124I Radiolabeled Basiliximab for CD25-Targeted Immuno-PET Imaging of Activated T Cells.

Activated T cells played critical roles in immunotherapy and adoptive T cell therapy, and a non-invasive imaging strategy can provide us useful information concerning the transportation, accumulation, and homing of T cells in vivo. In this paper, by utilizing the long half-life radionuclide iodine-124 (124I) and CD25 specific monoclonal antibody Basiliximab, we have fabricated a novel probe, namely, 124I-Basiliximab, which was highly promising in the immuno-PET imaging of T cells. In vitro, 124I-Basiliximab had superior affinity to CD25 protein (Kd = 5.31 nM) and exhibited much higher accumulation in CD25 high-expression lymphoma cell line Karpas299 than that in CD25-negative cell line Daudi. In vivo, 124I-Basiliximab was excreted slowly from the body of mice, rendering it a relatively high effective dose (0.393 mSv/MBq) when applied in the immuno-PET imaging. In Karpas299 tumor xenograft, 124I-Basiliximab probe was observed to accumulate in the tumor quickly after tracer administration, with the optimal image acquired at 24 h post-injection. More importantly, PHA-activated hPBMC had much higher uptake of 124I-Basiliximab, indicating the potential utility of 124I-Basiliximab to discriminate activated hPBMC from its non-activated status. In summary, 124I-Basiliximab was fabricated for the first time, which can be applied in CD25-targeted immuno-PET imaging of activated T cells in vivo.