Immunity to Mutated Ras. Researchers asked whether or not
oncogenic proteins can be targeted for vaccine and T-cell
therapy. They first examine mutated ras as a prototype. Ras is
activated by point mutations that are common in diverse tumors.
Ras is present in about 15 percent of all human tumors,
including 50 percent of colon cancer and 95 percent of pancreas
cancer. Animal experiments demonstrated that ras can function as
a tumor-specific antigen, eliciting both helper T-cell and CTL
responses that can decrease the growth of tumor in vitro and in
vivo. Researchers have also found existent immune responses in a
few patients with pancreatic and colon cancers. Most are
antibody responses to normal ras, but a small number have a very
restricted antibody response to the mutated protein. Other
patients have a very specific T-cell response to the mutated
segment of ras, but there is a problem in trying to focus immune
attack against a single epitope. More importantly, oncogenic
proteins that are activated by mutat