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pathway when evaluated using the AREc32
cell line 39 . Although such advances in test
method development are impressive there
is still a need to understand whether
sensitiser-induced changes in these
cell stress pathways simply confirm
the inherent chemical reactivity of the
sensitiser (section 1 above) or whether
they provide additional information.
4. DC Maturation
Independent of their interactions with
keratinocytes, the phenotypic changes that
LCs/DCs undergo upon sensitiser exposure
have been extensively studied over the last
20 years and form the basis for several DCbased
predictive methods 22,42,43 . Two DC
maturation test methods currently under
evaluation, the h-CLAT 44 and the MUSST
test 45 are based upon the measurement
of relative changes in cell surface receptor
expression (CD54 and CD86 in the h-CLAT
test, and CD86 in the U937/CD86 test).
In addition, the VITOSens approach
developed by Hooyberghs et al. 46-47 used
an algorithm to interpret changes in key
genes following exposure of a cord bloodcell
derived DC model to the chemical of
interest.
Clearly a mechanistic rationale can
be postulated for the inclusion of skin
inflammation and DC maturation test
methods in a non-animal toolbox for
skin sensitisation; however we have yet
to identify a need for these data when
modelling the hapten-specific T cell
response.
5. T Cell Proliferation
Naïve T cell proliferation in response to
chemical treatment is a robust indicator
that a substance is immunogenic, and
several publications are concerned with
demonstrating the experimental feasibility
of inducing a naïve T-cell proliferation in
vitro following co-culture with chemical
sensitiser-treated DCs or LCs 48-49 . However,
the sensitivity of these approaches has not
been demonstrated to date, as significant
proliferative responses have generally only
been detectable following stimulation
with sensitisers of strong potency. From
our own experience, the complexity of
DC:T-cell co-culture protocols make these
approaches both labour intensive and
difficult to standardise. Furthermore,
our SSP platform analysis of dLN cell
dynamics has highlighted the importance
of LN trafficking in driving the sensitiserspecific
proliferative response 25 , i.e. a
dynamic system is needed. Such trafficking
will be difficult to reproduce in vitro, due
to the static nature of the standard DC:
T cell co-culture methods. Therefore, we
are keen to explore the apparent benefits
of modifying these protocols to exclude
the regulatory T cell fraction 50 and to
investigate the potential benefits of novel
tissue engineering technologies 51 .
In May 2010, Unilever held a workshop
(London, UK) to explore the relationship
between sensitiser-induced T cell
responses and sensitiser potency with
experts from various disciplines including
immunology, mathematical modelling,
and risk assessment (Kimber et al.;
manuscript in preparation). After 2 days
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