Human IgG Fc-engineering for enhanced plasma half-life, mucosal distribution and killing of cancer cells and bacteria

Monoclonal IgG antibodies constitute the fastest growing class of therapeutics. Thus, there is an intense interest to design more potent antibody formats, where long plasma half-life is a commercially competitive differentiator affecting dosing, frequency of administration and thereby potentially patient compliance. Here, we report on an Fc-engineered variant with three amino acid substitutions Q311R/M428E/N434W (REW), that enhances plasma half-life and mucosal distribution, as well as allows for needle-free delivery across respiratory epithelial barriers in human FcRn transgenic mice. In addition, the Fc-engineered variant improves on-target complement-mediated killing of cancer cells as well as both gram-positive and gram-negative bacteria. Hence, this versatile Fc technology should be broadly applicable in antibody design aiming for long-acting prophylactic or therapeutic interventions.

Different glycosylation pattern of human IgG1 and IgG3 antibodies isolated from transiently as well as permanently transfected cell lines

The effector functions of IgG depend on the presence of carbohydrates attached to asparagine 297 in the Fc-portion. In this report, glycosylation profiles of recombinant wild-type and mutant IgG1 and IgG3 antibodies produced from three cell lines were analysed using LC-ESI-Orbitrap. Clear differences were detected between IgG1 and IgG3 glycoforms, where IgG1 generally contained fucosylated glycoforms, whilst IgG3 mainly were non-fucosylated. When using NS-0 and J558L cells for permanent transfection, IgG1 wt glycoforms differed between the two cell lines, whilst IgG3 wt glycoforms did not. Transiently transfected HEK 293E cells were used to produce IgG1 and IgG3 wt and mutants, affecting complement activation. Cell supernatants were harvested at early and late time points and analysed separately. IgGs harvested late showed simpler and less developed glycosylation structure compared to those harvested early. The IgG harvested early was slightly more effective in complement activation than those harvested late, whilst the antibody-dependent cell-mediated cytotoxicity was unaltered. Generally, the glycosylation pattern of the mutants tested, including a hinge truncate mutant of IgG3, did not differ significantly from the wild-type IgGs. The striking difference in glycosylation pattern of IgG1 compared to IgG3 therefore appears not to be due to the long hinge region of IgG3 (62 amino acids) relative to the IgG1 hinge region (15 amino acids). Furthermore, mutation variants at or near the C1q binding site showed similar glycosylation structure and difference in their complement activation activity observed earlier is thus most likely due to differences in protein structure only.

Structural difference in the complement activation site of human IgG1 and IgG3

The C1q binding epicentre on IgG molecules involves residues Asp(270), Lys(322), Pro(329) and Pro(331) in the C(H)2 domain. IgG1 and IgG3 are usually the most efficient of the four human IgG subclasses in activating complement and they both share all these residues. To reveal possible differences in the structural requirement for complement activation, we created a number of NIP (5-iodo-4-hydroxy-3-nitro-phenacetyl) specific IgG1 and IgG3 antibodies with parallel mutations in or near the putative C1q binding site. The mutants were tested simultaneously for antibody induced, antibody-dependent complement-mediated lysis (ADCML) at high and low antigen concentration on the target cells using sera of human, rabbit and guinea pig as complement source. In addition, we tested the antibodies against target cells decorated with the NP hapten, which has 10-fold lower affinity for the antibodies compared to the NIP hapten. We also used ELISA methods to measure complement activation. We observed a clear difference between IgG1 and IgG3 localized to residues Asp(270), Leu(334), Leu(335). For all these residues, and especially for Asp(270), IgG1 was heavily reduced in complement activation, while IgG3 was only moderated reduced, by alanine substitution. This difference was independent of the long hinge region of IgG3, demonstrated by hinge region truncation of this isotype such that it resembles that of IgG1. This report indicates the presence of structural differences between human IgG1 and IgG3 in the C1q binding site, and points to a specialization of the two isotypes with respect to complement activation.