Development and validation of a bioassay for interleukin-2.

A reliable and precise method for the determination of IL-2 activity, based on stimulation of CTLL cell proliferation, was developed. Cells were incubated with different concentrations of IL-2 for 24 h in microtiter plates. The stimulatory effect was measured on a plate-reading spectrophotometer by reading the optical density of formazan, which is produced by viable cells from 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). The bioassay was designed as a four-dose parallel line test, fulfilling pharmacopoeial requirements for assay validity, and the inter-assay relative standard deviation (RSD) for a group of four experiments was 2.6%. The International Standard for human IL-2 and the Reference Reagent for Recombinant DNA-derived IL-2 were employed for potency determinations. The method was found suitable for potency assessments of pharmaceutical formulations of IL-2.