FIG. 2.

MLV(LCMV) pseudotypes retain infectivity upon ultracentrifugation. TELCeB cells were infected with LCMV or amphotropic helper virus. Supernatants were harvested and frozen. The MLV(LCMV) and amphotropic pseudotype titers were determined. Equal quantities of the infectious vector were pelleted by ultracentrifugation and then subjected to purification on a 0 to 40% Urografin gradient. Vector titers and densities in each fraction were determined. ○, amphotropic pseudotype; □, MLV(LCMV) pseudotype.