Delayed vaginal SHIV infection in VRC01 and anti-α4β7 treated rhesus macaques

Broadly neutralizing antibodies targeting HIV: Progress and challenges

Anti-HIV broadly neutralizing antibodies (bNAbs) offer a novel approach to treating, preventing, or curing HIV. Pre-clinical models and clinical trials involving the passive transfer of bNAbs have demonstrated that they can control viremia and potentially serve as alternatives or complement antiretroviral therapy (ART). However, antibody decay, persistent latent reservoirs, and resistance impede bNAb treatment. This review discusses recent advancements and obstacles in applying bNAbs and proposes strategies to enhance their therapeutic potential. These strategies include multi-epitope targeting, antibody half-life extension, combining with current and newer antiretrovirals, and sustained antibody secretion.

α4β7high CD4+ T cells are prone to be infected by HIV-1 and associated with HIV-1 disease progression

INTRODUCTION

To investigate the characteristics of β7^high CD4⁺ T cells during HIV-1 infection and the relationship between β7^high CD4⁺ T cells and HIV-1 disease progress.

METHODS

This study enrolled 124 HIV-1-infected patients, including 80 treatment naïve patients (TNs), 41 patients who underwent antiretroviral therapy (ARTs), and three long-term no progression patients (LTNPs). Nineteen matched healthy subjects were included as controls (HCs). The characteristics and frequency of β7^high CD4⁺ T cells were analyzed using flow cytometry. An in vitro culture experiment was used to study HIV-1 infection of β7^high CD4⁺ T cells. Real-time polymerase chain reaction was performed to quantify HIV-1 DNA and CA-RNA levels.

RESULTS

The frequency of β7^high CD4⁺ T in the peripheral blood was significantly decreased and negatively correlated with disease progression during chronic HIV-1 infection. A large proportion of β7^high CD4⁺ T cells showed Th17 phenotype. Furthermore, β7^high CD4⁺ T cells were preferentially infected by HIV-1 in vitro and in vivo. There were no significant differences of HIV-1 DNA, and CA-RNA levels between β7^high CD4⁺ T and β7^low CD4⁺ T subsets in HIV-1 infected individuals after antiviral treatment.

CONCLUSION

The β7^high CD4⁺ T cells were negatively correlated with disease progression during chronic HIV-1 infection. β7^high CD4⁺ T cells are susceptible to infection with HIV-1 and HIV-1 latent cells.

Blocking α4β7 integrin delays viral rebound in SHIVSF162P3-infected macaques treated with anti-HIV broadly neutralizing antibodies

Anti-HIV broadly neutralizing antibodies (bNAbs) may favor development of antiviral immunity by engaging the immune system during immunotherapy. Targeting integrin α4β7 with an anti-α4β7 monoclonal antibody (Rh-α4β7) affects immune responses in SIV/SHIV-infected macaques. To explore the therapeutic potential of combining bNAbs with α4β7 integrin blockade, SHIVSF162P3-infected, viremic rhesus macaques were treated with bNAbs only (VRC07-523LS and PGT128 anti-HIV antibodies) or a combination of bNAbs and Rh-α4β7 or were left untreated as a control. Treatment with bNAbs alone decreased viremia below 200 copies/ml in all macaques, but seven of eight macaques (87.5%) in the bNAbs-only group rebounded within a median of 3 weeks (95% CI: 2 to 9). In contrast, three of six macaques treated with a combination of Rh-α4β7 and bNAbs (50%) maintained a viremia below 200 copies/ml until the end of the follow-up period; viremia in the other three macaques rebounded within a median of 6 weeks (95% CI: 5 to 11). Thus, there was a modest delay in viral rebound in the macaques treated with the combination antibody therapy compared to bNAbs alone. Our study suggests that α4β7 integrin blockade may prolong virologic control by bNAbs in SHIVSF162P3-infected macaques.

