PEDS Advance Access originally published online on August 17, 2004
Protein Engineering Design and Selection 2004 17(5):481-489; doi:10.1093/protein/gzh056
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Humanization of the anti-CEA T84.66 antibody based on crystal structure data
1Department of Radioimmunotherapy, 6Division of Radiology and 7Division of Radiation Oncology, City of Hope National Medical Center, 1500 East Duarte Road, Duarte, CA 91010, 4Division of Information Sciences and 5Division of Immunology, Beckman Research Institute of the City of Hope, Duarte, CA 91010 and 8Department of Molecular and Medical Pharmacology, Crump Institute for Molecular Imaging, University of California School of Medicine, Los Angeles, CA 90095, USA
3 To whom correspondence should be addressed. E-mail: pyazaki{at}coh.org
Chimeric T84.66 (cT84.66) is a monoclonal antibody (mAb) of high specificity and affinity for the tumor-associated carcinoembryonic antigen (CEA). Radiolabeled cT84.66 has demonstrated utility in the clinic as a reagent for the radioimmunoscintigraphy and radioimmunotherapy of CEA-positive colorectal and breast malignancies. To extend the therapeutic efficacy of T84.66, humanization by complementary determining region (CDR) grafting was employed. CDR grafting is a well-established technique, though often a series of framework back-mutations is required to restore high affinity. Recently, the crystal structure of the T84.66 diabody (scFv dimer) derived from the murine T84.66 mAb was determined, facilitating the humanization process by the availability of crystal structure data for both the graft donor and graft acceptor. A search of the Protein Data Bank revealed close structural similarity (r.m.s.d. of 1.07 Å) between the Fv of T84.66 and the Fv of 4D5v8, a humanized anti-p185HER2 antibody marketed as Herceptin® (Trastuzumab). This resulted in two humanized versions of the T84.66 M5A and M5B mAbs that differed only in the number of murine residues present in the C-terminal half of CDR-H2. Biochemical analysis and animal biodistribution studies were conducted to evaluate the humanized mAbs. The M5A, M5B and cT84.66 mAbs showed sub-nanomolar affinity for CEA and as radiolabeled mAbs exhibited specific tumor localization in tumor bearing mice. The T84.66 M5A mAb was selected for clinical development due to a slightly higher tumor uptake and a larger content of human residues, and was renamed hT84.66. A limited-scale production and animal imaging study have demonstrated hT84.66's ability to support clinical trials. Planned clinical trials will determine the effective utilization of this structure-based approach in the development of a promising new therapeutic.
Received April 9, 2004; accepted June 3, 2004.
Edited by Hennie Hoogenboom
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  T. Olafsen, V. E. Kenanova, G. Sundaresan, A.-L. Anderson, D. Crow, P. J. Yazaki, L. Li, M. F. Press, S. S. Gambhir, L. E. Williams, et al. Optimizing Radiolabeled Engineered Anti-p185HER2 Antibody Fragments for In vivo Imaging Cancer Res., July 1, 2005; 65(13): 5907 - 5916. [Abstract] [Full Text] [PDF]
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