Correction: Kalimuthu et al. Regulated Mesenchymal Stem Cells Mediated Colon Cancer Therapy Assessed by Reporter Gene Based Optical Imaging. Int. J. Mol. Sci. 2018, 19, 1002

The authors wish to make the following correction to this paper [1]. The authors state that the scientific conclusions remain unaffected. This correction was approved by the Academic Editor. The original publication has also been updated.

• Error in Figures

In the original publication, there was a mistake in Figure 1B,C, and Figure 2 (DOX(−) MSC-Tet-TK) as published. The error occurred due to erroneous copying of images during figure assembly. The corrected version of Figure 1B,C, and Figure 2 (DOX(−) MSC-Tet-TK) appears below.

• Figure 1B

• Figure 1C

• Figure 2. (DOX(−) MSC-Tet-TK).

• Error in Figure Legends

In the original publication, there were typographical errors in the legends for Figures 2 and 3. The correct legends appear below.

• Figure 2. Fluc activity of MSC-Tet-TK and MSC-TK cells after ganciclovir (GCV) treatment for 48 h. Fluc activity was measured by bioluminescent imaging (BLI), and the quantitation for MSC-Tet-TK and MSC-TK cells is shown in the right-hand panel. Values obtained from three experiments are expressed as the mean ± standard deviation (SD), ** p < 0.01, *** p < 0.001 (by Student’s t-test). p/s, photons/second.

• Figure 3. Bystander effect of MSC-Tet-TK and MSC-TK cells. (A) Rluc activity in co-cultures (1:1) of naive MSCs and CT26/Rluc cells treated with the indicated concentrations of GCV for 48 h. (B) BLI images of the Rluc activity and quantitation data of CT26/Rluc in co-cultures (1:1) of MSC-TK or MSC-Tet-TK cells in the absence or presence of doxycycline (DOX(−) and DOX 2 μg/mL, respectively). Three experiments are expressed as the mean ± standard deviation (SD), * p < 0.05, ** p < 0.01, *** p < 0.001 (by Student’s t-test). p/s, photons/second.

• Text Correction

There was an error in the original publication [1]: an error in the figure results. A correction has been made to the Results Section, in the subsection “Characterization of MSC-Tet-TK and MSC-TK”, Paragraph Number 1:

• 2.1. Characterization of MSC-Tet-TK and MSC-TK

The transduced MSC-Tet-TK and MSC-TK cells were created by retroviral transfection, and eGFP-positive cells were sorted by FACS Aria III. Cells with an eGFP concentration of more than 50% were used for further study. The expression of MSC-TK cell eGFP and MSC-Tet-TK cell eGFP after induction with DOX (2 µg/mL) for 24 h (Figure 1A) was confirmed by confocal microscopy images. The morphology of MSC-Tet-TK cells are heterogeneous and not uniform, because MSCs are a heterogeneous cell population. MSC-Tet-TK cells with eGFP positive revealed more rod-like morphology than others, which might be related to the genetic alteration. Some of the MSC-TK cells revealed higher eGFP signals due to higher eGFP expression, because protein synthesis can vary with individual cells, withdifferent copy numbers of the transduced gene. The Fluc activity of MSC-TK cells increased with increasing cell numbers (Figure 1B, R² = 0.90). The BLI signal in MSC-Tet-TK cells increased 15-, 21-, 25-, and 29-fold with increasing concentrations of DOX (0.25, 0.5, 1, and 2 µg/mL), whereas no signal was observed in DOX(−) cells (Figure 1C). Furthermore, we found that Fluc activity increased 17-, 19-, 20-, 20-, 15-, and 7-fold with increasing DOX treatment (0.5 to 4 µg/mL) for 48 h and then decreased at 8 and 16 µg/mL DOX (Figure S1). Therefore, in this study, we elected to use 2 µg/mL DOX for transgene activation.