title: Cytotoxic activity of disulfide-stabilized recombinant immunotoxin RFB4(dsFv)-PE38 (BL22) toward fresh malignant cells from patients with B-cell leukemias.
abstract: Chemical conjugates of anti-CD22 monoclonal antibodies and toxins have been used to treat CD22+ hematological malignancies. A new anti-CD22 recombinant immunotoxin RFB4(dsFv)-PE38, composed of the Fv portion of the monoclonal antibody RFB4 fused to a truncated form of Pseudomonas exotoxin A, is being developed to target CD22+ tumor cells. To explore the potential clinical utility of this recombinant toxin in treating patients with B-cell malignancies, the fresh cells of patients were incubated ex vivo with RFB4(dsFv)-PE38. Specific cytotoxicity was demonstrated in the malignant cells of 25 of 28 patients with a variety of B-cell malignancies, including acute and chronic lymphocytic leukemias and large cell, mantle cell, and follicular lymphomas. The IC50S, the concentrations necessary for 50% inhibition of protein synthesis, were 3-10 ng/ml in five patients and 10-50 ng/ml in seven patients. Cytotoxicity correlated with cell death upon direct examination of the malignant cells. Significant cytotoxicity was observed with cells containing as few as 350 CD22 sites/cell. A more active derivative of RFB4(dsFv)-PE38, RFB4(dsFv)-PE38KDEL, was produced and was slightly to more than 10-fold more cytotoxic toward patient cells and about twice as toxic to mice. Thus, RFB4(dsFv)-PE38 was specifically cytotoxic toward malignant cells from patients with B-cell leukemias. These data support the testing of RFB4(dsFv)-PE38 in patients with CD22+ leukemias and lymphomas, which is presently under way.
authors.affiliation: Laboratory of Molecular Biology, Division of Cancer Biology, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Kreitman
authors.forename: I
authors.initials: I
authors.lastname: Margulies
authors.forename: M
authors.initials: M
authors.lastname: Stetler-Stevenson
authors.forename: Q C
authors.initials: QC
authors.lastname: Wang
authors.forename: D J
authors.initials: DJ
authors.lastname: FitzGerald
authors.forename: I
authors.initials: I
authors.lastname: Pastan
mesh_terms: D000911:Antibodies, Monoclonal / Q000235:genetics / Q000494:pharmacology*; D000918:Antibody Specificity; D015703:Antigens, CD / Q000276:immunology*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000276:immunology*; D001665:Binding Sites; D015815:Cell Adhesion Molecules; D016923:Cell Death / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003602:Cytotoxicity, Immunologic; D004274:DNA, Recombinant / Q000235:genetics; D004220:Disulfides / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007128:Immunoglobulin Fragments / Q000235:genetics / Q000494:pharmacology; D000922:Immunotoxins / Q000235:genetics / Q000276:immunology / Q000494:pharmacology*; D020128:Inhibitory Concentration 50; D037102:Lectins; D015448:Leukemia, B-Cell / Q000188:drug therapy* / Q000276:immunology / Q000473:pathology; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000187:drug effects; D009154:Mutation; D010957:Plasmids; D014176:Protein Biosynthesis; D011506:Proteins / Q000187:drug effects; D051918:Sialic Acid Binding Ig-like Lectin 2; D013997:Time Factors; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; C497867:CD22 protein, human; D015815:Cell Adhesion Molecules; D004274:DNA, Recombinant; D004220:Disulfides; D007128:Immunoglobulin Fragments; D000922:Immunotoxins; D037102:Lectins; D011506:Proteins; D051918:Sialic Acid Binding Ig-like Lectin 2; C055966:immunoglobulin Fv