HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Perosa, F. Articles by Dammacco, F. Search for Related Content PubMed PubMed Citation Articles by Perosa, F. Articles by Dammacco, F.

Two Structurally Different Rituximab-Specific CD20 Mimotope Peptides Reveal That Rituximab Recognizes Two Different CD20-Associated Epitopes¹

Federico Perosa^2,*, Elvira Favoino^*, Chiara Vicenti^*, Andrea Guarnera, Vito Racanelli^*, Vito De Pinto and Franco Dammacco^*

^* Department of Internal Medicine and Clinical Oncology, University of Bari Medical School, Bari, Italy; and Department of Chemical Sciences, Section of Molecular Biology, University of Catania, Catania, Italy

Peptide mimotopes of the CD20 epitope recognized by rituximab are useful tools for studying this therapeutic mAb’s functional properties. We previously identified two structurally different peptides that are both effective mimotopes: a 7-mer cyclic peptide (Rp15-C) bearing the antigenic motif a/sNPS that matches ¹⁷⁰ANPS¹⁷³ of the extracellular loop of CD20, and a 12-mer linear peptide (Rp5-L) containing the antigenic motif WPxWLE lacking sequence homology to CD20. In this study, we investigated whether the different structures of Rp15-C and Rp5-L reflect the mimicry of the same or different CD20 epitopes recognized by rituximab. Using immunochemical methods, we found that, like Rp15-C, Rp5-L mimics the raft-associated form of CD20 (by inhibiting rituximab binding to CD20 in vitro). Rp5-L and Rp15-C elicit, in immunized mice, anti-CD20 Abs that stain CD20⁺ cells with a punctate pattern similar to that of rituximab. However, only anti-Rp5-L Abs recognize denatured CD20. When phage-display peptide libraries were panned with anti-Rp5-L, phage clones were enriched that expressed the consensus qWPxwL, similar to the antigenic motif WPxWLE, but not matching a/sNPS. Finally, WPxWLE and ANPS share some, but not all, contact sites within the rituximab Ag-combining site, indicating that WPxWLE is not an exact replica of Rp15-C (or CD20) ANPS. Altogether, these results indicate that the two structurally different peptides are also conformationally different, and suggest that rituximab recognizes two different CD20-associated epitopes.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by a grant (2007–2008) from Associazione Italiana per la Ricerca sul Cancro, Milan, Italy.

² Address correspondence and reprint requests to Dr. Federico Perosa, Department of Internal Medicine and Clinical Oncology, University of Bari Medical School, Piazza G. Cesare 11, I-70124 Bari, Italy. E-mail address: f.perosa{at}dimo.uniba.it

³ Abbreviations used in this paper: PDPL, phage-display peptide library; CTB, cholera toxin subunit B; KLH, keyhole limpet hemocyanin.