A single injection of anti-HIV-1 antibodies protects against repeated SHIV challenges

TLR-Agonist Mediated Enhancement of Antibody-Dependent Effector Functions as Strategy For an HIV-1 Cure

Background

The current treatment for HIV-1 is based on blocking various stages in the viral replication cycle using combination antiretroviral therapy (ART). Even though ART effectively controls the infection, it is not curative, and patients must therefore continue treatment life-long.

Aim

Here we review recent literature investigating the single or combined effect of toll-like receptor (TLR) agonists and broadly neutralizing antibodies (bNAbs) with the objective to evaluate the evidence for this combination as a means towards an HIV-1 cure.

Results

Multiple preclinical studies found significantly enhanced killing of HIV-1 infected cells by TLR agonist-induced innate immune activation or by Fc-mediated effector functions following bNAb administration. However, monotherapy with either agent did not lead to sustained HIV-1 remission in clinical trials among individuals on long-term ART. Notably, findings in non-human primates suggest that a combination of TLR agonists and bNAbs may be able to induce long-term remission after ART cessation and this approach is currently being further investigated in clinical trials.

Conclusion

Preclinical findings show beneficial effects of either TLR agonist or bNAb administration for enhancing the elimination of HIV-1 infected cells. Further, TLR agonist-mediated stimulation of innate effector functions in combination with bNAbs may enhance antibody-dependent cellular cytotoxicity and non-human primate studies have shown promising results for this combination strategy. Factors such as immune exhaustion, proviral bNAb sensitivity and time of intervention might impact the clinical success.

HIV Broadly Neutralizing Antibodies Expressed as IgG3 Preserve Neutralization Potency and Show Improved Fc Effector Function

The ability of several broadly neutralizing antibodies (bNAbs) to protect against HIV infection is enhanced through Fc receptor binding. Antibody isotype modulates this effect, with IgG3 associated with improved HIV control and vaccine efficacy. We recently showed that an IgG3 variant of bNAb CAP256-VRC26.25 exhibited more potent neutralization and phagocytosis than its IgG1 counterpart. Here, we expanded this analysis to include additional bNAbs targeting all major epitopes. A total of 15 bNAbs were expressed as IgG1 or IgG3, and pairs were assessed for neutralization potency against the multi-subtype global panel of 11 HIV strains. Binding to the neonatal Fc receptor (FcRn) and Fcγ receptors were measured using ELISA and antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis were measured using infectious viruses and global panel Env SOSIP trimers, respectively. IgG3 bNAbs generally showed similar or increased (up to 60 fold) neutralization potency than IgG1 versions, though the effect was virus-specific. This improvement was statistically significant for CAP256-VRC26.25, 35022, PGT135 and CAP255.G3. IgG3 bNAbs also showed significantly improved binding to FcγRIIa which correlated with enhanced phagocytosis of all trimeric Env antigens. Differences in ADCC were epitope-specific, with IgG3 bNAbs to the MPER, CD4 binding site and gp120-gp41 interface showing increased ADCC. We also explored the pH dependence of IgG1 and IgG3 variants for FcRn binding, as this determines the half-life of antibodies. We observed reduced pH dependence, associated with shorter half-lives for IgG3 bNAbs, with κ-light chains. However, IgG3 bNAbs that use λ-light chains showed similar pH dependence to their IgG1 counterparts. This study supports the manipulation of the constant region to improve both the neutralizing and Fc effector activity of bNAbs, and suggests that IgG3 versions of bNAbs may be preferable for passive immunity given their polyfunctionality.

