A new method to produce site specifically PEGylated or bivalent single-domain antibodies has been developed by Prof. Steven Liang group at Harvard University (Enzyme-Mediated Modification of Single-Domain Antibodies for Imaging Modalities with Different Characteristics, Angew. Chem. Int. Ed., DOI: 10.1002/anie.201507596).
They used camelid single-domain antibody fragments (VHHs) as the smallest antigen-binding derivatives, which lend themselves to enzymatic modification and have been used in a variety of applications, including imaging. They found that the antibody-PEG conjugation reaction conditions enable full retention of the biological activity of the fusion partners. And the attachment of small PEG groups could be used as a tool to “tune” the persistence of a VHH in the circulation. Moreover, PEGylation can decrease the immunogenicity of VHHs, which is important in cases in which repeated administration is required. The PEGylated fluorescent VHHs showed improved staining in vivo, with larger PEG substituents giving stronger signals in FACS, whereby PEG substituents with a higher molecular weight gave stronger signals. Finally, immune-PET of two different models of tumor-bearing mice showed that the DC8 dimer and DC13 dimer detected not only lymphoid organs, as expected, but also showed the location of ectopic melanoma and pancreatic tumor grafts.
Original manuscript: onlinelibrary.wiley.com/doi/10.1002/anie.201507596/abstract