In this study, we aimed to investigate the morphological changes of repairing fistula with transplanting AMSCs into fistula tissue in an animal model of TEF. Results showed that the AMSCs group received more benefit than control group in healing and inflammation aspects. The use of AMSCs led to less mortality, less rate of pulmonary infection and better degree of closure.
Mesenchymal stem cells (MSCs), which are referred to as stromal progenitor cells are self-renewing and expandable stem cells. MSCs from amount sites, including bone marrow and adipose tissue, may have immunomodulatory properties, thereby indicating a possible use for MSCs in regenerative medicine and tissue engineering[11].
In contrast to bone marrow-derived stem cells, adipose-derived stem cells are abundant in adipose tissue and are easy to harvest and expand in vitro, which makes them a describe cell type for regenerative cell therapy[12].
In our result, all animals present severe symptoms like acute cough, airway chocking, and vomiting in the first postoperative week. The mortality caused by refluxing of gastric contents was different in two group (fig 1). There are not any researches have been reported yet. Combining the subsequent results about pulmonary infection. we suspect the stem cell may reduce the risk of postoperative and reflux mortality in the first week.
There were many reports that MSCs have been used to cure, including bone repair, cardiovascular disease, plastic surgery, idiopathic pulmonary fibrosis, chronic liver injury, acute renal injury, and so on[13]. However, few studies using in vivo animal models had provided evidence on healing effects of MSCs in TEF. There are several researches about the efficacy of various approaches on TEF animal model (fig 2). In term of survival time, the surgery retains a longest survival rate and time.in Yang et al study[14], all TEF animals received a long survival time up to 56 d. it is longer than survival time of stent and stem cell. In the research of Wagner[15], the healing effects of covered stent, the longest survival time was 36 d which still need an additional tracheal stent. The longest survival time by one esophageal stent was only 30 d. Our survival day was 35 d in stem cell group, lower than Yang but longer than Wagner. In the rate of pneumonia, the aspiration pneumonia occurred in Wagner and our study after the first postoperative week compared with the surgery study. In our experiment, the pulmonary infection presents a severe consolidation in even whole lungs (upper lobes and lower lobes) in the control group. On the contrary, the contamination was concentrated in the upper lobes in the experimental group. The current researches about stem cells have showed the relative curative effect on the pneumonia. But we believe the fistula closure effect from stem cells is the main motivation to avoid pulmonary infection. The open fistula leads to the persistence of reflux of gastric, which lead to the infection in upper lobs in the early postoperative stage (1~2 week). In the middle stage, the closure of fistula prevents the erosion in lung caused by the reflux in the experimental group (3 week). This procedure was not occurred in the control group, which lead the severe lesion in the lower lobs in the later stage. The infection which involved in whole lung bring about the death of two animals (2102, 2014) in control group.
Although there are not reports on the healing research of TEF by stem cells, there are many cases for the bronchopleural fistula on the stem cell in the healing of the bronchial stumps.
The earliest report of stem cell in treatment of trachea fistula is form Agero et al in 2008[16]. he reported a case that a bronchopleural fistula patient was used autologous adipose-derived stem cell suspended in fibrin glue to close the fistula successfully. That is the first report on the treatment of tracheal fistula by autologous cell therapy. Prudencio et al[17] reported that two patients with bronchopleural fistula received a successful closure, and no treatment -related adverse reactions recurred in the 3 year follow up. Francesco et al[18] reported that bone marrow-derived stem cells were effectively closes bronchopleural fistula in animal model by extraluminal fibroblast proliferation and collagenous matrix development, which is similar with our results. In 2015, he reported the succeed in tracheobronchial dehiscence after stem cell infusion[19]. In 2016, Johnathon et al[20] combined the bio-absorbable mesh and autologous stem cell, and the stem cell-seeded matrix graft was used to repair a multiply recurrent postpneumonectomy bronchopleural fistula successfully. That is the first application of combination with bio-material and stem cell in tracheal fistula therapy. In the meantime, the difficulty spot we met is also that stem cells lack adhesive carrier in fistula transplantation. Partial stem cells injected into submembrane were leaked into outside. The leak of cells might be the reason that the animals in group 3 present a different healing degree. According to our previous research, the cardiac septal defect occlude (Amplazer occlude) has an eminent load capacity of various cells in vitro. However, the occlude alone could not have a long-term curative effect to fistula in our precious animal study. The difficulty in epithelialization and growth of miscellaneous bacteria are the limitation for the new occlude. Hence, the stem cells might ameliorate the problem according to the good epithelialized result from our research. The combination may be another new clinical strategy of the treatment of TEF.
In the current study, we reported the various effects of MSCs transplantation on TEF such as following: (1) reduce the death risk in early stage of TEF; (2) relieve the pneumonia and reduce the accumulation of secretion; (3) accelerate the closure of TEF in some degree; (4) increase in collagen synthesis because of fibroblast from stem cell.
In conclusion, this was the first study to use locally transplanted cell therapy for the healing of TEF. AMSCs therapy significantly accelerated the healing degree of TEF. That may be a potential therapeutic strategy to acquired TEF if combine the appropriative stent which can load stem cell efficiently.