VIRIONS RELEASED FROM CELLS TRANSFECTED WITH A MOLECULAR CLONE OF HUMAN T-CELL LEUKEMIA-VIRUS TYPE-I GIVE RISE TO PRIMARY AND SECONDARY INFECTIONS OF T-CELLS

The ability of molecular clones of human T-cell leukemia virus type I (HTLV-I) to direct the synthesis of infectious virions has not previou sly been demonstrated. An HTLV-I provirus originating from an adult T- cell leukemia patient was cloned into a plasmid vector and is designat ed pCS-HTLV. This molecular clone was shown to direct the synthesis of viral mRNAs and proteins in transiently transfected cells; in additio n, virus structural proteins were released into the culture medium. Vi ral proteins were assembled into virions that sedimented at a buoyant density characteristic of retrovirus particles and whose morphology wa s verified by electron microscopy. Virions concentrated from transient ly transfected cell supernatants were incubated with primary cord bloo d lymphocytes or with transformed T-cell lines to establish that these particles were infectious. Expression of spliced, viral mRNAs in the T-cell cultures after both primary and secondary infections with cell- free virus revealed that pCS-HTLV encodes an infectious provirus.