Biological Therapies for Cancer: Q & A - National Cancer Institute

What are interleukins?
"Like interferons, interleukins (ILs) are cytokines that occur naturally in the body and can be made in the laboratory. Many interleukins have been identified; interleukin-2 (IL–2 or aldesleukin) has been the most widely studied in cancer treatment. IL–2 stimulates the growth and activity of many immune cells, such as lymphocytes, that can destroy cancer cells. The FDA has approved IL–2 for the treatment of metastatic kidney cancer and metastatic melanoma.
Researchers continue to study the benefits of interleukins to treat a number of other cancers, including leukemia, lymphoma, and brain, colorectal, ovarian, breast, and prostate cancers."