Generation of lymphocyte cell lines coexpressing CD4 and wild-type or mutant HIV type 1 glycoproteins: implications for HIV type 1 Env-induced cell lysis

The Interplay of HIV and Autophagy in Early Infection

HIV/AIDS is still a global threat despite the notable efforts made by the scientific and health communities to understand viral infection, to design new drugs or to improve existing ones, as well as to develop advanced therapies and vaccine designs for functional cure and viral eradication. The identification and analysis of HIV-1 positive individuals that naturally control viral replication in the absence of antiretroviral treatment has provided clues about cellular processes that could interact with viral proteins and RNA and define subsequent viral replication and clinical progression. This is the case of autophagy, a degradative process that not only maintains cell homeostasis by recycling misfolded/old cellular elements to obtain nutrients, but is also relevant in the innate and adaptive immunity against viruses, such as HIV-1. Several studies suggest that early steps of HIV-1 infection, such as virus binding to CD4 or membrane fusion, allow the virus to modulate autophagy pathways preparing cells to be permissive for viral infection. Confirming this interplay, strategies based on autophagy modulation are able to inhibit early steps of HIV-1 infection. Moreover, autophagy dysregulation in late steps of the HIV-1 replication cycle may promote autophagic cell-death of CD4⁺ T cells or control of HIV-1 latency, likely contributing to disease progression and HIV persistence in infected individuals. In this scenario, understanding the molecular mechanisms underlying HIV/autophagy interplay may contribute to the development of new strategies to control HIV-1 replication. Therefore, the aim of this review is to summarize the knowledge of the interplay between autophagy and the early events of HIV-1 infection, and how autophagy modulation could impair or benefit HIV-1 infection and persistence, impacting viral pathogenesis, immune control of viral replication, and clinical progression of HIV-1 infected patients.

A neutralization assay for chikungunya virus infections in a multiplex format

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We established a CHIKV neutralization assay in a 384-well format.

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We used CHIKV pseudotyped lentiviral vectors encoding luciferase.

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We showed specific neutralization activity of patient sera.

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We developed a new multiplex neutralization assay for CHIKV.

Chikungunya virus (CHIKV) is a mosquito-transmitted Alphavirus that causes chikungunya fever and has infected millions of people mainly in developing countries. The associated disease is characterized by rash, high fever and severe arthritis that can persist for years. Since the epidemic on La Réunion in 2006, CHIKV has adapted to Aedes albopictus, which also inhabits temperate regions of the eastern and western hemispheres, including Europe and the United States. A. albopictus might continue migrating north with continuing climate change and CHIKV would then no longer be confined to the developing nations. No treatment or licensed CHIKV vaccine exists. A CHIKV neutralization assay in a 384-well format by using CHIKV-pseudotyped lentiviral vectors was established. This assay system can be used for entry inhibitor screening under a reduced safety level (S2). Production of CHIKV-pseudotyped lentiviral vectors and the reaction volume are optimized. A dose dependent, specific neutralization of CHIKV-pseudotyped vectors with sera of CHIKV-infected individuals could be measured in a 384-well format. A safe and simple multiplex assay for the analysis of CHIKV neutralizing activities was developed and will be able to improve drug and vaccine development as well as it would improve the understanding of CHIKV epidemics regarding antibody responses.

Analysis of the exposure of induced HIV glycoprotein epitopes in a potential HIV pseudovirion vaccine

Functionally conserved HIV-Env epitopes, which are induced during the process of Env-mediated membrane fusion, represent interesting immunogens, which may elicit broad neutralising antibody responses. In this report, we analyse a pseudovirion (PV)-based HIV vaccine preparation, potentially enriched in such induced Env-conformations. The vaccine has been prepared by mixing and incubating Env-PVs, with incorporated fusion-defective Env, with PVs, which have incorporated functional CD4 and CXCR4 proteins. Here, we demonstrate that three different monoclonal antibodies (CG10, 17b and 48d), recognising a region of gp120 overlapping with the coreceptor binding site, and a further antibody, 8F101, recognising a CD4-induced epitope outside of the coreceptor site, bind to Env molecules in the putative PV vaccine mixture but not at all, or less strongly, to native Env-PVs. In all cases, antibody binding required an interaction of the Env-PVs with CD4 whereas CXCR4 was dispensible. These results confirm that in the PV vaccine preparation, CD4-induced Env epitopes are accessible and that these, as well as other induced epitopes "downstream" from CD4 binding, may function as immunogens to elicit potentially cross-neutralising humoral immune responses.