Contribution to HIV Prevention and Treatment by Antibody-Mediated Effector Function and Advances in Broadly Neutralizing Antibody Delivery by Vectored Immunoprophylaxis

HIV-1 broadly neutralizing antibodies (bNAbs) targeting the viral envelope have shown significant promise in both HIV prevention and viral clearance, including pivotal results against sensitive strains in the recent Antibody Mediated Prevention (AMP) trial. Studies of bNAb passive transfer in infected patients have demonstrated transient reduction of viral load at high concentrations that rebounds as bNAb is cleared from circulation. While neutralization is a crucial component of therapeutic efficacy, numerous studies have demonstrated that bNAbs can also mediate effector functions, such as antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and antibody-dependent complement deposition (ADCD). These functions have been shown to contribute towards protection in several models of HIV acquisition and in viral clearance during chronic infection, however the role of target epitope in facilitating these functions, as well as the contribution of individual innate functions in protection and viral clearance remain areas of active investigation. Despite their potential, the transient nature of antibody passive transfer limits the widespread use of bNAbs. To overcome this, we and others have demonstrated vectored antibody delivery capable of yielding long-lasting expression of bNAbs in vivo. Two clinical trials have shown that adeno-associated virus (AAV) delivery of bNAbs is safe and capable of sustained bNAb expression for over 18 months following a single intramuscular administration. Here, we review key concepts of effector functions mediated by bNAbs against HIV infection and the potential for vectored immunoprophylaxis as a means of producing bNAbs in patients.

Preventive HIV Vaccines-Leveraging on Lessons from the Past to Pave the Way Forward

Almost four decades on, since the 1980’s, with hundreds of HIV vaccine candidates tested in both non-human primates and humans, and several HIV vaccines trials later, an efficacious HIV vaccine continues to evade us. The enormous worldwide genetic diversity of HIV, combined with HIV’s inherent recombination and high mutation rates, has hampered the development of an effective vaccine. Despite the advent of antiretrovirals as pre-exposure prophylaxis and preventative treatment, which have shown to be effective, HIV infections continue to proliferate, highlighting the great need for a vaccine. Here, we provide a brief history for the HIV vaccine field, with the most recent disappointments and advancements. We also provide an update on current passive immunity trials, testing proof of the concept of the most clinically advanced broadly neutralizing monoclonal antibodies for HIV prevention. Finally, we include mucosal immunity, the importance of vaccine-elicited immune responses and the challenges thereof in the most vulnerable environment–the female genital tract and the rectal surfaces of the gastrointestinal tract for heterosexual and men who have sex with men transmissions, respectively.

Immunotherapy during the acute SHIV infection of macaques confers long-term suppression of viremia

We report that combination bNAb immunotherapy initiated on day 3 post-infection (PI) maintained durable CD8+ T cell-mediated suppression of SHIVAD8 viremia and preinoculation levels of CD4+ T cells in 9 of 13 treated monkeys during nearly 6 yr of observation, as assessed by successive CD8+ T cell-depletion experiments. In an extension of that study, two treatment interventions (bNAbs alone or cART plus bNAbs) beginning on week 2 PI were conducted and conferred controller status to 7 of 12 monkeys that was also dependent on control mediated by CD8+ cells. However, the median time to suppression of plasma viremia following intervention on week 2 was markedly delayed (85 wk) compared with combination bNAb immunotherapy initiated on day 3 (39 wk). In both cases, the principal correlate of virus control was the induction of CD8+ T cellular immunity.

Enhanced Ability of Plant-Derived PGT121 Glycovariants To Eliminate HIV-1-Infected Cells

