Characterization of envelope glycoprotein mutants for human T-cell leukemia virus type 1 infectivity and immortalization

The human T-cell leukemia virus type 1 (HTLV-1) envelope protein is require d for virus spread. This study further characterizes the role of the envelo pe protein in HTLV-1 immortalization. Viruses with single amino acid substi tutions within the SU protein at residue 75, 81, 95, 101, 105, or 195 or wi th a C-terminal cytoplasmic domain truncation (CT), as well as an envelope- null (EN) virus, were generated within an infectious molecular clone, ACH. Transfection of 293T cells resulted in the release of similar amounts of vi rus particles from all of the mutants as determined by p19 enzyme-linked im munosorbent assay and immunoblot analysis of Gag in cell lysates and supern atants. The virus particles from all mutants except ACH-101, ACH-CT, and AC H-EN were infectious for B5 macaque cells in cell-free and cell-to-cell tra nsmission assays and were capable of immortalizing transfected CD4(+) lymph ocytes. These results indicate that HTLV-1 spread is required for immortali zation.