SMAC Mimetic Plus Triple-Combination Bispecific HIVxCD3 Retargeting Molecules in SHIV.C.CH505-Infected, Antiretroviral Therapy-Suppressed Rhesus Macaques

The "shock-and-kill" human immunodeficiency virus type 1 (HIV-1) cure strategy involves latency reversal followed by immune-mediated clearance of infected cells. We have previously shown that activation of the noncanonical NF-κB pathway using an inhibitor of apoptosis (IAP), AZD5582, reverses HIV/simian immunodeficiency virus (SIV) latency. Here, we combined AZD5582 with bispecific HIVxCD3 DART molecules to determine the impact of this approach on persistence. Rhesus macaques (RMs) (n = 13) were infected with simian/human immunodeficiency virus SHIV.C.CH505.375H.dCT, and triple antiretroviral therapy (ART) was initiated after 16 weeks. After 42 weeks of ART, 8 RMs received a cocktail of 3 HIVxCD3 DART molecules having human A32, 7B2, or PGT145 anti-HIV-1 envelope (Env) specificities paired with a human anti-CD3 specificity that is rhesus cross-reactive. The remaining 5 ART-suppressed RMs served as controls. For 10 weeks, a DART molecule cocktail was administered weekly (each molecule at 1 mg/kg of body weight), followed 2 days later by AZD5582 (0.1 mg/kg). DART molecule serum concentrations were well above those considered adequate for redirected killing activity against Env-expressing target cells but began to decline after 3 to 6 weekly doses, coincident with the development of antidrug antibodies (ADAs) against each of the DART molecules. The combination of AZD5582 and the DART molecule cocktail did not increase on-ART viremia or cell-associated SHIV RNA in CD4+ T cells and did not reduce the viral reservoir size in animals on ART. The lack of latency reversal in the model used in this study may be related to low pre-ART viral loads (median, <105 copies/ml) and low preintervention reservoir sizes (median, <102 SHIV DNA copies/million blood CD4+ T cells). Future studies to assess the efficacy of Env-targeting DART molecules or other clearance agents to reduce viral reservoirs after latency reversal may be more suited to models that better minimize immunogenicity and have a greater viral burden.IMPORTANCE The most significant barrier to an HIV-1 cure is the existence of the latently infected viral reservoir that gives rise to rebound viremia upon cessation of ART. Here, we tested a novel combination approach of latency reversal with AZD5582 and clearance with bispecific HIVxCD3 DART molecules in SHIV.C.CH505-infected, ART-suppressed rhesus macaques. We demonstrate that the DART molecules were not capable of clearing infected cells in vivo, attributed to the lack of quantifiable latency reversal in this model with low levels of persistent SHIV DNA prior to intervention as well as DART molecule immunogenicity.

A Rare Mutation in an Infant-Derived HIV-1 Envelope Glycoprotein Alters Interprotomer Stability and Susceptibility to Broadly Neutralizing Antibodies Targeting the Trimer Apex

