  The US and Hungarian statistical records of the years 1900 and 1896,
respectively, before the dramatic medical advances, show 32% and 27% deaths
attributable to infections, whereas only 5% and 2% due to cancer. These data
can be interpreted to mean that (i) the immune system evolved for purging
nascent selfish cells, which establish natural chimerism littering the soma and
the germline by conspecific alien cells and (ii) defense against pathogens that
represent xenogeneic aliens appeared later in evolution.
  `Liberating' T cells from the semantic trap of immunity and the shackles of
the `two-signal' model of T cell activation, we point out theoretical grounds
that the immune response to cancer is conceptually different from the immune
response to infection. We argue for a one-signal model (with stochastic
influences) as the explanation for T cell activation in preference to the
widely accepted two-signal model of co-stimulation. Convincing evidence for our
one-signal model emerged from the widespread autoimmune adverse events in 64.2%
of advanced melanoma patients treated with the anti-CTLA-4 antibody
(ipilimumab) that blocks an immune checkpoint. Harnessing the unleashed
autoimmune power of T cells could be rewarding to defeat cancer. Assuming that
immunization against isogeneic tumors also would be effective is a fallacy.
