Development and Characterization of Immortalized Cerebral Endothelial Cell Lines

Several groups have reported the isolation and in vitro pharmacological characterization of brain microvessel endothelial cells (BMECs) of various origins: bovine, porcine, murine, or human (1 –3 ). Brain capillaries are almost completely ensheathed by astrocyte processes, which are believed to provide the cerebral endothelium with specific stimuli responsible for the development and maintenance of the blood-brain barrier (BBB) phenotype (4 ). Considering that the absence of such environmental stimuli might prevent BMECs from retaining in culture the fully differentiated phenotype of the BBB found in vivo, some investigators have proposed a co-culture system where BMECs are grown in the presence of primary astrocytes or astrocyte-conditioned medium. In these experimental conditions, in vitro models of the BBB, essentially based on bovine or porcine BMECs, have been both proposed and validated (5 ,6 ). However, a number of drawbacks still limit the extensive use of these models in basic research and in drug-screening processes: 1) their use is time consuming and needs a considerable know-how which may hamper their routine use in nonexpert laboratories, 2) most available models are based on bovine or porcine BMECs, which may constitute a serious limitation for immunological studies or for studies with species-specific bacterial pathogens like Neisseria meningitidis or viruses like HIV and HTLV-I, and 3) BMECs rapidly de-differentiate in vitro, losing the characteristics of BBB endothelial cells after a few passages in culture, which limits their use for biochemical or pharmacological studies.