Alternative PCa vaccine strategy: Better tolerated than standard method

Giving patients a continuous low dose of an immune system booster, a method known as metronomic dosing, as part of a therapeutic prostate cancer vaccine strategy is safe and produces similar immune responses to, and fewer side effects than, the more common dosing method, which is not well tolerated by many patients, according to a study by researchers at the National Cancer Institute.

“Developing an alternative method of administering vaccine therapy that is well tolerated by most patients and produces similar immune responses to standard methods may help further the development of vaccine therapies for prostate cancer,” said lead author James L. Gulley, MD, PhD, of the NCI Center for Cancer Research.

The vaccine used in this study is designed to stimulate an immune response against PSA. Researchers examined the side effects and immune responses of patients treated with a three-pronged approach: the vaccine, radiation therapy, and an alternative dosing regimen of interleukin-2 (IL-2). All patients had localized prostate cancer, had not undergone prostatectomy, and were candidates for first-line radiation therapy.

In this study, the researchers sought to decrease the known side effects associated with IL-2. To do this, the team treated 18 patients with the vaccine and radiation therapy, but with smaller daily doses of IL-2 for 14 days of each 28-day treatment cycle. With metronomic dosing, less than a quarter of the patients had side effects that required their dose of IL-2 to be reduced, Dr. Gulley and colleagues reported in Clinical Cancer Research (2008; 14:5284-91).

The team also found that metronomic dosing of IL-2 produced effects on immune cell populations and immune responses that were similar to those observed previously with standard dosing. Five of eight evaluated patients had at least a three-fold increase in immune cells directed against PSA. In addition, similar to standard dosing, metronomic dosing of IL-2 induced immune responses against other prostate cancer antigens in some patients.