North showed in the 1980s/1990s that mice, given a lethal dose of a transplantable tumor, first generate protective CTL, responsible for “concomitant immunity.” The sustained presence of these CTL is inhibited by the subsequent generation of “suppressor” CD4 T cells (8, 58, 59), see Figure 1B, and so to tumor progression. Here, CD4 is linked to neoplasm.