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Adopted:29 July 2016
Corrected 7 February 2017 - Corrected version will be submitted to Council adoption over the summer in2017
Corrections are highlighted in yellow in the text

OECD GUIDELINE FOR THE TESTING OF CHEMICALSIn Vitro Skin Sensitisation: human Cell Line Activation Test (h-CLAT)INTRODUCTION
1. A skin sensitiser refers to a substance that will lead to an allergic response following skin contact as
defined by the United Nations Globally Harmonized System of Classification and Labelling of Chemicals(UN GHS) (1). This Test Guideline (TG) describes the in vitro procedure called human Cell Line
Activation test (h-CLAT), to be used for supporting the discrimination between skin sensitisers and nonsensitisers in accordance with the UN GHS (1).
2. There is general agreement regarding the key biological events underlying skin sensitisation. The current
knowledge of the chemical and biological mechanisms associated with skin sensitisation has beensummarised in the form of an Adverse Outcome Pathway (AOP) (2), starting with the molecular initiating
event through intermediate events to the adverse effect, namely allergic contact dermatitis. In this instance,
the molecular initiating event (i.e. the first key event) is the covalent binding of electrophilic substances tonucleophilic centres in skin proteins. The second key event in this AOP takes place in the keratinocytes
and includes inflammatory responses as well as changes in gene expression associated with specific cellsignalling pathways such as the antioxidant/electrophile response element (ARE)-dependent pathways. The
third key event is the activation of dendritic cells (DC), typically assessed by expression of specific cellsurface markers, chemokines and cytokines. The fourth key event is T-cell proliferation, which is indirectly
assessed in the murine Local Lymph Node Assay (LLNA) (3).
3. The assessment of skin sensitisation has typically involved the use of laboratory animals. The classicalmethods that use guinea-pigs, the Guinea Pig Maximisation Test (GPMT) of Magnusson and Kligman, andthe Buehler Test (TG 406) (4), assess both the induction and elicitation phases of skin sensitisation. The
murine tests, the LLNA (TG 429) (3) and its two non-radioactive modifications, LLNA: DA (TG 442 A)(5) and LLNA: BrdU-ELISA (TG 442 B) (6), all assess exclusively the induction response, and have also
gained acceptance, since they provide an advantage over the guinea pig tests in terms of animal welfare
together with an objective measurement of the induction phase of skin sensitisation.
4. More recently mechanistically-based in chemico (OECD TG 442C; Direct Peptide Reactivity Assay
addressing the first key event of the skin sensitisation AOP) (7) and in vitro (OECD TG 442D; ARE-Nrf2
Luciferase Test Method addressing the second key event of the skin sensitisation AOP) (8) test methods
have been adopted for contributing to the evaluation of the skin sensitisation hazard potential of chemicals.
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This Guideline was adopted by the OECD Council by written procedure on 29 July 2016 [C(2016)103].

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However, a combination of non-animal methods (in silico, in chemico, in vitro) within Integrated
Approaches to Testing and Assessment (IATA) will be needed to be able to fully substitute for the animal
tests currently in use given the restricted AOP mechanistic coverage of each of the currently available nonanimal test methods (2)(9).
5. The h-CLAT method is proposed to address the third key event of the skin sensitisation AOP by
quantifying changes in the expression of cell surface markers associated with the process of activation of
monocytes and DC (i.e. CD86 and CD54), in the human monocytic leukaemia cell line THP-1, following
exposure to sensitisers (10). The measured expression levels of CD86 and CD54 cell surface markers arethen used for supporting the discrimination between skin sensitisers and non-sensitisers.
6. The h-CLAT method has been evaluated in a European Union Reference Laboratory for Alternatives toAnimal Testing (EURL ECVAM)-coordinated validation study and subsequent independent peer review
by the EURL ECVAM Scientific Advisory Committee (ESAC). Considering all available evidence andinput from regulators and stakeholders, the h-CLAT was recommended by EURL ECVAM (11) to be usedas part of an IATA to support the discrimination between sensitisers and non-sensitisers for the purpose ofhazard classification and labelling. Examples of the use of h-CLAT data in combination with otherinformation are reported in the literature (12) (13) (14) (15) (16) (17) (18) (19).
7. Definitions are provided in Annex I.

INITIAL CONSIDERATIONS AND LIMITATIONS
8. Skin sensitisers have been reported to induce the expression of cell membrane markers associated withDC activation (2). Test methods such as the h-CLAT which measure markers of monocyte activation andmay be related to DC activation (20) are therefore considered relevant for the assessment of the skinsensitisation potential of chemicals. However, since DC activation represents only one key event of theskin sensitisation AOP, information generated with test methods measuring markers of DC activation may
not be sufficient on its own to conclude on the absence of skin sensitisation potential of chemicals.
Therefore, data generated with the h-CLAT method should be considered in the context of integrated
approaches, such as IATA, and combined with other complementary information e.g. derived from in vitro
assays addressing other key events of the skin sensitisation AOP as well as non-testing methods, including
read-across from chemical analogues.
9. The test method described in this Test Guideline can be used to support the discrimination between skinsensitisers (i.e. UN GHS Category 1) and non-sensitisers in the context of IATA. This Test Guidelinecannot be used on its own, neither to sub-categorise skin sensitisers into subcategories 1A and 1B as
defined by UN GHS (1), for authorities implementing these two optional subcategories, nor to predict
potency for safety assessment decisions. However, depending on the regulatory framework, a positive
result with the h-CLAT may be used on its own to classify a chemical into UN GHS category 1.
10. The h-CLAT method proved to be transferable to laboratories experienced in cell culture techniques
and flow cytometry analysis. The level of reproducibility in predictions that can be expected from the test
method is in the order of 80% within and between laboratories (11) (21). Results generated in thevalidation study (22) and other published studies (23) overall indicate that, compared with LLNA results,
the accuracy in distinguishing skin sensitisers (i.e. UN GHS Cat.1) from non-sensitisers is 85% (N=142)
with a sensitivity of 93% (94/101) and a specificity of 66% (27/41) (based on a re-analysis by EURLECVAM (21) considering all existing data and not considering negative results for chemicals with a Log
Kow greater than 3.5 as described in paragraph 12). False negative predictions with the h-CLAT are more

