Vaccinal effect of HIV-1 antibody therapy

Trade-off between the antiviral and vaccinal effects of antibody therapy in the humoral response to HIV

Antibody therapy for HIV-1 infection exerts two broad effects: a drug-like, antiviral effect, which rapidly lowers the viral load, and a vaccinal effect, which may control the viral load long-term by improving the immune response. Here, we elucidate a trade-off between these two effects as they pertain to the humoral response, which may compromise antibody therapy aimed at eliciting long-term HIV-1 remission. We developed a multi-scale computational model that combined within-host viral dynamics and stochastic simulations of the germinal centre (GC) reaction, enabling simultaneous quantification of the antiviral and vaccinal effects of antibody therapy. The model predicted that increasing antibody dosage or antibody-antigen affinity increased immune complex formation and enhanced GC output. Beyond a point, however, a strong antiviral effect reduced antigen levels substantially, extinguishing GCs and limiting the humoral response. We found signatures of this trade-off in clinical studies. Accounting for the trade-off could be important in optimizing antibody therapy for HIV-1 remission.

Interventions during Early Infection: Opening a Window for an HIV Cure?

Although combination antiretroviral therapy (ART) has been a landmark achievement for the treatment of human immunodeficiency virus (HIV), an HIV cure has remained elusive. Elimination of latent HIV reservoirs that persist throughout HIV infection is the most challenging barrier to an HIV cure. The progressive HIV infection is marked by the increasing size and diversity of latent HIV reservoirs until an effective immune response is mobilized, which can control but not eliminate HIV infection. The stalemate between HIV replication and the immune response is manifested by the establishment of a viral set point. ART initiation during the early stage limits HIV reservoir development, preserves immune function, improves the quality of life, and may lead to ART-free viral remission in a few people living with HIV (PLWH). However, for the overwhelming majority of PLWH, early ART initiation alone does not cure HIV, and lifelong ART is needed to sustain viral suppression. A critical area of research is focused on determining whether HIV could be functionally cured if additional treatments are provided alongside early ART. Several HIV interventions including Block and Lock, Shock and Kill, broadly neutralizing antibody (bNAb) therapy, adoptive CD8+ T cell therapy, and gene therapy have demonstrated delayed viral rebound and/or viral remission in animal models and/or some PLWH. Whether or not their application during early infection can improve the success of HIV remission is less studied. Herein, we review the current state of clinical and investigative HIV interventions and discuss their potential to improve the likelihood of post-treatment remission if initiated during early infection.

Dual neutralization of influenza virus hemagglutinin and neuraminidase by a bispecific antibody leads to improved antiviral activity

Targeting multiple viral proteins is pivotal for sustained suppression of highly mutable viruses. In recent years, broadly neutralizing antibodies that target the influenza virus hemagglutinin and neuraminidase glycoproteins have been developed, and antibody monotherapy has been tested in preclinical and clinical studies to treat or prevent influenza virus infection. However, the impact of dual neutralization of the hemagglutinin and neuraminidase on the course of infection, as well as its therapeutic potential, has not been thoroughly tested. For this purpose, we generated a bispecific antibody that neutralizes both the hemagglutinin and the neuraminidase of influenza viruses. We demonstrated that this bispecific antibody has a dual-antiviral activity as it blocks infection and prevents the release of progeny viruses from the infected cells. We show that dual neutralization of the hemagglutinin and the neuraminidase by a bispecific antibody is advantageous over monoclonal antibody combination as it resulted an improved neutralization capacity and augmented the antibody effector functions. Notably, the bispecific antibody showed enhanced antiviral activity in influenza virus-infected mice, reduced mice mortality, and limited the virus mutation profile upon antibody administration. Thus, dual neutralization of the hemagglutinin and neuraminidase could be effective in controlling influenza virus infection.

Mucosal administration of anti-bacterial antibodies provide long-term cross-protection against Pseudomonas aeruginosa respiratory infection

Bacterial respiratory infections, either acute or chronic, are major threats to human health. Direct mucosal administration, through the airways, of therapeutic antibodies (Abs) offers a tremendous opportunity to benefit patients with respiratory infections. The mode of action of anti-infective Abs relies on pathogen neutralization and crystallizable fragment (Fc)-mediated recruitment of immune effectors to facilitate their elimination. Using a mouse model of acute pneumonia induced by Pseudomonas aeruginosa, we depicted the immunomodulatory mode of action of a neutralizing anti-bacterial Abs. Beyond the rapid and efficient containment of the primary infection, the Abs delivered through the airways harnessed genuine innate and adaptive immune responses to provide long-term protection, preventing secondary bacterial infection. In vitro antigen-presenting cells stimulation assay, as well as in vivo bacterial challenges and serum transfer experiments indicate an essential contribution of immune complexes with the Abs and pathogen in the induction of the sustained and protective anti-bacterial humoral response. Interestingly, the long-lasting response protected partially against secondary infections with heterologous P. aeruginosa strains. Overall, our findings suggest that Abs delivered mucosally promotes bacteria neutralization and provides protection against secondary infection. This opens novel perspectives for the development of anti-infective Abs delivered to the lung mucosa, to treat respiratory infections.

