CD4 and neoplasm: The terms αx(Ti+Tu)1+bxWX, αy(Ti+Tu)1+byWY, and αn(Ti+Tu)1+bnWN represent that IFN-γ is activated by both susceptible and infected tumor cells, and secreted by activated CD8+ T [20,30], CD4+ T cells [20,25], and NK cells [31] at a constant rate αx, αy, and αn, respectively.