18F-FDG labelling of hematopoietic stem cells: Dynamic study of bone marrow homing by PET–CT imaging and impact on cell functionality

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 [18F] fluorodeoxyglucose (18F-FDG) and to follow early HSPC homing through PET–CT in mice. Purified CB HSPCs were radiolabelled with 18F-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 18F-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 18F-FDG-labelled HSPCs, the biodistribution of which was followed using micro-PET–CT. 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 18F-FDG. The activity of the obtained 18F-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.