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CAMPATH-1 antibodies have a long and successful history in the treatment of leukaemia, autoimmune disease and transplant rejection. The first antibody to undergo "humanisation", CAMPATH-1H, permits treatment with limited patient anti-globulin response. It recognises the CD52 antigen which is a small glycosylphosphatidylinositol(GPI)-anchored protein expressed on lymphocytes and mediates cell depletion. We present the 1.9 A structure of the CAMPATH-1H Fab complexed [corrected] with an analogue of the antigenic determinant of CD52. Analysis of the CAMPATH-1H binding site reveals that in contrast to most antibodies CDR L3 plays a dominant role in antigen binding. Furthermore CDR H3, which is essential for effective antigen recognition in most antibodies, participates in only two main-chain interactions in CAMPATH-1H. The CAMPATH-1H binding site is highly basic; ionic interaction with the enthanolamine phosphate of the CD52 GPI anchor has long been hypothesised to be important in antigen binding. The structure reveals a number of important specific ionic interactions, including Lys53H but not Lys52bH as had previously been suggested. Prolonged treatment with CAMPATH-1H can lead to patient anti-idiotype responses which may be exacerbated by the unusually high number of basic residues in the antibody. This suggests that a strategy where redundant basic residues are replaced with neutral counterparts may be effective in further reducing the immunogenicity of this versatile and widely used antibody.

Original publication

DOI

10.1006/jmbi.1999.2750

Type

Journal article

Journal

J Mol Biol

Publication Date

04/06/1999

Volume

289

Pages

293 - 301

Keywords

Alemtuzumab, Amino Acid Sequence, Animals, Antibodies, Monoclonal, Antibodies, Monoclonal, Humanized, Antibodies, Neoplasm, Antigens, CD, Antigens, Neoplasm, Antineoplastic Agents, Binding Sites, Antibody, CD52 Antigen, CHO Cells, Computer Graphics, Cricetinae, Crystallography, X-Ray, Glycoproteins, Immunoglobulin Fab Fragments, Models, Molecular, Molecular Sequence Data, Protein Conformation, Protein Structure, Secondary, Recombinant Proteins, Transfection