Stem Cell-Based Product Biomanufacturing: From Cultivation Modalities to Population Based-Models

The engineering of bioprocesses for stem-cell based therapy products can benefit from the implementation of the quality by design paradigm in the manufacturing of biopharmaceutics. This approach requires better understanding of process parameters and product characteristics. The list of involved tasks is extensive but this presentation will focus on three core aspects. First, different cultivation modes are available for stem cell expansion and differentiation. Stirred suspension bioreactors, which are commonly used for high-density culture of vaccine and biosimilar producer cells, allow the propagation of stem cells as aggregates, on microcarriers or after encapsulation affording process design flexibility. Selection of the culture modality is largely dictated by attributes of the final cell type(s) including sensitivity to shear, and dependence of commitment on concentration gradients and paracrine signals. Second, cell growth in these systems is intimately influenced by the formulation of media and surfaces shaping the culture environment. After years of intense research efforts, the development is coming to fruition of chemically defined, xeno-free media and substrates conforming to current good manufacturing practices (cGMP) for pluripotent cell cultivation and directed differentiation along specific trajectories. The increasing reliance on small molecules to replace growth factors and cytokines has the benefits of reduced cost and increased medium stability. Third, stem cell bioprocess engineering is expected to gain significantly from mathematical models capturing the heterogeneity of stem/progenitor cell ensembles. Population-based models with multiple process variables as inputs quantified via process analytical technology can be used to map and control process (e.g. differentiation strength) or product attributes (cell phenotype or function) within a given design space. These models can be combined with next-generation sequencing and proteomic data to gain insight into ways by which gene/protein networks interact with the process environment and guide optimization efforts. Despite the significant strides noted in the areas discussed here, integration of approaches from a broad range of disciplines will be essential for the realization of robust, economical processes for stem cell-based product manufacturing.