Performance of a proliferation chamber with external stirred conditioning tank (PC-ESCT) was evaluated to expand a cell line as a model of suspendable stem cells. A hematopoietic cell line (U937) showed considerable cell proliferation in the PC-ESCT at seeding densities of 10(4) and 10(5) cells/mL (97.5 +/- 1.7 and 24.5 +/- 1.9-fold), as compared to the cultures in T-flask (80 +/- 2.8 and 21.5 +/- 1.4-fold) and stirred tank bioreactor (STB) (no detectable increase and 2.85 +/- 0.8-fold) after 8 days of culture. The round-shaped cells appeared dominantly in the T-flask and PC-ESCT cultures, while few cells could maintain their original phenotype or survive in the STB system during the culture period. The cell surface marker analysis of CD14 for testing self-renewing proliferation of the cells also coincide with the cell appearance and quantitative morphological analysis based on the roundness parameter. The present study showed the potential of the PC-ESCT for the expansion of suspendable stem cells in vitro. (C) 2015 Elsevier Ltd. All rights reserved.