Key Point

Mesenchymal stem cells can differentiate into AECs, ex vivo. By means of a virus vector, the stem cells can be gene corrected in CF patients.

NEW ORLEANS—Cystic fibrosis (CF), caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, affects the transport of chloride across airway epithelium. This in turn causes impaired lung defenses, frequent infections, and death, often by as early as age 30. However, new research has shown that ex vivo, adult stem cells can differentiate into airway epithelial cells (AECs). Moreover, the CFTR defect in stem cells from CF patients can be corrected using a virus vector.¹

STEM CELLS TESTED

Guoshun Wang, DVM, PhD, and colleagues assessed the ability of mesenchymal stem cells (MSCs) from two controls to differentiate into AECs. MSCs are distinct from hematopoietic stem cells, which were not used. The researchers then tested whether MSCs from three CF patients could be CFTR-corrected and able to secrete chloride, in the same manner as healthy cells. According to Dr. Wang, an Assistant Professor of Medicine and Genetics at the Louisiana State University Health Sciences Center, “Stem cells can be cultured, expanded, and gene-corrected ex vivo. Furthermore, gene-corrected CF stem cells are able to contribute the apical chloride secretion when co-cultured with CF airway epithelial cells.”

HOW STEM CELL THERAPY WORKS

After being cultured with AECs for two weeks, some MSCs from controls differentiated into AECs. The differentiated cells expressed epithelia-specific genes. In addition, the cells contained occludin, a tight junction protein. Moreover, CFTR was expressed in these cells. These results demonstrate that stem cells taken from healthy people and cultured with mature AECs can indeed become fully functioning AECs.

The researchers then evaluated whether autologous cell-based therapy in CF patients would be a viable approach. Bone marrow was aspirated from three homozygous ΔF508 CF patients, and the MSCs were isolated and expanded. Using a viral vector (Moloney murine leukemia virus-CFTR-neo), the researchers transduced CFTR into the cells.

“We complemented the CF-stem cells with a normal copy of CFTR by viral vector–mediated gene transfer,” commented Dr. Wang. After three days, the cells were successfully gene corrected. These corrected cells retained their pluripotency (they had the ability to differentiate into adipogenic, osteogenic, and chondrogenic cells), indicating that the gene-corrected stem cells from CF patients have the same differentiation potential as stem cells from healthy people.

Lastly, the researchers determined whether the gene-corrected stem cells in CF patients were functional—in other words, if they were able to secrete chloride as do healthy cells. To do this, both gene-corrected and non–gene-corrected stem cells from CF patients were cultured with CF AECs in a dose-dependent fashion (0% to 20%). After one month, radioactive chloride was applied to the basal culture medium. The corrected CF stem cells secreted significantly more chloride to the apical side after cyclic adenosine monophosphate (cAMP) stimulation than did MSCs without gene correction, indicating that chloride transport function was partially restored in the epithelium.

A TREATMENT FOR HUMAN CF?

The data provide proof of principle that CFTR-corrected stem cells may one day be a treatment for CF; they have the potential to improve chloride secretion, and thus, possibly modify airway-surface liquid composition and host defense in the lung. The researchers acknowledged that in vivo studies would need to be performed to confirm their data. Using autologous stem cell transplantation in humans with CF is a long way off, and one potential barrier is “recruiting enough stem cells to the lung and inducing them to differentiate into airway epithelial cells,” explained Dr. Wang. However, stem cells show great promise, and only future research can determine if this promise is borne out in humans.

—Tamara Gibb

Reference
1. Wang G, Bunnell BA, Painter RG, et al. Adult stem cells from bone marrow stroma differentiate into airway epithelial cells: potential therapy for cystic fibrosis. PNAS. 2005;102:186-191.

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