The science behind cancer immunotherapy

The different approaches to cancer immunotherapy all work in different ways. The non-specific approach, using immune stimulants, aims at stimulating a generalized immune response. The hope is that this will also enhance the response directed against the cancer cells in a tumor. This approach involves the injection of cancer patients with man-made (recombinant) versions of immune system messengers called cytokines. These are produced naturally in a healthy person’s immune system, but in much smaller quantities than used to treat cancer patients.

Passive specific immunotherapy

Passive specific immunotherapy is based on giving patients monoclonal antibodies (mAbs). Monoclonal antibodies are man-made copies of natural antibodies. 'Monoclonal' simply means 'all one type'. In cancer treatment, the antibodies are designed to attach themselves to one particular antigen found on the surface of the cancer cell. Monoclonal antibodies attack or block one or more of the factors that enable a cancer to grow or to spread. They are relatively easy to produce in pure form, in comparison with the antibodies collected from donated blood that have been used to give passive immunity in diseases such as rabies. Some therapeutic mAbs, such as trastuzumab and rituximab, have become standard therapies for some tumors [Acres et al., 2007, #18697].

Active specific immunotherapy

Active specific immunotherapy approaches rely on the patient's own immune system to generate an anti-cancer immune response. The ultimate goal of active specific immunotherapy is to stimulate killer T-cells to bind to cancer antigens and destroy cancer cells. This is done by presenting a cancer antigen to the immune system. The antigen can either be derived from the patient or produced synthetically. The immune system will react to this antigen and start an immune response. The end result is the stimulation of killer T-cells, which will bind to the specific cancer antigen and kill the cancer cell that displays it.

In active specific immunotherapy, strategies include combining cancer-associated antigens with immunological stimulants called adjuvants, or with chemical messengers called cytokines. These enhance the natural anti-cancer response. Active approaches have the advantage over passive approaches in that they can induce the immune system to develop the most specific immune response, with the potential to control tumor growth and eventually cause complete disappearance (regression) of the tumor. [Mitchell, 2002, #96750].