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likely to concern chemicals showing a low to moderate skin sensitisation potency (i.e. UN GHS
subcategory 1B) than chemicals showing a high skin sensitisation potency (i.e. UN GHS subcategory 1A)(12) (22) (24). Taken together, this information indicates the usefulness of the h-CLAT method tocontribute to the identification of skin sensitisation hazards. However, the accuracy values given here forthe h-CLAT as a stand-alone test method are only indicative, since the test method should be considered in
combination with other sources of information in the context of an IATA and in accordance with theprovisions of paragraph 9 above. Furthermore, when evaluating non-animal methods for skin sensitisation, it
should be kept in mind that the LLNA test as well as other animal tests may not fully reflect the situation inhumans.
11. The term "test chemical" is used in this Test Guideline to refer to what is being tested1 and is not
related to the applicability of the h-CLAT to the testing of mono-constituent substances, multi-constituent
substances and/or mixtures. On the basis of the data currently available, the h-CLAT method was shown tobe applicable to test chemicals covering a variety of organic functional groups, reaction mechanisms, skinsensitisation potency (as determined in in vivo studies) and physicochemical properties (11) (23) (24).
Limited information is currently available on the applicability of the h-CLAT method to multi-constituent
substances/mixtures (24). The test method is nevertheless technically applicable to the testing of multiconstituent substances and mixtures. However, before use of this Test Guideline on a mixture forgenerating data for an intended regulatory purpose, it should be considered whether, and if so why, it may
provide adequate results for that purpose2. Such considerations are not needed when there is a regulatory
requirement for the testing of the mixture. Moreover, when testing multi-constituent substances or mixtures,consideration should be given to possible interference of cytotoxic constituents with the observed
responses.
12. The h-CLAT method is applicable to test chemicals soluble or that form a stable dispersion (i.e. a
colloid or suspension in which the test chemical does not settle or separate from the solvent/vehicle into
different phases) in an appropriate solvent/vehicle (see paragraph 21). Test chemicals with a Log Kow
greater than 3.5 tend to produce false negative results (23). Therefore negative results with test chemicals
with a Log Kow greater than 3.5 should not be considered. However, positive results obtained with test
chemicals with a Log Kow greater than 3.5 could still be used to support the identification of the test
chemical as a skin sensitiser. Furthermore, because of the limited metabolic capability of the cell line used(25) and because of the experimental conditions, pro-haptens (i.e. substances requiring enzymatic
activation for example via P450 enzymes) and pre-haptens (i.e. substances activated by oxidation) in
particular with a slow oxidation rate may also provide negative results in the h-CLAT (24). Fluorescent test
chemicals can be assessed with the h-CLAT (26), nevertheless, strong fluorescent test chemicals emittingat the same wavelength as fluorescein isothiocyanate (FITC) or as propidium iodide (PI), will interferewith the flow cytometric detection and thus cannot be correctly evaluated using FITC-conjugatedantibodies or PI. In such a case, other fluorochrome-tagged antibodies or other cytotoxicity markers,
respectively, can be used as long as it can be shown they provide similar results as the FITC-tagged
antibodies (see paragraph 31) or PI (see paragraph 25) e.g. by testing the proficiency substances in Annex
II. In the light of the above, negative results should be interpreted in the context of the stated limitations
and together with other information sources within the framework of IATA. In cases where there isevidence demonstrating the non-applicability of the h-CLAT method to other specific categories of test
chemicals, it should not be used for those specific categories.
13. As described above, the h-CLAT method supports the discrimination between skin sensitisers from
non-sensitisers. However, it may also potentially contribute to the assessment of sensitising potency (12)1

In June 2013, the Joint Meeting agreed that where possible, a more consistent use of the term "testchemical" describing what is being tested should be applied in new and updated Test Guidelines.

2

This sentence was proposed and agreed at the April 2014 WNT meeting.

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OECD/OCDE(13) (17) when used in integrated approaches such as IATA. Nevertheless, further work, preferably basedon human data, is required to determine how h-CLAT results may possibly inform potency assessment.

PRINCIPLE OF THE TEST
14. The h-CLAT method is an in vitro assay that quantifies changes of cell surface marker expression (i.e.
CD86 and CD54) on a human monocytic leukemia cell line, THP-1 cells, following 24 hours exposure to
the test chemical. These surface molecules are typical markers of monocytic THP-1 activation and may
mimic DC activation, which plays a critical role in T-cell priming. The changes of surface marker
expression are measured by flow cytometry following cell staining with fluorochrome-tagged antibodies.
Cytotoxicity measurement is also conducted concurrently to assess whether upregulation of surface marker
expression occurs at sub-cytotoxic concentrations. The relative fluorescence intensity of surface markers
compared to solvent/vehicle control are calculated and used in the prediction model (see paragraph 33), to
support the discrimination between sensitisers and non-sensitisers

DEMONSTRATION OF PROFICIENCY
15. Prior to routine use of the test method described in this Test Guideline, laboratories should demonstratetechnical proficiency, using the 10 Proficiency Substances listed in Annex II. Moreover, test method users
should maintain an historical database of data generated with the reactivity checks (see paragraph 18) andwith the positive and solvent/vehicle controls (see paragraphs 27-29), and use these data to confirm thereproducibility of the test method in their laboratory is maintained over time.

PROCEDURE
16. This Test Guideline is based on the h-CLAT DataBase service on ALternative Methods to animal
experimentation (DB-ALM) protocol no. 158 (27) which represents the protocol used for the EURLECVAM-coordinated validation study. It is recommended that this protocol is used when implementing
and using the h-CLAT method in the laboratory. The following is a description of the main components
and procedures for the h-CLAT method, which comprises two steps: dose finding assay and CD86/CD54
expression measurement.
Preparation of cells
17. The human monocytic leukaemia cell line, THP-1, should be used for performing the h-CLAT method.
It is recommended that cells (TIB-202™) are obtained from a well-qualified cell bank, such as theAmerican Type Culture Collection.
18. THP-1 cells are cultured, at 37°C under 5% CO2 and humidified atmosphere, in RPMI-1640 medium
supplemented with 10% foetal bovine serum (FBS), 0.05 mM 2-mercaptoethanol, 100 units/mL penicillinand 100 µg/mL streptomycin. The use of penicillin and streptomycin in the culture medium can be avoided.
However, in such a case users should verify that the absence of antibiotics in the culture medium has no
impact on the results, for example by testing the proficiency substances listed in Annex II. In any case, inorder to minimise the risk of contamination, good cell culture practices should be followed independentlyof the presence or not of antibiotics in the cell culture medium. THP-1 cells are routinely seeded every 2-3
days at the density of 0.1 to 0.2 × 106 cells/mL. They should be maintained at densities from 0.1 to 1.0 ×

