OBJECTIVETo explore the feasibility of tracing mesenchymal stem cells in vivo with scintigraphy.

METHODSTransferrin receptor expression of cultured mesenchymal stem cells (hMSCs) was quantified with radioligand-receptor binding assay before the cells were transplanted into the spinal cord of rabbits. (131)I-labeled transferrin was then administered into the subarachnoid space of the rabbits, and scintigraphic images were acquired with a gamma camera at different time points after the administration. In the control experiments, (131)I-labeled human serum albumin was used in stead of (131)I-transferrin as the tracer, or only PBS was injected without stem cell transplantation. The images were semi-quantitatively analyzed with region of interest (ROI) techniques, and the phosphor imaging on the spinal sections were performed.

RESULTSRadioligand-receptor binding assay showed 10 770 binding sites with high affinity (KD=0.982 nmol/L) for Fe saturated transferrin on each human mesenchymal cell. Visible accumulation of radioactivity at the cell transplantation sites was observed 16 h and 24 h after intrathecal injection of (131)I-transferrin tracer, but not in two control groups. ROI analysis showed that the difference between (131)I-transferrin and the control groups was statistically significant (P<0.05). Phosphor imaging further verified that it was the specific coupling of transferrin to the implanted cells that resulted in radioactivity accumulation at the transplantation sites.

CONCLUSIONSTransferrin receptor imaging is capable of in vivo tracing of the implanted stem cells, and has the potential for use in non-invasive monitoring for stem cell transplantation therapy after further technical improvements.