Standardization of immune quality controls on clinical-grade mesenchymal stromal cells of different origin produced according to GMP rules

The versatile and wide range application of Mesenchymal Stromal Cells (MSC) for a diverse set of clinical indications has generated a great and increasing interest in MSC as potential therapeutic agents during last years. Research on MSC biology is progressing rapidly, as illustrated by the growing number of clinical trials using MSC. Some of them are taking advance of the immunosuppressive ability of MSC to treat some immunological based disease like GvHD or Multiple Sclerosis. MSC exhibit a wide range of immunosuppressive properties that target virtually any cell of the immune system and these properties can be easily affected and hampered by culture conditions. Therefore, to assess the immunological properties of clinical-grade MSC obtained from different laboratories it is crucial to design fully standardized and reproducible in vitro assays; otherwise, only not comparable, and frequent contradictory results could be achieved. We aimed to compare immune modulatory properties of clinical-grade MSC using a combination of fully standardized in vitro assays. BMMSC expanded with FCS (BMMSC-FCS) or PL (BMMSC-PL), and ADSC-PL were analyzed in parallel in two independent laboratories (Stem Cell Research Laboratory of the University of Verona and the INSERM Institute in Rennes, France). Standardized functional assays revealed that resting MSC inhibited proliferation of T and NK cells, but not B cells. ADSC-PL were the most potent in inhibiting T-cell growth, a property ascribed to IFN-γ-dependent indoleamine 2,3-dioxygenase activity. MSC did not stimulate allogeneic T cell proliferation but were efficiently lysed by activated NK cells. The systematic use of quantitative and reproducible validation techniques highlights differences in immunological properties of MSC produced using various clinical-grade processes. Among all cell tested, ADSC-PL emerge as the best promising candidate for future clinical trials.