During the past 20 years, there have been many reports of the presence of inflammatory and immune-cell infiltrates in various neoplasms, including colorectal cancer. Initially, these findings were thought to indicate that although the immune system can recognize autologous tumor cells, it mounts an ineffective response to them. In the 1990s, functional studies demonstrated the presence of HLA-restricted T cells specific for colorectal cancer in populations of tumor-infiltrating lymphocytes and peripheral-blood mononuclear cells from patients with colorectal cancer. Since there were negligible numbers of such T cells in the blood of control subjects, the findings indicated that some of the . . .