High throughput performance-based selection and expansion of clonal progenitor populations resident in human articular cartilage to characterize sub-populations for effective cartilage stem cell therapies

Abstract

Background & Aim Enormous heterogeneity in autogenous tissue sources of mesenchymal stromal cells (MSCs) with respect to the quantity and quality of the stem and progenitor cells that serve as the starting materials for cellular therapeutics limits delivery of safe, effective and reliable cellular therapies. The goal of this study is to identify the subset of the progenitors with systematically characterized critical quality attributes (CQAs) that can be selectively expanded to obtain clonal cell populations with better quality and reproducibility that can help improve stem cell therapies. Methods, Results & Conclusion Articular cartilage (Outerbridge grade 1-2) obtained from six knee arthroplasty patient's were enzymatically digested to isolate cells for 2-D cell culture assay. Large field of view images were acquired daily to capture images of the progenitors and their progeny for standardized ASTM-based automated image analysis to define and quantify CQAs of the stem/progenitor cells. Based on the CQAs identified, 24 clonal populations from each patient were picked using Cell XTMrobotic device in rapid, precise, repeatable and rigorously documented manner. Of the 24 clonal colonies, twelve fastest growing clones were expanded to 20 doublings for trilineage differentiation assay and RNA sequencing analysis. Preliminary assessment indicated wide variation in morphological and biological characteristics of progenitor and their progeny: circularity (median: 0.665; range:0.15-0.93), area (median: 116.4µm2; range:51.9-204.2µm2), doubling time (median:32.9h; rangse:26.9-41.2h) and colony density (median:6.5%;range:2.3-20.7%). Differences seen between two representative clonal populations with respect to the trilineage differentiation potential and gene expression seen at 20 doublings is shown in Figure 1 and 2 respectively. A complete detailed assessment of all the clonal populations and their culture-expanded population (n=72) will help us identify the CQAs that will aid in selection of quality clones. An improved understanding of the heterogeneity of progenitor cells resident in adult cartilage will also improve the rigor of cell sourcing and targeting decisions for pharmacological and cellular therapies. The automated methods for rapid and high precision analysis and management of cell populations that we have built into Cell X™ represent an important advancement in the tools that are available in the field for stem cell research and manufacturing.