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106 cells/mL. Prior to using them for testing, the cells should be qualified by conducting a reactivity check.
The reactivity check of the cells should be performed using the positive controls, 2,4-dinitrochlorobenzene(DNCB) (CAS n. 97-00-7, ≥ 99% purity) and nickel sulfate (NiSO4) (CAS n. 10101-97-0, ≥ 99% purity)and the negative control, lactic acid (LA) (CAS n. 50-21-5, ≥ 85% purity), two weeks after thawing. BothDNCB and NiSO4 should produce a positive response of both CD86 and CD54 cell surface markers, andLA should produce a negative response of both CD86 and CD54 cell surface markers. Only the cells which
passed the reactivity check are to be used for the assay. Cells can be propagated up to two months afterthawing. Passage number should not exceed 30. The reactivity check should be performed according to theprocedures described in paragraphs 27-31.
19. For testing, THP-1 cells are seeded at a density of either 0.1 × 106 cells/mL or 0.2 × 106 cells/mL, andpre-cultured in culture flasks for 72 hours or for 48 hours, respectively. It is important that the cell density
in the culture flask just after the pre-culture period be as consistent as possible in each experiment (byusing one of the two pre-culture conditions described above), because the cell density in the culture flask
just after pre-culture could affect the CD86/CD54 expression induced by allergens (28). On the day of
testing, cells harvested from culture flask are resuspended with fresh culture medium at 2 × 10 6 cells/mL.
Then, cells are distributed into a 24 well flat-bottom plate with 500 µL (1 × 106 cells/well) or a 96-wellflat-bottom plate with 80 µL (1.6 × 105 cells/well).
Dose finding assay
20. A dose finding assay is performed to determine the CV75, being the test chemical concentration that
results in 75% cell viability (CV) compared to the solvent/vehicle control. The CV75 value is used todetermine the concentration of test chemicals for the CD86/CD54 expression measurement (see paragraphs
27-31).
Preparation of test chemicals and control substances
21. The test chemicals and control substances are prepared on the day of testing. For the h-CLAT method,
test chemicals are dissolved or stably dispersed (see also paragraph 12) in saline or medium as firstsolvent/vehicle options or dimethyl sulfoxide (DMSO,  99% purity) as a second solvent/vehicle option if
the test chemical is not soluble or does not form a stable dispersion in the previous two solvents/vehicles,
to final concentrations of 100 mg/mL (in saline or medium) or 500 mg/mL (in DMSO). Other
solvents/vehicles than those described above may be used if sufficient scientific rationale is provided.
Stability of the test chemical in the final solvent/vehicle should be taken into account.
22. Starting from the 100 mg/mL (in saline or medium) or 500 mg/mL (in DMSO) stock solutions of thetest chemicals, the following dilution steps should be taken:− For saline or medium as solvent/vehicle: Eight stock solutions (eight concentrations) are prepared,by two-fold serial dilutions using the corresponding solvent/vehicle. These stock solutions are thenfurther diluted 50-fold into culture medium (working solutions). If the top final concentration in theplate of 1000 µg/mL is non-toxic, the maximum concentration should be re-determined by
performing a new cytotoxicity test. The final concentration in the plate should not exceed 5000
µg/mL for test chemicals dissolved or stably dispersed in saline or medium.
− For DMSO as solvent/vehicle: Eight stock solutions (eight concentrations) are prepared, by two-foldserial dilutions using the corresponding solvent/vehicle. These stock solutions are then further
diluted 250-fold into culture medium (working solutions).The final concentration in plate should notexceed 1000 µg/mL even if this concentration is non-toxic.

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The working solutions are finally used for exposure by adding an equal volume of working solution to thevolume of THP-1 cell suspension in the plate (see also paragraph 24) to achieve a further two-fold dilution(usually, the final range of concentrations in the plate is 7.81–1000 µg/mL).
23. The solvent/vehicle control used in the h-CLAT method is culture medium (for test chemicals
solubilised or stably dispersed (see paragraph 12) either with medium or saline) or DMSO (for test
chemicals solubilised or stably dispersed in DMSO) tested at a single final concentration in the plate of
0.2%. It undergoes the same dilution as described for the working solutions in paragraph 22.
Application of test chemicals and control substances
24. The culture medium or working solutions described in paragraphs 22 and 23 are mixed 1:1 (v/v) withthe cell suspensions prepared in the 24-well or 96-well flat-bottom plate (see paragraph 19). The treatedplates are then incubated for 24±0.5 hours at 37°C under 5% CO2. Care should be taken to avoid
evaporation of volatile test chemicals and cross-contamination between wells by test chemicals, e.g. by
sealing the plate prior to the incubation with the test chemicals (29).
Propidium iodide (PI) staining
25. After 24±0.5 hours of exposure, cells are transferred into sample tubes and collected by centrifugation.
The supernatants are discarded and the remaining cells are resuspended with 200 µL (in case of 96-well) or
600 µL (in case of 24-well) of a phosphate buffered saline containing 0.1% bovine serum albumin(staining buffer). 200 µL of cell suspension is transferred into 96-well round-bottom plate (in case of 96well) or micro tube (in case of 24-well) and washed twice with 200 µL (in case of 96-well) or 600 µL (incase of 24-well) of staining buffer. Finally, cells are resuspended in staining buffer (e.g. 400 µL) and PI
solution (e.g. 20 µL) is added (for example, final concentration of PI is 0.625 µg/mL). Other cytotoxicity
markers, such as 7-Aminoactinomycin D (7-AAD), Trypan blue or others may be used if the alternative
stains can be shown to provide similar results as PI, for example by testing the proficiency substances inAnnex II.
Cytotoxicity measurement by flow cytometry and estimation of CV75 value
26. The PI uptake is analysed using flow cytometry with the acquisition channel FL-3. A total of 10,000
living cells (PI negative) are acquired. The cell viability can be calculated using the following equation by
the cytometer analysis program. When the cell viability is low, up to 30,000 cells including dead cells
should be acquired. Alternatively, data can be acquired for one minute after the initiation of the analysis.
Cell Viability =Number of living cells

× 100

Total Number of acquired cells
The CV75 value (see paragraph 20), i.e. a concentration showing 75% of THP-1 cell survival (25%cytotoxicity), is calculated by log-linear interpolation using the following equation:

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Where:
a is the minimum value of cell viability over 75%
c is the maximum value of cell viability below 75%
b and d are the concentrations showing the value of cell viability a and c respectively

Cell viability (%)

100

a

50
c
0
1

b d
10
100
1000
Test dose (g/mL)

Other approaches to derive the CV75 can be used as long as it isdemonstrated that this has no impact on the results (e.g. by testing
the proficiency substances).
CD86/CD54 expression measurement

