In vivo tracking of ¹⁴C thymidine labeled mesenchymal stem cells using ultra-sensitive accelerator mass spectrometry
Dr Gwan-ho Lee1, Mr Min‑Seok Oh1,2, Mr Seul‑Gi Lee2, Prof C‑Yoon Kim2, Dr Jong Han Song1, Prof. Hyung Min Chung2, Dr Byung‑Yong Yu1
1Korea Institute Of Science And Technology, Seoul, South Korea, 2Konkuk University, Seoul, South Korea
Therapeutic effects of stem cells have been established but confirmation of the safety and the efficacy of stem cells is still required. This requires development of methods for quantification of stem cells that after introduction into the test organism. Commonly used methods for quantifying administered stem cells to organs are limited, with problems including limited sensitivity and damage to cells by the materials used during the labeling process.
To overcome these problems in particular, we radiolabeled the DNA of human stem cells (AD-MSCs) grown in vitro with a trace amount of ¹⁴C thymidine with low radioactivity (5 nCi/mL, 24.2 ng/mL) that would have minimal effects on the properties and function of the stem cells.
We additionally demonstrate the utility of both liquid scintillator counter (LSC) and accelerator mass spectrometry (AMS) in investigating the distribution and quantification of radioisotope labeled adipocyte derived mesenchymal stem cells (AD-MSCs) after intravenous (IV) transplantation. The high sensitivity of AMS enabled quantification down to the single ¹⁴C-labeled AD-MSCs cell level in various tissue while it was found that the sensitivity of LSC was below that of AMS. For LSC, AD-MSCs were only detected in the lung with the highest number of cells existing within the organ at 4 hr post-transplantation. This sharply decreased over time with little to no trace left by 72 hr. In contrast, AMS was able to detect a small number of cells located in all other tested organs but difficult to quantify larger numbers such as the lung’s case due to over-detection. At 4 hr post-transplantation, the number of AD-MSCs per mg located in the spleen and liver was 19 ± 8 and 14 ± 1, respectively. And even lesser amounts or single cells were detected in the heart and kidney (1 ± 0 infused cells number/mg) while no cells were detected in the brain. This approach can show the results of a vital pattern of distribution for stem cells such as MSCs which is essential for both research and therapeutic purposes.
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