The activity of broadly neutralizing antibodies (bNAbs) targeting HIV-1 depends on pleiotropic functions, including viral neutralization and the elimination of HIV-1-infected cells. Several in vivo studies have suggested that passive administration of bNAbs represents a valuable strategy for the prevention or treatment of HIV-1. In addition, different strategies are currently being tested to scale up the production of bNAbs to obtain the large quantities of antibodies required for clinical trials. Production of antibodies in plants permits low-cost and large-scale production of valuable therapeutics; furthermore, pertinent to this work, it also includes an advanced glycoengineering platform. In this study, we used Nicotiana benthamiana to produce different Fc-glycovariants of a potent bNAb, PGT121, with near-homogeneous profiles and evaluated their antiviral activities. Structural analyses identified a close similarity in overall structure and glycosylation patterns of Fc regions for these plant-derived Abs and mammalian cell-derived Abs. When tested for Fc-effector activities, afucosylated PGT121 showed significantly enhanced FcγRIIIa interaction and antibody dependent cellular cytotoxicity (ADCC) against primary HIV-1-infected cells, both in vitro and ex vivo. However, the overall galactosylation profiles of plant PGT121 did not affect ADCC activities against infected primary CD4+ T cells. Our results suggest that the abrogation of the Fc N-linked glycan fucosylation of PGT121 is a worthwhile strategy to boost its Fc-effector functionality. IMPORTANCE PGT121 is a highly potent bNAb and its antiviral activities for HIV-1 prevention and therapy are currently being evaluated in clinical trials. The importance of its Fc-effector functions in clearing HIV-1-infected cells is also under investigation. Our results highlight enhanced Fc-effector activities of afucosylated PGT121 MAbs that could be important in a therapeutic context to accelerate infected cell clearance and slow disease progression. Future studies to evaluate the potential of plant-produced afucosylated PGT121 in controlling HIV-1 replication in vivo are warranted.

Advances in simian--human immunodeficiency viruses for nonhuman primate studies of HIV prevention and cure

PURPOSE OF REVIEW

Simian--human immunodeficiency viruses (SHIVs), chimeric viruses that encode HIV-1 Env within an SIV backbone, are key reagents for nonhuman primate studies of antibody-based vaccines, broadly neutralizing antibodies (bnAbs), and other Env-targeting reagents. Here, we discuss the provenance and characteristics of currently relevant SHIVs, novel technical advances, recent discoveries enabled by SHIV challenge studies, and the continued development of SHIVs for persistence and cure experiments.

RECENT FINDINGS

SHIV SF162P3, SHIV AD8EO, and transmitter/founder SHIVs with Env375 mutations are now common reagents in nonhuman primate studies, with increased use and validation establishing their properties and potential applications. Genetic barcoding of SIV and SHIV, which allows tracing of individual lineages and elucidation of viral kinetics from transmission through latency has expanded the experimental capacity of SHIV models. SHIV challenge studies have determined the neutralizing antibody titers that correlate with protection for passive and active immunization and enabled complementary human and nonhuman primate studies of vaccine development. SHIV models of latency continue to evolve, aided by descriptions of SHIV persistence on ART and the proviral landscape.

SUMMARY

Recent advances and more thorough characterization of SHIVs allow for expanded applications and greater confidence in experimental results.

Long-acting injectable HIV therapies: the next frontier

PURPOSE OF REVIEW

There has been significant development of long-acting injectable therapy for the management of HIV in recent years that has the potential to revolutionise HIV care as we know it. This review summarises the data and outlines the potential challenges in the field of long-acting antiretroviral therapy (ART).

RECENT FINDINGS

In recent years, monthly and two monthly long-acting injectable ART in the form of cabotegravir and rilpivirine has shown safety and efficacy in large-scale phase 3 randomised control trials. Also, agents with novel mechanisms of action, such as Lenacapavir, have been tested in early-phase studies and are currently being tested in phase 2-3 clinical trials; if successful, this may allow six-monthly dosing schedules.

SUMMARY

However, despite evidence that suggests that these therapies are efficacious and acceptable to patients, the challenge of integrating these agents into our current healthcare infrastructure and making these novel agents cost-effective and available to the populations most likely to benefit remains. The next frontier for long-acting therapy will be to introduce these agents in a real-world setting ensuring that the groups most in need of long-acting therapy are not left behind.

