The concept of grafting mannose 6-phosphonate derivatives (M6Pn), named AMFA, on therapeutic proteins was first developed for the improvement of enzyme delivery in lysosomal storage disorders. This glycoengineering increases the cellular uptake of the protein via the cation-independent mannose 6-phosphate receptor (M6PR) which further allows their targeting to the lysosomes. In the present study, we investigated the extent to which the direct grafting of AMFA onto a drug, here a monoclonal antibody (mAb), affects the cell uptake and recycling of the antibody. The antibodies infliximab (IFX) and adalimumab (ADA), directed against the tumor necrosis factor α (TNFα), grafted with AMFA acquired an affinity for the M6PR, resulting in a >3-fold increase in drug release in cells. Subsequently, the impact of AMFA grafting to the Fc portion of mAb on its affinity for the neonatal Fc receptor (FcRn), which is the key receptor for antibody recycling, was evaluated. Whether one to three AMFA moieties were grafted, FcRn-mediated recycling of mAb were not affected. AMFA grafting did not impair the pharmacokinetics of both ADA and IFX and presented a high stability since AMFA were still bound to mAb in the plasma of mice 21 days after the treatment. In conclusion, this type of antibody engineering with a reduced number of AMFA confers M6PR targeting property and increases endocytosis, and yet appears fully compatible with FcRn binding and with antibody recycling and transcytosis.