Efficient gene transfer by a human immunodeficiency virus type 1 (HIV-1)-derived vector utilizing a stable HIV packaging cell line

By transfecting fibroblast cells with an HIV-1-MN molecular clone with a deletion of the major packaging sequence, we have developed a stable HIV-1 packaging cell line, Ψ422. Ψ422 cells form syncytia with CD4-positive cells, correctly express HIV-1 structural proteins, and produce a large amount of mature particles with normal reverse transcriptase activity. Yet these particles, in which RNA was not detected by reverse transcriptase–PCR, are not infectious. When stably transfected with an HIV-1-based retroviral vector, the Ψ422 cell line produces virions capable of transducing CD4-positive cells with high efficiency (up to 10(5) cells per ml). The availability of this stable noninfectious HIV-1 packaging cell line capable of generating high-titer HIV-1 vectors represents a new step toward the use of an HIV-1 delivery system in gene therapy.