Distinct Stromal Cell Factor Combinations Can Separately Control Hematopoietic Stem Cell Survival, Proliferation, and Self-Renewal

Hematopoietic stem cells (HSCs) are identified by their ability to sustain prolonged blood cell production in vivo, although recent evidence suggests that durable self-renewal (DSR) is shared by HSC subtypes with distinct self-perpetuating differentiation programs. Net expansions of DSR-HSCs occur in vivo, but molecularly defined conditions that support similar responses in vitro are lacking. We hypothesized that this might require a combination of factors that differentially promote HSC viability, proliferation, and self-renewal. We now demonstrate that HSC survival and maintenance of DSR potential are variably supported by different Steel factor (SF)-containing cocktails with similar HSC-mitogenic activities. In addition, stromal cells produce other factors, including nerve growth factor and collagen 1, that can antagonize the apoptosis of initially quiescent adult HSCs and, in combination with SF and interleukin-11, produce >15-fold net expansions of DSR-HSCs ex vivo within 7 days. These findings point to the molecular basis of HSC control and expansion. [Display omitted] •HSC viability, mitogenesis, and self-renewal are differentially controlled•Stromal cells produce nonmitogenic factors that directly sustain HSC viability•More adult bone marrow cells can produce HSCs than display HSC activity directly•Nerve growth factor and collagen 1 promote serially transplantable HSCs Wohrer et al. now show that different factors secreted by stromal cells separately control the survival, proliferation, and self-renewal of hematopoietic stem cells. These factors are thus required in combination to stimulate net expansions of these cells with full retention of their original stem cell properties.