Aglycosylated antibodies and the methods of making and using them: WO2008030564

Construction and expression of a human/mouse chimeric CD19 monoclonal antibody: Successful modification of a murine IgM to a chimeric IgG

CD19 is a specific surface marker of B cells. A murine IgM-subtype antibody, 2E8, was generated previously and assigned to the CD19 category by the 6th International Workshop and Conference on Human Leukocyte Differentiation Antigens in 1996. In the present study, the 2E8 Fv gene was inserted into a baculovirus shuttle vector and novel protein was expressed in an IgG1 form in the Sf9 insect cell line. VH_2E8 and VL_2E8 genes were cloned and inserted into the baculovirus shuttle vector pAc-κ-CH3 to form pAc-κ-CH3-VH_2E8-VL_2E8. Sf9 cells were then transfected with the reconstructed baculovirus shuttle vector. Novel protein expressed by the Sf9 cells was identified by immunofluorescence and western blot analysis, while activity levels were analyzed by flow cytometry (FCM). Sequencing demonstrated that the VH_2E8 and VL_2E8 fragments were inserted into pAc-κ-CH3 correctly. The immunofluorescence, western blot analysis and FCM results indicated that active recombinant antibody was expressed in the cytoplasm of Sf9 cells, but not in the culture supernatant. Thus, functional recombinant antibody was expressed successfully in the cytoplasm of Sf9 cells, but was not secreted into the culture supernatant. Therefore, the present study demonstrates that it is possible to modify mouse IgM to mouse-human chimeric IgG1 while retaining reasonable biological activity.

Revisiting the role of glycosylation in the structure of human IgG Fc

Binding of the Fc domain of Immunoglobulin G (IgG) to Fcγ receptors on leukocytes can initiate a series of signaling events resulting in antibody-dependent cell-mediated cytotoxicity (ADCC) and other important immune responses. Fc domains lacking glycosylation at N297 have greatly diminished Fcγ receptor binding and lack the ability to initiate a robust ADCC response. Earlier structural studies of Fc domains with either full length or truncated N297 glycans led to the proposal that these glycans can stabilize an "open" Fc conformation recognized by Fcγ receptors. We determined the structure of an E. coli expressed, aglycosylated human Fc domain at 3.1 Å resolution and observed significant disorder in the C'E loop, a region critical for Fcγ receptor binding, as well as a decrease in distance between the C(H)2 domains relative to glycosylated Fc structures. However, comparison of the aglycosylated human Fc structure with enzymatically deglycosylated Fc structures revealed large differences in the relative orientations and distances between C(H)2 domains. To provide a better appreciation of the physiologically relevant conformation of the Fc domain in solution, we determined Radii of Gyration (R(g)) by small-angle X-ray scattering (SAXS) and found that the aglycosylated Fc displays a larger R(g) than glycosylated Fc, suggesting a more open C(H)2 orientation under these conditions. Moreover, the R(g) of aglycosylated Fc was reduced by mutations at the C(H)2-C(H)3 interface (E382V/M428I), which confer highly selective binding to FcγRI and novel biological activities.

Galactosylation variations in marketed therapeutic antibodies

There are currently ~25 recombinant full-length IgGs (rIgGs) in the market that have been approved by regulatory agencies as biotherapeutics to treat various human diseases. Most of these are based on IgG1k framework and are either chimeric, humanized or human antibodies manufactured using either Chinese hamster ovary (CHO) cells or mouse myeloma cells as the expression system. Because CHO and mouse myeloma cells are mammalian cells, rIgGs produced in these cell lines are typically N-glycosylated at the conserved asparagine (Asn) residues in the CH2 domain of the Fc, which is also the case with serum IgGs. The Fc glycans present in these rIgGs are for the most part complex biantennary oligosaccharides with heterogeneity associated with the presence or the absence of several different terminal sugars. The major Fc glycans of rIgGs contain 0 or 1 or 2 (G0, G1 and G2, respectively) terminal galactose residues as non-reducing termini and their relative proportions may vary depending on the cell culture conditions in which they were expressed. Since glycosylation is strongly associated with antibody effector functions and terminal galactosylation may affect some of those functions, a panel of commercially available therapeutic rIgGs expressed in CHO cells and mouse myeloma cells were examined for their galactosylation patterns. The results suggest that the rIgGs expressed in CHO cells are generally less galactosylated compared to the rIgGs expressed in mouse myeloma cells. Accordingly, rIgGs produced in CHO cells tend to contain higher levels of G0 glycans compared with rIgGs produced in mouse myeloma cell lines. Despite the apparent wide variability in galactose content, adverse events or safety issues have not been associated with specific galactosylation patterns of therapeutic antibodies. Nevertheless, galactosylation may have an effect on the mechanisms of action of some therapeutic antibodies (e.g., effector pathways) and hence further studies to assess effects on product efficacy may be warranted for such antibodies. For antibodies that do not require effector functions for biological activity, however, setting a narrow specification range for galactose content may be unnecessary.

Mutational deglycosylation of the Fc portion of immunoglobulin G causes O-sulfation of tyrosine adjacently preceding the originally glycosylated site

Mutagenesis directed to a specific glycosylation site has been widely used to examine biological roles of individual glycans. However, occurrence of any post-translational modification on such deglycosylated mutants has not yet been well characterized. Here we performed mass spectrometric analyses of the Fc fragment of an unglycosylated mutant of mouse immunoglobulin G2b, whose conserved N-glycosylation site, i.e. Asn297, was substituted with alanine. We found that a major part of this mutant is sulfated at Tyr296, which adjacently precedes the originally glycosylated site. Our findings demonstrate that mutational deglycosylation can induce an unexpected post-translational modification in the protein.