of neoplastic cells”(Thomas 1982, p. 330). Thomas was convinced that humans
produce tumors all the time but keep them under control, thanks to the action of
the immune system. Burnet later expanded this idea and coined the term
immunological surveillance (sometimes calledimmunosurveillance)(Burnet
1970). According to immunological surveillance, the immune system is capable
of detecting and eliminating the“altered self”(Houghton 1994), that is,“new
antigens”(Burnet 1970, p. 7) (antigens that are different from those of the body,
also called“neoantigens”(Schumacher and Schreiber 2015)). In the 1970s, the
idea of immunological surveillance started to decline because several experi-
ments suggested that immunodeficient mice did not have a higher susceptibility
to spontaneous or chemically induced tumors (Stutman 1974). As a result it was
almost entirely abandoned for several years. A clear indication of this is the fact
that the highly influential review on the“hallmarks of cancer”by Hanahan and
Weinberg published in 2000 (Hanahan and Weinberg 2000) ignores the role of
the immune system in cancer (this was corrected in (Hanahan and Weinberg
2011 )).
At the beginning of the 2000s, a series of experiments showed the impact of
the immune system on cancer development (Shankaran et al. 2001; Dunn et al.
2002). The supposedly immunodeficient mice used in experiments from the
1970s onward to invalidate the idea of immunosurveillance in fact had an
immune system (they had NK cells,γδT cells, and even someαβT cells)
(Dunn et al. 2002). During this period, the involvement of both innate and
adaptive immune components in cancer control was demonstrated (immuno-
chemical or functional ablations of NKT,γδT cells, NK cells,αβT cells, IFN-γ,
and interleukin 12 all lead to increased susceptibility to cancer).
4.2 The Dual Action of the Immune System in Both Restraining
and Promoting Cancer: Immunoediting and Beyond
Although much emphasis has been put on the capacity of the immune system to
restrain cancer, the immune system can also, perhaps paradoxically, promote
cancer (de Visser et al. 2006). Here again, both the innate and adaptive compo-
nents of the immune system can participate in such cancer-promoting processes.
One important step in the realization that the immune system can favor cancer
development was the switch from the concept of immunosurveillance to that of
immunoediting (Dunn et al. 2002). Several researchers working on immuno-
surveillance noted that the action of the immune system could lead to the
selection of more resistant tumor cells. Highly immunogenic tumor cells are
eliminated by the immune system, but this process leaves behind tumor variants
of reduced immunogenicity (or that have acquired other mechanisms to evade
32 Elements in the Philosophy of Biology