High-efficiency intracellular magnetic labeling with novel superparamagnetic-tat peptide conjugates

A biocompatible, dextran coated superparamagnetic iron oxide particle was d erivatized with a peptide sequence from the HIV-tat protein to improve intr acellular magnetic labeling of different target cells. The conjugate had a mean particle size of 41 nm and contained an average of 6.7 tat peptides. D erivatized particles were internalized into lymphocytes over 100-fold more efficiently than nonmodified particles, resulting in up to 12.7 x 10(6) par ticles/cell. Internalized particles localized in cytoplasm and nuclear comp artments as demonstrated by fluorescence microscopy and immunohistochemistr y. Labeled cells were highly magnetic, were detectable by NMR imaging, and could be retained on magnetic-separation columns. The described method has potential applications for in vivo tracking of magnetically labeled cells b y MR imaging and for recovering intracellularly labeled cells from organs.