Preservation of differentiation and clonogenic potential of human hematopoietic stem and progenitor cells during lyophilization and ambient storage

Abstract

Progenitor cell therapies show great promise, but their potential for clinical applications requires improved storage and transportation. Desiccated cells stored at ambient temperature would provide economic and practical advantages over approaches employing cell freezing and subzero temperature storage. The objectives of this study were to assess a method for loading the stabilizing sugar, trehalose, into hematopoietic stem and progenitor cells (HPC) and to evaluate the effects of subsequent freeze-drying and storage at ambient temperature on differentiation and clonogenic potential. HPC were isolated from human umbilical cord blood and loaded with trehalose using an endogenous cell surface receptor, termed P2Z. Solution containing trehalose-loaded HPC was placed into vials, which were transferred to a tray freeze-dryer and removed during each step of the freeze-drying process to assess differentiation and clonogenic potential. Control groups for these experiments were freshly isolated HPC. Control cells formed 1450±230 CFU-GM, 430±140 BFU-E, and 50±40 CFUGEMM per 50 μL. Compared to the values for the control cells, there was no statistical difference observed for cells removed at the end of the freezing step or at the end of primary drying. There was a gradual decrease in the number of CFU-GM and BFU-E for cells removed at different temperatures during secondary drying; however, there were no significant differences in the number of CFU-GEMM. To determine storage stability of lyophilized HPC, cells were stored for 4 weeks at 25oC in the dark. Cells reconstituted immediately after lyophilization produced 580690 CFU-GM (~40%, relative to unprocessed controls p<0.0001), 170670 BFU-E (~40%, p,0.0001), and 41622 CFU-GEMM (~82%, p = 0.4171), and cells reconstituted after 28 days at room temperature produced 5136170 CFU-GM (~35%, relative to unprocessed controls, p <0.0001), 112668 BFU-E (~26%, p<0.0001), and 36617 CFU-GEMM (~82%, p = 0.2164) These studies are the first to document high level retention of CFU-GEMM following lyophilization and storage for 4 weeks at 25uC. This type of flexible storage stability would potentially permit the ability to ship and store HPC without the need for refrigeration. © 2010 Buchanan et al.