Chemical modification of an ecotropic murine leukemia virus results in redirection of its target cell specificity

An ecotropic virus was chemically modified in order to determine whether its target cell specificity could be altered. We hypothesized that chemical coupling of galactose residues to a virus might permit specific infection of hepatocytes mediated by asialoglycoprotein receptors unique to these cells. To test this hypothesis, we took advantage of the fact that: 1) artificial asialoglycoproteins can be created by chemical coupling of lactose to proteins; and 2) viruses that are ecotropic have a narrow species specificity. An ecotropic, rodent-specific, replication-defective murine leukemia virus containing the gene for beta-galactosidase was chemically modified with lactose to contain 5.9 mumol of lactose per mg of viral RNA. Modified and unmodified viruses were incubated for 5 days with HepG2, a human hepatoma line that possesses asialoglycoprotein receptors, and SK Hep1, a human cell line that does not. As expected from the ecotropism, unmodified virus did not produce beta-galactosidase activity in either cell type. Modified virus did not produce beta-galactosidase activity in SK Hep1 cells. However, modified virus did produce beta-galactosidase activity, 71.2 units/mg of cell protein, in the human receptor (+) HepG2 cells. Interestingly, modification of the virus also resulted in decreased enzyme activity in previously susceptible host rodent cells. Competition with modified virus by an excess of an asialoglycoprotein completely prevented development of enzymatic activity in HepG2 cells. Histochemical treatment of cells with 5-bromo-4-chloro-3-indoyl beta-D-galactoside to detect in situ beta-galactosidase activity demonstrated that only HepG2 cells treated with modified virus were positive and that 36% of these cells were stained after 5 days. These data indicate that chemical modification of a virus can result in a redirection of the infectivity of the virus toward hepatocyte-derived cells mediated by the presence of asialoglycoprotein receptors.