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Monocytes are a subpopulation of peripheral blood leukocytes, which when appropriately activated by the regulatory hormones of the immune system, are capable of becoming macrophages--potent effector cells for immune response to tumors and parasites. A complementary DNA for the T lymphocyte-derived lymphokine, granulocyte-macrophage colony-stimulating factor (GM-CSF), has been cloned, and recombinant GM-CSF protein has been expressed in yeast and purified to homogeneity. This purified human recombinant GM-CSF stimulated peripheral blood monocytes in vitro to become cytotoxic for the malignant melanoma cell line A375. Another T cell-derived lymphokine, gamma-interferon (IFN-gamma), also stimulated peripheral blood monocytes to become tumoricidal against this malignant cell line. When IFN-gamma activates monocytes to become tumoricidal, additional stimulation by exogenously added lipopolysaccharide is required. No such exogenous signals were required for the activation of monocytes by GM-CSF.

Direct isolation of human central nervous system stem cells (CNS‐SC) based on cell surface markers yields a highly purified stem cell population that can extensively expand in vitro and exhibit multilineage differentiation potential both in vitro and in vivo. The CNS‐SC were isolated from fetal brain tissue using the cell surface markers CD133+, CD34–, CD45–, and CD24–/lo (CD133+ cells). Fluorescence‐activated cell sorted (FACS) CD133+ cells continue to expand exponentially as neurospheres while retaining multipotential differentiation capacity for >10 passages. CD133–, CD34–, and CD45– sorted cells (∼95% of total fetal brain tissue) fail to initiate neurospheres. Neurosphere cells transplanted into neonatal immunodeficient NOD‐SCID mice proliferated, migrated, and differentiated in a site‐specific manner. However, it has been difficult to evaluate human cell engraftment, because many of the available monoclonal antibodies against neural cells (β‐tubulin III and glial fibrillary acidic protein) are not species specific. To trace the progeny of human cells after transplantation, CD133+‐derived neurosphere cells were transduced with lentiviral vectors containing enhanced green fluorescent protein (eGFP) expressed downstream of the phosphoglycerate kinase promoter. After transduction, GFP+ cells were enriched by FACS, expanded, and transplanted into the lateral ventricular space of neonatal immunodeficient NOD‐SCID brain. The progeny of transplanted cells were detected by either GFP fluorescence or antibody against GFP. GFP+ cells were present in the subventricular zone‐rostral migrating stream, olfactory bulb, and hippocampus as well as nonneurogenic sites, such as cerebellum, cerebral cortex, and striatum. Antibody against GFP revealed that some of the cells displayed differentiating dendrites and processes with neurons or glia cells. Thus, marking human CNS‐SC with reporter genes introduced by lentiviral vectors is a useful tool with which to characterize migration and differentiation of human cells in this mouse transplantation model. © 2002 Wiley‐Liss, Inc.

Messenger RNA from HeLa cells contains, as part of the polynucleotide chain, RNase-resistant sequences that are labeled by adenosine but not by uridine. Heterogeneous nuclear RNA also contains adenylate-rich RNase-resistant regions, but in lower proportion than messenger RNA. Hybridization to DNA of 32P-labeled messenger RNA reveals that some of the adenylate-rich region is included in the rapidly-hybridizing fraction.