Time (arbitrary units)

Fig. 11.7 Effect of dendritic cell vaccination on tumor dynamics assuming that the growth rate of the tumor has evolved to high values, where only the tolerance outcome is stable, (a) A single vaccination event induces a temporary reduction in tumor load, followed by a relapse, (b) Repeated vaccination events can drive the tumor load below a threshold which corresponds to extinction in practical terms. Parameters were chosen as follows: r=1.5; k=10; d=0.1; 7 =1; A=1; 5i=0.01; a=0.5; 52=1.5; tj =0.5; e=l; q=0.5; ¡j. =0.1.

which practically corresponds to extinction (Figure 11.7).

Next, we consider the more benign scenario in which the tumor has not progressed that far and the CTL control equilibrium is still stable. Now a single vaccination event can shift the dynamics from the tolerance outcome to the CTL control outcome (Figure 11.8). The reason is that an elevation in the number of presenting dendritic cells shifts the system into a space where the trajectories lead to CTL control and not to tolerance. This is likely to be achieved if the size of the tumor is not very large. The larger the size of the tumor, the stronger the vaccination has to be (higher A*) in

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