DEBORAH CASTELLETTI:  FRIDAY 31 MARCH 2006, 15:05

T-cell and B-cell epitopes triggering a human immune response against ricin A-chain

D. Castelletti, M. Tommasi, R. Schnell¹, A. Engert¹, and M. Colombatti
Section of Immunology, Department of Pathology, University of Verona, Italy; ¹Klinik I für Innere Medizin, Universität Köln, Germany

Ricin A-chain-based immunotoxins (RTA-IT) have yielded promising results mainly in the treatment of leukaemia and lymphomas. However, in most of the reported studies generation of neutralizing anti-IT antibodies have limited their clinical impact. Investigating the immunologic profile of RTA represents a crucial pre-requisite to elaborate epitope-targeted immunomodulating strategies.

A peptide scan approach enabled to map T-cell epitopes of RTA recognized by anti-RTA T-cell clones, generated from in vitro immunizations of peripheral blood mononuclear cells (PBMC) of healthy donors. T-cell proliferative response to the whole antigen and to RTA-derived peptides was assayed in the presence of homozygous B-lymphoblastoid cell lines, thus allowing to define two minimal T-cell epitopes, i.e. I175-Y183 and M174-I184, presented in the context of HLA-DRB1*03011 and HLA-DRB1*11011, respectively. Alanine substitutions of the I175-Y183 peptide allowed to evaluate the role of discrete residues in T-cell activation, e.g. I175 as the primary anchor. One Altered Peptide Ligand behaved as antagonist by preventing T-cells from being activated by the wild-type I175-Y183 peptide. Anti-RTA antibodies elicited in Hodgkin’s lymphoma patients treated with an anti-CD25 RTA-based IT were purified by immunoaffinity and assayed in ELISA for the binding ability to a panel of RTA-derived peptides. A major linear B-cell epitope was found, located within the stretch L161-I175 of RTA and close to the dominant T-cell epitope. Anti-L161-I175 antibodies recognized folded RTA and affected the toxin’s biological activity by inhibiting RTA-based IT cytotoxicity in vitro .

PREVIOS ABSTRACT    NEXT ABSTRACT   BACK TO PROGRAM