[Distribution and differentiation of marrow mesenchymal cells in tumor tissue: experimental with rabbits]

To study the distribution of bone marrow mesenchymal stem cells (MSCs) in tumor tissue and the possibility of MSCs differentiating into myofibroblast under the induction of local tumor microenvironment.

MSC were isolated from 24 New Zealand rabbits, and cultured. Then vx-2 tumor tissue was transplanted under the bladder mucosa of each animal. Then the rabbits were randomly divided into 2 equal groups: control group and test group. One week after the transplantation, the autologous F2 passage MSCs marked by diamino-phenyl-indole (DAPI) were transplanted into the tumor tissue of the test group and DMEM medium was infused into the tumor tissue of the control group. Ultrasonography was performed 1, 2, 3, and 4 week(s) after the vx-2 tumor mass was transplanted. The maximum bladder tumor diameters of each animal were recorded and the mean value of each group was calculated. One animal in each group with its tumor diameter closest to the average value of the very group was put to death in the third week and all the left animals were killed in the fourth week to observe the tumor development. Another rabbit underwent same treatment as that in the test group was put to death to observe the distribution of MSCs in the tumor tissue one week after self-MSC transplantation. Immunofluorescence was used to trace the MSCs in the tumor tissue. Double labeling immunofluorescence for alpha-smooth muscle actin (alpha-SMA) and vimentin was performed to identify whether MSCs could differentiate into myofibroblasts.

Ultrasonography showed no tumor mass one week after the vx-2 tumor mass transplantation. In the second week, the mean maximum tumor diameter of the control group was 0.70 +/- 0.14 cm, not significantly different from that of the test group (0.78 +/- 0.14 cm, t = 1.308, P = 0.204), however, the mean maximum tumor diameter in the third and fourth weeks of the control group were 1.8 +/- 0.4 cm and 2.3 +/- 0.6 cm respectively, both significantly shorter than those of the test group (2.2 +/- 0.3 cm and 3.8 +/- 0.9 cm respectively, both P < 0.05). Microscopy showed that MSCs were distributed uniformly in the tumor tissue one week after transplantation while most of the MSCs were distributed in the tumor stroma three weeks after transplantation. Double labeling immunofluorescence showed an increase of alpha-SMA and vimentin expression three weeks after MSC engraftment.

MSCs are initially distributed uniformly in the tumor tissue and then distributed mainly in the tumor stroma. Furthermore, MSCs accelerate tumor development and can differentiate into myofibroblasts under the induction of tumor microenvironment.