title: Recombinant immunotoxin engineered for low immunogenicity and antigenicity by identifying and silencing human B-cell epitopes.
abstract: Recombinant immunotoxins (RITs) are hybrid proteins used to treat cancer. These proteins are composed of an Fv that reacts with cancer cells joined to a portion of Pseudomonas exotoxin A, which kills the cell. Because the toxin is a foreign protein, it can induce neutralizing antibodies and thereby limit the number of doses a patient can receive. We previously identified seven major mouse B-cell epitopes in the toxin, and subsequently silenced them using point mutations that converted large hydrophilic amino acids to alanine, yet retained full antitumor activity. Here we present results in which we identify and silence human B-cell epitopes in the RIT HA22. We obtained B cells from patients with antibodies to RITs, isolated the corresponding variable fragments (Fvs), and constructed a phage-display library containing Fvs that bind to the RITs. We then used alanine scanning mutagenesis to locate the epitopes. We found that human and mouse epitopes frequently overlap but are not identical. Most mutations that remove mouse epitopes did not remove human epitopes. Using the epitope information, we constructed a variant immunotoxin, HA22-LR-LO10, which has low reactivity with human antisera, yet has high cytotoxic and antitumor activity and can be given to mice at high doses without excess toxicity. The toxin portion of this RIT (LR-LO10) can be used with Fvs targeting other cancer antigens and is suitable for clinical development.
authors: Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors: Wenhai
authors: W
authors: Liu
authors: Masanori
authors: M
authors: Onda
authors: Byungkook
authors: B
authors: Lee
authors: Robert J
authors: RJ
authors: Kreitman
authors: Raffit
authors: R
authors: Hassan
authors: Laiman
authors: L
authors: Xiang
authors: Ira
authors: I
authors: Pastan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000970:Antineoplastic Agents / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D018985:Epitopes, B-Lymphocyte / Q000276:immunology*; D006801:Humans; D007167:Immunotherapy / Q000379:methods*; D000922:Immunotoxins / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000493:pharmacokinetics; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009369:Neoplasms / Q000188:drug therapy* / Q000276:immunology; D019151:Peptide Library; D015202:Protein Engineering / Q000379:methods; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000493:pharmacokinetics; D057127:Single-Chain Antibodies / Q000276:immunology; D018709:Statistics, Nonparametric
chemical_list: D000970:Antineoplastic Agents; D018985:Epitopes, B-Lymphocyte; D000922:Immunotoxins; D019151:Peptide Library; D011994:Recombinant Proteins; D057127:Single-Chain Antibodies