Possible new cancer therapy shrinks tumors in melanoma patients, Science authors report

A treatment that replaces most of the body's immune system with cancer fighting cells shrank the melanomas of some seriously ill patients, researchers report. The findings appear in the journal Science, published by the American Association for the Advancement of Science.

The therapy takes advantage of the immune system's ability to deliver a specially targeted assault on an unwanted invader, and helps boost that assault by multiplying the number of immune cells involved inside the patient's body.

This approach may also work for treating other cancer types, as well as infectious diseases, such as AIDS, according to the researchers.

Unlike many other cancer studies, which are done on mice, this study was done on human patients, who had not responded to standard therapies.

"To be able to do something as complex as this in humans, where every human is different and every tumor is different, has been quite difficult," said study author Steven Rosenberg of the National Cancer Institute.

The body's immune system can produce a set of T cells that attack tumors, but often these alone aren't a match for aggressive cancer. In the past, researchers have tried to boost these cells' numbers by extracting some from patients, inducing them to multiply in culture, and then transferring the expanded population back into the patients. The cells generally failed to "stick," however and disappeared quickly after the transfer.

By suppressing the patients' immune systems to "make room" for the new cells, as physicians do during a tissue transplant, Rosenberg and his colleagues induced the transferred cells to remain and grow in the body and start killing the tumor cells. In two cases, the transferred cells repopulated the patients' blood, becoming the dominant type of active T cell.

"It's very rare to be able to sustain large numbers of T cells in the body," said Rosenberg. "When your body fights the flu, maybe three percent of the T cells are active. In one of our patients, 90 percent of the T cells were active, and they sustained themselves for over four months. That's a striking occurrence."

The researchers studied 13 patients in the advanced stages of melanoma that had resisted the usual treatments. The researchers removed parts of the patients' tumors, which contained relatively small amounts of anti-tumor T cells, and grew the T cells in culture, until they had multiplied by approximately 1,000 times.

Before transferring the cells to the patients, Rosenberg's team gave the patients a round of chemotherapy that suppressed their immune systems' tendency to reject new cells. A few days after the T cell transfer, the number of tumor-fighting T cells shot up in more than half of the patients. After the transfer, the cells proliferated and traveled to the tumor sites, the scientists found.

"We generated and grew cells in the body to numbers that have never been approached before," Rosenberg said.