title: WITHDRAWN: Letter to the Editor.
abstract: This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.
authors.affiliation: University of Pennsylvania, Wistar Institute, Aventis Pasteur, 4650 Wismer Road, Doylestown, PA 18901, United States. Electronic address: stanley.plotkin@aventis.com.
authors.forename: S A
authors.initials: SA
authors.lastname: Plotkin