Background: Treatment with the IgG1 anti-TNF antibodies infliximab and adalimumab achieves complete mucosal healing in a considerable proportion of patients with Crohn's disease. In contrast, the Fab' fragment certolizumab showed only 4% endoscopic remission. These observations suggest that the Fc-region of anti-TNF contributes to the induction of mucosal healing. We have previously showed that anti-TNF induces CD206+ regulatory macrophages and that these macrophages were increased in the lamina propria of anti-TNF responders, but not in non-responders. Here, we investigate the importance of Fc-gamma receptor (FcgR) engagement by anti-TNF for achieving therapeutic efficacy in IBD.
Methods: Rag1−/− mice lacking all activating FcgR were generated. We constructed hypo-fucosylated anti-murine TNF and hypo-fucosylated adalimumab. In vivo studies were performed in the T-cell transfer colitis model. For in vitro studies, T-cell proliferation and CD206+ macrophage percentages were measured in mixed lymphocyte reactions containing human PBMC from healthy donors.
Results: Anti-TNF treatment achieved near complete intestinal healing in the T-cell transfer model. However, mice lacking FcgR were completely unresponsive to anti-TNF therapy. In line with our previous human data, colons of mice treated with anti-TNF contained increased amounts of CD206+ macrophages, but this effect was completely abrogated in animals mice lacking FcgR. In vitro studies revealed that blocking FcgR III impaired the generation of human CD206+ macrophages. Further emphasizing the role of FcgRIII, CD206+ macrophage formation was increased in cultures composed of cells homozygous for high affinity FcgRIIIa158V compared to low affinity FcγRIIIa158F. Interestingly, hypo-fucosylation of the antibody Fc region enhances binding affinity specifically for FcgRIIIa. Indeed, hypo-fucosylation of anti-TNF increased the amount of CD206+ macrophages in vitro, especially for cells expressing low affinity FcgRIIIa158F. Finally, hypo-fucosylated anti-TNF increased the generation of CD206+ macrophages in the colon and displayed significantly improved therapeutic efficacy in vivo.
Conclusions: FcgR engagement by anti-TNF is required for the therapeutic efficacy in IBD. Increasing the Fc binding affinity of anti-TNF with hypo-fucosylation significantly improved therapeutic outcome. Anti-TNF therapy currently achieves mucosal healing in less than 50% of patients, antibody glycoengineering could be an effective future strategy and might be of special interest for patients carrying the low affinity FcgRIIIa158F allotype.