Single-Cell Radiotracer Allocation via Immunomagnetic Sorting to Disentangle PET Signals at Cellular Resolution

Abstract

With great interest, our independent groups of scientists located in Korea and Germany recognized the use of a very similar methodologic approach to quantify the uptake of radioactive glucose (¹⁸F-FDG) at the cellular level. The focus of our investigations was to disentangle microglial ¹⁸F-FDG uptake. To do so, CD11b immunomagnetic cell sorting was applied to isolate microglia cells after in vivo ¹⁸F-FDG injection, to allow simple quantification via a γ-counter. Importantly, this technique reveals a snapshot of cellular glucose uptake in living mice at the time of injection since ¹⁸F-FDG is trapped by hexokinase phosphorylation without a further opportunity to be metabolized. Both studies indicated high ¹⁸F-FDG uptake of single CD11b-positive microglia cells and a significant increase in microglial ¹⁸F-FDG uptake when this cell type is activated in the presence of amyloid pathology. Furthermore, another study noticed that immunomagnetic cell sorting after tracer injection facilitated determination of high ¹⁸F-FDG uptake in myeloid cells in a range of tumor models. Here, we aim to discuss the rationale for single-cell radiotracer allocation via immunomagnetic cell sorting (scRadiotracing) by providing examples of promising applications of this innovative technology in neuroscience, oncology, and radiochemistry.

Keywords: 18F-FDG; PET; cell sorting; cellular resolution; scRadiotracing; tracer uptake.

FIGURE 1.

Workflow of scRadiotracing to determine microglial ¹⁸F-FDG uptake in brain at cellular resolution. After tracer injection into tail vein, brain is removed during tracer-specific uptake period. After generation of single-cell suspension, immunomagnetic cell separation is used to separate fractions of enriched cells from their depleted counterparts, which contain bound radioactivity. Fluorescent labeling, γ-counting, and flow cytometry are used to calculate radioactivity per cell as primary readout. Time to complete each step is indicated, together with summed time during workflow. CD11b is used to detect microglia. p.i. = after injection; S/N = south and north pole of the magnet. (Courtesy of Miltenyi Biotec B.V. & Co. KG. All rights reserved. Copyright © 2022.)