There are really five ways to improve the workings of an immune system . They are analogous to ways you could make an army more effective if it was fighting a battle in the field. You could increase the number of your troops, both foot soldiers and more specialized units. You could help the troops focus their efforts more effectively by helping them communicate with each other. You could quickly replace any troops already lost in the fight. You could give them more precise weapons. Or you could make sure their efforts aren't wasted in a scattershot way by clearly identifying or highlighting the targets they're shooting at.
In a similar way, cancer immunotherapy can be conveniently characterized by five broad strategies.
• Active stimulation This is based on the idea that everyone has some intrinsic antitumor immunity and that if
the defensive cells can just be aroused in some way they may have an effect against cancer cells. There are both
non-specific and specific strategies involved.
The non-specific strategy uses bacterial or chemical booster substances (adjuvants) to "turn on" a whole
range of immune cells—macrophages, natural killer cells and other non-specific killer cells. One effect of
stimulating macrophages is that T cells are activated too.
The specific strategy uses the tumor cells themselves or tumor-associated antigens to trigger specific
"effector" cells such as killer T cells. These are often called tumor vaccines.
