LLNA variability: An essential ingredient for a comprehensive assessment of non-animal skin sensitization test methods and strategies

Abstract

The development of non-animal skin sensitization test methods and strategies is quickly progressing. Either individually or in combination, the predictive capacity is usually described in comparison to local lymph node assay (LLNA) results. In this process an important lesson from other endpoints, such as skin or eye irritation, i.e., that the variability of reference test results – here the LLNA – must be accounted for, has not yet been fully acknowledged.
In order to provide assessors as well as method and strategy developers with appropriate estimates, the variability of EC3 values from repeated substance testing in the LLNA was investigated using the publicly available NICEATM (NTP Interagency Center for the Evaluation of Alternative Toxicological Methods) LLNA database. Repeat experiments taking the vehicle into account (76 substances) or combining data over different vehicles (38 substances) were analyzed.
In general, variability was higher when different vehicles were used. In terms of skin sensitization potential, i.e., discriminating sensitizers from non-sensitizers, the false positive rate ranged from 14-20%, while the false negative rate was 4-5%. In terms of skin sensitization potency, the rate to assign a substance to the next higher or next lower potency class was approx.10-15% each. In addition, general estimates for EC3 variability are provided that can be used for modelling purposes.
This analysis stresses the importance of considering the LLNA variability in the assessment of skin sensitization test methods and strategies and provides estimates thereof.