HEMATOPOIESIS ON CELLULOSE ESTER MEMBRANES .13. A COMBINATION OF CLONED STROMAL CELLS IS NEEDED TO ESTABLISH A HEMATOPOIETIC MICROENVIRONMENT SUPPORTIVE OF TRILINEAL HEMATOPOIESIS

A mixture of stromal cells from murine bone marrow placed upon cellulo se ester membranes (CEM) and then implanted intraperitoneally (i.p.) i n mice results in a regenerated hematopoietic microenvironment which s upports trilineal hematopoiesis. We used this model to study the capac ity of 5 cloned murine stromal cell lines of marrow origin to support hematopoiesis in vivo: MBA-1 (fibroblast); MBA-2 (endothelial); MBA-13 (fibroendothelial; 14F1.1 (endothelial-adipose); and 14M1.4 (macropha ge); 10(7) stromal cells of a single cell line were applied to 1.5 cm CEM, which were folded into tubes and implanted i.p. into mice. Simila rly, combinations of 4, 3 and 2 stromal cell lines were applied to CEM and implanted i.p. Single lines were implanted into syngeneic hosts o f the same murine strain from which the clone was derived and into nud e mice. Combinations of stromal cells were implanted only in nude mice to avoid allogeneic incompatibility. CEM implants were removed after intervals of 5 to 36 weeks and examined histologically. 1) Stromal cel ls of a single phenotype did not develop hematopoiesis. 2) A combinati on of 4 stromal phenotypes (MBA-1, MBA-2, MBA-13 and 14F1.1) formed a hematopoietic microenvironment supportive of trilineal hematopoiesis a nd bone. 3) The combination of 14F1.1 (endothelial adipose) + a second stromal phenotype-MBA-1 (fibroblast) or MBA-2 (endothelial) or MBA-13 (fibroendothelial) also supported trilineal hematopoiesis and bone. 4 ) CEM coated with MBA-13 or MBA-1 developed bone but no hematopoiesis. The endothelial-adipose phenotype appears to be essential to support hematopoiesis but requires other types of stromal cells-fibroblast, fi broendothelial or endothelial phenotype.