A versatile approach for the site-specific modification of recombinant antibodies using a combination of enzyme-mediated bioconjugation and click chemistry.

A unique two-step modular system for site-specific antibody modification and conjugation is reported. The first step of this approach uses enzymatic bioconjugation with the transpeptidase Sortase A for incorporation of strained cyclooctyne functional groups. The second step of this modular approach involves the azide-alkyne cycloaddition click reaction. The versatility of the two-step approach has been exemplified by the selective incorporation of fluorescent dyes and a positron-emitting copper-64 radiotracer for fluorescence and positron-emission tomography imaging of activated platelets, platelet aggregates, and thrombi, respectively. This flexible and versatile approach could be readily adapted to incorporate a large array of tailor-made functional groups using reliable click chemistry whilst preserving the activity of the antibody or other sensitive biological macromolecules.

Phosphorylated self-peptides alter human leukocyte antigen class I-restricted antigen presentation and generate tumor-specific epitopes.

Human leukocyte antigen (HLA) class I molecules present a variety of posttranslationally modified epitopes at the cell surface, although the consequences of such presentation remain largely unclear. Phosphorylation plays a critical cellular role, and deregulation in phosphate metabolism is associated with disease, including autoimmunity and tumor immunity. We have solved the high-resolution structures of 3 HLA A2-restricted phosphopeptides associated with tumor immunity and compared them with the structures of their nonphosphorylated counterparts. Phosphorylation of the epitope was observed to affect the structure and mobility of the bound epitope. In addition, the phosphoamino acid stabilized the HLA peptide complex in an epitope-specific manner and was observed to exhibit discrete flexibility within the antigen-binding cleft. Collectively, our data suggest that phosphorylation generates neoepitopes that represent demanding targets for T-cell receptor ligation. These findings provide insights into the mode of phosphopeptide presentation by HLA as well as providing a platform for the rational design of a generation of posttranslationally modified tumor vaccines.