Baf250a^E2E3/E2E3 stromal cell cultures support the in vitro self-renewal of progenitor/stem cell populations. (A) Enumeration of mesenchymal stem/progenitor cells in WT, Baf250a^E2E3/+, and Baf250a^E2E3/E2E3 FL cell populations. Each circular symbol represents individual FL population. Note the statistically significant difference between the WT, or Baf250a^E2E3/+, and the Baf250a^E2E3/E2E3 FL (unpaired t test, and 2-tailed P value determined). (B) Maintenance of CAFCday28 in the presence of WT or Baf250a^E2E3/E2E3 stromal cells. Primary stromal cell cultures (4-cm - 10-cm dishes for each genotype) were established using pools of 4 FL cell populations. BM cells isolated from recipients of WT or Baf250a^E2E3/E2E3 FL (2 recipients per genotype, > 85% of donor-derived PBL) were cocultured with stromal cell cultures for 28 days. CAFCday28 frequency at the beginning of experiment (t₀), or after 28-day maintenance in stromal cocultures, were determined by plating an aliquot of the input BM cells, or entire cellular content of the stromal cocultures, at limit dilution on pre-established AFT024 cell layers. Results are mean (± SD), of 2 independent experiments performed in duplicate and are presented as the number of CAFC per 3 × 10⁷ input BM cells. (C) Baf250a^E2E3/E2E3 stromal cell cultures support self-renewal of progenitor/stem cell populations. WT BM cells were seeded at limit dilution on pre-established WT or Baf250a^E2E3/E2E3 stromal cell layers in 96-well trays (4 independent stromal cell cultures for each genotype). After 4-week coculture, all wells estimated to comprise a single cobblestone area were replated on freshly established WT or Baf250a^E2E3/E2E3 stromal cell layers, and the frequency of secondary CAFCday28 was determined after additional 4-week maintenance.