Chronic obstructive pulmonary disease (COPD) has emerged as a serious public health concern in recent years and is predicted to become the fourth leading cause of death worldwide by 2030 (Mathers and Loncar, 2006). COPD of the feline is treated with medications including bronchodilators, inhaled steroids, oral steroids, phosphodiesterase-4 inhibitors, theophylline, and antibiotics; lung therapies, such as oxygen therapy and pulmonary rehabilitation programs; and surgeries including lung volume reduction surgery, lung transplantation, and bullectomy. However, these treatments have limited efficacy and serious side effects (McEvoy and Niewoehner, 1997; McEvoy and Niewoehner, 2000; Chang et al., 2019).

There have been several reports in the literature recently using stem cells to treat lung-related diseases. In the murine asthma model, Th2-related cytokines were decreased to maintain Th1/Th2 balance after mesenchymal stem cells injection, thereby regulating immunity (Nemeth et al., 2010; Park et al., 2010; Kavanagh and Mahon, 2011). In feline asthma, stem cell therapy reduced lung attenuation compared to an untreated stem cells in the asthmatic cat (Trzil et al., 2016).

In this study, we treated a COPD cat using amniotic membrane-derived stem cells, which have similar stemness to mesenchymal stem cells but are non-invasively and easily obtainable with large amounts.

A 15-year-old, neutered female cat weighing 4.6 kg was diagnosed with COPD at the age of 10 with a severe cough. Clinical symptoms were coughing, gagging, and breathing difficulty more than 10 times every day. X-rays showed a bronchial pattern throughout the lung field, a typical aspect of COPD (Fig. 1A). We counted the number of coughs per day; a cough was regarded when she started a coughing and it continuously maintained. Sometimes she has breathing difficulty after severe coughing. She was treated with antibiotics and prednisolone when she had severe coughing. Usually she was given doxycycline as antibiotics (5 mg/kg twice a day) and prednisolone to suppress immune system (1 to 5 mg/kg twice a day). However, the effect of the medicine was decreased and finally was non-responsive. Therefore, stem cell therapy was performed 3 times on days 0, 7, and 23.

Figure 1.Chest x-ray results of COPD cat. Chest X-ray before stem cell treatment and after conventional drug treatment (A). Chest X-ray after one week of stem cell transplantation (B).

Stem cells from the feline amniotic membrane were isolated by referring to the method (Fig. 2A). Briefly, we obtained amniotic membranes during the cesarean section surgery on full term pregnancy (60 days). The feline placenta was washed with sterile phosphate buffered saline (PBS), thereafter, the amniotic membrane was mechanically separated from the allantoic sac, and enzymatic digestion was performed using 0.1% collagenase solution to isolate amniotic-derived mesenchymal stem cells (Vidane et al., 2014).

Figure 2.Stem cells used for the treatment of COPD therapy and coughing index. Morphology of mesenchymal stem cell isolated from cat amniotic membrane (A). Coughing index in patients with COPD. After stem cell therapy, the frequency of coughing decreased sharply (B).

The patient was premedicated with cefazolin (25 mg/kg intravenously) and dexamethasone (0.1 mg/kg intravenously) prior to stem cell transplantation, thereafter, allogeneic stem cells were infused intravenously. The 1 × 10⁶ cell/kg stem cells were mixed in normal saline with 200 IU heparin sulfate and administered intravenously with a syringe pump-operating with 10 mL/kg/hr injection speed. The dose was based on previous studies, and proved not to be associated with adverse events as well (Quimby et al., 2013; Noh et al., 2021). The patient appeared clinically normal and stable during and after infusions.

The patient coughed an average of 3 to 25 times a day before stem cell transplantation. There was no clincal improvement in chest X-ray examination after 1 week of stem cell treatment (Fig. 1B), but the number of coughs was significantly reduced to once or not a day (Fig. 2B) and there were no side effects like hypersensitivity, vomiting, throat pain, bleeding, pneumonae, and graft failure. Appetite and activity were clinically improved compared to before stem cell transplantation and there was no dyspnea or nausea. Later on, she additionally had 6 times stem cell transplants after a month of first transplantation series, and we observed the patient post stem cell transplantation for 6 months and confirmed that there was no longer any coughing.

Stem cell transplantation in animal models of COPD has in vivo safety, immunogenicity, pharmacokinetics, and therapeutic value in many cases of preclinical studies. In addition, various tissue-derived stem cells were safe and effective for intravenous and intratracheal injection in animal models of COPD (Liu et al., 2016). In our case report, we could see a big improvement after a transplantation of stem cell, and additionally appetite was also increased compared to before the stem cell therapy. The immunomodulation and anti-inflammatory abilities of stem cells are thought to be important in the treatment of COPD.

Chronic inflammation is known to be a major cause of COPD, asthma, and interstitial lung disease (ILD). Immunomodulation and anti-inflammatory abilities of mesenchymal stem cells are effective in the treatment in various animal models. When bone marrow-derived stem cells were transplanted in a COPD mouse animal model, pro-inflammatory mediators including TNF-α, IL-1β, MCP-1, and IL-6 and proteases such as MMP9 and MMP12 were down-regulated, and VEGF and its receptors were up-regulated (Guan et al., 2013). Antiapoptotic properties of mesenchymal stem cells increased cell proliferation in the damaged area and improved the pulmonary vascularity, which is followed by restoring emphysema (Zhen et al., 2010; Huh et al., 2011). Mesenchymal stem cells also reduced Th2-associated cytokines to maintain Th1/Th2 balance and promote immune tolerance through Treg proliferation (Nemeth et al., 2010).

The amnion is a valuable source which a large number of stem cells can be easily obtained by a non-invasive method and is the similar stemness of mesenchymal stem cells (De Coppi et al., 2007). Since allogeneic mesenchymal stem cells lack the expression of MHC I and MHC II and have immune tolerance in allografts, they can be safely used in clinical practice (Patel et al., 2008; Lee et al., 2011). The amniotic membrane-derived stem cells also have the aforementioned benefits and can be widely used for animal stem cell therapy.

In this study, the cat has great improvement clinically by stem cell transplantation rather than conventional drug treatment in cat with COPD. As we know, COPD for cats and human is difficult to be treated without continuous medicine such as immune suppressants. The medicine potentially has side effects and inconvenience. In addition, life quality would be worsen with medicine. Therefore, stem cell transplantation will be another great solution for respiratory disorders in humans and animals.

None.

Conceptualization, T.K. and J.J.; data curation, T.K. and J.J.; formal analysis, S.A.N. and J.J.; funding acquisition, J.J.; investigation, J.J.; methodology, J.J.; project administration, J.J.; resources, S.A.N. and J.J.; software, T.K.; supervision, J.J.; validation, J.J.; visualization, S.A.N. and T.K.; writing - original draft, T.K. and J.J.; writing - review & editing, T.K. and J.J.

This study was supported by grants from the National Research Foundation of Korea (NRF-2019M3A9H1103582).

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No potential conflict of interest relevant to this article was reported.