Characterization of human cartilage-derived progenitor heterogeneity for cellular therapy strategies using time-lapse phase-contrast imaging

Abstract

Background & Aim Cartilage tissue, one of the most popular sources of tissue for cartilage repair, contains a heterogeneous population of progenitors. However, only a subset of this population possess the significant biological potential to proliferate and differentiate to form cartilage. The goal of this study is to define the static and dynamic characteristics of these progenitors and progeny which can systematically serve as critical quality attributes (CQAs) for selection and expansion to obtain clonal cell populations with better quality and reproducibility to enable delivery of safe, effective and reliable cellular therapies. Methods, Results & Conclusion Articular cartilage (Outerbridge grade 1-2) obtained from nine knee arthroplasty patient's were enzymatically digested to isolate cells for 2-D cell culture assay. Large field of view phase contrast images were acquired hourly to capture images of the progenitors and their progeny (colony) for standardized ASTM-based automated colony-forming unit (CFU) analysis to define and quantify CQAs of the stem/progenitor cells and their progeny, which include: 1) lag-time for first division, 2) circularity, 3) area, 4) feret's diameter, 5) effective proliferation rate, and 6) colony density. Of the 225 colonies obtained from nine patients, 87 colonies (38.7%) were clonal (colony derived from single progenitor) and 138 colonies (61.3%) were non-clonal (colony derived from clumps of cells or multiple-single progenitors), as determined from the time-lapse video (Fig. 1). For the clonal colonies assessed, a wide variation was observed in morphological and biological characteristics of progenitor and their progeny as shown in Fig. 2: Lag time (median:3.8days; range:1.04-7days), circularity (median: 0.48; range:0.12-0.95), area (median: 534.4µm2; range:113.9-1988.9µm2), feret's diameter (median: 13.9µm; range:5.8-37.1µm) and colony density (median:16.9%;range:3.6-55%). 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 CQAs identified via this process can be reliably and reproducibly used for selection and expansion to obtain clonal cell populations to improve efficacy of cell therapy products.