Effect of formulation and freeze-drying on the long-term stability of rDNA-derived cytokines.

Lyophilized recombinant DNA-derived cytokine preparations intended for use as International Reference Material have been processed in such a way as to give batches of preparations which possess homogeneity and high stability, in order that each cytokine standard has a reasonable use of some 10 to 20 years. This has been achieved by exercising careful control at every stage of the lyophilization process. All cytokines were ampouled in microgram quantities with relatively large quantities (milligrams) of bulking agent such as albumin and carbohydrate which were shown to have no effect on the biological activity of the cytokine. Residual moisture present in the preparations and their uptake was measured by Karl-Fischer titration and found to vary from 0.5% to 4% moisture. On storage over phosphorus pentoxide these values were reduced to 0.1% to 0.5% with good reproducibility throughout the batch. Reconstitution of the freeze-dried plug was readily achieved in seconds. The stability of freeze-dried preparations of several cytokines was monitored by observing changes in biological activity after accelerated degradation studies. To date, several freeze-dried preparations have shown no loss in activity after storage at temperatures up to +56 degrees C for one year.