A single amino-acid change in a highly conserved motif of gp41 elicits HIV-1 neutralization and protects against CD4 depletion.

BACKGROUND: The induction of neutralizing antibodies against conserved regions of the human immunodeficiency virus type 1 (HIV-1) envelope protein is a major goal of vaccine strategies. We previously identified 3S, a critical conserved motif of gp41 that induces the NKp44L ligand of an activating NK receptor. In vivo, anti-3S antibodies protect against the natural killer (NK) cell-mediated CD4 depletion that occurs without efficient viral neutralization. METHODS: Specific substitutions within the 3S peptide motif were prepared by directed mutagenesis. Virus production was monitored by measuring the p24 production. Neutralization assays were performed with immune-purified antibodies from immunized mice and a cohort of HIV-infected patients. Expression of NKp44L on CD4(+) T cells and degranulation assay on activating NK cells were both performed by flow cytometry. RESULTS: Here, we show that specific substitutions in the 3S motif reduce viral infection without affecting gp41 production, while decreasing both its capacity to induce NKp44L expression on CD4(+) T cells and its sensitivity to autologous NK cells. Generation of antibodies in mice against the W614 specific position in the 3S motif elicited a capacity to neutralize cross-clade viruses, notable in its magnitude, breadth, and durability. Antibodies against this 3S variant were also detected in sera from some HIV-1-infected patients, demonstrating both neutralization activity and protection against CD4 depletion. CONCLUSIONS: These findings suggest that a specific substitution in a 3S-based immunogen might allow the generation of specific antibodies, providing a foundation for a rational vaccine that combine a capacity to neutralize HIV-1 and to protect CD4(+) T cells.

Perspectives for immunotherapy: which applications might achieve an HIV functional cure?

The major advances achieved in devising successful combined antiretroviral therapy (cART) have enabled the sustained control of HIV replication. However, this is associated with costly lifelong treatment, partial immune restoration, chronic inflammation and persistent viral reservoirs. In this context, new therapeutic strategies deserve investigation as adjuncts to cART so as to potentiate immune responses that are capable of completely containing HIV pathogenicity, particularly if cART is discontinued. This may seem a dauntingly high hurdle given the results to date. This review outlines the key research efforts that have recently resurrected immunotherapeutic options, and some of the approaches tested to date. These areas include promising cytokines or vaccine strategies, using different viral or non-viral vectors based on polyvalent "mosaic" antigens and highly conserved HIV envelope peptides, broadly neutralizing antibodies or new properties of antibodies to improve the control of immune system homeostasis. These novel immunotherapeutic strategies appear promising per se, or in combination with TLR-agonists in order to bypass the complexity of the interplay between immune activation, massive CD4+ T-cell loss and viral persistence.

NKp44L expression on CD4+ T cells is associated with impaired immunological recovery in HIV-infected patients under highly active antiretroviral therapy.

OBJECTIVE: HIV-infected immunological nonresponders (InRs) patients fail to show satisfactory CD4+ T-cell recovery despite virologically effective HAART. We propose that NKp44L, the cellular ligand of an activating natural killer (NK) receptor, expressed only on uninfected bystander CD4+ T cells from HIV-1 infected patients, could play a major role in this phenomenon by sensitizing these cells to NK killing. DESIGN: Phenotype and multifunctional status of CD4+ T cells, especially the subsets expressing and not expressing NKp44L, were characterized for HIV-infected patients receiving HAART for at least 2 years, during which their viral load remained less than 40 copies/ml; 53 were InRs (CD4 cell count always <350 cells/µl), and 82 immunological responders (CD4 cell count always ≥350 cells/µl). Flow cytometry determined NKp44L expression in association with specific markers of proliferation, maturation, activation, homeostasis, and intracellular cytokine production. Degranulation of NKp44+ determined the functional capacity of NK cells. RESULTS: InRs exhibited high levels of NKp44L+CD4+ T cells. Compared with NKp44L negative cells, the frequency of naive CD45RA+CCR7+ T cells expressing NKp44L fell (P < 0.001) and their proliferative capacity grew. Moreover, apoptosis and a unique ability to produce multiple cytokines (IL-2, IFN-γ, and TNF-α) without or after phytohemagglutinin or anti-CD3/CD28 stimulation distinguished NKp44L+ T cells. CONCLUSION: InR status is associated to a significant expansion of highly differentiated, multifunctional and apoptotic CD4+ T cells expressing NKp44L. This could explain a rapid CD4+ T-cell turnover in InR preventing immune recovery. These data suggest a new target for developing therapeutic strategies to prevent NKp44L expression and then stimulating immune recovery in InRs.

Specific anti-gp41 antibodies predict HIV-1 disease progression.

The immunodeficiency-defining AIDS results from a progressive decline of CD4 cell count. We previously showed that 3S, a unique motif of the HIV-1 gp41 envelop protein, is highly conserved in HIV-1 strains and induces expression of NKp44L, rendering CD4 cells sensitive to NK killing. Here we found from a well-characterized cohort of 244 untreated HIV-1 seroconverters that high levels of anti-3S antibodies significantly delay spontaneous disease progression in the first years after seroconversion; this effect was not mediated through baseline viral load or CD4. These results could have important implications both for clinical care and better understanding of pathogenicity.