RHEACELL GmbH & Co. KG

Background: The ability of mesenchymal stromal cells (MSCs) to facilitate regenerative responses in inflamed and injured tissues, coupled with preclinical data suggesting potential to restore defective collagen VII at the dermo-epidermal junction, has raised the hope that MSCs may provide an effective disease-modifying therapy for patients suffering from recessive dystrophic epidermolysis bullosa (RDEB).Methods: We present a descriptive analysis of the clinical research on systemic MSC administration to RDEB patients available in PubMed, including six early-phase studies and one case report, involving 59 patients who received 1-3 intravenous infusions of MSCs from various sources.Results: Based on 133 MSC infusions, a total of 44 mostly mild adverse events were reported as definitely, possibly or likely related to the study treatment, only two of which led to treatment discontinuation. Improvements were seen in skin manifestations, disease activity, pain, pruritus and quality of life, with considerable heterogeneity in reported outcome variables and measurement tools between studies, and large inter-patient variability within studies.Conclusions: Although the current evidence base is limited, reflecting the typical challenges of clinical research in rare diseases, the reported results suggest potential treatment benefits for patients and provide a rationale for continuing to pursue this therapeutic approach.

Given the high level of product complexity and limited regulatory guidance, designing and implementing appropriate potency assays is often the most challenging part of establishing a quality control testing matrix for a cell-based medicinal product. Among the most elusive tasks are the selection of suitable read-out parameters, the development of assay designs that most closely model the pathophysiological conditions, and the validation of the methods. Here we describe these challenges and how they were addressed in developing an assay that measures the anti-inflammatory potency of mesenchymal stromal cells (MSCs) in an M1 macrophage-dominated inflammatory environment.

An in vitro inflammation model was established by coculturing skin-derived ABCB5⁺ MSCs with THP-1 monocyte-derived M1-polarized macrophages. Readout was the amount of interleukin 1 receptor antagonist (IL-1RA) secreted by the MSCs in the coculture, measured by an enzyme-linked immunosorbent assay.

IL-1RA was quantified with guideline-concordant selectivity, accuracy and precision over a relevant concentration range. Consistent induction of the macrophage markers CD36 and CD80 indicated successful macrophage differentiation and M1 polarization of THP-1 cells, which was functionally confirmed by release of proinflammatory tumor necrosis factor α. Testing a wide range of MSC/macrophage ratios revealed the optimal ratio for near-maximal stimulation of MSCs to secrete IL-1RA, providing absolute maximum levels per individual MSC that can be used for future comparison with clinical efficacy. Batch release testing of 71 consecutively manufactured MSC batches showed a low overall failure rate and a high comparability between donors.

We describe the systematic development and validation of a therapeutically relevant, straightforward, robust and reproducible potency assay to measure the immunomodulatory capacity of MSCs in M1 macrophage-driven inflammation. The insights into the challenges and how they were addressed may also be helpful to developers of potency assays related to other cellular functions and clinical indications.