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Background Aims: Advanced therapy medicinal products (ATMPs) are novel drugs based on genes, cells or tissues developed to treat many different diseases. Stability studies of each new ATMP need to be performed to define its shelf life and guarantee efficacy and safety upon infusion, and these are presently based on guidelines originally drafted for standard pharmaceutical drugs, which have properties and are stored in conditions quite different from cell products. The aim of this report is to provide evidence-based information for stability studies on ATMPs that will facilitate the interlaboratory harmonization of practices in this area., Methods: We have collected and analyzed the results of stability studies on 19 different cell-based experimental ATMPs, produced by five authorized cell factories forming the Lombardy "Plagencell network" for use in 36 approved phase I/II clinical trials; most were cryopreserved and stored in liquid nitrogen vapors for 1 to 13 years., Results: The cell attributes collected in stability studies included cell viability, immunophenotype and potency assays, in particular immunosuppression, cytotoxicity, cytokine release and proliferation/differentiation capacity. Microbiological attributes including sterility, endotoxin levels and mycoplasma contamination were also analyzed. All drug products (DPs), cryopreserved in various excipients containing 10% DMSO and in different primary containers, were very stable long term at <-150°C and did not show any tendency for diminished viability or efficacy for up to 13.5 years., Conclusions: Our data indicate that new guidelines for stability studies, specific for ATMPs and based on risk analyses, should be drafted to harmonize practices, significantly reduce the costs of stability studies without diminishing safety. Some specific suggestions are presented in the discussion., (Copyright © 2022 International Society for Cell & Gene Therapy. Published by Elsevier Inc. All rights reserved.)

Background Aims: Mesenchymal stromal cells (MSCs) exert broad immunomodulatory functions. We recently demonstrated a strong suppressive effect of MSCs on virus-specific CD8(+) T-cell proliferation. Here, we further explored the underlying mechanism., Methods: The role of indoleamine 2,3-dioxygenase (IDO) in inhibition of virus-specific CD8(+) T-cell proliferation by human MSCs was investigated using a mixed lymphocyte peptide culture assay, IDO intracellular staining and IDO inhibition through 1-methyl-DL-tryptophan (1-MT). Moreover, the influence of the number of passages and the seeding density of MSCs on their IDO expression and immunosuppressive ability were investigated., Results: MSCs with low IDO expression exhibited a reduced suppressive effect on both allo-antigen- and cytomegalovirus (CMV)-specific CD8(+) T-cell proliferation. 1-MT could partially abrogate the suppressive effect. MSCs inhibited CMV-specific CD8(+) T-cell proliferation regardless of the number of passages and the seeding density. IDO expression of MSCs was not significantly affected by the number of passages or the seeding density. In addition, the interferon (IFN)-γ level in the culture system was crucial for MSCs to inhibit the proliferation of CMV-specific CD8(+) T cells., Summary: MSCs inhibit virus-specific CD8(+) T-cell proliferation through IFN-γ-induced IDO activity, resolving current conflicting reports on this issue and indicating the potential need for prophylaxis and surveillance of virus infection in patients treated with MSCs. In addition, our study makes a contribution to the development of MSC potency assay for clinical use., (Copyright © 2016 International Society for Cellular Therapy. Published by Elsevier Inc. All rights reserved.)

Mesenchymal stromal cells (MSCs) as a pharmaceutical for ailments characterized by pathogenic autoimmune, alloimmune and inflammatory processes now cover the spectrum of early- to late-phase clinical trials in both industry and academic sponsored studies. There is a broad consensus that despite different tissue sourcing and varied culture expansion protocols, human MSC-like cell products likely share fundamental mechanisms of action mediating their anti-inflammatory and tissue repair functionalities. Identification of functional markers of potency and reduction to practice of standardized, easily deployable methods of measurements of such would benefit the field. This would satisfy both mechanistic research as well as development of release potency assays to meet Regulatory Authority requirements for conduct of advanced clinical studies and their eventual registration. In response to this unmet need, the International Society for Cellular Therapy (ISCT) addressed the issue at an international workshop in May 2015 as part of the 21st ISCT annual meeting in Las Vegas. The scope of the workshop was focused on discussing potency assays germane to immunomodulation by MSC-like products in clinical indications targeting immune disorders. We here provide consensus perspective arising from this forum. We propose that focused analysis of selected MSC markers robustly deployed by in vitro licensing and metricized with a matrix of assays should be responsive to requirements from Regulatory Authorities. Workshop participants identified three preferred analytic methods that could inform a matrix assay approach: quantitative RNA analysis of selected gene products; flow cytometry analysis of functionally relevant surface markers and protein-based assay of secretome. We also advocate that potency assays acceptable to the Regulatory Authorities be rendered publicly accessible in an "open-access" manner, such as through publication or database collection., (Copyright © 2015 International Society for Cellular Therapy. Published by Elsevier Inc. All rights reserved.)