Restriction of Macrophage infection During HIV and SIV infection: The Role of Antibodies and Coreceptor Use Plasticity in Enforcing Cd4-Dependent Entry and Shaping Tropism in Vivo

The pathogenesis of HIV and SIV infection is determined to a large extent by adaptations of the virus that enable it to infect different cell types and either destroy these cells, or establish long-term reservoirs of viral replication. CD4+ T cells are the predominant targets of HIV and SIV infection in vivo, although some variants of these viruses have the ability to efficiently infect macrophages, which express exceedingly low levels of CD4. I sought to understand the selective forces that normally favor CD4+ T cell infection while restricting macrophage infection in vivo. To investigate these forces, I examined viral envelope glycoprotein (Env) variants that emerged during an in vivo SIV infection model in which extensive tissue macrophage infection was observed in experimentally CD4+ T cell-depleted rhesus macaques. I found that plasma-derived viral Envs from these animals had a remarkable ability to mediate entry into cells expressing CCR5 but lacking CD4, a phenotypic hallmark of macrophage-tropic viruses. These CD4-independent Env variants were highly sensitive to neutralization by anti-Env antibodies, as well as to control SIV+ plasma. However, plasma from CD4+ T cell-depleted animals could not neutralize CD4-independent Envs. This suggests that CD4+ T cells enforce CD4-dependent SIV entry by supporting the production of anti-Env antibodies that normally prevent the emergence of macrophage-tropic virus. In further studies, I asked whether other forces might restrict the emergence of CD4-independent Envs in vivo by examining entry coreceptor use by these Envs. Despite the ability of CD4-independent Envs to mediate robust entry in the presence of high cell surface levels of rhesus macaque CCR5, they were impaired in their use of human CCR5, rhesus macaque GPR15, and low levels of rhesus macaque CCR5. These phenotypes indicated that CD4-independent entry is accompanied by reduced plasticity in coreceptor usage, possibly restricting the virus in its range of potential target cells in vivo. Future studies will examine whether antibody-mediated enforcement of CD4 tropism and coreceptor usage are selective pressures that also explain the conservation of CD4-dependent entry during HIV-1 infection. It is possible that these forces can be manipulated to reshape viral tropism and eliminate HIV-1 macrophage reservoirs

Glycoside analogs of beta-galactosylceramide, a novel class of small molecule antiviral agents that inhibit HIV-1 entry.

International audienceThe interaction between HIV gp120 and galactose-containing cell surface glycolipids such as GalCer or Gb3 is known to facilitate HIV binding to both CD4+ as well as CD4- cells. In an effort to develop small molecule HIV-1 entry inhibitors with improved solubility and efficacy, we have synthesized a series of C-glycoside analogs of GalCer and tested their anti HIV-1 activity. The analogs were tested for gp120 binding using a HIV-1 (IIIB) V3-loop specific peptide. Two of the six analogs that interfered with gp120 binding also inhibited HIV Env-mediated cell-to-cell fusion and viral entry in the absence of any significant cytotoxicity. Analogs with two side chains did not show inhibition of fusion and/or infection under identical conditions. The inhibition of virus infection seen by these compounds was not coreceptor dependent, as they inhibited CXCR4, CCR5 as well as dual tropic viruses. These compounds showed inhibition of HIV entry at early steps in viral infection since the compounds were inactive if added post viral entry. Temperature-arrested state experiments showed that the compounds act at the level of virus attachment to the cells likely at a pre-CD4 engagement step. These compounds also showed inhibition of VSV glycoprotein-pseudotyped virus. The results presented here show that the glycoside derivatives of GalCer with simple side chains may serve as a novel class of small molecule HIV-1 entry inhibitors that would be active against a number of HIV isolates as well as other enveloped viruses

Global genomic analysis reveals rapid control of a robust innate response in SIV-infected sooty mangabeys

Natural SIV infection of sooty mangabeys (SMs) is nonprogressive despite chronic virus replication. Strikingly, it is characterized by low levels of immune activation, while pathogenic SIV infection of rhesus macaques (RMs) is associated with chronic immune activation. To elucidate the mechanisms underlying this intriguing phenotype, we used high-density oligonucleotide microarrays to longitudinally assess host gene expression in SIV-infected SMs and RMs. We found that acute SIV infection of SMs was consistently associated with a robust innate immune response, including widespread upregulation of IFN-stimulated genes (ISGs) in blood and lymph nodes. While SMs exhibited a rapid resolution of ISG expression and immune activation, both responses were observed chronically in RMs. Systems biology analysis indicated that expression of the lymphocyte inhibitory receptor LAG3, a marker of T cell exhaustion, correlated with immune activation in SIV-infected RMs but not SMs. Our findings suggest that active immune regulatory mechanisms, rather than intrinsically attenuated innate immune responses, underlie the low levels of immune activation characteristic of SMs chronically infected with SIV