To investigate the effect of MSCs on the growth of breast cancer cells by constructing a co-culture model of the interaction between MSCs and breast cancer cells.

Human umbilical cord was infected with the third generation of sin lentivirus vector containing fluorescent gene, and then MSCs and breast cancer cells MDA-MB-231, MCF-7 were extracted. Breast cancer cells MDA-MB-231 and MCF-7 were cultured respectively, and then control groups were established. Two breast cancer cells were co-cultured with MSCs respectively, to detect the change of proliferation ability of breast cancer cells under the effect of MSCs. Flow cytometry (FACS) was used to detect the expression of cell surface markers. Independent sample t-test was used for comparison between two groups, one-way ANOVA was used for comparison between multiple groups, and Dunnet-t test was used for multiple comparisons.

MSCs promote tumor cell growth during co-culture with breast cancer cells. After 3 days co-cultre, the number of MDA-MB-231 cells in the co-culture group was significantly higher than that in the single MDA-MB-231 culture group (5.50 ± 0.71) × 10³ vs (1.63 ± 0.41) × 10³. The difference became more significantly at 7 days co-culture (81.25 ± 7.40) × 10³ vs (26.25 ± 4.15) × 10³ (P < 0.001) .After co-culture, the expression of stem cell specific marker CD90 could be promoted by MSCs. The expression rate of MCF-7 was only (1.38±0.30) ﹪ at 2 days co-culture and (92.45±2.04) ﹪ at 9 days co-culture. The stem cells grew around the tumor cells and became longer. Meanwhile, a new hybrid cell (hybrid fusion cell) was found, which can simultaneously express green and red fluorescence and was more sensitive to chemotherapeutic drugs.

Human MSCs could promote the growth of breast cancer cells, accompanied by the morphological changes of MSCs and the appearance of hybrid fusion cells. Breast cancer cells could express CD90 and only in MSCs.