Department of Biological Technologies, Wyeth Research, 35 CambridgePark Drive, Cambridge, MA 02140, USA. ahill@wyeth.com|Department of Biological Technologies, Wyeth Research, 35 CambridgePark Drive, Cambridge, MA 02140, USA. ahill@wyeth.com|Department of Biological Technologies, Wyeth Research, 35 CambridgePark Drive, Cambridge, MA 02140, USA. ahill@wyeth.com|Department of Biological Technologies, Wyeth Research, 35 CambridgePark Drive, Cambridge, MA 02140, USA. ahill@wyeth.com