Partial characterization of a novel stromal cell-derived pre-B-cell growth factor active on normal and immortalized pre-B cells.

Characterization of three stromal cell lines that support the proliferation of murine pre-B cells showed that they all exhibit a fibroblast-like morphology, but express laminin and collagen type IV, and behave as pre-adipocytes. One of these lines was used as a feeder for the isolation of feeder-dependent (A8 cells) and feeder-independent (H9 cells) pre-B-cell subclones present in a spontaneously immortalized line of pre-B cells that originally arose in a long-term lymphoid marrow culture. Both pre-B subclones show the same JH gene rearrangement and are strongly BP-1 positive but differ from most pre-B-cell lines described to date in that they do not express immunoglobulin (Ig), B220, or T200. Cell density experiments confirmed that A8 cells do not proliferate (or survive) in the absence of an appropriate feeder layer when cultured alone at concentrations less than 10(5) cells/ml, but greater than 10(5) cells/ml can undergo a short-lived burst of proliferation. In contrast, H9 cells are readily maintained as an autonomous line at concentrations greater than 10(4) cells/ml, but their growth is suboptimal in the absence of stromal cells at lower concentrations, and at less than 3000 cells/ml, their ability to proliferate ceases. Additional experiments demonstrated that at least part of the supportive function of the stromal cells is due to their ability to produce a low molecular weight, heat-resistant factor that is active on normal pre-B cells as well as both A8 and H9 cells, and appears to be different from any previously described hemopoietic growth factor.