A dominant linear B‐cell epitope of ricin A‐chain is the target of a neutralizing antibody response in Hodgkin's lymphoma patients treated with an anti‐CD25 immunotoxin

Hodgkin's lymphoma patients treated with an anti‐CD25 Ricin toxin A‐chain (RTA)‐based Immunotoxin (RFT5.dgA) develop an immune response against the toxic moiety of the immunoconjugate. The anti‐RTA antibody response of 15 patients showing different clinical features and receiving different total amounts of RFT5.dgA was therefore studied in detail, considering antibody titre, IgG and IgM content, average binding efficacy and ability to inhibit in vitro the cytotoxicity of a RTA‐based Immunotoxin. No correlations were found between these parameters and the clinical features of the patients or the total amount of Immunotoxin administered. However, using a peptide scan approach we have identified a continuous epitope recognized by all patients studied, located within the stretch L161‐I175 of the RTA primary sequence, close to a previously identified T‐cell epitope. The ability of anti‐L161‐I175 antibodies to recognize folded RTA and to affect the biological activity of RTA by inhibiting RTA‐IT cytotoxicity in vitro revealed that they may exert an important role in IT neutralization in vivo. Discovery of RTA immunodominant epitopes which are the target of anti‐RTA immune response may lead to the development of immunomodulating strategies and to more successful treatment schedules.

[1]  J. M. Zimmerman,et al.  The characterization of amino acid sequences in proteins by statistical methods. , 1968, Journal of theoretical biology.

[2]  L. Roberts,et al.  Expression of ricin A chain in Escherichia coli , 1987, FEBS letters.

[3]  R. Chignola,et al.  Sensitivity of human leukemia cells in exponential or stationary growth phase to anti-CD5 immunotoxins. Role of intracellular processing events. , 1994, Journal of immunology.

[4]  J. Lopez-Ribot,et al.  Identification of Continuous B-Cell Epitopes on the Protein Moiety of the 58-Kilodalton Cell Wall Mannoprotein ofCandida albicans Belonging to a Family of Immunodominant Fungal Antigens , 2001, Infection and Immunity.

[5]  R. Chignola,et al.  Self-potentiation of Ligand-Toxin Conjugates Containing Ricin A Chain Fused with Viral Structures (*) , 1995, The Journal of Biological Chemistry.

[6]  F. Turrini,et al.  Mapping Antigenic Sites of an Immunodominant Surface Lipoprotein of Mycoplasma agalactiae, AvgC, with the Use of Synthetic Peptides , 2002, Infection and Immunity.

[7]  J. Robertus,et al.  Structure of ricin A‐chain at 2.5 Å , 1991, Proteins.

[8]  Richard A. Lerner,et al.  Immunogenic structure of the influenza virus hemagglutinin , 1982, Cell.

[9]  V. Diehl,et al.  Immunotoxins constructed with anti‐CD25 monoclonal antibodies and deglycosylated ricin a‐chain have potent anti‐tumour effects against human hodgkin cells in vitro and solid hodgkin tumours in mice , 1991, International journal of cancer.

[10]  K. R. Woods,et al.  A computer program for predicting protein antigenic determinants. , 1983, Molecular immunology.

[11]  S. Rosen,et al.  Phase I trial of H65-RTA immunoconjugate in patients with cutaneous T-cell lymphoma. , 1991, Blood.

[12]  S. Wood,et al.  Crystal structure of momordin, a type I Ribosome Inactivating Protein from the seeds of Momordica charantia , 1994, FEBS letters.

[13]  R. F. Weaver,et al.  Genomic cloning and characterization of a ricin gene from Ricinus communis. , 1985, Nucleic acids research.

[14]  G. Fracasso,et al.  Identification of ricin A‐chain HLA class II‐restricted epitopes by human T‐cell clones , 2001, Clinical and experimental immunology.

[15]  S L Wiener.  Strategies for the prevention of a successful biological warfare aerosol attack. , 1996, Military medicine.

