Ex vivo expansion of CD34+ cells in a noncontact transwell system with C17.2 cells. Enriched CD34+ cells were cultured for 8 days in a transwell system in the presence of cytokines T6F, with or without pre-established C17.2 cells. C17.2 cells promoted the expansion of various stem and progenitor cell populations. n=8. **P⩽0.01.