Rectal tissue and vaginal tissue from intravenous VRC01 recipients show protection against ex vivo HIV-1 challenge

BackgroundVRC01, a potent, broadly neutralizing monoclonal antibody, inhibits simian-HIV infection in animal models. The HVTN 104 study assessed the safety and pharmacokinetics of VRC01 in humans. We extend the clinical evaluation to determine intravenously infused VRC01 distribution and protective function at mucosal sites of HIV-1 entry.MethodsHealthy, HIV-1-uninfected men (n = 7) and women (n = 5) receiving VRC01 every 2 months provided mucosal and serum samples once, 4-13 days after infusion. Eleven male and 8 female HIV-seronegative volunteers provided untreated control samples. VRC01 levels were measured in serum, secretions, and tissue, and HIV-1 inhibition was determined in tissue explants.ResultsMedian VRC01 levels were quantifiable in serum (96.2 μg/mL or 1.3 pg/ng protein), rectal tissue (0.11 pg/ng protein), rectal secretions (0.13 pg/ng protein), vaginal tissue (0.1 pg/ng protein), and cervical secretions (0.44 pg/ng protein) from all recipients. VRC01/IgG ratios in male serum correlated with those in paired rectal tissue (r = 0.893, P = 0.012) and rectal secretions (r = 0.9643, P = 0.003). Ex vivo HIV-1Bal26 challenge infected 4 of 21 rectal explants from VRC01 recipients versus 20 of 22 from controls (P = 0.005); HIV-1Du422.1 infected 20 of 21 rectal explants from VRC01 recipients and 12 of 12 from controls (P = 0.639). HIV-1Bal26 infected 0 of 14 vaginal explants of VRC01 recipients compared with 23 of 28 control explants (P = 0.003).ConclusionIntravenous VRC01 distributes into the female genital and male rectal mucosa and retains anti-HIV-1 functionality, inhibiting a highly neutralization-sensitive but not a highly resistant HIV-1 strain in mucosal tissue. These findings lend insight into VRC01 mucosal infiltration and provide perspective on in vivo protective efficacy.FundingNational Institute of Allergy and Infectious Diseases and Bill & Melinda Gates Foundation.

Broadly neutralizing antibody-mediated protection of macaques against repeated intravenous exposures to simian-human immunodeficiency virus

OBJECTIVE

The opioid epidemic has increased parentally acquired HIV infection. To inform the development of a long-acting prevention strategy, we evaluated the protective efficacy of broadly neutralizing antibodies (bNAbs) against intravenous simian-human immunodeficiency virus (SHIV) infection in macaques.

DESIGN

Five cynomolgus macaques were injected once subcutaneously with 10-1074 and 3BNC117 (10 mg each kg-1) and were repeatedly challenged intravenously once weekly with SHIVAD8-EO (130 TCID50), until infection was confirmed via plasma viral load assay. Two control macaques, which received no antibody, were challenged identically.

METHODS

Plasma viremia was monitored via RT-qPCR assay. bNAb concentrations were determined longitudinally in plasma samples via TZM-bl neutralization assays using virions pseudotyped with 10-1074-sensitive (X2088_c9) or 3BNC117-sensitive (Q769.d22) HIV envelope proteins.

RESULTS

Passively immunized macaques were protected against a median of five weekly intravenous SHIV challenges, as compared to untreated controls, which were infected following a single challenge. Of the two bNAbs, 10-1074 exhibited relatively longer persistence in vivo. The median plasma level of 10-1074 at SHIV breakthrough was 1.1 μg ml-1 (range: 0.6-1.6 μg ml-1), whereas 3BNC117 was undetectable. Probit modeling estimated that 6.6 μg ml-1 of 10-1074 in plasma corresponded to a 99% reduction in per-challenge infection probability, as compared to controls.

CONCLUSIONS

Significant protection against repeated intravenous SHIV challenges was observed following administration of 10-1074 and 3BNC117 and was due primarily to 10-1074. Our findings extend preclinical studies of bNAb-mediated protection against mucosal SHIV acquisition and support the possibility that intermittent subcutaneous injections of 10-1074 could serve as long-acting preexposure prophylaxis for persons who inject drugs.