[16]  L. Barbieri,et al.  Purification and conjugation of type 1 ribosome-inactivating proteins. , 2001, Methods in molecular biology.

[17]  M. Kimura,et al.  Conserved amino acid residues in ribosome-inactivating proteins from plants. , 1991, Biochimie.

[18]  L. Roberts,et al.  Nucleotide sequence of cloned cDNA coding for preproricin. , 1985, European journal of biochemistry.

[19]  L. Weiner,et al.  Phase I evaluation of an anti-breast carcinoma monoclonal antibody 260F9-recombinant ricin A chain immunoconjugate. , 1989, Cancer research.

[20]  A. Lanzavecchia,et al.  Modulation of antigen processing by bound antibodies can boost or suppress class II major histocompatibility complex presentation of different T cell determinants , 1995, The Journal of experimental medicine.

[21]  A. Monzingo,et al.  The 2.5 A structure of pokeweed antiviral protein. , 1993, Journal of molecular biology.

[22]  E. Sausville,et al.  The emerging role of ricin A-chain immunotoxins in leukemia and lymphoma. , 1998, Current topics in microbiology and immunology.

[23]  J. Berzofsky,et al.  T cell recognition of hypervariable region-1 from hepatitis C virus envelope protein with multiple class II MHC molecules in mice and humans: preferential help for induction of antibodies to the hypervariable region. , 1999, Journal of immunology.

[24]  S. Steinberg,et al.  Continuous infusion of the anti-CD22 immunotoxin IgG-RFB4-SMPT-dgA in patients with B-cell lymphoma: a phase I study. , 1995, Blood.

[25]  E. Vitetta,et al.  Immunotoxins: an update. , 1996, Annual review of immunology.

[26]  J. Janin,et al.  Surface and inside volumes in globular proteins , 1979, Nature.

[27]  E. Oldfield,et al.  Tumor regression with regional distribution of the targeted toxin TF-CRM107 in patients with malignant brain tumors , 1997, Nature Medicine.

[28]  V. Diehl,et al.  A phase-I study of an anti-CD25 ricin A-chain immunotoxin (RFT5-SMPT-dgA) in patients with refractory Hodgkin's lymphoma. , 1997, Blood.

[29]  Ira Pastan,et al.  Immunotoxins in cancer therapy. , 1999, Current opinion in investigational drugs.

[30]  J. Uhr,et al.  Immunotoxins: magic bullets or misguided missiles? , 1993, Trends in pharmacological sciences.

[31]  W J Harris,et al.  Humanized antibodies. , 1993, Trends in pharmacological sciences.

[32]  M. A. Olson,et al.  Prediction of a conserved, neutralizing epitope in ribosome-inactivating proteins. , 1999, International journal of biological macromolecules.

[33]  M S Doscher,et al.  Solid-phase peptide synthesis. , 1977, Methods in enzymology.

[34]  L. Roberts,et al.  Ribosome inactivating proteins of plants. , 1991, Seminars in cell biology.

[35]  A. Monzingo,et al.  Structure of recombinant ricin A chain at 2.3 Å , 1993, Protein science : a publication of the Protein Society.

[36]  R. Macklis,et al.  Selective depletion of bone marrow T lymphocytes with anti-CD5 monoclonal antibodies: effective prophylaxis for graft-versus-host disease in patients with hematologic malignancies. , 1991, Blood.

[37]  S. Herrera,et al.  Plasmodium vivax malaria vaccine development. , 2001, Molecular immunology.

[38]  V. Diehl,et al.  Treatment of refractory Hodgkin's lymphoma patients with an anti-CD25 ricin A-chain immunotoxin , 2000, Leukemia.

[39]  R. W. Baldwin,et al.  Phase I study of monoclonal antibody-ricin A chain immunotoxin XomaZyme-791 in patients with metastatic colon cancer. , 1989, Cancer research.