High Affinity Nanobodies against the Trypanosome brucei VSG Are Potent Trypanolytic Agents that Block Endocytosis

• DOI: 10.1371/journal.ppat.1002072
• Publication Date: 2011-11-26T22:56:59Z
• Authors: Benoît Stijlemans; Guy Caljon; Senthil Kumar A. ...; Dirk Saerens; Katja Conrath; David Pérez-Morga; Jeremy N. Skepper; Alexandros Nikolaou; Lea Brys; Etienne Pays; Stefan Magez; Mark C. Field; Patrick De Baetse...; Serge Muyldermans
• Keywords: Antigenic variation; Internalization

The African trypanosome Trypanosoma brucei, which persists within the bloodstream of mammalian host, has evolved potent mechanisms for immune evasion. Specifically, antigenic variation variant-specific surface glycoprotein (VSG) and a highly active endocytosis recycling coat efficiently delay killing mediated by anti-VSG antibodies. Consequently, conventional VSG-specific intact immunoglobulins are non-trypanocidal in absence complement. In sharp contrast, monovalent antigen-binding fragments, including 15 kDa nanobodies (Nb) derived from camelid heavy-chain antibodies (HCAbs) recognizing VSG epitopes, lyse trypanosomes both vitro vivo. This Nb-mediated lysis is preceded very rapid immobilisation parasites, massive enlargement flagellar pocket major blockade endocytosis. accompanied severe metabolic perturbations reflected reduced intracellular ATP-levels loss mitochondrial membrane potential, culminating cell death. Modification Nbs through site-directed mutagenesis reconstitution into HCAbs, combined with unveiling trypanolytic activity papain proteolysis, demonstrates that Fabs requires low molecular weight, monovalency high affinity. We propose generation weight impede offers new opportunity developing novel trypanosomiasis therapeutics. addition, these data suggest domain an anti-microbial antibody harbours biological functionality latent immunoglobulin revealed only upon release fragment.