Still looking for cancer immunotherapy.

Still looking for cancer immunotherapy

An estimated three out of four families in the United Stateswill be directly affected by cancer, says the American Cancer Society. But, thanks to aggressive cancer research, innovative approaches to cure and treatment of the disease have improved the chances of survival. Last week, scientists presented recent data on potential treatments--particularly those involving the immune system.

In cancer, immune therapy may involve stimulating thepatient's own response, or substituting for that response with outside factors like antitumor antibodies. Monoclonal antibodies --made by tumor cells joined to antibody-producing cells--are possible anticancer candidates.

However, those present at the seminar agreed that the use ofmonoclonal antibodies alone may be neither potent enough nor specific enough in treating cancer. To bolster the antibodies' effect, Jack A. Roth, from M.D. Anderson Hospital and Tumor Institute in Houston, suggests that linking those antibodies to substances that are toxic to cells will form an immunotoxin capable of selectively destroying cancer cells.

In animal experiments, Roth has successfully treated metastases(cancer spread beyond the initial site) using an immunotoxin made from a monoclonal antibody against the tumor, and with a plant product called ricin, which inhibits protein synthesis; one molecule of ricin can kill a cancer cell. The antibody alone does not kill the tumor cells, but the hybrid antibody-ricin reduces the number of tumor cells by 1,000- to 10,000-fold, says Roth. And adding a veterinary antibiotic called monensin to the treatment system increases the immunotoxin's killing ability another 10-fold.

Moving immunology from the laboratory into the operatingroom, a team at the Huntington Medical Research Institutes in Pasadena, Calif., is treating primary malignant brain tumors with surgery followed by insertion of stimulated immune cells. The invariably fatal brain tumors appear in about 15,000 new cases each year in the United States, with an average life expectancy of one year following initial diagnosis.

According to Huntington's Deane B. Jacques, immune cellstaken from the patient's peripheral blood are stimulated with interleukin-2 and then replaced into the brain. Interleukin-2 causes white blood cells to turn into cancer-killing cells. The procedure is similar to an immune-stimulating approach developed at the National Cancer Institute in Bethesda, Md. (SN: 12/7/85, p.359), with differences in the type of interleukin-2 and cell populations used. Another aspect that distinguishes the Pasadena technique is that the stimulated cells are not administered throughout the body, but are placed directly into the hole left by the excised tumor.

For brain tumor patients, life is measured in days rather thanmonths or years. But Jacques's patients survived longer than the three-month life expectancy often seen following failure to respond to conventional treatment. (All the patients studied had previously been treated with conventional therapy, including surgery and radiation.) Of the first 19 patients treated, nine are still alive, with an average survival time of 55 weeks. Those who have died of their disease survived an average of 38 weeks. In some, the tumors continue to shrink months after the special surgery, which appears to have minimal toxic effects on the body, says Jacques.

Jacques admits that the procedure is "highly experimental,'with much to be learned about optimizing it. Because two patients had remained free of tumors for about two years following immunotherapy, the physicians had hoped the cancer had been cured. But a patient who apparently had been free of tumors for two years returned last month with new malignant growth, and Jacques says he now questions whether "cure,' rather than just prolonging life expectancy, is possible.