A cell-permeable nanobody to restore F508del cystic fibrosis transmembrane conductance regulator activity.

Nanobodies are emerging as attractive biopharmaceuticals due to their small size, stability and target specificity. However, their therapeutic use has largely been restricted to extracellular targets because of a lack of efficient delivery methods. This limitation is particularly relevant for diseases caused by dysfunctional intracellular proteins, such as cystic fibrosis. Here we show that cell-permeable nanobodies can modulate an intracellular disease-relevant target: the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel carrying the common F508del mutation. By combining a CFTR-binding nanobody with cell-penetrating peptides, we achieved intracellular delivery in cystic fibrosis bronchial epithelial cells. The delivered nanobody stabilizes misfolded F508del-CFTR, promotes its maturation and trafficking to the apical membrane and restores chloride channel activity. Moreover, the cell-permeable nanobody enhances the efficacy of approved CFTR modulator drug combination in primary airway epithelial cultures from patients with cystic fibrosis. These findings establish cell-permeable nanobodies as promising biopharmaceuticals for intracellular protein targeting and therapeutic modulation.