Background
Local application of adipose-derived mesenchymal stem cells (ADSCs) is a promising method for the treatment of perianal fistula in patients with Crohn’s disease. More clinical and experimental studies are needed including the technique of in vivo monitoring. The aim of the study was to evaluate the fistula healing after application of ADSCs in perifistular tissue.

Materials and Methods
Coecostomy was used as a fistula model in 11 Lewis rats. The adipose tissue was harvested from transgenic donor expressing firefly luciferase (LEW-Tg(Rosa-luc)11Jmsk; Jichi Medical School). The ADSCs were isolated using collagenase and injected (1-2*106 cells/ml) in perifistular tissue. After application of D-luciferin (25mg/kg), rats were imaged in IVIS Lumina camera on days 0, 2, 7, 14 and 30. Fistula drainage assessment (FDA) was used to evaluate fistula healing.

Results
The fistula was identified as healed in 4/11 animals. Bioluminescence was strongest 2 days after application (4,46*105 (5,1*104-2,7*106). The radiance decreased as follows 1,15*105 (4,05*104 - 6,4*105) on day 7; 7,29*104 (9,36*103-2,88*105) on day 14 and 2,94*104 (4,93*103-1,70*105) on day 30 (values are medians in p/s/cm2/sr). There was a trend to higher luminescence in animals with healed fistula (30 days after injection - 8,23*104 (1,18*104- 1,70*105) vs. 2,75*104 (4,93*103-6,88*104); p=0,18).

Conclusion
Local application of ADSCs can lead to fistula healing. The effect of ADSCs was confirmed by higher luminescence in healed rats 30 days after implanatation.

Supported by NT13708