The objective of this study is to develop an in vitro potency assay to replace the guinea pig death test portion of the official release test for the diptheria component. VERO cells will be used as a target for the diptheria toxin. After screening several lot of fetal bovine serum for diptheria antitoxin, a lot has been approved and purchased. After examining several methods for determining viable cells, the Neutral Red Assay has been selected. The U.S. Standard Diptheria Toxin Lot 35119 will be used for the cell death assay. It is currently used in the animal death test and will be used in the rabbit skin test. A reproducible minimum cytopathic dose is being established for the 4 day assay. Inhibition of cell death will be measured using the U.S. Standard Diptheria Antitoxin, Immune Serum Globulin, IGIV and guinea pig immune serum.
