Immunotherapeutic agents have become important additions to the list o
f anti-cancer treatments; further progress will require more informati
on about how the immune system can respond to tumor cells. Tumor cells
can avoid eliciting an immune response through several mechanisms. Un
derstanding these mechanisms may Suggest strategies to manipulate tumo
r cells so that they trigger an effective immune response. Another str
ategy being developed is to improve the therapeutic index of cytokines
so that better anti-tumor effects can be elicited with less toxicity.