Preparation of the test chemicals and control substances
27. The appropriate solvent/vehicle (saline, medium or DMSO; see paragraph 21) is used to dissolve or
stably disperse the test chemicals. The test chemicals are first diluted to the concentration corresponding to
100-fold (for saline or medium) or 500-fold (for DMSO) of the 1.2 × CV75 determined in the dose finding
assay (see paragraph 26). If the CV75 cannot be determined (i.e. if sufficient cytotoxicity is not observedin the dose finding assay), the highest soluble or stably dispersed concentration of test chemical preparedwith each solvent/vehicle should be used as starting concentration. Please note that the final concentrationin the plate should not exceed 5000 µg/mL (in case of saline or medium) or 1000 µg/mL (in case of
DMSO). Then, 1.2-fold serial dilutions are made using the corresponding solvent/vehicle to obtain thestock solutions (eight concentrations ranging from 100×1.2 × CV75 to 100×0.335 × CV75 (for saline or
medium) or from 500×1.2 × CV75 to 500×0.335 × CV75 (for DMSO)) to be tested in the h-CLAT method(see DB-ALM protocol NO. 158 for an example of dosing scheme). The stock solutions are then further
diluted 50-fold (for saline or medium) or 250-fold (for DMSO) into the culture medium (working
solutions). These working solutions are finally used for exposure with a further final two-fold dilution
factor in the plate. If the results do not meet the acceptance criteria described in the paragraphs 35 and 36
regarding cell viability, the dose finding assay may be repeated to determine a more precise CV75. Please
note that only 24-well plates can be used for CD86/CD54 expression measurement.
28. The solvent/vehicle control is prepared as described in paragraph 23. The positive control used in the hCLAT method is DNCB (see paragraph 18), for which stock solutions are prepared in DMSO and diluted
as described for the stock solutions in paragraph 27. DNCB should be used as the positive control for
CD86/CD54 expression measurement at a final single concentration in the plate (typically 4.0 µg/mL). To
obtain a 4.0 µg/mL concentration of DNCB in the plate, a 2 mg/mL stock solution of DNCB in DMSO is
prepared and further diluted 250-fold with culture medium to a 8 µg/mL working solution. Alternatively,
the CV75 of DNCB, which is determined in each test facility, could be also used as the positive control
concentration. Other suitable positive controls may be used if historical data are available to derivecomparable run acceptance criteria. For positive controls, the final single concentration in the plate should
not exceed 5000 µg/mL (in case of saline or medium) or 1000 µg/mL (in case of DMSO). The run
acceptance criteria are the same as those described for the test chemical (see paragraph 35), except for thelast acceptance criterion since the positive control is tested at a single concentration.

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Application of test chemicals and control substances
29. For each test chemical and control substance, one experiment is needed to obtain a prediction. Eachexperiment consists of at least two independent runs for CD86/CD54 expression measurement (seeparagraphs 33 and 34). Each independent run is performed on a different day or on the same day provided
that for each run: a) independent fresh stock solutions and working solutions of the test chemical andantibody solutions are prepared and b) independently harvested cells are used (i.e. cells are collected fromdifferent culture flasks); however, cells may come from the same passage. Test chemicals and control
substances prepared as working solutions (500 µL) are mixed with 500 µL of suspended cells (1x106 cells)
at 1:1 ratio, and cells are incubated for 24±0.5 hours as described in paragraphs 27 and 28. In each run, asingle replicate for each concentration of the test chemical and control substance is sufficient because aprediction is obtained from at least two independent runs.
Cell staining and analysis
30. After 24±0.5 hours of exposure, cells are transferred from 24 well plate into sample tubes, collected bycentrifugation and then washed twice with 1mL of staining buffer (if necessary, additional washing steps
may be done). After washing, cells are blocked with 600 µL of blocking solution (staining buffer
containing 0.01% (w/v) globulin (Cohn fraction II, III, Human: SIGMA, #G2388-10G)) and incubated at
4°C for 15 min. After blocking, cells are split in three aliquots of 180 µL into a 96-well round-bottom plateor micro tube.
31. After centrifugation, cells are stained with 50 µL of FITC-labelled anti-CD86, anti-CD54 or mouse
IgG1 (isotype) antibodies at 4°C for 30 min. The antibodies described in the h-CLAT DB-ALM protocol
no. 158 (27) should be used by diluting 3:25 (v/v, for CD86 (BD-PharMingen, #555657; Clone: Fun-1)) or
3:50 (v/v, for CD54 (DAKO, #F7143; Clone: 6.5B5) and IgG1 (DAKO, #X0927)) with staining buffer.
These antibody dilution factors were defined by the test method developers as those providing the best
signal-to-noise ratio. Based on the experience of the test method developers, the fluorescence intensity of
the antibodies is usually consistent between different lots. However, users may consider titrating theantibodies in their own laboratory's conditions to define the best concentrations for use. Other
fluorochrome-tagged anti-CD86 and/or anti-CD54 antibodies may be used if they can be shown to provide
similar results as FITC-conjugated antibodies, for example by testing the proficiency substances in Annex
II. It should be noted that changing the clone or supplier of the antibodies as described in the h-CLAT DBALM protocol no. 158 (27) may affect the results. After washing twice with 150 µL or more of staining
buffer three times, cells are resuspended in staining buffer (e.g. 400 µL), and the PI solution (e.g. 20 µL to
obtain a final concentration of 0.625 µg/mL) or another cytotoxicity marker's solution (see paragraph 25) is
added. The expression levels of CD86 and CD54, and cell viability are analysed using flow cytometry.

DATA AND REPORTING
Data evaluation
32. The expression of CD86 and CD54 is analysed with flow cytometry with the acquisition channel FL-1.
Based on the geometric mean fluorescence intensity (MFI), the relative fluorescence intensity (RFI) of
CD86 and CD54 for positive control (ctrl) cells and chemical-treated cells are calculated according to thefollowing equation:

RFI =MFI of chemical-treated cells − MFI of chemical-treated isotype control
x100
cells
MFI of solvent/vehicle-treated ctrl cells − MFI of solvent/vehicle-treated isotype ctrl
cells
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The cell viability from the isotype control (ctrl) cells (which are stained with mouse IgG1 (isotype)antibodies) is also calculated according to the equation described in paragraph 26.
Prediction model
33. For CD86/CD54 expression measurement, each test chemical is tested in at least two independent runs
to derive a single prediction (POSITIVE or NEGATIVE). An h-CLAT prediction is considered POSITIVE
if at least one of the following conditions is met in 2 of 2 or in at least 2 of 3 independent runs, otherwise
the h-CLAT prediction is considered NEGATIVE (Figure 1):− The RFI of CD86 is equal to or greater than 150% at any tested concentration (with cell viability ≥50%);− The RFI of CD54 is equal to or greater than 200% at any tested concentration (with cell viability ≥50%).
Based on the above, if the first two runs are both positive for CD86 and/or are both positive for CD54, theh-CLAT prediction is considered POSITIVE and a third run does not need to be conducted. Similarly, if
the first two runs are negative for both markers, the h-CLAT prediction is considered NEGATIVE (withdue consideration of the provisions of paragraph 36) without the need for a third run. If however, the firsttwo runs are not concordant for at least one of the markers (CD54 or CD86), a third run is needed and thefinal prediction will be based on the majority result of the three individual runs (i.e. 2 out of 3). In thisrespect, it should be noted that if two independent runs are conducted and one is only positive for CD86
(hereinafter referred to as P1) and the other is only positive for CD54 (hereinafter referred to as P2), a third
run is required. If this third run is negative for both markers (hereinafter referred to as N), the h-CLAT
prediction is considered NEGATIVE. On the other hand, if the third run is positive for either marker (P 1 or
P2) or for both markers (hereinafter referred to as P12), the h-CLAT prediction is considered POSITIVE.