An exploration of how broadly neutralizing antibodies might induce HIV remission: the 'vaccinal' effect

PURPOSE OF REVIEW

Broadly neutralizing antibodies (bNAbs) are a potential new therapeutic strategy to treat HIV infection. This review explores possible mechanisms of action of bNAbs and summarizes the current evidence supporting their immunomodulatory properties, which might lead to sustained virological remission - the 'vaccinal effect'.

RECENT FINDINGS

Antiretroviral therapy (ART) is required to confer lasting HIV suppression; stopping ART almost invariably leads to HIV recrudescence from a persistent pool of virally infected cells - the HIV reservoir. HIV-specific broadly neutralizing antibodies (bNAbs) may confer viral control after ART cessation predominantly through blockade of viral entry into uninfected target cells. In some human and animal studies, HIV bNAbs also conferred lasting viral suppression after therapeutic bNAb plasma levels had declined. Immune-modulatory mechanisms have been postulated to underlie this observation - the 'vaccinal effect'. Hypothesized mechanisms include the formation of immune complexes between bNAbs and HIV envelope protein, thereby enhancing antigen presentation and uptake by immune cells, with boosted adaptive immune responses subsequently controlling the HIV reservoir.

SUMMARY

There is emerging evidence for potent antiviral efficacy of bNAb therapy. Whether bNAbs can induce sustained viral suppression after dropping below therapeutic levels remains controversial. Mechanistic data from on-going and future clinical trials will help answer these questions.

Broadly neutralizing anti-HIV-1 antibodies tether viral particles at the surface of infected cells

Broadly neutralizing antibodies (bNAbs) targeting the HIV-1 envelope glycoprotein (Env) are promising molecules for therapeutic or prophylactic interventions. Beyond neutralization, bNAbs exert Fc-dependent functions including antibody-dependent cellular cytotoxicity and activation of the complement. Here, we show that a subset of bNAbs targeting the CD4 binding site and the V1/V2 or V3 loops inhibit viral release from infected cells. We combined immunofluorescence, scanning electron microscopy, transmission electron microscopy and immunogold staining to reveal that some bNAbs form large aggregates of virions at the surface of infected cells. This activity correlates with the capacity of bNAbs to bind to Env at the cell surface and to neutralize cell-free viral particles. We further show that antibody bivalency is required for viral retention, and that aggregated virions are neutralized. We have thus identified an additional antiviral activity of bNAbs, which block HIV-1 release by tethering viral particles at the surface of infected cells.

Broadly neutralizing antibodies (bNAbs) neutralize HIV-1 and exert Fc-dependent activities against infected cells. Here, Dufloo et al. show that bNAbs also block HIV-1 release by trapping viral particles at the surface of infected cells.

Differential and sequential immunomodulatory role of neutrophils and Ly6Chi inflammatory monocytes during antiviral antibody therapy

Antiviral monoclonal antibodies (mAbs) can generate protective immunity through Fc-FcγRs interactions. We previously showed a role for immune complexes (ICs) in the enhancement of antiviral T-cell responses through FcγR-mediated activation of dendritic cells (DCs). Here we addressed how mAb therapy in retrovirus-infected mice affects the activation of neutrophils and inflammatory monocytes, two FcγR-expressing innate effector cells rapidly recruited to sites of infection. We found that both cell-types activated in vitro by viral ICs secreted chemokines able to recruit monocytes and neutrophils themselves. Moreover, inflammatory cytokines potentiated chemokines and cytokines release by IC-activated cells and induced FcγRIV upregulation. Similarly, infection and mAb-treatment upregulated FcγRIV on neutrophils and inflammatory monocytes and enhanced their cytokines/chemokines secretion. Notably, upon antibody therapy neutrophils and inflammatory monocytes displayed distinct functional activation states and sequentially modulated the antiviral immune response by secreting Th1-type polarizing cytokines and chemokines, which occurred in a FcγRIV-dependent manner. Consistently, FcγRIV- blocking in mAb-treated, infected mice led to reduced immune protection. Our work provides new findings on the immunomodulatory role of neutrophils and monocytes in the enhancement of immune responses upon antiviral mAb therapy.

