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Why does the immune system not work to fight cancers?

The origin of the development of cancer is the alteration of the genetic material of one of our cells. Cancer is therefore a disease involving the actual functioning of our cells, which gradually lose control of their proliferation, become immortal and develop in an uncontrolled manner within the body.

They do this, in particular, when the immune system, which in theory is there to destroy agents that present a danger to the body, does not react efficiently. Why does the immune system remain “silent” when faced with tumor cells? Does it react at times, but ineffectively? Some questions remain unanswered.

For a long time, the immune system’s inability to recognize and attack the body’s cells has been used to explain its “passivity” in response to the development of a tumor. Indeed, the immune system has many control mechanisms to stop it from over-reacting and to prevent self-destructive phenomena, known as autoimmunity. Although they originate in the body, tumor cells nonetheless have certain distinctive signs which could possibly alert the immune system. This was demonstrated by the discovery of tumor antigens in 1991. These are present on the surface of tumor cells, and sometimes seem to be able to activate an immune response. A number of therapeutic options based on antigens have been explored, but without success. 

In addition to all the others, the tumor cells have the ability to “melt” into the surrounding tissues, and to deceive the immune system by making it believe that they are not dangerous, explains Dr Christophe Le Tourneau, medical oncologist responsible for early trials at Institut Curie.

Activation of the immune system by itself is therefore not sufficient to elicit a response. At the same time, several obstacles must be removed in order to destroy tumor cells.

Only precise knowledge of all of these mechanisms will unlock the immune system and allow it to act against cancer. Very promising results have been obtained using therapeutic molecules capable of blocking immunosuppressive mechanisms; they utilize all of the steps needed to activate the immune system.