1. Department of Cancer Research, Merck and Company, Sumneytown Pike, West Point, PA 19454, U.S.A.
2. Department of Biological Chemistry, Merck and Company, Sumneytown Pike, West Point, PA 19454, U.S.A.
3. Department of Bioprocess Engineering, Merck and Company, Sumneytown Pike, West Point, PA 19454, U.S.A.