The effect of the removal of sialic acid, galactose and total carbohydrate on the functional activity of Campath-1H.

A monoclonal human IgG1, Campath-1H, was digested with glycosidases to assess the effect of carbohydrate on the functional activities of an IgG1. Removal of the complete carbohydrate moiety abolished complement lysis activity and antibody-dependent cell-mediated cytotoxicity, but left antigen binding activity and protein A binding activity intact. Removal of terminal sialic acid residues through glycopeptidase F digestion was not found to affect any of the tested IgG activities. Removal of the majority of the galactose residues from desialylated Campath-1H was found to reduce but not abolish complement lysis activity. Other activities were not affected by degalactosylation. This indicates a rare separation of complement lysis activity and antibody-dependent cell-mediated cytotoxicity of IgG in the way they behave under controlled conditions. This paper underlines the overall importance of carbohydrate in IgG function and stresses the relative contributions of some of the carbohydrate residues.

High-performance liquid chromatographic mapping of the oligosaccharides released from the humanised immunoglobulin, CAMPATH 1H.

A sensitive and reproducible method for the routine mapping of oligosaccharides in a humanised immunoglobulin (IgG) is described. The method involves the enzymic release of intact glycans using the endoglycosidase glycopeptidase-F, and subsequent derivatisation with 1-phenyl-3-methyl-5-pyrazolone to facilitate analysis by high-performance liquid chromatography (HPLC). The heterogeneous oligosaccharide chains are separated by a phosphate buffer-acetonitrile gradient reversed-phase HPLC method and monitored by ultraviolet detection at 245 nm, allowing the detection of picomole amounts. A number of standard oligosaccharides are similarly derivatised to enable classification of the types of structures present from a comparison of retention times.

Mass spectrometry of the humanized monoclonal antibody CAMPATH 1H.

Two mass spectrometric techniques, electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) have been used to study the intact humanized monoclonal antibody CAMPATH 1H, its fully and partially deglycosylated species, and 13 fragments prepared from it. The transformed ESI mass spectra of the glycosylated species gave complex patterns of molecular masses (M(r's). These have been substantially assigned to the presence of a mixture of glycoforms, each resulting from the combination of a single protein species with specific glycans of four distinct masses. The MALDI mass spectra of the glycosylated species, with the exception of that of the smallest fragment Fc/2, which indicated the presence of three of the glycans, gave single M(r) values comparable to the mean M(r) calculated from the ESI results. The M(r) values for the 10 prepared nonglycosylated species support the validity of the published amino acid sequence for the antibody and define the cleavage sites for the enzymic fragmentations. It is concluded that mass measurement of the Fc/2 fragment using ESI techniques provides a convenient means of preliminary assessment of the major glycosylated entities.