- People with cancer can have a weak immune system as a result of the cancer itself, or from prior treatments. . Still, treatments that stimulate the immune system have been shown to be effective against a number of different cancers. Recombinant human interleukin-15 (rhIL-15) is a drug that is designed to boost the immune system. Researchers are interested in seeing if rhIL-15 can strengthen the immune system's response against cancer. The drug will be given through a vein without a break for 10 days (240 hours).