Tag Archive for: quantitative skin sensitizing potency assessment

Quantitative assessment of sensitizing potency using a dose-response adaptation of GARDskin

Nature Scientific Reports 11, 18904 (2021), https://doi.org/10.1038/s41598-021-98247-7

Robin Gradin, Andy Forreryd, Ulrika Mattson, Anders Jerre, Henrik Johansson


Hundreds of chemicals have been identified as skin sensitizers. These are chemicals that possess the ability to induce hypersensitivity reactions in humans, giving rise to a condition termed allergic contact dermatitis. The capacity to limit hazardous exposure to such chemicals depends upon the ability to accurately identify and characterize their skin sensitizing potency. This has traditionally been accomplished using animal models, but their widespread use offers challenges from both an ethical and a scientific perspective. Comprehensive efforts have been made by the scientific community to develop new approach methodologies (NAMs) capable of replacing in vivo assays, which have successfully yielded several methods that can identify skin sensitizers. However, there is still a lack of new approaches that can effectively measure skin sensitizing potency. We present a novel methodology for quantitative assessment of skin sensitizing potency, which is founded on the already established protocols of the GARDskin assay. This approach analyses dose-response relationships in the GARDskin assay to identify chemical-specific concentrations that are sufficient to induce a positive response in the assay. We here compare results for 22 skin sensitizers analyzed using this method with both human and LLNA potency reference data and show that the results correlate strongly and significantly with both metrics (rLLNA = 0.81, p = 9.1 × 10–5; rHuman = 0.74, p = 1.5 × 10–3).

In conclusion, the results suggest that the proposed GARDskin dose-response methodology provides a novel non-animal approach for quantitative potency assessment, which could represent an important step towards reducing the need for in vivo experiments.


Key words: GARD, GARDskin, GARDskin Dose-Response, in vitro, sensitization, potency, chemical sensitizers, quantitative risk assessment


Full article
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Dose-Response Analysis in GARD™ for Assessment of Skin Sensitizer Potency

Poster presented at ACT 2020

J. Schmidt, A. Forreryd, R. Gradin, H. Johansson.
SenzaGen Inc., Raleigh, NC., SenzaGen AB, Lund, Sweden.

Link to the poster



  • As an adaptation from the GARDskin assay, GARDskin Dose-Response is suitable for quantitative skin sensitizing potency assessment of chemicals.
  • The experimental readout, referred to as cDV0, corresponds to the lowest dose required to elicit a positive response in GARDskin. As such, experimental protocols are analogous to the LLNA, in which the cDV0 corresponds to the EC3-value.
  • The cDV0 may be used to directly monitor sensitizing potency, or further used to extrapolate LLNA EC3-values, estimation of Human Potency categories, or CLP 1A/1B classifications.


Several non-animal methods for identifying skin sensitizers have been developed with acceptable prediction performance. However, advancement of alternative methods for skin sensitizing potency assessment is still missing although a highly sought-after endpoint. The GARDskin assay is a genomics-based in vitro assay for hazard assessment of skin sensitizers, currently progressing towards regulatory acceptance. Here, we introduce GARDskin Dose-Response (DR), in which test chemicals are evaluated by the GARDskin assay in an extended range of concentrations, in order to investigate the dose-response relationship between GARDskin classifications and test chemical concentration.

For this work, 29 chemicals of various sensitizing potencies were used to evaluate the efficacy of applying the assay in this manner. Each chemical was analyzed at several concentrations using a slightly modified GARDskin protocol. At each concentration, a decision-value was produced and a classification prediction (sensitizing or non-sensitizing) was made by the GARDskin algorithm. Afterwards, the lowest concentration where a test item would provide a positive GARDskin prediction was found using linear interpolation. This concentration (cDV0) was then hypothesized to reflect the test items skin sensitizing potency. Furthermore, when comparing cDV0 to LLNA EC3 values, a statistically significant correlation was realized between the values (correlation coefficient =0.74, p-value=4.1*10-4).

These results suggest that modifying the GARDskin protocol to accommodate dose-response measurements can provide sensitizing potency information analogous to the gold-standard in vivo methods. This presentation will further explain the testing process, expand on results, and demonstrate how this method can be used for decision-making throughout all stages of product development, without having to use animal experimentation.