues reported that overall, the vaccine was well tolerated. Four subjects had low-grade fevers and flu-like symptoms, and four patients had inflammation at the site of the injection that subsided after two to three days.

Vieweg said that the immunological data, which is sometimes not collected in such early trials, is highly important in proving that the cancer vaccine is working in the patient and other influences are not at work.

"Some studies examine only if there is a reduction in tumor growth, but this would only show part of the story," he said. "You wouldn't see the subclinical changes in the body that might indicate that a vaccine is promising."

The Duke study was not designed to track tumor regression because the small trial was aimed at determining only whether the vaccine was safe and effective in stimulating T cell response. However, the researchers tracked PSA levels in seven of the 13 patients. Six were excluded because they required radiation treatments for preexisting tumors or they took herbal supplements that could impact PSA levels. In the remaining seven, six had a significant decrease in PSA levels and three patients exhibited a decrease in free-circulating tumor cells detected in the blood.

The next step is to use fully mature dendritic cells and program them to carry multiple tumor antigens rather than just PSA. Vieweg cautioned that a possible side effect of a more potent vaccine might be that it could overactivate the immune system and cause T cells to attack healthy cells.

However, Vieweg said that if such a problem were to occur, it could be adjusted easily by withholding vaccine booster shots, changing the dose or changing the antigen.