Kinetics of tumor cell population changes.

The model defines three different tumor cell types: un-intoxicated, intoxicated, and dead cells, with densities ρ1, ρ2, and ρ3, respectively. The un-intoxicated cells proliferate, but the intoxicated and dead cells do not. The conversion from un-intoxicated to dead cells is irreversible. The number of the surface antigen molecules on an un-intoxicated cell remains constant, but it decays on an intoxicated cell through endocytosis and shedding without supply of newly synthesized internal antigen. Both protein synthesis and endocytosis have stopped in the dead cell, but the shedding and the on and off reaction between the surface antigen and immunotoxin still go on. The dead cells are removed from the tissue, presumably by macrophages, at a certain rate.