If cancer cells are able to divide in a repeated approach under the radar of the immune system, it would be rather tough to stop cancer from coming into being and further developing. In addition, some cancer cells are capable of inhibiting immunocytes in the aspect of proliferation and attacking action. As a result, in order to render immunity stronger than cancer cells, it is doable to proliferate and activate immunocytes in vitro and then inject them back into the body, which perfectly explains the operation principles of immunocyte therapy.