title: Identification of ricin A-chain HLA class II-restricted epitopes by human T-cell clones.
abstract: The identification of ricin toxin A-chain (RTA) epitopes and the molecular context in which they are recognized will allow strategies to be devised that prevent/suppress an anti-RTA immune response in patients treated with RTA-based immunotoxins. RTA-specific human T-cell lines and T-cell clones were produced by in vitro priming of PBMC. The T-cell clones used a limited set of Vbeta chains (Vbeta1, Vbeta2 and Vbeta8) to recognize RTA epitopes. The use of RTA deletion mutants demonstrated that T-cell lines and T-cell clones from three out of four donors responded to RTA epitopes within the domain D124-Q223, whereas one donor recognized the region I1-D124. The response to RTA peptides of T-cell lines and T-cell clones from two donors allowed the identification of immunogenic segments (D124-G140 and L161-T190) recognized in the context of different HLA-DRB1 alleles (HLA-DRB1*0801, and HLA-DRB1*11011 and B1*03011, respectively). The response to L161-T190 was investigated in greater detail. We found that the HLA-DRB1*03011 allele presents a minimal epitope represented by the sequence I175-Y183 of RTA, whereas the HLA-DRB1*11011 allele presents the minimal epitope M174-I184. RTA peptides and an I175A RTA point mutant allowed us to identify I175 as a crucial residue for the epitope(s) recognized by the two HLA-DRB1 alleles. Failure of T-cell clones to recognize ribosome inactivating proteins (RIPs) showing sequences similar but not identical to RTA further confirmed the role of I175 as a key residue for the epitope recognized in the context of HLA-DRB1*11011/03011 alleles.
authors.affiliation: Section of Immunology, Department of Pathology, University of Verona, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Tommasi
authors.forename: D
authors.initials: D
authors.lastname: Castelletti
authors.forename: M
authors.initials: M
authors.lastname: Pasti
authors.forename: G
authors.initials: G
authors.lastname: Fracasso
authors.forename: I
authors.initials: I
authors.lastname: Lorenzetti
authors.forename: S
authors.initials: S
authors.lastname: Sartoris
authors.forename: C
authors.initials: C
authors.lastname: Pera
authors.forename: G B
authors.initials: GB
authors.lastname: Ferrara
authors.forename: G
authors.initials: G
authors.lastname: Tridente
authors.forename: M
authors.initials: M
authors.lastname: Colombatti
mesh_terms: D000595:Amino Acid Sequence; D002999:Clone Cells; D000939:Epitopes; D019673:Genes, T-Cell Receptor alpha; D006684:HLA-DR Antigens / Q000276:immunology*; D015803:HLA-DR3 Antigen / Q000276:immunology; D059811:HLA-DRB1 Chains; D006801:Humans; D000922:Immunotoxins; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000276:immunology; D012276:Ricin / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*; D006377:T-Lymphocytes, Helper-Inducer; D014611:Vaccination
chemical_list: D000939:Epitopes; D006684:HLA-DR Antigens; D015803:HLA-DR3 Antigen; D059811:HLA-DRB1 Chains; C553518:HLA-DRB1*11:01:01 antigen; D000922:Immunotoxins; D010446:Peptide Fragments; D012276:Ricin