Cellular magnetic resonance with iron oxide nanoparticles : long-term persistence of SPIO signal in the CNS after transplanted cell death

To study the specificity of cellular MRI based on superparamagnetic iron oxide particles (SPIOs), especially within the CNS. MATERIALS & METHODS: A microglial cell line was engineered for the expression of a suicide gene, the receptor of diphtheria toxin (DT), and two reporter genes, green fluorescent protein and luciferase, in order to induce, in a controlled manner, cell death and test it through bioluminescence. SPIO-labeled DT-sensitive and control DT-insensitive cells were transplanted into the brains of mice, which underwent serial MRI and bioluminescence studies before and up to 90 days after DT-induced cell death. RESULTS: No variations in SPIO signal voids were detected along longitudinal monitoring in brain hemispheres transplanted with DT-sensitive cells. Ex vivo analyses showed persistence of iron nanoparticle deposits at transplantation sites. CONCLUSION: Due to the long-term persistence of signal after transplanted cell death, caution is advised when SPIOs are employed for cell tracking.