The envelope glycoprotein (Env) of human immunodeficiency virus type 1 (HIV-1) is the sole target of broadly neutralizing antibodies (bnAbs). Several mechanisms, such as the acquisition of mutations, variability of the loop length, and alterations in the glycan pattern, are employed by the virus to shield neutralizing epitopes on Env to sustain survival and infectivity within the host. The identification of mutations that lead to viral evasion of the host immune response is essential for the optimization and engineering of Env-based trimeric immunogens. Here, we report a rare leucine-to-phenylalanine escape mutation (L184F) at the base of hypervariable loop 2 (population frequency of 0.0045%) in a 9-month-old perinatally HIV-1-infected infant broad neutralizer. The L184F mutation altered the trimer conformation by modulating intramolecular interactions stabilizing the trimer apex and led to viral escape from autologous plasma bnAbs and known N160 glycan-targeted bnAbs. The L184F amino acid change led to the acquisition of a relatively open trimeric conformation, often associated with tier 1 HIV-1 isolates and increased susceptibility to neutralization by polyclonal plasma antibodies of weak neutralizers. While there was no impact of the L184F mutation on free virus transmission, a reduction in cell-to-cell transmission was observed. In conclusion, we report a naturally selected viral mutation, L184F, that influenced a change in the conformation of the Env trimer apex as a mechanism of escape from contemporaneous plasma V2 apex-targeted nAbs. Further studies should be undertaken to define viral mutations acquired during natural infection, to escape selection pressure exerted by bnAbs, to inform vaccine design and bnAb-based therapeutic strategies.IMPORTANCE The design of HIV-1 envelope-based immunogens capable of eliciting broadly neutralizing antibodies (bnAbs) is currently under active research. Some of the most potent bnAbs target the quaternary epitope at the V2 apex of the HIV-1 Env trimer. By studying naturally circulating viruses from a perinatally HIV-1-infected infant with plasma neutralizing antibodies targeted to the V2 apex, we identified a rare leucine-to-phenylalanine substitution, in two out of six functional viral clones, that destabilized the trimer apex. This single-amino-acid alteration impaired the interprotomeric interactions that stabilize the trimer apex, resulting in an open trimer conformation and escape from broadly neutralizing autologous plasma antibodies and known V2 apex-directed bnAbs, thereby favoring viral evasion of the early bnAb response of the infected host. Defining the mechanisms by which naturally occurring viral mutations influence the sensitivity of HIV-1 to bnAbs will provide information for the development of vaccines and bnAbs as anti-HIV-1 reagents.

Broadly neutralizing plasma antibodies effective against autologous circulating viruses in infants with multivariant HIV-1 infection

Broadly neutralizing antibodies (bnAbs) develop in a subset of HIV-1 infected individuals over 2-3 years of infection. Infected infants develop plasma bnAbs frequently and as early as 1-year post-infection suggesting factors governing bnAb induction in infants are distinct from adults. Understanding viral characteristics in infected infants with early bnAb responses will provide key information about antigenic triggers driving B cell maturation pathways towards induction of bnAbs. Herein, we evaluate the presence of plasma bnAbs in a cohort of 51 HIV-1 clade-C infected infants and identify viral factors associated with early bnAb responses. Plasma bnAbs targeting V2-apex on the env are predominant in infant elite and broad neutralizers. Circulating viral variants in infant elite neutralizers are susceptible to V2-apex bnAbs. In infant elite neutralizers, multivariant infection is associated with plasma bnAbs targeting diverse autologous viruses. Our data provides information supportive of polyvalent vaccination approaches capable of inducing V2-apex bnAbs against HIV-1.

Anti-α4β7 monoclonal antibody-conjugated nanoparticles block integrin α4β7 on intravaginal T cells in rhesus macaques

Intravenous administration of anti-α₄β₇ monoclonal antibody in macaques decreases simian immunodeficiency virus (SIV) vaginal infection and reduces gut SIV loads. Because of potential side effects of systemic administration, a prophylactic strategy based on mucosal administration of anti-α₄β₇ antibody may be safer and more effective. With this in mind, we developed a novel intravaginal formulation consisting of anti-α₄β₇ monoclonal antibody-conjugated nanoparticles (NPs) loaded in a 1% hydroxyethylcellulose (HEC) gel (NP-α₄β₇ gel). When intravaginally administered as a single dose in a rhesus macaque model, the formulation preferentially bound to CD4⁺ or CD3⁺ T cells expressing high levels of α₄β₇, and occupied ~40% of α₄β₇ expressed by these subsets and ~25% of all cells expressing α₄β₇ Blocking of the α₄β₇ was restricted to the vaginal tract without any changes detected systemically.

