gp96 null hematopoietic progenitors fail to proliferate and differentiate in BM stromal cell cultures. Purified WT and gp96 KO BM Lin⁻c-kit⁺ progenitor cells were cultured on BM stromal cell OP9 or OP9-DL1 for 3 weeks and analyzed for cell growth and differentiation. (A-B) Kinetic analysis of cell proliferation. (C-D) Flow cytometric analysis of T- and B-cell development after 3 weeks of coculture. (E) Bright field image of day 5 coculture of WT or KO Lin⁻c-kit⁺ progenitors on OP9 (original magnification ×100). Dotted circle denotes “cobblestone” colony. A few KO progenitors were indicated by. Three experiments were performed with similar results.