BackgroundMesenchymal stromal cells (MSC) are largely investigated in clinical trials aiming to control inappropriate immune reactions (GVHD, Crohn’s disease, solid organ transplantation). As the percentage of MSC precursors in bone marrow is very low, these must be expanded in vitro to obtain therapeutic cell doses. We describe here the constitution of an allogeneic human third-party MSC bank from screened healthy volunteer donors in compliance with quality specifications and ISCT-release criteria and report follow-up of different aspects of this activity since 2007.Methods68 clinical-grade large-scale MSC cultures were completed and analyzed. The whole process was described, including volunteer donor screening, bone marrow collection, mononuclear cell isolation and expansion over 4 weeks, harvesting, cryopreservation, release, administration and quality controls of the cells (including microbiology, phenotype, and potency assays).ResultsFrom 59 validated donors, 68 cultures were completed (mean of final yields: 886 × 106 cells/culture) and a total of 464 MSC aliquots have been produced and stored in liquid nitrogen (mean of 132.8 × 106 cells/bag). Each MSC batch underwent extensive testing to verify its conformity with EBMT and ISCT release criteria and was individually validated. As of June 1 2015, 314 bags have been released and infused to patients included in 6 different clinical protocols. All thawed MSC units satisfied to release criteria and no infusion-related toxicity was reported.ConclusionIn conclusion, despite low passage cultures, we have been able to create an allogeneic “off-the-shelf” MSC bank with a large number of frozen aliquots and report here an efficient clinical-grade MSC banking activity in place for more than 7 years. Our challenge now is to produce MSC in compliance with good manufacturing practices (GMP) as, in the meantime, MSC have become considered as advanced therapy medicinal products (ATMP). Another significant challenge remains the development of relevant potency assay.

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Background We investigated the ability of clinical‐grade enriched human regulatory T cells (Treg) to attenuate experimental xenogeneic graft‐versus‐host disease (GVHD) induced by peripheral blood mononuclear cells (PBMNCs; autologous to Treg) infusion in NSG mice, as well as verified their inability to induce xenogeneic GVHD when infused alone. Study Design and Methods Human Treg were isolated from peripheral blood apheresis products with a cell separation system (CliniMACS, Miltenyi Biotec GmbH) using a two‐step procedure (simultaneous CD8 and CD19 depletion followed by CD25‐positive selection) in six independent experiments with six different healthy volunteer donors. Sublethally (2.5 Gy) irradiated NSG mice were given 2 × 106 cytapheresis (PBMNC) product cells intravenously (IV) without (PBMNC group) or with 1 × 106 Treg (PBMNC + Treg group), while other NSG mice received 2 × 106 enriched Treg alone (also in IV; Treg group). Results The first five procedures were successful at obtaining a relatively pure Treg population (defined as >50%), while the sixth procedure, due to a technical problem, was not (Treg purity, 42%). Treg cotransfusion significantly delayed death from xenogeneic GVHD in the first five experiments, (p < 0.0001) but not in the sixth experiment. Importantly, none of the mice given enriched Treg alone (Treg group) experienced clinical signs of GVHD, while, interestingly, the CD4+ cells found in these mice 26 days after transplantation were mainly conventional T cells (median CD25+FoxP3+ cells among human CD4+ total cells were only 2.1, 3.1, and 12.2% in spleen, marrow, and blood, respectively). Conclusions Infusion of clinical‐grade enriched Treg delayed the occurrence of xenogeneic GVHD without inducing toxicity in this murine model.