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Figure 1: Prediction model used in the h-CLAT test method. An h-CLAT prediction should beconsidered in the framework of an IATA and in accordance with the provision of paragraphs 9, 11 and 12.
P1: run with only CD86 positive; P2; run with only CD54 positive; P12: run with both CD86 and CD54
positive; N: run with neither CD86 nor CD54 positive. *The boxes show the relevant combinations ofresults from the first two runs, independently of the order in which they may be obtained. #The boxes show
the relevant combinations of results from the three runs on the basis of the results obtained in the first two
runs shown in the box above, but do not reflect the order in which they may be obtained.
34. For the test chemicals predicted as POSITIVE with the h-CLAT, optionally, two Effective
Concentrations (EC) values, the EC150 for CD86 and EC200 for CD54, i.e. the concentration at which thetest chemicals induced a RFI of 150 or 200, may be determined. These EC values potentially could
contribute to the assessment of sensitising potency (3) when used in integrated approaches such as IATA
(12) (13) (14) (15) (16). They can be calculated by the following equations:
EC150 (for CD86) = Bconcentration + [(150 - BRFI) / (ARFI - BRFI) × (Aconcentration - Bconcentration)]
EC200 (for CD54) = Bconcentration + [(200 - BRFI) / (ARFI - BRFI) × (Aconcentration - Bconcentration)]where
Aconcentrationis the lowest concentration in µg/mL with RFI > 150 (CD86) or 200 (CD54)
Bconcentration is the highest concentration in µg/mL with RFI < 150 (CD86) or 200 (CD54)
ARFI is the RFI at the lowest concentration with RFI > 150 (CD86) or 200 (CD54)

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BRFI is the RFI at the highest concentration with RFI < 150 (CD86) or 200 (CD54)
For the purpose of more precisely deriving the EC150 and EC200 values, three independent runs for
CD86/CD54 expression measurement may be required. The final EC150 and EC200 values are thendetermined as the median value of the ECs calculated from the three independent runs. When only two of
three independent runs meet the criteria for positivity (see paragraph 33), the higher EC150 or EC200 of
the two calculated values is adopted.
Acceptance criteria
35. The following acceptance criteria should be met when using the h-CLAT method (22) (27).
-The cell viabilities of medium and solvent/vehicle controls should be higher than 90%.

-

In the solvent/vehicle control, RFI values of both CD86 and CD54 should not exceed the positive
criteria (CD86 RFI  150% and CD54 RFI  200%). RFI values of the solvent/vehicle control arecalculated by using the formula described in paragraph 32 ("MFI of chemical" should be replacedwith "MFI of solvent/vehicle", and "MFI of solvent/vehicle" should be replaced with "MFI of(medium) control").

-

For both medium and solvent/vehicle controls, the MFI ratio of both CD86 and CD54 to isotype
control should be > 105%.

-

In the positive control (DNCB), RFI values of both CD86 and CD54 should meet the positive criteria(CD86 RFI  150 and CD54 RFI  200) and cell viability should be more than 50%.

-

For the test chemical, the cell viability should be more than 50% in at least four tested concentrations
in each run.

36. Negative results are acceptable only for test chemicals exhibiting a cell viability of less than 90% at thehighest concentration tested (i.e. 1.2 × CV75 according to the serial dilution scheme described in paragraph27). If the cell viability at 1.2 × CV75 is equal or above 90% the negative result should be discarded. Insuch a case it is recommended to try to refine the dose selection by repeating the CV75 determination. Itshould be noted that when 5000 µg/mL in saline (or medium or other solvents/vehicles), 1000 µg/mL in
DMSO or the highest soluble concentration is used as the maximal test concentration of a test chemical, anegative result is acceptable even if the cell viability is above 90%.
Test report
37. The test report should include the following information.
Test chemical- Mono-constituent substanceChemical identification, such as IUPAC or CAS name(s), CAS number(s), SMILES or InChI
code, structural formula, and/or other identifiers;Physical appearance, Log Kow, water solubility, DMSO solubility, molecular weight, andadditional relevant physicochemical properties, to the extent available;

Purity, chemical identity of impurities as appropriate and practically feasible, etc.;
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OECD/OCDETreatment prior to testing, if applicable (e.g. warming, grinding);Concentration(s) tested;

Storage conditions and stability to the extent available;Justification for choice of solvent/vehicle for each test chemical.

- Multi-constituent substance, UVCB and mixture:Characterisation as far as possible by e.g. chemical identity (see above), purity, quantitative
occurrence and relevant physicochemical properties (see above) of the constituents, to theextent available;Physical appearance, water solubility, DMSO solubility and additional relevant
physicochemical properties, to the extent available;

Molecular weight or apparent molecular weight in case of mixtures/polymers of known
compositions or other information relevant for the conduct of the study;Treatment prior to testing, if applicable (e.g. warming, grinding);Concentration(s) tested;

Storage conditions and stability to the extent available;Justification for choice of solvent/vehicle for each test chemical.

Controls- Positive control


Chemical identification, such as IUPAC or CAS name(s), CAS number(s), SMILES or InChI
code, structural formula, and/or other identifiers;Physical appearance, Log Kow, water solubility, DMSO solubility, molecular weight, andadditional relevant physicochemical properties, to the extent available and where applicable;

Purity, chemical identity of impurities as appropriate and practically feasible, etc.;Treatment prior to testing, if applicable (e.g. warming, grinding);Concentration(s) tested;

Storage conditions and stability to the extent available;

Reference to historical positive control results demonstrating suitable run acceptance criteria,
if applicable.

- Negative and solvent/vehicle control


Chemical identification, such as IUPAC or CAS name(s), CAS number(s), SMILES or InChI
code, structural formula, and/or other identifiers;Purity, chemical identity of impurities as appropriate and practically feasible, etc.;Physical appearance, molecular weight, and additional relevant physicochemical properties in
the case other control solvent/vehicle than those mentioned in the Test Guideline are used andto the extent available;

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Storage conditions and stability to the extent available;Justification for choice of solvent/vehicle for each test chemical.

