In the antigen (Ag) positive environment, if in the presence of activated T cells, NK cells are activated, complete tumour rejection ensues. If they fail to activate NK cells early enough, antigen escape variants develop and tumour is not rejected. In the antigen negative environment, in the absence of T cell activation, there is no tumour rejection. In the Ag+/- mix tumour environment, again if the activated T cells fail to activate NK cells early enough, there is no tumour rejection. When both the effectors are activated, there is complete tumour rejection.