Immune Responses and Viral Persistence in Simian/Human Immunodeficiency Virus SHIV.C.CH848-Infected Rhesus Macaques

SHIVs have been extensively used in a nonhuman primate (NHP) model for HIV research. In this study, we investigated viral reservoirs in tissues and immune responses in an NHP model inoculated with newly generated transmitted/founder HIV-1 clade C-based SHIV.C.CH848.

Chimeric simian/human immunodeficiency viruses (SHIVs) are widely used in nonhuman primate models to recapitulate human immunodeficiency virus (HIV) infection in humans, yet most SHIVs fail to establish persistent viral infection. We investigated immunological and virological events in rhesus macaques infected with the newly developed SHIV.C.CH848 (SHIVC) and treated with combined antiretroviral therapy (cART). Similar to HIV/simian immunodeficiency virus (SIV) infection, SHIV.C.CH848 infection established viral reservoirs in CD4⁺ T cells and myeloid cells, accompanied by productive infection and depletion of CD4⁺ T cells in systemic and lymphoid tissues throughout SHIV infection. Despite 6 months of cART-suppressed viral replication, integrated proviral DNA levels remained stable, especially in CD4⁺ T cells, and the viral rebound was also observed after ART interruption. Autologous neutralizing antibodies to the parental HIV-1 strain CH848 were detected, with limited viral evolution at 5 months postinfection. In comparison, heterogenous neutralizing antibodies in SHIV.C.CH848-infected macaques were not detected except for 1 (1 of 10) animal at 2 years postinfection. These findings suggest that SHIV.C.CH848, a novel class of transmitted/founder SHIVs, can establish sustained viremia and viral reservoirs in rhesus macaques with clinical immunodeficiency consequences, providing a valuable SHIV model for HIV research.

IMPORTANCE SHIVs have been extensively used in a nonhuman primate (NHP) model for HIV research. In this study, we investigated viral reservoirs in tissues and immune responses in an NHP model inoculated with newly generated transmitted/founder HIV-1 clade C-based SHIV.C.CH848. The data show that transmitted founder (T/F) SHIVC infection of macaques more closely recapitulates the virological and clinical features of HIV infection, including persistent viremia and viral rebound once antiretroviral therapy is discontinued. These results suggest this CCR5-tropic, SHIVC strain is valuable for testing responses to HIV vaccines and therapeutics.

Eliminating postnatal HIV transmission in high incidence areas: need for complementary biomedical interventions

The rate of mother-to-child transmission (MTCT) of HIV from breastfeeding is increasing relative to other causes of MTCT. Early effective preconception and antenatal antiretroviral therapy (ART) reduces intrauterine and intrapartum MTCT, whereas maternal post-partum HIV acquisition, untreated maternal HIV, and suboptimal postnatal maternal ART adherence increase the risk of MTCT through breastfeeding. Although the absolute number of cases of MTCT acquired through breastfeeding is decreasing, the rate of decrease is less than the decrease in intrauterine and intrapartum MTCT. Unless current strategies are universally applied, they might not be sufficient to eliminate MTCT due to breastfeeding. Urgent action is needed to evaluate and implement additional preventive biomedical strategies in high HIV prevalence and incidence settings to eliminate MTCT from breastfeeding. Preventive strategies include: pre-exposure prophylaxis in breastfeeding women who have an increased risk of acquiring HIV; postnatal reinforcement strategies, such as maternal retesting for HIV, maternal care reinforcement, and prophylaxis in infants exposed to HIV via breastmilk; and active (vaccine) or passive immunoprophylaxis with long-acting broadly neutralising antibodies.

Residual Proviral Reservoirs: A High Risk for HIV Persistence and Driving Forces for Viral Rebound after Analytical Treatment Interruption

Antiretroviral therapy (ART) has dramatically suppressed human immunodeficiency virus (HIV) replication and become undetectable viremia. However, a small number of residual replication-competent HIV proviruses can still persist in a latent state even with lifelong ART, fueling viral rebound in HIV-infected patient subjects after treatment interruption. Therefore, the proviral reservoirs distributed in tissues in the body represent a major obstacle to a cure for HIV infection. Given unavailable HIV vaccine and a failure to eradicate HIV proviral reservoirs by current treatment, it is crucial to develop new therapeutic strategies to eliminate proviral reservoirs for ART-free HIV remission (functional cure), including a sterilizing cure (eradication of HIV reservoirs). This review highlights recent advances in the establishment and persistence of HIV proviral reservoirs, their detection, and potential eradication strategies.

