CD8(+) T lymphocytes have been shown to produce unidentified soluble factors active in suppressing HIV-1 replication. In this study, we purified an HIV-1 suppressing activity from the culture supernatant of an immortalized CD8(+) T cell clone, derived from an HIV-1 infected long-term nonprogressor, and identified this activity as the amino-terminal fragment (ATF) of urokinase-type plasminogen activator (uPA), ATF is catalytically inactive, but suppresses the release of viral particles from the HIV-1 infected cell lines via binding to its receptor CD87, In contrast, cell proliferation and the secretion of an HIV-1 LTR driven reporter gene product were not affected by ATF. These findings suggest that ATF may inhibit the assembly and budding of HIV-1, which provides a novel therapeutic strategy for AIDS.