American Fluoroseal Corporation

Feeder layers consisting of fibroblasts or other connective tissue elements have been employed since 1955 to enhance the growth of cultured cells, presumably by conditioning the substrate with trophic factors and other cell products. 

This method was first applied to the culture of bone marrow cells by Dexter and co-workers who demonstrated that hematopoietic stem cell renewal was sustained in cultures inoculated onto a preestablished support layer of medullary stromal cells. Earlier attempts to culture hematopoietic cells in the absence of this support layer promoted only the terminal differentiation of the stem cells in the initial inoculum with no evidence of self-renewal. Several different types of cells have been identified in the stromal compartment of the bone marrow.

These include macrophages which support erythropoiesis and influence  granulopoiesis, reticular cells which have been implicated in the synthesis of extracellular matrix components endothelial cells which are associated with granulopoiesis and have been reported to elaborate colony stimulating factors and interstitial (type Ill) collagen, several subsets of fibroblasts which synthesize other collagens and essential components of the marrow microenvironment, and adipocytes which are associated with mature granulocytic precursors in long-term bone marrow cultures (LTBMC) and the perisinal region of marrow in vivo.  Stromal cells appear to regulate hematopoiesis by synthesizing colony stimulating factors (CSF) and other trophic substances and form the  hematopoietic microenvironment.

Qualitative differences in stroma capable of supporting myelopoiesis and erythropoiesis have been reported. Other studies indicate that stromal cell regeneration precedes hematopoietic recovery after local bone marrow injury and following bone marrow transplantation (BMT). 

The influence of stromal cell monolayers at different stages of confluence on suspended nylon screen (LTMBC) is described in the present paper. Also included is data indicating that an immortal cell line of human fetal fibroblasts can support the initial seeding and long-term growth of human and nonhuman primate but not rat bone marrow cells.