Monitoring immune activity across tissues remains a key challenge in both basic and translational immunology. Select immune cell compartments can be visualized with positron emission tomography (PET) imaging using small-molecule-based or antibody-based probes that target specific immune cell markers, such as CD8 for cytotoxic T cells, CD4 for helper T cells and CD11b for myeloid cells. However, these probes do not offer a holistic view of total immune cell activity across the body. To bridge this gap and to offer maximum sensitivity while maintaining high specificity, we developed CD45-PET imaging, a pan-leukocyte imaging modality that targets a protein expressed on all nucleated haematopoietic cells.

CD45-PET imaging uses radioactively labelled antibody fragments, such as nanobodies or minibodies, that specifically target the CD45 antigen expressed on immune cells. Unlike full-length antibodies, these smaller fragments have much shorter half-lives in the blood, enabling high-specificity imaging within hours to a day, reducing patient radiation exposure and simplifying imaging logistics.