Paolo Lusso

CD46 Is a Cellular Receptor for Human Herpesvirus 6

Human herpesvirus 6 (HHV-6) is the etiologic agent of exanthema subitum, causes opportunistic infections in immunocompromised patients, and has been implicated in multiple sclerosis and in the progression of AIDS. Here, we show that the two major HHV-6 subgroups (A and B) use human CD46 as a cellular receptor. Downregulation of surface CD46 was documented during the course of HHV-6 infection. Both acute infection and cell fusion mediated by HHV-6 were specifically inhibited by a monoclonal antibody to CD46; fusion was also blocked by soluble CD46. Nonhuman cells that were resistant to HHV-6 fusion and entry became susceptible upon expression of recombinant human CD46. The use of a ubiquitous immunoregulatory receptor opens novel perspectives for understanding the tropism and pathogenicity of HHV-6.

Structural determinants of CCR5 recognition and HIV-1 blockade in RANTES.

Certain chemokines act as natural antagonists of human immunodeficiency virus (HIV) by blocking key viral coreceptors, such as CCR5 and CXCR4, on the surface of susceptible cells. Elucidating the structural determinants of the receptor-binding and HIV-inhibitory functions of these chemokines is essential for the rational design of derivative molecules of therapeutic value. Here, we identify the structural determinants of CCR5 recognition and antiviral activity of the CC chemokine RANTES, showing that critical residues form a solvent-exposed hydrophobic patch on the surface of the molecule. Moreover, we demonstrate that the biological function is critically dependent on dimerization, resulting in the exposure of a large (∼180 Å2), continuous hydrophobic surface. Relevant to the development of novel therapeutic approaches, we designed a retroinverted RANTES peptide mimetic that maintained both HIV- and chemotaxis-antagonistic functions.

Enhancement of the HIV-1 inhibitory activity of RANTES by modification of the N-terminal region: dissociation from CCR5 activation

Although selected chemokines act as natural inhibitors of human immunodeficiency virus (HIV) infection, their inherent proinflammatory activity may limit a therapeutic use. To elucidate whether the antiviral and signaling functions of RANTES can be dissociated, several recombinant analogues mutated at the N terminus were generated and functionally compared with the wild‐type (WT) molecule, as well as with three previously described mutants. Substitution of selected residues within the N‐terminal region caused a marked loss of antiviral potency. By contrast, two unique analogues (C1.C5‐RANTES and L‐RANTES) exhibited an increased antiviral activity against different CXCR4‐negative HIV‐1 isolates grown in primary mononuclear cells or in macrophages. This enhanced HIV‐blocking activity was associated with an increased binding affinity for CCR5. Both C1.C5‐RANTES and L‐RANTES showed a dramatically reduced ability to trigger intracellular calcium mobilization via CCR3 or CCR5, while potently antagonizing the action of the WT chemokine. By contrast, two previously described analogues (RANTES3–68 and AOP‐RANTES) maintained a WT ability to trigger CCR5‐mediated signaling, while a third one (RANTES9–68) showed a dramatic loss of antiviral activity. These data demonstrate that the antiviral and signaling functions of RANTES can be uncoupled, opening new perspectives for the development of chemokine‐based therapeutic approaches for HIV infection.