Quantitative in vivo comparisons of the Fcγ receptor-dependent agonist activities of different fucosylation variants of an immunoglobulin G antibody

Although it has been shown that functions of immunoglobulin G (IgG) antibodies (Abs) that depend on binding to certain Fcγ receptors (FcγR) can be influenced by Fc glycan fucosylation, quantitative in vivo analyses comparing the effects of different levels of fucose are still lacking. We used a simple mouse model to compare FcγR-dependent T cell activation induced by different fucosylation variants of a hamster/human IgG1 chimeric version of anti-mouse CD3 monoclonal Ab, 145-2C11 (2C11). Initial studies supported the expectation that this agonist activity by 2C11 was a reflection of FcγR binding, including comparisons of human IgG1 and IgG4 variants of 2C11 that showed the IgG4 to be dramatically less active at inducing T cell activation. Dose–response analyses in mice then showed that a sample of the human IgG1 version of 2C11 Ab in which 40% of the Fc glycans in the population of Ab molecules were fucosylated was 3–5 times more potent than a sample with 90% of its Fc glycans fucosylated. A sample with 10% fucosylation showed the same activity as the 40% fucosylated sample, revealing that complete absence of fucose was not necessary to achieve maximal Fc function in this model. In vitro binding to recombinant mouse FcγRs by the 2C11 variants revealed interesting relationships between fucose content and receptor affinity, and suggested the involvement of FcγRIV in mediating 2C11 activity in vivo. These analyses showed that low-fucose human IgG1 Abs indeed show greater FcγR-dependent activities in mice, but that Abs with moderate levels of fucose may be just as potent as Abs with very low or no fucose.