Genetic construction and characterization of an anti-monkey CD3 single-chain immunotoxin with a truncated diphtheria toxin.
We have previously developed a chemically conjugated anti-rhesus monkey CD3 immunotoxin FN18-CRM9 that can deplete in vivo T cells and induce long term tolerance of mismatched renal allograft in rhesus monkeys. This immunotoxin is a monkey analogue of anti-human CD3 immunotoxin UCHT1-CRM9. In this study, we cloned the light and heavy chain variable regions of anti-monkey CD3 monoclonal antibody FN18 and constructed a single-chain Fv (sFv) by linking variable light and variable heavy regions with a (Gly4Ser)3 linker. The single-chain immunotoxin DT390-FN18sFv was constructed by ligating the sFv to the carboxyl terminus of DT390, a truncated form of diphtheria toxin. The DT390-FN18sFv fusion protein was expressed in Escherichia coli and purified with Ni-RTA affinity and anion exchange columns. Similar to the chemically conjugated immunotoxin FN18-CRM9, DT390-FN18sFv can also specifically inhibit protein synthesis in primary monkey T cells in a dose-dependent manner. DT390-FN18sFv at 10(-7) mol/L or FN18-CRM9 at 10(-8) mol/L is sufficient to reduce protein synthesis of monkey primary T cells to less than 5% of the control. The 50% inhibition dosage (IC50) of FN18-CRM9 is 1 x 10(-10) mol/L, while the IC50 of DT390-FN18sFv is 1 x 10(-8) mol/ L, reflecting the lowered affinity of monovalent Fab' FN18 to its parental divalent antibody. The availability of functional FN18sFv will provide the basis for the construction of divalent anti-CD3 immunotoxins for preclinical studies on the induction of tolerance in organ transplantation and experimental autoimmune diseases.
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Section on Biophysical Chemistry, National Institute of Mental Health, National Institutes of Health, Bethesda, Maryland 20892-4034, USA.
Hu
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Thompson
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Stavrou
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Scharff
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Neville
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D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D017252:CD3 Complex / Q000235:genetics*; D002469:Cell Separation; D003001:Cloning, Molecular; D003602:Cytotoxicity, Immunologic; D004167:Diphtheria Toxin / Q000235:genetics*; D004926:Escherichia coli / Q000378:metabolism; D005453:Fluorescence; D006825:Hybridomas / Q000378:metabolism; D000922:Immunotoxins / Q000235:genetics* / Q000302:isolation & purification; D008253:Macaca mulatta / Q000276:immunology; D008969:Molecular Sequence Data; D009154:Mutation; D013601:T-Lymphocytes / Q000276:immunology
D017252:CD3 Complex; D004167:Diphtheria Toxin; D000922:Immunotoxins; D000246:Adenosine Diphosphate Ribose