|Title||Affinity is an important determinant of the anti-trypanosome activity of nanobodies.|
|Publication Type||Journal Article|
|Year of Publication||2012|
|Authors||Caljon, G., B. Stijlemans, D. Saerens, J. Van Den Abbeele, S. Muyldermans, S. Magez, and P. De Baetselier|
|Journal||PLoS Negl Trop Dis|
|Type of Article||parasites|
|Keywords||Animals, Antibodies, Protozoan, Antibody Affinity, Mice, Mice, Inbred C57BL, Microbial Viability, Single-Domain Antibodies, Trypanosoma brucei brucei|
BACKGROUND: The discovery of Nanobodies (Nbs) with a direct toxic activity against African trypanosomes is a recent advancement towards a new strategy against these extracellular parasites. The anti-trypanosomal activity relies on perturbing the highly active recycling of the Variant-specific Surface Glycoprotein (VSG) that occurs in the parasite's flagellar pocket.METHODOLOGY/PRINCIPAL FINDINGS: Here we expand the existing panel of Nbs with anti-Trypanosoma brucei potential and identify four categories based on their epitope specificity. We modified the binding properties of previously identified Nanobodies Nb_An05 and Nb_An33 by site-directed mutagenesis in the paratope and found this to strongly affect trypanotoxicity despite retention of antigen-targeting properties. Affinity measurements for all identified anti-trypanosomal Nbs reveal a strong correlation between trypanotoxicity and affinity (K(D)), suggesting that it is a crucial determinant for this activity. Half maximal effective (50%) affinity of 57 nM was calculated from the non-linear dose-response curves. In line with these observations, Nb humanizing mutations only preserved the trypanotoxic activity if the K(D) remained unaffected.CONCLUSIONS/SIGNIFICANCE: This study reveals that the binding properties of Nanobodies need to be compatible with achieving an occupancy of >95% saturation of the parasite surface VSG in order to exert an anti-trypanosomal activity. As such, Nb-based approaches directed against the VSG target would require binding to an accessible, conserved epitope with high affinity.
|Alternate Journal||PLoS Negl Trop Dis|
|PubMed Central ID||PMC3499403|
Affinity is an important determinant of the anti-trypanosome activity of nanobodies.