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Clinical and Vaccine Immunology, June 2008, p. 946-953, Vol. 15, No. 6
1071-412X/08/$08.00+0     doi:10.1128/CVI.00003-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Interlaboratory Comparison of Results of an Anthrax Lethal Toxin Neutralization Assay for Assessment of Functional Antibodies in Multiple Species

Precision Bioassay, Burlington, Vermont,¹ Battelle Eastern Science and Technology Center, Aberdeen, Maryland,² Battelle Biomedical Research Center, West Jefferson, Ohio,³ Division of Microbiology and Infectious Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland⁴

Received 4 January 2008/ Returned for modification 8 February 2008/ Accepted 31 March 2008

The anthrax lethal toxin neutralization assay (TNA) will likely be used to correlate the protection offered by new anthrax vaccines in animal models to the immunogenicity that will be provided in humans. TNA data are being generated in several different laboratories to measure the immune responses in rabbits, nonhuman primates, and humans. In order to compare data among species and laboratories, a collaborative study was conducted in which 108 samples from the three species were analyzed in seven independent laboratories. Six of the seven laboratories had participated in an interlaboratory technology transfer of the TNA. Analysis of the titration curves generated by samples from each species indicated that the behaviors of the samples from all species were similar; the upper and lower asymptotes and the slopes of the curves were less than 30% divergent from those for human reference material. Dilutional linearity was consistent among samples from each species, with spike to effective dilution at 50% inhibition (ED₅₀) slopes of less than 1.2 for all species. Agreement among the laboratories with consensus values was within 10% of the ED₅₀s for all samples and within 7.5% of the quotients of the test sample ED₅₀ and the reference standard ED₅₀ (NF₅₀s) for all samples. The relative standard deviations obtained when data from all laboratories and for all species were combined were 45% for the ED₅₀s and 35% for the NF₅₀s. These precision data suggest that the NF₅₀ readout may normalize the values generated by different laboratories. This study demonstrates that the TNA is a panspecies assay that can be performed in several different laboratories with a high degree of quantitative agreement and precision.

Published ahead of print on 16 April 2008.