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Kan
Chi Hon
HOW DO CANCER
CELLS
ESCAPE
IMMUNITY
SURVEILLANCE?
Our key immunity cells
are
the
"T
cells", the cytotoxic T
lym-
phocytes (CTL) and the "T helper"
(TH) cells but "tumor specific anti-
gens"
of
cancers
manage
to
es-
cape our
immunity. Antigen-pre-
senting
cells
(APC) e.9.,
dendritic
cells,
activated macrophages
and
"B
cells"
serve
to
process
our
"danger" signals but
cunning
can-
cer
cells pose
no
danger
at
all.
The
activation signals of natural killer
(NK)
and
lymphokine-activated
killer (LAK) cells are also blocked.
Cancer cells have
not
only a
"co-
coon" but also immuno-suppres-
sion factors: transforming growth
factor-beta
(TGF-B),
vascular
en-
dothelial growth
factor
(VEGF),
prostaglandins
(PGs), interleukin-
10
(lL-10),
macrophage colony
stimulating factor, etc. As our
T
cells
are inactivated
or
deleted and
our TH cells, inhibited, eradicating
as
much
tumor
as
feasible
should
precede restoration
of
immunity.
As our
immunity
is
attacked
by
cancer, restoring immunity
in the
presence
of
tumor bulk
is
"flogging
a
dead horse"- most inappropriate.
lnterestingly,
caspase-cascade
activation (through circulating me-
diators
-
soluble Fas/Fas
ligand
(sFas/Fasl))
leading to
apoptosis
of
our
key
cells
may be modified
experimentally by agents
like
PSP.
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