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Test method conditions-

Name and address of the sponsor, test facility and study director;-

Description of test method used;-

Cell line used, its storage conditions and source (e.g. the facility from which they were obtained);-

Flow cytometry used (e.g. model), including instrument settings, globulin, antibodies and cytotoxicity
marker used;-

The procedure used to demonstrate proficiency of the laboratory in performing the test method bytesting of proficiency substances, and the procedure used to demonstrate reproducible performance ofthe test method over time, e.g. historical control data and/or historical reactivity checks’ data.

Test acceptance criteria-

Cell viability, MFI and RFI values obtained with the solvent/vehicle control in comparison to theacceptance ranges;- Cell viability and RFI values obtained with the positive control in comparison to the acceptance
ranges;-Cell viability of all tested concentrations of the tested chemical.

Test procedure-

Number of runs used;
Test chemical concentrations, application and exposure time used (if different than the one
recommended)
Duration of exposure (if different than the one recommended);
Description of evaluation and decision criteria used;
Description of any modifications of the test procedure.

-

Results--

Tabulation of the data, including CV75 (if applicable), individual geometric MFI, RFI, cell viability
values, EC150/EC200 values (if applicable) obtained for the test chemical and for the positive control
in each run, and an indication of the rating of the test chemical according to the prediction model;
Description of any other relevant observations, if applicable.

Discussion of the results-

Discussion of the results obtained with the h-CLAT method;

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Consideration of the test method results within the context of an IATA, if other relevant information
is available.

Conclusions

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LITERATURE
1. United Nations UN (2013), Globally Harmonized System of Classification and Labelling of Chemicals(GHS). Fifth revised edition. New York & Geneva: United Nations Publications. ISBN: 978-92-1117006-1. Available at: [http://www.unece.org/trans/danger/publi/ghs/ghs_rev05/05files_e.html].
2. OECD (2012), The Adverse Outcome Pathway for Skin Sensitisation Initiated by Covalent Binding toProteins. Part 1: Scientific Evidence. Series on Testing and Assessment No. 168. Available at:
http://www.oecd.org/officialdocuments/publicdisplaydocumentpdf/?cote=ENV/JM/MONO(2012)10/P
ART1&docLanguage=En
3. OECD (2010), The Local Lymph Node Assay. OECD Guideline for the Testing of Chemicals No. 429,
Organisation for Economic Cooperation and Development, Paris. Available at:
http://www.oecd.org/env/testguidelines
4. OECD (1992), Skin Sensitisation. OECD Guideline for the Testing of Chemicals No. 406, Organisation
for Economic Cooperation and Development, Paris. Available at:
http://www.oecd.org/env/testguidelines
5. OECD (2010), Skin Sensitisation: Local Lymph Node Assay: DA. OECD Guideline for the Testing ofChemicals No. 442A, Organisation for Economic Cooperation and Development, Paris. Available at:
http://www.oecd.org/env/testguidelines
6. OECD (2010), Skin sensitisation: Local Lymph Node Assay: BrdU-ELISA. OECD Guideline for the
Testing of Chemicals No. 442B, Organisation for Economic Cooperation and Development, Paris.
Available at: http://www.oecd.org/env/testguidelines
7. OECD (2015), OECD Guideline for the Testing of Chemicals No. 442C: In Chemico Skin Sensitisation:
Direct Peptide Reactivity Assay (DPRA). Paris, France: Organisation for Economic Cooperation andDevelopment. Available at: http://www.oecd.org/env/testguidelines
8. OECD (2015), OECD Guideline for the Testing of Chemicals No. 442D: In Vitro Skin Sensitisation:
ARE-Nrf2 Luciferase Test Method. Paris, France: Organisation for Economic Cooperation andDevelopment. Available at: http://www.oecd.org/env/testguidelines
9. Adler S, Basketter D, Creton S, Pelkonen O, van Benthem J, Zuang V, Andersen KE, Angers-Loustau A,
Aptula A, Bal-Price A, Benfenati E, Bernauer U, Bessems J, Bois FY, Boobis A, Brandon E, Bremer S,
Broschard T, Casati S, Coecke S, Corvi R, Cronin M, Daston G, Dekant W, Felter S, Grignard E,
Gundert-Remy U, Heinonen T, Kimber I, Kleinjans J, Komulainen H, Kreiling R, Kreysa J, Leite SB,
Loizou G, Maxwell G, Mazzatorta P, Munn S, Pfuhler S, Phrakonkham P, Piersma A, Poth A, Prieto P,
Repetto G, Rogiers V, Schoeters G, Schwarz M, Serafimova R, Tähti H, Testai E, van Delft J, vanLoveren H, Vinken M, Worth A, Zaldivar JM. (2011), Alternative (non-animal) methods for cosmetics
testing: current status and future prospects-2010. Archives of Toxicology 85, 367-485.
10. Ashikaga T, Yoshida Y, Hirota M, Yoneyama K, Itagaki H, Sakaguchi H, Miyazawa M, Ito Y, Suzuki
H, Toyoda H. (2006), Development of an in vitro skin sensitization test using human cell lines: The
human Cell Line Activation Test (h-CLAT) I. Optimization of the h-CLAT protocol. Toxicol. In Vitro
20, 767–773.
11. EC EURL-ECVAM (2013), Recommendation on the human Cell Line Activation Test (h-CLAT) forskinsensitisation
testing.
Accessibleat:https://eurl-ecvam.jrc.ec.europa.eu/eurl-ecvamrecommendations
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12. Takenouchi O, Fukui S, Okamoto K, Kurotani S, Imai N, Fujishiro M, Kyotani D, Kato Y, Kasahara T,
Fujita M, Toyoda A, Sekiya D, Watanabe S, Seto H, Hirota M, Ashikaga T, Miyazawa M. (2015), Test
battery with the human cell line activation test, direct peptide reactivity assay and DEREK based on a
139 chemical data set for predicting skin sensitizing potential and potency of chemicals. J Appl Toxicol.
35, 1318-1332.
13. Hirota M, Fukui S, Okamoto K, Kurotani S, Imai N, Fujishiro M, Kyotani D, Kato Y, Kasahara T,
Fujita M, Toyoda A, Sekiya D, Watanabe S, Seto H, Takenouchi O, Ashikaga T, Miyazawa M. (2015),
Evaluation of combinations of in vitro sensitization test descriptors for the artificial neural networkbased risk assessment model of skin sensitization. J Appl Toxicol. 35, 1333-1347.
14. Bauch C,kolle SN, Ramirez T, Fabian E, Mehling A, Teubner W, van Ravenzwaay B, Landsiedel R.
(2012), Putting the parts together: combining in vitro methods to test for skin sensitizing potencials.
Regul Toxicol Parmacol. 63, 489-504.
15. Van der Veen JW, Rorije E, Emter R, Natch A, van Loveren H, Ezendam J. (2014), Evaluating theperformance of integrated approaches for hazard identification of skin sensitizing chemicals. Regul
Toxicol Pharmacol. 69, 371-379.
16. Urbisch D, Mehling A, Guth K, Ramirez T, Honarvar N, Kolle S, Landsiedel R, Jaworska J, Kern PS,
Gerberick F, Natsch A, Emter R, Ashikaga T, Miyazawa M, Sakaguchi H. (2015), Assessing skinsensitization hazard in mice and men using non-animal test methods. Regul Toxicol Parmacol. 71, 337351.
17. Jaworska JS, Natsch A, Ryan C, Strickland J, Ashikaga T, Miyazawa M. (2015), Bayesian integrated
testing strategy (ITS) for skin sensitization potency assessment: a decision support system forquantitative weight of evidence and adaptive testing strategy. Arch Toxicol. 89, 2355-2383.
18. Strickland J, Zang Q, Kleinstreuer N, Paris M, Lehmann DM, Choksi N, Matheson J, Jacobs A, Lowit
A, Allen D, Casey W. (2016), Integrated decision strategies for skin sensitization hazard. J Appl
Toxicol. DOI 10.1002/jat.3281.
19. Nukada Y, Ashikaga T, Miyazawa M, Hirota M, Sakaguchi H, Sasa H, Nishiyama N. (2012),
Prediction of skin sensitization potency of chemicals by human Cell Line Activation Test (h-CLAT)
and an attempt at classifying skin sensitization potency. Toxicol. In Vitro 26, 1150-60.
20. Miyazawa M, Ito Y, Yoshida Y, Sakaguchi H, Suzuki H. (2007), Phenotypic alterations and cytokine
production in THP-1 cells in response to allergens. Toxicol. In Vitro 21, 428-437.
21. EC EURL ECVAM (2015), Re-analysis of the within and between laboratory reproducibility of thehuman Cell Line Activation Test (h-CLAT). Accessible at: https://eurl-ecvam.jrc.ec.europa.eu/eurlecvam-recommendations/eurl-ecvam-recommendation-on-the-human-cell-line-activation-test-h-clatfor-skin-sensitisation-testing
22. EC EURL ECVAM (2012), human Cell Line Activation Test (h-CLAT) Validation Study Report
Accessible at: https://eurl-ecvam.jrc.ec.europa.eu/eurl-ecvam-recommendations
23. Takenouchi O, Miyazawa M, Saito K, Ashikaga T, Sakaguchi H. (2013), Predictive performance of thehuman Cell Line Activation Test (h-CLAT) for lipophilic with high octanol-water partition coefficients.
J. Toxicol. Sci. 38, 599-609.
24. Ashikaga T, Sakaguchi H, Sono S, Kosaka N, Ishikawa M, Nukada Y, Miyazawa M, Ito Y,