Broadly neutralizing HIV-1 antibody reactivity in HIV tests: implications for diagnostics

OBJECTIVE

Passive immunization with broadly neutralizing antibodies (bNAbs) is under evaluation for HIV prevention. BNAbs target gp120 or gp41, two HIV envelope antigens commonly present in diagnostic tests. Depending on bNAb type and dose administered to humans, serum levels can reach nearly 1 mg/ml and wane over several weeks to months. We investigated the reactivity of bNAbs in HIV serological tests to inform diagnostic testing practices for persons treated with these products.

DESIGN AND METHODS

The antigp120 bNAbs VRCO1, PGT121, PGT145, 3BNC117, 10-1074 and N6 and antigp41 bNAbs 10E8 and 10E8v4 were tested with the laboratory-based Bio-Rad Ag/Ab Combo assay, the point-of-care single-use Determine Combo, OraQuick, Reveal G4, SureCheck, Uni-Gold, INSTI and DPP HIV-1/2 assays, and the supplemental Geenius and HIV-1 Western Blot assays.

RESULTS

At 1 mg/ml, all bNAbs were nonreactive in four screening tests. OraQuick, SureCheck, Reveal G4 and INSTI detected at least two bNAbs each; SureCheck exhibited reactivity to six bNAbs. Geenius was HIV-1 indeterminate (gp160+) with all bNAbs except PGT121, which was HIV antibody-negative. HIV-1 Western Blot was indeterminate (gp41+/gp160+) with 10E8 and 10E8v4 and negative with the remaining bNAbs. There was no correlation between the test antigen construct(s) and bNAb reactivity.

CONCLUSION

We identified a laboratory-based Ag/Ab EIA and three single-use rapid HIV tests that are nonreactive against a panel of bNAbs supporting some diagnostic tests can distinguish HIV-1 infection events among persons receiving bNAb immunoprophylaxis. Evaluation of HIV diagnostic tests prior to clinical use may identify suitable serologic assays for persons administered bNAbs.

Prevention of diabetes-associated fibrosis: Strategies in FcRn-targeted nanosystems for oral drug delivery

Diabetes mellitus is a chronic disease with an elevated risk of micro- and macrovascular complications, such as fibrosis. To prevent diabetes-associated fibrosis, the symptomatology of diabetes must be controlled, which is commonly done by subcutaneous injection of antidiabetic peptides. To minimize the pain and distress associated with such injections, there is an urgent need for non-invasive oral transmucosal drug delivery strategies. However, orally administered peptide-based drugs are exposed to harsh conditions in the gastrointestinal tract and poorly cross the selective intestinal epithelium. Thus, targeting of drugs to receptors expressed in epithelial cells, such as the neonatal Fc receptor (FcRn), may therefore enhance uptake and transport through mucosal barriers. This review compiles how in-depth studies of FcRn biology and engineering of receptor-binding molecules may pave the way for design of new classes of FcRn-targeted nanosystems. Tailored strategies may open new avenues for oral drug delivery and provide better treatment options for diabetes and, consequently, fibrosis prevention.

CD8 Effector T Cells Function Synergistically With Broadly Neutralizing Antibodies to Enhance Suppression of HIV Infection

HIV-specific CD8 T cells and broadly neutralizing antibodies (bNAbs) both contribute to the control of viremia, but in most cases, neither can completely suppress viral replication. To date, therapeutic vaccines have not been successful in eliciting HIV-specific CD8 T cell or bNAb responses that are capable of preventing long-term viral rebound upon ART cessation. These challenges suggest that a combinatorial approach that harnesses both bNAbs and CD8 T cell responses may be necessary for long term control of viral replication. In this study we demonstrate a synergistic interaction between CD8 T cells and bNAbs using an in vitro model. Our data suggest that this combinatorial approach is very effective at suppressing viral replication in vitro and should be considered in future therapeutic studies.

