Mesenchymal stromal cells(MSCs),known for their therapeutic bioactivity,find widespread application as cellular drugs for treating various diseases.MSCs obtained from patients or donors require extensive large-scale expansion for clinical applications.However,the conventional method of cultivating MSCs involves several manual processes and yields inconsistent batch-to-batch quality.Consequently,it has not been scalable as a cell therapy[1].

To overcome the limitations of conventional planar cell culture,van Wezel initially proposed a system for culturing cells in suspension using microcarriers and successfully proliferated rabbit embryonic skin cells and human embryonic lung cells [2].Subsequently,microcarrier technology has been employed across various pharmaceutical applications,leading to the development and commercialization of a diverse array of microcarriers with distinct physicochemical properties.SoloHill Engineering Inc.has introduced several microcarriers,including Plastic,Collagen,Glass,Hillex?CT,ProNectin?F,and FACT III,all of which facilitate MSC expansion [3-6].Commercial microcarriers such as CultiSpher S(Sigma),SphereCol (Advanced BioMatrix),Cytodex 1 (GE Healthcare),and Cytodex 3(GE Healthcare)have demonstrated enhanced chondrogenic differentiation of MSCs [5-7].Nonetheless,the single-use cell production volume,operational convenience,biocompatibility,and biodegradability of these microcarriers need further enhancement.The presence of microcarrier remnants in the final product has raised safety concerns[1].A team led by Yanan Du [8] has introduced an automated closed industrial-scale cell production (ACISCP) platform employing Good Manufacturing Practice (GMP)-grade 3D TableTrix?microcarriers.This approach facilitates the suspension culture of clinical-grade MSCs on an industrial scale.Approved as a drug excipient by both the U.S.Food and Drug Administration and the Center for Drug Evaluation,China,3D TableTrix?constitutes a dissolvable and porous microcarrier with open pores that enable cellular attachment to inner walls,closely resembling in vivo microenvironments.The chemical and physical characteristics of the microcarrier can be precisely tailored,allowing customized designs of cellular microenvironments according to the culturing cell type.This technology eliminates the use of trypsin or TrypLE?to detach MSCs from the culture matrix,which are substances that compromise cell viability and quality.In comparison to conventional microcarriers,the 3D TableTrix can be rapidly dissolved within 1 h using a specialized reagent,3D FloTrix Digest,leading to approximately 100% cell harvesting and facilitating MSC harvesting[9].

The most significant advantage of this system lies in its resolution of the challenge surrounding industrial-scale expansion of MSCs.MSCs underwent a three-stage expansion process utilizing 1,5,and 15 L vivaSPIN bioreactors,respectively.After introducing 1.5×107MSCs and 0.6 g 3D TableTrix into a 1 L vivaSPIN bioreactor,cell expansion took place in the 5 and 15 L bioreactors,resulting in a yield of 2.09×1010cells from two 15 L bioreactors,reflecting a cumulative 1975-fold expansion achieved within 13 days.It is noteworthy that the ACISCP platform facilitated automated MSC harvesting through enzymatic digestion of 3D TableTrix,obviating the need for manual digestion.Furthermore,MSCs derived from ACISCP adhered to existing quality standards for therapeutic cell products,offering numerous advantages over traditional 2D culture models,including safety,purity,homogeneity,chromosomal stability,and immunomodulatory potency [8].

The ACISCP cell manufacturing system represents a fully enclosed and automated industrial-scale platform for cell production.Equipped with an automated monitoring and control system,this platform significantly reduces the necessity for human intervention and effectively mitigates the risk of microorganism contamination.The system holds considerable potential for enhancing process efficiency,curtailing associated costs,ensuring reproducibility,and maintaining product uniformity.Therefore,this system emerges as a promising tool for addressing the limitations inherent in monolayer culture,thereby enabling automated industrial-scale manufacturing of clinical-grade MSCs within a single batch,adequately catering to the demands of a substantial patient population.Furthermore,the system can also offer comprehensive industrial solutions for other categories of adherent cells and their derivatives,including vesicles or exosomes.

To align with the rigorous regulations governing drug manufacturing,the ACISCP system must adhere to GMP standards,despite the GMP-grade classification of the 3D TableTrix microcarriers.Consequently,additional efforts are required to ensure the conformity of the ACISCP system with device manufacturing regulations and to facilitate its transition from an academic research endeavor to a fully commercialized product.This progression can facilitate the large-scale industrial production of clinicalgrade MSCs,thereby facilitating consistent advancements in stem cell-based therapies with clinical applications.

Declaration of competing interest

The authors declare that there are no conflicts of interest.