Mature monocytic cells enter tissues and engraft

The goal of this study was to identify the circulating cell that is the imm ediate precursor of tissue macrophages. ROSA 26 marrow mononuclear cells (c ontaining the beta-geo transgene that encodes beta-galactosidase and neomyc in resistance activities) were cultured in the presence of macrophage colon y-stimulating factor and flt3 Ligand for 6 days to generate monocytic cells at all stages of maturation. Expanded monocyte cells (EMC), the immature ( ER-MP12(+)) and more mature (ER-MP20(+)) subpopulations, were transplanted into irradiated B6/129 F2 mice. beta-gal staining of tissue sections from a nimals 15 min after transplantation demonstrated that the donor cells lande d randomly. By 3 h, donor cells in lung and liver were more frequent in ani mals transplanted with ER-MP20(+) (more mature) EMC than in animals transpl anted with unseparated EMC or fresh marrow mononuclear cells, a pattern tha t persisted at 3 and 7 days. At 3 days, donor cells were found in spleen, l iver, lung, and brain (rarely) as clusters as well as individual cells. By 7 and 14 days, the clusters had increased in size, and the cells expressed the macrophage antigen F4/80, suggesting that further replication and diffe rentiation had occurred. PCR for the neogene was used to quantitate the amo unt of donor DNA in tissues from transplanted animals and confirmed that ER -MP20(+) EMC preferentially engrafted, These data demonstrate that a mature monocytic cell gives rise to tissue macrophages. Because these cells can b e expanded and manipulated in vitro, they may be a suitable target populati on for gene therapy of lysosomal storage diseases.