3D Culture of MSCs in Bioreactors - the Importance of Microcarriers
Updated: Oct 7, 2020
Advances in clinical manufacturing processes are central in developing functional cell therapies, including those involving mesenchymal stem cells (MSCs). As well as challenges in consistently and reliably generating cells with the necessary therapeutic attributes (for example, self-renewal, immunomodulatory, and regenerative capacity), there is also the issue of producing batches of cells at the required scale to be therapeutically meaningful for the wider population (1).
Bioreactors are closed systems that enable the growth of cells in a highly controllable, consistent, and scalable manner. These platforms could be a potential solution to various manufacturing issues associated with the expansion of MSCs. As such, many innovative technologies have been implemented to maximize their feasibility for producing large batches of clinical-grade MSCs.
Bioreactors and 3D cultures
A challenge with MSCs is that they are adherent cells traditionally grown as 2D cultures. However, 3D cultures represent the in vivo microenvironment; they facilitate cell-cell adhesion and communication and improve morphology, pluripotency, and proliferative potential.
Bioreactors usually support the growth of suspension cultures. To overcome this and facilitate 3D culture, MSCs are often grown on adherent substrates, which act as a supporting matrix for suspension growth. These supporting matrices, which are usually in the form of ‘microcarriers’ also provide a greater surface area for cell growth, enabling large-scale manufacturing (2). The selection of the correct supporting matrices is essential to ensure the therapeutic potential of the MSCs is maintained.
One such example of a microcarrier that enables the 3D culture of bone marrow-derived MSCs is gelatin microspheres. These were recently found to support the differentiation of bone marrow-derived MSCs into chondrocytes for cartilage tissue engineering (2). It has been suggested that the effectiveness of gelatin could be due to the combination of amino acids found in gelatin, which recapitulate the conditions in the native extracellular matrix.
The Next Generation of Microcarriers
There are some practical hurdles associated with microcarriers. For instance, they must be effectively removed from the cultures prior to harvesting the cells. Additionally, preparing microcarriers for culture requires sterilization procedures, balancing them with culture media, and coating with proteins. These steps are time-consuming and technically challenging when scaling up to large volumes (3). Thus, there is a significant demand for novel microcarrier solutions that are easy-to-use in bioreactor systems and biodegradable (4).
Recently, scientists in Beijing employed a dissolvable macroporous gelatin-based microcarrier system. These microcarriers (3D TableTrix™) are commercially available as pre-weighed sterile tablets which readily absorb liquid and disperse into individual microcarriers in solution. A complementary dissolution reagent (3D FloTrix™ Digest) also dissolves the carriers, enabling the highly efficient recovery of cells during harvest (3). The MSCs manufactured in this manner also retained their differentiation potential and remain suitable for treatment.
In the future, we can expect further innovations in the technologies we use to grow MSCs. High-performance microcarriers are an important step towards reliably generating MSCs on a large scale.
This blog is part of a series on the production of MSCs in bioreactors. Next week, we will explore more recent innovations that have helped advance the production of MSCs for clinical use in the future.
References
1. Levy, O. et al. Shattering barriers toward clinically meaningful MSC therapies. Science advances vol. 6 eaba6884 (2020). doi: 10.1126/sciadv.aba6884
2. Sulaiman, S. et al. 3d culture of MSCS on a gelatin microsphere in a dynamic culture system enhances chondrogenesis. Int. J. Mol. Sci. (2020) doi:10.3390/ijms21082688.
3. Yan, X. et al. Dispersible and Dissolvable Porous Microcarrier Tablets Enable Efficient Large-Scale Human Mesenchymal Stem Cell Expansion. Tissue Eng. - Part C Methods (2020) doi:10.1089/ten.tec.2020.0039.
4. Lam, A. T. L. et al. Biodegradable poly-ε-caprolactone microcarriers for efficient production of human mesenchymal stromal cells and secreted cytokines in batch and fed-batch bioreactors. Cytotherapy 19, 419–432 (2017). doi: 10.1016/j.jcyt.2016.11.009.