Proliferation of HEL cells under various coculture conditions with a murine hematopoietic supportive stromal cell line, HESS-5 cells. HEL cells (2 × 10⁵ cells) were cultured without stromal cells (□), or cocultured with HESS-5 cells with direct cell contact (○) or without cell contact (•) in RPMI-1640 medium supplemented with 0.1% (wt/vol) BSA in triplicate wells. The cell contact between HEL cells and HESS-5 cells was prevented by a microporous membrane on the confluent cell layer of HESS-5 cells. The results are expressed as mean values ± SD of the mean.