Infection by retroviral vectors outside of their host range in the presence of replication-defective adenovirus

Retrovirus infection is normally limited to cells within a specific host range which express a cognate receptor that is recognized by the product of the env gene. We describe retrovirus infection of cells outside of their normal host range when the infection is performed in the presence of a replication-defective adenovirus (dl312). In the presence of adenovirus, several different ecotropic vectors are shown to infect human cell lines (HeLa and PLC/PRF), and a xenotropic vector is shown to infect murine cells (NIH 3T3). Infectivity is demonstrated by 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal) staining, selection with G418 for neomycin resistance, and PCR identification of the provirus in infected cells. Infectivity is quantitatively dependent upon both the concentration of adenovirus (10(6) to 10(8) PFU/ml) and the concentration of retrovirus. Infection requires the simultaneous presence of adenovirus in the retrovirus infection medium and is not stimulated by preincubation and removal of adenovirus from the cells before retrovirus infection. The presence of adenovirus is shown to enhance the uptake of fluorescently labeled retrovirus particles into cells outside of their normal host range, demonstrating that the adenovirus enhances viral entry into cells in the absence of the recognized cognate receptor. This observation suggests new opportunities for developing safe retroviral vectors for gene therapy and new mechanisms for the pathogenesis of retroviral disease.