Stem cell products derived from mesenchymal stem cells (MSCs) have been widely used in clinical trials, and a few products have been already commercialized. However, the therapeutic effects of clinical-grade MSCs are still controversial owing to mixed results from recent clinical trials. A potential solution to overcome this hurdle may be to use clonal stem cells as the starting cell material to increase the homogeneity of the final stem cell products. We have previously developed an alternative isolation and culture protocol for establishing a population of clonal MSCs (cMSCs) from single colony forming unit (CFU)-derived colonies. In this study, we established a good manufacturing practice (GMP)-compatible procedure for the clinical-grade production of human bone marrow-derived cMSCs based on the subfractionation culturing method. We optimized the culture procedures to expand and obtain a clonal population of final MSC products from single CFU-derived colonies in a GMP facility. The characterization results of the final cMSC products met our preset criteria. Animal toxicity tests were performed in a good laboratory practice facility, and showed no toxicity or tumor formation in vivo. These tests include single injection toxicity, multiple injection toxicity, biodistribution analysis, and tumorigenicity tests in vivo. No chromosomal abnormalities were detected by in situ karyotyping using oligo-fluorescence in situ hydridization (oligo-FISH), providing evidence of genetic stability of the clinical-grade cMSC products. The manufacture and quality control results indicated that our GMP methodology could produce sufficient clonal population of MSC products from a small amount of bone marrow aspirate to treat a number of patients.

Successful therapy for radiation-induced salivary gland (SG) hypofunction is currently unavailable; however, tissue-specific stem cells are expected to be promising candidates for SG regeneration. Here, we present our method for the establishment of single cell-derived clonal stem cells from mouse SGs and describe their characteristics. Salivary gland-derived clonal stem cells (SGSCs) were isolated and expanded in vitro by a modified subfractionation culture method. The properties of SGSCs were examined with respect to their marker expression, gene expression, differentiation potential, and in vitro immunosuppressive activity relative to bone marrow-derived mesenchymal stem cells (BM-MSCs). SGSCs appeared to largely share the characteristics of BM-MSCs based on their marker expression, whereas they differentially expressed some genes, including AQP5, E-Cadherin, Laminin, ZO-1, and COL4. SGSCs showed the ability to differentiate into fat, bone, and cartilage cell types, as well as into α-amylase-producing and hepatocyte-like cells after appropriate induction. The in vitro immunosuppressive activity of SGSCs was found to be more potent than that of BM-MSCs. These results showed that SGSCs possess the properties of MSCs with some differential gene expression and they are salivary-specific stem cells with both epithelial and mesenchymal properties. The biological functions of SGSCs and their relevance to SG epithelial progenitor cells require further investigation.