In vivo cellular imaging of magnetically labeled hybridomas in the spleen with a 1.5-T clinical MRI system.

The feasibility of in vivo cellular imaging using a 1.5 T clinical magnet was studied in the mouse. Hybridoma cells were labeled with anionic gamma-Fe2O3 superparamagnetic iron oxide nanoparticles. These were internalized by the endocytose pathway. Both electron spin resonance and magnetophoresis as a measure of the labeled cells migration velocity under a magnetic field were used to quantify particle uptake. A fast (< 2 hr) and substantial (up to 5 pg of iron per cell) internalization of nanoparticles by hybridomas was found, with good agreement between the two methods used. Hybridomas labeled with 2.5 pg iron per cell were injected intraperitoneally to male Swiss nude mice. A decrease in the spleen signal, suggesting a "homing" of labeled hybridomas to this organ, was found 24 hr later by MRI performed at 1.5 T. Furthermore, in labeled cells recovered from the spleen by ex vivo magnetic sorting, a mean of 0.5 pg iron per cell was found, i.e., a value five times lower than that of the injected hybridomas. This finding is consistent with in vivo proliferation of these cells. In addition, the amount of labeled hybridomas present in the spleen was found to correlate with MRI signal intensity. Copyright 2004 Wiley-Liss, Inc.