Safety and Immunological Evaluation of Interleukin-21 Plus Anti-α4β7 mAb Combination Therapy in Rhesus Macaques

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections compromise gut immunological barriers, inducing high levels of inflammation and a severe depletion of intestinal CD4+ T cells. Expression of α4β7 integrin promotes homing of activated T cells to intestinal sites where they become preferentially infected; blockade of α4β7 with an anti-α4β7 monoclonal antibody (mAb) prior to infection has been reported to reduce gut SIV viremia in rhesus macaques (RMs). Interleukin-21 (IL-21) administration in antiretroviral therapy-treated, SIV-infected RMs reduces gut inflammation and improves gut integrity. We therefore hypothesized that the combination of IL-21 and anti-α4β7 mAb therapies could synergize to reduce inflammation and HIV persistence. We co-administered two intravenous doses of rhesus anti-α4β7 mAb (50 mg/kg) combined with seven weekly subcutaneous infusions of IL-21-IgFc (100 μg/kg) in four healthy, SIV-uninfected RMs to evaluate the safety and immunological profiles of this intervention in blood and gut. Co-administration of IL-21 and anti-α4β7 mAb showed no toxicity at the given dosages as assessed by multiple hematological and chemical parameters and did not alter the bioavailability of the therapeutics or result in the generation of antibodies against the anti-α4β7 mAb or IL-21-IgFc. Upon treatment, the frequency of CD4 memory T cells expressing β7 increased in blood and decreased in gut, consistent with an inhibition of activated CD4 T-cell homing to the gut. Furthermore, the frequency of T cells expressing proliferation and immune activation markers decreased in blood and, more profoundly, in gut. The combined IL-21 plus anti-α4β7 mAb therapy is well-tolerated in SIV-uninfected RMs and reduces the gut homing of α4β7+ CD4 T cells as well as the levels of gut immune activation.

Integrin α4β7 in HIV-1 infection: A critical review

Over the past decade, a series of observations linking α4β7, the principal gut-homing integrin, with various aspects of HIV-1 infection have generated considerable interest in the field of HIV-1 research. After the initial report that the major HIV-1 envelope glycoprotein, gp120, can bind to α4β7, intensive research efforts have been focused on the role of α4β7 as a key factor in HIV-1 pathogenesis and as a potential target for prevention and treatment. The interaction between α4β7 and its natural ligand, MAdCAM-1, directs infected CD4⁺ T cells and HIV-1 virions carrying incorporated α4β7 to the gut mucosa, which may facilitate HIV-1 seeding and replication in the intestinal compartment during the early stages of infection. In addition, cells that express high levels of α4β7, such as Th17 cells, represent preferential targets for infection, and their frequency in the circulation was shown to correlate with susceptibility to HIV-1 infection and disease progression. A number of in vivo studies in nonhuman primates have investigated whether blockage of α4β7 may affect SIV transmission and pathogenesis. Administration of a primatized anti-α4β7 antibody that blocks MAdCAM-1 binding to α4β7 was reported to reduce SIV mucosal transmission in rhesus macaques. However, the mechanism responsible for such a protective effect is still undefined, and conflicting results have been reported on the effects of the same antibody, in combination with ART, during the early chronic phase of SIV infection. Thus, despite a series of tantalizing results accrued over the past decade, the jury is still out on the role of α4β7 in HIV-1 infection.

Analytical Treatment Interruption after Short-Term Antiretroviral Therapy in a Postnatally Simian-Human Immunodeficiency Virus-Infected Infant Rhesus Macaque Model