Inhibition of human immunodeficiency virus type-1 (HIV-1) glycoprotein-mediated cell-cell fusion by immunor (IM28)

Background

Immunor (IM28), an analog of dehydroepiandrosterone (DHEA), inhibits human immunodeficiency virus type-1 (HIV-1) by inhibiting reverse transcriptase. We assessed the ability of IM28 to inhibit the cell-cell fusion mediated by HIV envelope glycoprotein in an in vitro system. For this purpose, we co-cultured TF228.1.16, a T-cell line expressing stably HIV-1 glycoprotein envelopes, with an equal number of 293/CD4+, another T cell line expressing CD4, and with the SupT1 cell line with or without IM28.

Results

In the absence of IM28, TF228.1.16 fused with 293/CD4+, inducing numerous large syncytia. Syncytia appeared more rapidly when TF228.1.16 was co-cultured with SupT1 cells than when it was co-cultured with the 293/CD4+ cell line. IM28 (1.6 – 45 μg/ml) completely inhibits cell-cell fusion. IM28 also prevented the development of new syncytia in infected cells and protected naive SupT1 cells from HIV-1 infection. Evaluation of 50% inhibitory dose (IC50) of IM28 revealed a decrease in HIV-1 replication with an IC50 of 22 mM and 50% cytotoxicity dose (CC50) as determined on MT2 cells was 75 mM giving a selectivity index of 3.4

Conclusions

These findings suggest that IM28 exerts an inhibitory action on the env proteins that mediate cell-cell fusion between infected and healthy cells. They also suggest that IM28 interferes with biochemical processes to stop the progression of existing syncytia. This property may lead to the development of a new class of therapeutic drug.

Inter-retroviral fusion mediated by human immunodeficiency virus or murine leukemia virus glycoproteins: independence of cellular membranes and membrane vesicles

We have recently demonstrated for the first time that inter-retroviral membrane fusion, i.e., membrane fusion between individual retroviral particle populations with incorporated HIV-1 Env and cellular receptors, respectively, can occur (Sparacio et al. 2000, Virology 271: 248-252). We have extended these analyses here and confirmed that fusion between particles can occur in the extracellular medium independent of any cellular membranes and that luciferase transduction, mediated by the fused structures, is independent of significant potential contribution by contaminating membrane vesicles. We have additionally analyzed whether membrane fusion between HIV-like particles can be mediated by amphotropic murine leukemia virus (MuLV) glycoprotein and its respective cellular receptor, PiT-2. We demonstrate that PiT-2 can be incorporated into HIV-like particles and can fuse with MuLV-Env-carrying particles. This occurs only in the situation in which the incorporated MuLV-Env protein has been activated to fusion activity by HIV protease-mediated removal of the C-terminal R-peptide and is completely inhibited when the respective particles are generated in the presence of the HIV protease inhibitor, Saquinavir.

Membrane fusion between retroviral particles: host-range extension and vaccine prospects

We have analyzed if different populations of retroviral particles carrying the viral and cellular receptors of membrane viruses, respectively, are able to specifically fuse with each other. Using the glycoprotein of human immunodeficiency virus type 1 and its cellular receptor complex, we demonstrate that interviral membrane fusion can, indeed, occur and that the resultant fused viral structures are able to infect cells and transduce a marker gene. On the one hand, these results have relevance for the development of vaccine strategies based on fusion-induced conformational epitopes on the viral glycoprotein. However, in addition to this potential practical application, the results obtained (which were extended to include analyses with the vesicular stomatitis virus G protein and its cellular receptor) have far-reaching implications for in vivo situations in which simultaneous infections with different membrane viruses can occur.