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NishiyamaN, Itagaki H. (2010), A comparative evaluation of in vitro skin sensitisation tests: thehuman cell-line activation test (h-CLAT) versus the local lymph node assay (LLNA). Altern. Lab.
Anim. 38, 275-284.
25. Fabian E., Vogel D., Blatz V., Ramirez T., Kolle S., Eltze T., van Ravenzwaay B., Oesch F.,
Landsiedel R. (2013), Xenobiotic metabolizin enzyme activities in cells used for testing skinsensitization in vitro. Arch Toxicol 87, 1683-1969.
26. Okamoto K, Kato Y, Kosaka N, Mizuno M, Inaba H, Sono S, Ashikaga T, Nakamura T, Okamoto Y,
Sakaguchi H, Kishi M, Kuwahara H, Ohno Y. (2010), The Japanese ring study of a human Cell Line
Activation Test (h-CLAT) for predicting skin sensitization potential (6th report): A study forevaluating oxidative hair dye sensitization potential using h-CLAT. AATEX 15, 81-88.
27. DB-ALM (INVITTOX) (2014), Protocol 158: human Cell Line Activation Test (h-CLAT), 23pp.
Accessible at: http://ecvam-dbalm.jrc.ec.europa.eu/
28. Mizuno M, Yoshida M, Kodama T, Kosaka N, Okamato K, Sono S, Yamada T, Hasegawa S, Ashikaga
T, Kuwahara H, Sakaguchi H, Sato J, Ota N, Okamoto Y, Ohno Y. (2008), Effects of pre-culture
conditions on the human Cell Line Activation Test (h-CLAT) results; Results of the 4th Japanese interlaboratory study. AATEX 13, 70-82.
29. Sono S, Mizuno M, Kosaka N, Okamoto K, Kato Y, Inaba H, , Nakamura T, Kishi M, Kuwahara H,
Sakaguchi H, Okamoto Y, Ashikaga T, Ohno Y. (2010), The Japanese ring study of a human Cell Line
Activation Test (h-CLAT) for predicting skin sensitization potential (7th report): Evaluation of volatile,
poorly soluble fragrance materials. AATEX 15, 89-96.
30. OECD (2005), Guidance Document No.34 on “the Validation and International Acceptance of New or
Updated Test Methods for Hazard Assessment”. OECD Series on Testing and Assessment.
Organization for Economic Cooperation and Development, Paris, France, 2005, 96 pp.
31. ECETOC (2003). Contact sensitization: Classification according to potency. European Centre for
Ecotoxicology & Toxicology of Chemicals (Technical Report No. 87).
32. Ashikaga T, Sakaguchi H, Okamoto K, Mizuno M, Sato J, Yamada T, Yoshida M, Ota N, Hasegawa S,
Kodama T, Okamoto Y, Kuwahara H, Kosaka N, Sono S, Ohno Y. (2008), Assessment of the human
Cell Line Activation Test (h-CLAT) for Skin Sensitization; Results of the First Japanese Interlaboratory Study. AATEX 13, 27-35.

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OECD/OCDEANNEX I
DEFINITIONS

