HIV-1 infection triggers lateral membrane diffusion following interaction of the viral envelope with cell surface receptors. We show that these membrane changes are necessary for infection, as initial gp120-CD4 engagement leads to redistribution and clustering of membrane microdomains, enabling subsequent interaction of this complex with HIV-1 co-receptors. Disruption of cell membrane rafts by cholesterol depletion before viral exposure inhibits entry by both X4 and R5 strains of HIV-1, although viral replication in infected cells is unaffected by this treatment. This inhibitory effect is fully reversed by cholesterol replenishment of the cell membrane. These results indicate a general mechanism for HIV-1 envelope glycoprotein-mediated fusion by reorganization of membrane microdomains in the target cell, and offer new strategies for preventing HIV-1 infection.
Muller’s ratchet predicts fitness losses in small populations of asexual organisms because of the irreversible accumulation of deleterious mutations and genetic drift. This effect should be enhanced if population bottlenecks intervene and fixation of mutations is not compensated by recombination. To study whether Muller’s ratchet could operate in a retrovirus, 10 biological clones were derived from a human immunodeficiency virus type 1 (HIV-1) field isolate by MT-4 plaque assay. Each clone was subjected to 15 plaque-to-plaque passages. Surprisingly, genetic deterioration of viral clones was very drastic, and only 4 of the 10 initial clones were able to produce viable progeny after the serial plaque transfers. Two of the initial clones stopped forming plaques at passage 7, two others stopped at passage 13, and only four of the remaining six clones yielded infectious virus. Of these four, three displayed important fitness losses. Thus, despite virions carrying two copies of genomic RNA and the system displaying frequent recombination, HIV-1 manifested a drastic fitness loss as a result of an accentuation of Muller’s ratchet effect.
The emergence of drug-resistant variants during antiretroviral therapy is a serious obstacle to sustained suppression of the human immunodeficiency virus type 1 (HIV-1). For that reason, resistance assays are essential to guide clinicians in the selection of optimal treatment regimens. Genotypic assays are less expensive and results are available faster than phenotypic assays. However, in heavily experienced patients with multiple treatment failures interpretation of complex mutation patterns remains difficult, and in these cases phenotypic assays are recommended. This report describes a novel recombinant virus assay where protease (PR) and reverse transcriptase (RT) sequences derived from the plasma isolated from patients are introduced into the back-bone of an HIV molecular clone that expresses Renilla luciferase protein in the place of nef gene. All drug resistance profiles analyzed correlate with previously reported data and showed high reproducibility. This assay, in addition to a fast (completed in 10 days), precise, reproducible and automated method, presents several advantages as compared to other phenotypic assays. The system described below allows the generation of recombinant viruses with multiples cycles of replication carrying a reporter gene in their genomes. These features increase the sensitivity of the test, an important aspect to be considered in the evaluation of less fit viral isolates. In conclusion, the assay permits the quantitation of the level of resistance of clinical HIV-1 isolates to PR and RT inhibitors.
Several recent studies have identified HIV-infected patients able to produce a broad neutralizing response, and the detailed analyses of their sera have provided valuable information to improve future vaccine design. All these studies have excluded patients on antiretroviral treatment and with undetectable viral loads, who have an improved B cell profile compared to untreated patients. To better understand the induction of neutralizing antibodies in patients on antiretroviral treatment with undetectable viremia, we have screened 508 serum samples from 364 patients (173 treated and 191 untreated) for a broadly neutralizing antibody (bNAb) response using a new strategy based on the use of recombinant viruses. Sera able to neutralize a minipanel of 6 recombinant viruses, including envelopes from 5 different subtypes, were found in both groups. After IgG purification, we were able to confirm the presence of IgG-associated broadly neutralizing activity in 3.7% (7 of 191) of untreated patients with detectable viremia and 1.7% (3 of 174) of aviremic patients receiving antiretroviral treatment. We thus confirm the possibility of induction of a broad IgG-associated neutralizing response in patients on antiretroviral treatment, despite having undetectable viremia. This observation is in stark contrast to the data obtained from long-term nonprogressors, whose little neutralizing activity has been attributed to the low levels of viral replication.
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