Model-based estimation of myeloid hematopoietic progenitor cells in ex vivo cultures for cell and gene therapies

Ex vivo production of hematopoietic progenitor cells has potential applicat ions for cell therapy to alleviate cytopenias associated with chemotherapy and for gene therapy. In both therapies, progenitor and stem cells are cons idered crucial factors for therapeutic success. Assays for progenitor cells , however, take 2 weeks to complete, which is similar to the length of a ty pical culture. Therefore, a real-time estimation of the percentage or numbe r of progenitor cells, based on rapid measurements, would be useful for opt imization of feeding and harvest decisions. In this study, metabolic activi ty assays and flow cytometric analysis were used to estimate the content of progenitor cells. The measured metabolic activities are a collective contr ibution from all types of cells. Cells in granulomonocytic cultures have be en lumped into six cell types and metabolic rates have been modeled as a li near function of cell composition and growth rate and as a nonlinear functi on of cell density. Data from 24 experiments were utilized to determine the model parameters in a calibration step. These data include flow cytometric analysis of more mature hematopoietic cells, progenitor cell colony assays , total cell content, and metabolite concentrations, and cover a wide range of cell composition, cell density, and growth rate. After calibration, the model is able to deliver good predictions of progenitor cell content for c ultures with higher percentages of progenitor cells, as well as the peak pr ogenitor cell content, based only on parameters that can be rapidly measure d. With the aid of those predictions a harvest strategy was developed that will allow optimizing the harvest time based on the culture kinetics of eac h patient or donor inoculum, rather than using retrospective analysis to de termine a uniform harvest time. (C) 2000 John Wiley & Sons, Inc.