Karolinska Research Lectures: Hidde Ploegh
Hidde Ploegh, Whitehead Institute for Biomedical Research, Cambridge, USA
Title: “Imaging immunity”
Recent work in my laboratory has focused on applications of camelid-derived single domain antibodies. These protein, also referred to as VHHs or nanobodies, are small (~12 kDa), do not have a stringent requirement for disulfide bonds and/or glycosylation for their expression, and are readily modified chemically or enzymatically for a variety of applications. We have used cytoplasmic expression of VHHs to perturb protein-protein interactions inside the reducing environment of cells, as demonstrated for VHHs capable of interfering with the life cycle of influenza A virus or vesicular stomatitis virus. Cytoplasmic expression of VHHs specific for inflammasome components, such as the adapter protein Asc, can likewise inhibit IL-1 release. VHHs are therefore useful adjuncts to genetic tools such as RNA interference or Cas9/ CRISPR- based approaches.
We also exploit the small size and attendant short circulatory half-life of VHHs to generate reagents for non-invasive in vivo imaging by positron emission tomography. This approach makes it possible to make longitudinal observations in individual mice without the need to sacrifice the animal. We have applied this method to image anti-tumor immune responses longitudinally and show that the images obtained have prognostic value in therapies that exploit antibodies against CTLA4 for checkpoint blockade. To generate VHHs suitable for PET imaging, we make use of sortase to execute site-specific and quantitative labeling, a general approach that can be extended to other proteins of immunological interest, including surface-disposed receptors such as the B cell receptor for antigen.
Nobel Office, Nobel Forum