Fig. 4

Non-invasive visualization of IL-2c and of bound receptors by immunoPET/CT with ⁶⁴Cu-NOTA-IL-2c in naïve mice. a Size exclusion chromatography of ⁶⁴Cu-NOTA-IL-2c, demonstrating complex formation of the S4B6 anti-IL-2 mAb with IL-2; note the shift in the retention time compared to the uncomplexed S4B6 anti-IL-2 mAb; NOTA-conjugated anti-IL-2 mAb was incubated with IL-2 at a ratio of 1:2 at 37 °C for 30 min. 5 μg each of the ⁶⁴Cu-labeled NOTA-conjugated anti-IL-2 mAb and of IL-2c were run on an Enrich™ SEC 650 column. Frequency of CD122+ cells in spleen (b), lymph nodes (c), and thymus (d) of naïve mice (n = 3). e Representative coronal (C) and transverse (T) immunoPET/CT sections of untreated and CD122-depleted mice 24 h after injection of ⁶⁴Cu-NOTA-IL-2c (5 μg, 7.5 MBq). CD122-depleted mice were pre-treated with 0.25 mg depletion mAb (i.p.) 24 h before tracer injection. White ticks in the C-sections indicate the positions of the T-sections. The scanning duration was approximately 15–20 min. (f) Ex vivo biodistribution of radiotracer uptake 24 h after injection; n = 4 mice per group. Abbreviations: cLN – cervical lymph node, aLN – axillary lymph node, iLN – inguinal lymph node, mLN – mesenteric lymph node, Sp – spleen