Optimization of Freeze-Dried Formulations for the Preservation and Viability of Human Mesenchymal/Stromal Stem Cells

Aim: To overcome the logistical hurdles associated with cryostorage, cell therapy products would benefit from being stored as a (freeze-) dried product. However, there is currently unfortunately not a lot of focus in the field to evaluate formulations for their capabilities to preserve cells, especially not in dried states. Current strategies to tackle this challenging task lack cohesive and translationally applicable approaches to select promising formulations. At early stages of freeze-dried cell therapy product development an efficient and reliable approach to select suitable formulations is key to enable the development process. It was thus the aim of this study to offer an applicable approach that screens for potentially viable formulations for dried cell therapy products. Methodology: This comprehensive multi-step approach combines several reliable, complementary methods and comprises of measuring glass transition temperature, residual moisture, cell membrane integrity, morphology, viability, and proliferation to successively narrow the range of potentially applicable formulations. We employed this approach for a selected set of novel urea- and glucose-based formulations with clinically relevant human mesenchymal/stromal stem cells. Results: Some evaluated conditions yielded partially dried products and up to 38% viable and proliferating cells were retrieved from a formulation comprising of urea, glucose, sucrose, and mannitol. Other formulations comprising of urea, glucose, sucrose, PEG 8000, and PEG 400 yielded elegant cakes and high numbers of membrane intact cells (up to 95%). Conclusion: This approach presented here offers an efficient setup to screen formulations for their capabilities to protect cells during freeze-drying. The evaluated formulations benefit from employing well-tolerated pharmaceutical excipients, which makes them potentially applicable in cell therapy products. These promising findings invite for further investigations to improve (long term) product and cellular stability.