Accuracy: The closeness of agreement between test method results and accepted reference values. It is ameasure of test method performance and one aspect of relevance. The term is often used interchangeably
with concordance to mean the proportion of correct outcomes of a test method (30).
AOP (Adverse Outcome Pathway): sequence of events from the chemical structure of a target chemicalor group of similar chemicals through the molecular initiating event to an in vivo outcome of interest (2).
CV75: The estimated concentration showing 75% cell viability.
EC150: the concentrations showing the RFI values of 150 in CD86 expression
EC200: the concentrations showing the RFI values of 200 in CD54 expression
Flow cytometry: a cytometric technique in which cells suspended in a fluid flow one at a time through afocus of exciting light, which is scattered in patterns characteristic to the cells and their components; cells
are frequently labeled with fluorescent markers so that light is first absorbed and then emitted at alteredfrequencies.
Hazard: Inherent property of an agent or situation having the potential to cause adverse effects when an
organism, system or (sub) population is exposed to that agent.
IATA (Integrated Approach to Testing and Assessment): A structured approach used for hazard
identification (potential), hazard characterisation (potency) and/or safety assessment (potential/potency andexposure) of a chemical or group of chemicals, which strategically integrates and weights all relevant data
to inform regulatory decision regarding potential hazard and/or risk and/or the need for further targeted andtherefore minimal testing.
Medium control: An untreated replicate containing all components of a test system. This sample isprocessed with test chemical-treated samples and other control samples to determine whether thesolvent/vehicle interacts with the test system.
Mixture: A mixture or a solution composed of two or more substances in which they do not react.
Mono-constituent substance: A substance, defined by its quantitative composition, in which one main
constituent is present to at least 80% (w/w).
Multi-constituent substance: A substance, defined by its quantitative composition, in which more than
one main constituent is present in a concentration ≥ 10% (w/w) and < 80% (w/w). A multi-constituent
substance is the result of a manufacturing process. The difference between mixture and multi-constituent
substance is that a mixture is obtained by blending of two or more substances without chemical reaction. A
multi-constituent substance is the result of a chemical reaction.

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Positive control: A replicate containing all components of a test system and treated with a substanceknown to induce a positive response. To ensure that variability in the positive control response across time
can be assessed, the magnitude of the positive response should not be excessive.
Pre-haptens: chemicals which become sensitisers through abiotic transformation
Pro-haptens: chemicals requiring enzymatic activation to exert skin sensitisation potential
Relative fluorescence intensity (RFI): Relative values of geometric mean fluorescence intensity (MFI) in
chemical-treated cells compared to MFI in solvent/vehicle-treated cells.
Relevance: Description of relationship of the test to the effect of interest and whether it is meaningful anduseful for a particular purpose. It is the extent to which the test correctly measures or predicts the
biological effect of interest. Relevance incorporates consideration of the accuracy (concordance) of a test
method (30).
Reliability: Measures of the extent that a test method can be performed reproducibly within and between
laboratories over time, when performed using the same protocol. It is assessed by calculating intra- andinter-laboratory reproducibility and intra-laboratory repeatability (30).
Run: A run consists of one or more test chemicals tested concurrently with a solvent/vehicle control andwith a positive control.
Sensitivity: The proportion of all positive/active chemicals that are correctly classified by the test. It is ameasure of accuracy for a test method that produces categorical results, and is an important considerationin assessing the relevance of a test method (30).
Staining buffer: A phosphate buffered saline containing 0.1% bovine serum albumin.
Solvent/vehicle control: An untreated sample containing all components of a test system except of the test
chemical, but including the solvent/vehicle that is used. It is used to establish the baseline response for the
samples treated with the test chemical dissolved or stably dispersed in the same solvent/vehicle. Whentested with a concurrent medium control, this sample also demonstrates whether the solvent/vehicle
interacts with the test system.
Specificity: The proportion of all negative/inactive chemicals that are correctly classified by the test. It is ameasure of accuracy for a test method that produces categorical results and is an important consideration inassessing the relevance of a test method (30).
Substance: Chemical elements and their compounds in the natural state or obtained by any production
process, including any additive necessary to preserve the stability of the product and any impurities
deriving from the process used, but excluding any solvent which may be separated without affecting thestability of the substance or changing it composition.

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OECD/OCDE

Test chemical: The term "test chemical" is used to refer to what is being tested.
United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UNGHS): A system proposing the classification of chemicals (substances and mixtures) according tostandardised types and levels of physical, health and environmental hazards, and addressing corresponding
communication elements, such as pictograms, signal words, hazard statements, precautionary statements
and safety data sheets, so that to convey information on their adverse effects with a view to protect people(including employers, workers, transporters, consumers and emergency responders) and the environment(1).
UVCB: substances of unknown or variable composition, complex reaction products or biological materials.
Valid test method: A test method considered to have sufficient relevance and reliability for a specificpurpose and which is based on scientifically sound principles. A test method is never valid in an absolutesense, but only in relation to a defined purpose (30).

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ANNEX IIPROFICIENCY SUBSTANCES

Prior to routine use of a test method that adheres to this Test Guideline, laboratories should demonstratetechnical proficiency by correctly obtaining the expected h-CLAT prediction for the 10 substances
recommended in Table 1 and by obtaining CV75, EC150 and EC200 values that fall within the respective
reference range for at least 8 out of the 10 proficiency substances. Proficiency substances were selected torepresent the range of responses for skin sensitisation hazards. Other selection criteria were that thesubstances are commercially available, and that high-quality in vivo reference data as well as high quality
in vitro data generated with the h-CLAT method are available. Also, published reference data are available
for the h-CLAT method (11) (23).
Table 1: Recommended substances for demonstrating technical proficiency with the h-CLAT method
In vivoprediction1

CV75
Reference
Range in
g/mL2h-CLAT resultsfor CD86(EC150 Reference
Range in μg/mL)2

h-CLAT resultsfor CD54(EC200 Reference
Range in μg/mL)2

Proficiency substances

CASRN

Physicalstate

2,4-Dinitrochlorobenzene

97-00-7

Solid

Sensitiser(extreme)

2-12

Positive(0.5-10)

Positive(0.5-15)

4-Phenylenediamine

106-50-3

Solid

Sensitiser(strong)

5-95

Positive(<40)

Negative(>1.5)3

Nickel sulfate

10101-97-0

SolidSensitiser(moderate)

30-500

Positive(<100)

Positive(10-100)

2-Mercaptbenzothiazole

149-30-4

Solid

Sensitiser(moderate)

30-400

Negative(>10)3

Positive(10-140)

R(+)-Limonene

5989-27-5

LiquidSensitiser(weak)>20

Negative(>5)3

Positive(<250)

Imidazolidinyl urea

39236-46-9

SolidSensitiser(weak)

25-100

Positive(20-90)

Positive(20-75)Isopropanol

67-63-0LiquidNon-sensitiser>5000

Negative(>5000)

Negative(>5000)Glycerol

56-81-5

LiquidNon-sensitiser>5000

Lactic acid50-21-5

LiquidNon-sensitiser

1500-5000

4-Aminobenzoic acid150-13-0

Solid

Non-sensitiser>1000

Negative(>5000)
Negative(>5000)
Negative(>1000)

Negative(>5000)
Negative(>5000)
Negative(>1000)Abbreviations: CAS RN = Chemical Abstracts Service Registry Number
1
The in vivo hazard and (potency) prediction is based on LLNA data (11) (23). The in vivo potency isderived using the criteria proposed by ECETOC (31).
2Based on historical observed values (22) (32).
3Historically, a majority of negative results have been obtained for this marker and therefore a negative
result is mostly expected. The range provided was defined on the basis of the few historical positive
results observed. In case a positive result is obtained, the EC value should be within the reported
reference range.

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