Introduction Mesenchymal stromal cells (MSCs) have opened a new window to treat inflammatory and non-inflammatory diseases. Nonetheless, their clinical applications require rigorous control and monitoring procedures to ensure full compliance with the principles of good manufacturing practice (GMP). Various evaluations should be passed in conjunction with the development of these newly emerging therapeutic products from bench-to-bedside. These evaluations include in vitro characterization, preclinical studies, and clinical trials to ensure product safety and efficacy. Therefore, a robust and well-designed preclinical study is critical to confirm product safety. This study aims to determine the probable toxicity effects of local and systemic injections of cryopreserved human bone marrow-derived clonal MSCs (BM-cMSCs) during subacute and subchronic periods of time. Methods BM-cMSCs were characterized according to the International Society for Cell and Gene Therapy (ISCT) criteria for MSCs. Both safety and toxicity of the BM-cMSCs population produced under GMP-compatible conditions were assessed in both sexes of Sprague Dawley (SD) rats via systemic intravenous (IV) administration and local injection in intervertebral disc (IVD). Behavioral changes, clinical signs of toxicity, and changes in body weight, water and food consumption were the important variables for product toxicity testing over 14 consecutive days during the subacute period and 90 consecutive days during the subchronic period. At the end of the assessment periods, the rats were killed for histopathology analysis of the target tissues. The BM-cMSCs potential for tumorigenicity was checked in nude mice. Results Single IV and IVD injections of BM-cMSCs did not cause significant signs of clinical toxicity, or changes in laboratory and histopathology data during the subacute (14 day) and subchronic (90 day) periods. Ex vivo-expanded and cryopreserved BM-cMSCs did not induce tumor formation in nude mice. Conclusion The results suggest that local and systemic administrations of xenogeneic BM-cMSCs in both sexes of SD rats do not cause toxicity during the subacute and subchronic periods of time. Also, BM-cMSCs were non-tumorigenic in nude mice.

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease of unknown cause. The interaction of immune system cells and the secretion of inflammatory cytokines with synovial cells leads to severe inflammation in the affected joints. Currently, medications, including non‐steroidal anti‐inflammatory drugs, glucocorticoids, and more recently, disease‐modifying anti‐rheumatic drugs, are used to reduce inflammation. However, long‐term use of these drugs causes adverse effects or resistance in a considerable number of RA patients. Recent findings revealed the safety and efficacy of mesenchymal stromal cells (MSCs)‐based therapies both in RA animal models and clinical trials. Here, the beneficial effects of bone marrow‐derived heterogeneous MSCs (BM‐hMSCs) and Wharton jelly‐derived MSCs (WJ‐MSCs) at early passages were compared to BM‐derived clonal MSCs (BM‐cMSCs) at high passage number on a rat model of collagen‐induced arthritis. Results showed that systemic delivery of MSCs significantly reversed adverse changes in body weight, paw swelling, and arthritis score in all MSC‐treated groups. Radiological images and histological evaluation demonstrated the therapeutic effects of MSCs. There was a decrease in serum level of anti‐collagen type II immunoglobulin G and the inflammatory cytokines interleukin (IL)‐1β, IL‐6, IL‐17, and tumor necrosis factor‐α in all MSC‐treated groups. In contrast, an increase in inhibitory cytokines transforming growth factor‐β and IL‐10 was seen. Notably, the long‐term passages of BM‐cMSCs could alleviate RA symptoms similar to the early passages of WJ‐MSCs and BM‐hMSCs. The importance of BM‐cMSCs is the potential to establish cell banks with billions of cells derived from a single donor that could be a competitive cell‐based therapy to treat RA.