Immunomodulatory Role of NK Cells during Antiviral Antibody Therapy

Monoclonal antibodies (mAbs) are now considered as a therapeutic approach to prevent and treat severe viral infections. Using a mouse retroviral model, we showed that mAbs induce protective immunity (vaccinal effects). Here, we investigated the role of natural killer (NK) cells on this effect. NK cells are effector cells that are crucial to control viral propagation upon mAb treatment. However, their immunomodulatory activity during antiviral mAb immunotherapies has been little studied. Our data reveal that the mAb treatment of infected mice preserves the functional activation of NK cells. Importantly, functional NK cells play an essential role in preventing immune dysfunction and inducing antiviral protective immunity upon mAb therapy. Thus, NK cell depletion in mAb-treated, viral-infected mice leads to the upregulation of molecules involved in immunosuppressive pathways (i.e., PD-1, PD-L1 and CD39) on dendritic cells and T cells. NK cell depletion also abrogates the vaccinal effects induced by mAb therapy. Our data also reveal a role for IFNγ-producing NK cells in the enhancement of the B-cell responses through the potentiation of the B-cell helper properties of neutrophils. These findings suggest that preserved NK cell functions and counts might be required for achieving mAb-induced protective immunity. They open new prospects for improving antiviral immunotherapies.

Passive immunization with an extended half-life monoclonal antibody protects Rhesus macaques against aerosolized ricin toxin

Inhalation of ricin toxin (RT), a Category B biothreat agent, provokes an acute respiratory distress syndrome marked by pro-inflammatory cytokine and chemokine production, neutrophilic exudate, and pulmonary edema. The severity of RT exposure is attributed to the tropism of the toxin's B subunit (RTB) for alveolar macrophages and airway epithelial cells, coupled with the extraordinarily potent ribosome-inactivating properties of the toxin's enzymatic subunit (RTA). While there are currently no vaccines or treatments approved to prevent RT intoxication, we recently described a humanized anti-RTA IgG1 MAb, huPB10, that was able to rescue non-human primates (NHPs) from lethal dose RT aerosol challenge if administered by intravenous (IV) infusion within hours of toxin exposure. We have now engineered an extended serum half-life variant of that MAb, huPB10-LS, and evaluated it as a pre-exposure prophylactic. Five Rhesus macaques that received a single intravenous infusion (25 mg/kg) of huPB10-LS survived a lethal dose aerosol RT challenge 28 days later, whereas three control animals succumbed to RT intoxication within 48 h. The huPB10-LS treated animals remained clinically normal in the hours and days following toxin insult, suggesting that pre-existing antibody levels were sufficient to neutralize RT locally. Moreover, pro-inflammatory markers in sera and BAL fluids collected 24 h following RT challenge were significantly dampened in huPB10-LS treated animals, as compared to controls. Finally, we found that all five surviving animals, within days after RT exposure, had anti-RT serum IgG titers against epitopes other than huPB10-LS, indicative of active immunization by residual RT and/or RT-immune complexes.

Update on Fc-Mediated Antibody Functions Against HIV-1 Beyond Neutralization

Antibodies (Abs) are the major component of the humoral immune response and a key player in vaccination. The precise Ab-mediated inhibitory mechanisms leading to in vivo protection against HIV have not been elucidated. In addition to the desired viral capture and neutralizing Ab functions, complex Ab-dependent mechanisms that involve engaging immune effector cells to clear infected host cells, immune complexes, and opsonized virus have been proposed as being relevant. These inhibitory mechanisms involve Fc-mediated effector functions leading to Ab-dependent cellular cytotoxicity, phagocytosis, cell-mediated virus inhibition, aggregation, and complement inhibition. Indeed, the decreased risk of infection observed in the RV144 HIV-1 vaccine trial was correlated with the production of non-neutralizing inhibitory Abs, highlighting the role of Ab inhibitory functions besides neutralization. Moreover, Ab isotypes and subclasses recognizing specific HIV envelope epitopes as well as pecular Fc-receptor polymorphisms have been associated with disease progression. These findings further support the need to define which Fc-mediated Ab inhibitory functions leading to protection are critical for HIV vaccine design. Herein, based on our previous review Su & Moog Front Immunol 2014, we update the different inhibitory properties of HIV-specific Abs that may potentially contribute to HIV protection.