脊髓内移植间充质干细胞的转铁蛋白受体显像

Transferrin receptor imaging for tracing mesenchymal stem cells implanted in the spinal cord

目的探索放射性核素显像活体追踪移植干细胞的可能性。方法用放射性受体分析定量测定体外培养人间充质干细胞(hMSCs)的转铁蛋白受体表达。兔脊髓内移植人间充质干细胞,蛛网膜下腔注入131I标记铁胞和转铁蛋白后不同时间,用伽玛相机采集图像。感兴趣区(ROI)技术对图像进行半定量分析。磷屏放射自显影验证活体显像。结果hMSCs高表达转铁蛋白受体(10,770/细胞),并且对铁饱和转铁蛋白具有高亲和力(KD=0.982nmol/L)。实验组动物在注射显像剂后16和24h观察到了移植区放射性浓聚灶,而以PBS作为移植物和以131I标记的血清白蛋白作为显像剂的2个对照组均呈阴性显像,ROI分析显示实验组与对照组之间具有显著的统计学差别(P<0.05)。磷屏放射自显影证实了间充质干细胞移植部位能够特异结合铁饱和转铁蛋白。结论应用核素显像活体示踪移植干细胞具有可行性,经过进一步改进,有望为干细胞移植治疗提供无创的监测手段。

Objective To explore the feasibility of tracing mesenchymal stem cells in vivo with scintigraphy. Methods Transferrin 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, ^131I-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, ^131I-labeled human serum albumin was used in stead of ^131I-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. Results Radioligand-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 ^131I-transferrin tracer, but not in two control groups. ROI analysis showed that the difference between ^131I-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. Conclusions Transferrin 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.