F-FDG labelling of hematopoietic stem cells: Dynamic study of bone marrow homing by PET-CT imaging and impact on cell functionality.

Purpose Of The Study: After transplantation, cord blood (CB) hematopoietic stem and progenitor cells (HSPCs) are able to home to the bone marrow niche and to reconstitute the hematopoietic system. PET-CT imaging may be a useful method to monitor this parameter in different conditions. The aim of our study was to set up an efficient method for HSPC radiolabelling with [F] fluorodeoxyglucose (F-FDG) and to follow early HSPC homing through PET-CT in mice.

Materials And Methods: Purified CB HSPCs were radiolabelled with F-FDG at 37° C with various conditions of cell concentration, incubation time and radioactivity concentration in order to define the in vitro condition that allows both sufficient F-FDG uptake to get high quality PET imaging, and preservation of HSPC viability and functional properties during 3h after radiolabelling. Then, 24h after 2.25Gy irradiation, eight NOD-scid/γc mice were injected with F-FDG-labelled HSPCs, the biodistribution of which was followed using micro-PET-CT.

Results: The optimal incubation time was 45min with a stability of 48.3%±12.8% after 180min. The radio-uptake rate we obtained was 7.2%±1.7% with an activity of 5.6±2.1 MBq. Three hours after radiolabelling, viability was 96.7%±3.4%. Fifteen hours after radiolabelling, cell viability was 64.0%±2.3%, migration ability diminished from 51.0%±23.6% to 12.0%±9.1%, clonogenic capacity was null, and long-term engraftment in NSG mice also decreased compared to unlabelled cells. Micro-PET-CT experiments showed an accumulation of radiolabelled HSPCs for 2.5h after injection in the bone marrow and a slight elution of F-FDG.

Conclusion: The activity of the obtained F-FDG-labelled HSPCs was sufficient to perform the micro-PET-CT imaging. Although the radiolabelling had a significant toxicity on HSPCs 15h after labelling, this technique allowed monitoring the beginning of HSPC homing into the bone marrow.