B3

Antibody Name: B3(Fv)-PE38
References: Benhar, I., Padlan, E.A., Jung, S-H., Lee, B. and Pastan I. "Rapid humanization of the Fv of monoclonal antibody B3 by using framework exhange of the recombinant immunotoxin B3(Fv)-PE38" Proc. Natl. Acad. Sci. USA (1994) 91:12051-12055.
Donor Antibody: mouse
Acceptor Antibody: Human Fv fused to truncated form of Pseudomonas exotoxin (PE) (Single-chain immunotoxin).
Antigen: Lewis Y related Carbohydrate
Laboratory: National Institutes of Health, MD
Design: "Framework Exchange" - Identify different FR residues in highly homologous human VH or VL chains and mutate. Some mouse residues are kept. Thus some buried residues are humanised, and some exposed residues are kept mouse. A structural model was also built.
Frameworks: VH 56P1'CL | VL GM607
CDRs: All 6 VH and VL, Kabat Definition.
Backmutations: Veneering changes (mouse to human):
VH L11V G16R T40A E42G R44G A74S R75K S82aN 82b K83R S84A
VL S14T L15P D17E Q18P K45Q L83V
Additional changes: S100Q L104V
Backmutations of veneered residues (human to mouse):
VH E3K R19K A24T V89I Y91S
VL I2V V3L Q41G Additional change to restore activity
VH S82bR
Binding: Final humanised version was "similar" to mouse scFV in competition binding and cytotoxic activity assays. Also loss of immunogenic primate epitopes.
Expression: Expressed as inclusion bodies in E. coli strain BL21.
Comment: Positions 82b:H and 104:L were found to be important in restoring activity and binding.
Clinical Indication: Being developed as therapeutic agent to deliver radioisotopes or toxins to tumours and for diagnosis of cancer.

explanation of symbols and abbreviations

José Saldanha © 1997-8. Birkbeck College, London WC1E 7HX.