Soluble recombinant HTLV-1 surface glycoprotein competitively inhibits syncytia formation and viral infection of cells

Efficient entry into, and infection of, human cells by human T-cell leukaem ia virus type-1 (HTLV-1) is mediated by the viral envelope glycoproteins, g p46 and gp21. The gp46 surface glycoprotein binds to an as yet unidentified cell surface receptor, thereby, allowing the gp21 transmembrane glycoprote in to initiate fusion of the viral and cellular membranes. In the absence o f membrane fusion viral penetration and entry into the host cell cannot occ ur. The envelope glycoproteins are also a major target for neutralising ant ibodies and cytotoxic T lymphocytes following a protective immune response, and represent ideal constituents for a recombinant HTLV-1 vaccine. Given t he importance of the envelope proteins in HTLV-1 pathogenesis there is incr easing interest in obtaining sufficient quantities of these proteins for bi ochemical, biophysical and biological analyses. We have now developed a sys tem for production of large amounts of a glycosylated and functional form o f soluble recombinant gp46 (sRgp46). and have used this recombinant materia l for analysis of envelope function and receptor binding activity. We find that, the sRgp46 molecules expressed in our system are immunologically indi stinguishable from the native virally expressed surface glycoproteins that sRgp46 binds to T-cells in a dose dependent and saturable manner; and that cell surface binding by sRgp46 can be inhibited by neutralising antibodies. Importantly, we demonstrate that these sRgp46 molecules potently inhibit s yncytia formation and viral infection of target cells, and that regions out with the SU domain of envelope are not required for binding to target cells or for inhibiting membrane fusion. The sRgp46 produced in our study will p rovide new opportunities to investigate envelope-receptor interactions, and will be of utility in defining the conformationally sensitive antigenic de terminants of the HTLV-1 surface glycoprotein. (C) 2001 Elsevier Science B. V. All rights reserved.