Initial Cell Seeding Density in Culture Influences Hematopoietic Stem and Progenitor Cell Proliferation, Expansion...

Initial cell seeding density (CSD) has been identified as a key parameter that may determine the growth dynamics of hematopoietic cells in vitro. Herein, we have assessed hematopoietic cell growth in liquid cultures at different CSDs.

Two hematopoietic cell populations were cultured: CD34⁺ CD38^- cells (enriched for hematopoietic stem cells) and CD34⁺ CD38⁺ cells (enriched for hematopoietic progenitor cells) at doses of 1, 10, 100, or 1,000 cells/100 µL/well. Their proliferation, expansion, and differentiation were determined throughout 14 d of culture.

When cultured at a density of 1 cell per well, only 50% of the cells were able to proliferate. This was observed in both cell populations. At higher densities (100 or 1,000 cells/well), all culture wells showed proliferation. This suggests that either non-proliferating cells became proliferating under the influence of surrounding cells, or proliferating cells covered up and compensated for non-proliferating cells. Cell expansion was favored at intermediate densities (10 or 100 cells/well), whereas cell viability decreased at high densities (1,000 cells/well). Higher CSDs seemed to favor the generation of erythroid progenitors and accelerate cell differentiation.

Our results indicate that CD34⁺ CD38^- cells are more dependent on surrounding cells in culture than CD34⁺ CD38⁺ cells are. Further research is necessary to elucidate the actual mechanisms that control the division of primitive hematopoietic cells when cultured at such low cell densities.