Promotion of hematopoietic stem cell differentiation in vitro by a soluble mediator, allogeneic effect factor

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Abstract
This study was designed to investigate the effects of allogeneic effect factor (AEF), a soluble mediator derived from short‐term mixed lymphocyte cultures (MLC) of in vitro alloantigen‐primed T cells, on cultures of murine bone marrow cells. Cultures established under suboptimal conditions namely, in the absence of a pre‐established adherent cell layer as required in conventional Dextertype cultures–declined and lost their stem cell activity rapidly. In contrast, supplementation of these cultures, at initiation and thereafter, with AEF, but not with T cell growth factor (TCGF), induced cell growth and proliferation for several weeks. Such AEF‐supplemented cultures exhibited cellular heterogeneity and stem cell activity for significantly longer periods than the control cultures. Even in conventional Dexter cultures, established under optimal conditions, AEF had a beneficial effect on cellular growth and proliferation and myeloid progenitor cell (CFU‐C) activity. Furthermore, cells capable of synergizing with suboptimal numbers of mature T cells in con A‐induced mitogenic responses, shown by others to be pre‐T cells, were detected in the AEF‐supplemented cultures for several weeks.