Inhibition of cellular glycoprotein incorporation into human immunodeficiency virus-like particles by coexpression of additional cellular interaction partner

We examined the concepts of whether cellular surface glycoprotein overexpressed in heterologous cells can be efficiently incorporated into lentiviral particles and whether incorporation is blocked when a natural interaction partner is coexpressed. Human CD4 and a truncated version lacking the cytoplasmic C terminus, expressed in 293T cells, were efficiently incorporated into Env-defective human immunodeficiency virus type 1 virus-like particles. However, on coexpression of p56(lck), the natural binding partner of the CD4 C-terminal domain in T lymphocytes, incorporation of the wild-type CD4 was completely abolished, whereas incorporation of the C-terminally truncated mutant remained unaffected. Confocal microscopy and detergent solubility assays did not reveal any significant difference in the distribution of wild-type CD4 at the plasma membrane in the presence or absence of p56(lck). These results give some insight into the processes governing protein incorporation into the lipid bilayer of lentiviruses.

Pseudotyping of murine leukemia virus with the envelope glycoproteins of HIV generates a retroviral vector with specificity of infection for CD4-expressing cells

CD4-expressing T cells in lymphoid organs are infected by the primary strains of HIV and represent one of the main sources of virus replication. Gene therapy strategies are being developed that allow the transfer of exogenous genes into CD4(+) T lymphocytes whose expression might prevent viral infection or replication. Insights into the mechanisms that govern virus entry into the target cells can be exploited for this purpose. Major determinants of the tropism of infection are the CD4 molecules on the surface of the target cells and the viral envelope glycoproteins at the viral surface. The best characterized and most widely used gene transfer vectors are derived from Moloney murine leukemia virus (MuLV). To generate MuLV-based retroviral gene transfer vector particles with specificity of infection for CD4-expressing cells, we attempted to produce viral pseudotypes, consisting of MuLV capsid particles and the surface (SU) and transmembrane (TM) envelope glycoproteins gp120-SU and gp41-TM of HIV type 1 (HIV-1). Full-length HIV-1 envelope glycoproteins were expressed in the MuLV env-negative packaging cell line TELCeB6. Formation of infectious pseudotype particles was not observed. However, using a truncated variant of the transmembrane protein, lacking sequences of the carboxyl-terminal cytoplasmic domain, pseudotyped retroviruses were generated. Removal of the carboxyl-terminal domain of the transmembrane envelope protein of HIV-1 was therefore absolutely required for the generation of the viral pseudotypes. The virus was shown to infect CD4-expressing cell lines, and infection was prevented by antisera specific for gp120-SU. This retroviral vector should prove useful for the study of HIV infection events mediated by HIV-1 envelope glycoproteins, and for the targeting of CD4(+) cells during gene therapy of AIDS.

Inhibition of HIV-1, HIV-2 and SIV envelope glycoprotein-mediated cell fusion by calmodulin

Calmodulin, an EF-hand protein, inhibited the fusion between CD4+ human cells and cells stably expressing HIV-1 envelope proteins. Fusion was also inhibited when HIV-1, HIV-2 or SIV envelope glycoproteins were expressed by vaccinia virus (VV) recombinants, but calmodulin did not inhibit syncytia formation induced by measles virus glycoproteins. Calmodulin also inhibited fusion induced by vPE17, a VV-recombinant expressing a truncated form of HIV-1gp160 which lacks the two known calmodulin-binding sites located in the cytoplasmic domain of gp41. The inhibitory activity was specific to calmodulin among the EF-hand proteins. These observations may be important in understanding the mechanism of retroviral envelope glycoprotein-mediated cell fusion. Several possible mechanisms of action are discussed.

The Role of the Envelope Glycoprotein in the Depletion of T Helper Cells in Human Immunodeficiency Virus Infection

Infection with the human immunodeficiency virus (HIV) causes gradual depletion of CD4+ T helper lymphocytes and destruction of the lymphoid tissue, which ultimately leads to a fatal defect of the cellular immune system. Paramount to the understanding of the pathogenesis of HIV infection is to elucidate the mechanism which underlies the loss of T helper cells. Various ideas have been proposed in order to explain this issue. Several hypotheses have focused on the role of the envelope glycoprotein in this process. This review summarizes the data obtained and concepts proposed regarding the involvement of the HIV glycoprotein in the pathology of CD4+ T cell depletion.