To achieve long-term viral remission in human immunodeficiency virus (HIV)-infected children, novel strategies beyond early antiretroviral therapy (ART) will be necessary. Identifying clinical predictors of the time to viral rebound upon ART interruption will streamline the development of novel therapeutic strategies and accelerate their evaluation in clinical trials. However, identification of these biomarkers is logistically challenging in infants, due to sampling limitations and the potential risks of treatment interruption. To facilitate the identification of biomarkers predicting viral rebound, we have developed an infant rhesus macaque (RM) model of oral simian-human immunodeficiency virus (SHIV) SHIV.CH505.375H.dCT challenge and analytical treatment interruption (ATI) after short-term ART. We used this model to characterize SHIV replication kinetics and virus-specific immune responses during short-term ART or after ATI and demonstrated plasma viral rebound in 5 out of 6 (83%) infants. We observed a decline in humoral immune responses and partial dampening of systemic immune activation upon initiation of ART in these infants. Furthermore, we monitored SHIV replication and rebound kinetics in infant and adult RMs and found that both infants and adults demonstrated equally potent virus-specific humoral immune responses. Finally, we validated our models by confirming a well-established correlate of the time to viral rebound, namely, the pre-ART plasma viral load, as well as identified additional potential humoral immune correlates. Thus, this model of infant ART and viral rebound can be used and further optimized to define biomarkers of viral rebound following long-term ART as well as to preclinically assess novel therapies to achieve a pediatric HIV functional cure.IMPORTANCE Novel interventions that do not rely on daily adherence to ART are needed to achieve sustained viral remission for perinatally infected children, who currently rely on lifelong ART. Considering the risks and expense associated with ART interruption trials, the identification of biomarkers of viral rebound will prioritize promising therapeutic intervention strategies, including anti-HIV Env protein therapeutics. However, comprehensive studies to identify those biomarkers are logistically challenging in human infants, demanding the need for relevant nonhuman primate models of HIV rebound. In this study, we developed an infant RM model of oral infection with simian-human immunodeficiency virus expressing clade C HIV Env and short-term ART followed by ATI, longitudinally characterizing the immune responses to viral infection during ART and after ATI. Additionally, we compared this infant RM model to an analogous adult RM rebound model and identified virologic and immunologic correlates of the time to viral rebound after ATI.

A Tat/Rev Induced Limiting Dilution Assay to Measure Viral Reservoirs in Non-Human Primate Models of HIV Infection

The establishment of latent infection and poorly characterized viral reservoirs in tissues represent major obstacles to a definitive cure for HIV. Non-human primate (NHP) models of HIV infection are critical to elucidate pathogenic processes and an essential tool to test novel therapeutic strategies. Thus, the availability of novel assays to measure residual viral replication and reservoirs in NHP models may increase their utility in the search for an HIV cure. We developed a tat/rev induced limiting dilution assay to measure the frequency of CD4⁺ T cells that express multiply-spliced(ms)_SIV RNA in presence and absence of stimulation. We validated the assay using cell lines and cells from blood and lymph nodes of SIV infected macaques. In vitro, SIV/SHIV TILDA detects only cells expressing viral proteins. In SIV/SHIV-infected macaques, CD4⁺ T cells that express msSIV/SHIV RNA (TILDA data) were detected also in the setting of very low/undetectable viremia. TILDA data were significantly higher after stimulation and correlated with plasma viral load (pVL). Interestingly, TILDA data from early cART initiation correlated with peak and AUC pVL post-cART interruption. In summary, we developed an assay that may be useful in characterizing viral reservoirs and determining the effect of HIV interventions in NHP models.

V2-Specific Antibodies in HIV-1 Vaccine Research and Natural Infection: Controllers or Surrogate Markers

Most human immunodeficiency virus (HIV) vaccine trials have lacked efficacy and empirical vaccine lead targets are scarce. Thus far, the only independent correlate of reduced risk of HIV-1 acquisition in humans is elevated levels of V2-specific antibodies identified in the modestly protective RV144 vaccine trial. Ten years after RV144, human and non-human primate vaccine studies have reassessed the potential contribution of V2-specific antibodies to vaccine efficacy. In addition, studies of natural HIV-1 infection in humans have provided insight into the development of V1V2-directed antibody responses and their impact on clinical parameters and disease progression. Functionally diverse anti-V2 monoclonal antibodies were isolated and their structurally distinct V2 epitope regions characterized. After RV144, a plethora of research studies were performed using different model systems, immunogens, protocols, and challenge viruses. These diverse studies failed to provide a clear picture regarding the contribution of V2 antibodies to vaccine efficacy. Here, we summarize the biological functions and clinical findings associated with V2-specific antibodies and discuss their impact on HIV vaccine research.