Figure 5.

PEGylation increases sensitivity and decreases kidney retention of radiolabeled heavy-chain variable domains (VHHs). Mice were injected with ⁸⁹Zr-labeled anti-mouse CD8 nanobody (A), with or without a 20-kDa PEG molecule (B,C). Mice were imaged 2 h post injection (for the ‘no PEG’ VHH) or 24 h post injection (for the PEGylated VHH), which are the optimum timepoints for maximum signal-to-background ratio. RAG knockout animals, which lack all lymphocytes, did not yield an obvious signal, except in the organs of elimination (kidney, bladder) (D). To measure sensitivity of the approach, lymph nodes (LNs) were excised and CD8⁺ cells were counted. Results showed that a popliteal LN, with ∼70 000 CD8⁺ T cells, can be detected with a signal-to-background ratio of ∼7.

Data adopted from Rashidian et al. (2017, 2019).^54,55