Broadly Neutralizing Antibodies for HIV-1 Prevention

Given the absence of an effective vaccine for protection against HIV-1 infection, passive immunization strategies that utilize potent broadly neutralizing antibodies (bnAbs) to block acquisition of HIV-1 are being rigorously pursued in the clinical setting. bnAbs have demonstrated robust protection in preclinical animal models, and several leading bnAb candidates have shown favorable safety and pharmacokinetic profiles when tested individually or in combinations in early phase human clinical trials. Furthermore, passive administration of bnAbs in HIV-1 infected individuals has resulted in prolonged suppression of viral rebound following interruption of combination antiretroviral therapy, and robust antiviral activity when administered to viremic individuals. Recent results from the first efficacy trials testing repeated intravenous administrations of the anti-CD4 binding site bnAb VRC01 have demonstrated positive proof of concept that bnAb passive immunization can confer protection against HIV-1 infection in humans, but have also highlighted the considerable barriers that remain for such strategies to effectively contribute to control of the epidemic. In this review, we discuss the current status of clinical studies evaluating bnAbs for HIV-1 prevention, highlight lessons learned from the recent Antibody Mediated Prevention (AMP) efficacy trials, and provide an overview of strategies being employed to improve the breadth, potency, and durability of antiviral protection.

In vitro affinity maturation of broader and more-potent variants of the HIV-1-neutralizing antibody CAP256-VRC26.25

Three variable 2 (V2) loops of HIV-1 envelope glycoprotein (Env) trimer converge at the Env apex to form the epitope of an important classes of HIV-1 broadly neutralizing antibodies (bNAbs). These V2-glycan/apex antibodies are exceptionally potent but less broad (∼60 to 75%) than many other bNAbs. Their CDRH3 regions are typically long, acidic, and tyrosine sulfated. Tyrosine sulfation complicates efforts to improve these antibodies through techniques such as phage or yeast display. To improve the breadth of CAP256-VRC26.25 (VRC26.25), a very potent apex antibody, we adapted and extended a B cell display approach. Specifically, we used CRISPR/Cas12a to introduce VRC26.25 heavy- and light-chain genes into their respective loci in a B cell line, ensuring that each cell expresses a single VRC26.25 variant. We then diversified these loci through activation-induced cytidine deaminase-mediated hypermutation and homology-directed repair using randomized CDRH3 sequences as templates. Iterative sorting with soluble Env trimers and further randomization selected VRC26.25 variants with successively improving affinities. Three mutations in the CDRH3 region largely accounted for this improved affinity, and VRC26.25 modified with these mutations exhibited greater breadth and potency than the original antibody. Our data describe a broader and more-potent form of VRC26.25 as well as an approach useful for improving the breadth and potency of antibodies with functionally important posttranslational modifications.

Employing Broadly Neutralizing Antibodies as a Human Immunodeficiency Virus Prophylactic & Therapeutic Application

Despite the discovery that the human immunodeficiency virus 1 (HIV-1) is the pathogen of acquired immunodeficiency syndrome (AIDS) in 1983, there is still no effective anti-HIV-1 vaccine. The major obstacle to the development of HIV-1 vaccine is the extreme diversity of viral genome sequences. Nonetheless, a number of broadly neutralizing antibodies (bNAbs) against HIV-1 have been made and identified in this area. Novel strategies based on using these bNAbs as an efficacious preventive and/or therapeutic intervention have been applied in clinical. In this review, we summarize the recent development of bNAbs and its application in HIV-1 acquisition prevention as well as discuss the innovative approaches being used to try to convey protection within individuals at risk and being treated for HIV-1 infection.

Germinal Center T follicular helper (GC-Tfh) cell impairment in chronic HIV infection involves c-Maf signaling

We have recently demonstrated that the function of T follicular helper (Tfh) cells from lymph nodes (LN) of HIV-infected individuals is impaired. We found that these cells were unable to provide proper help to germinal center (GC)-B cells, as observed by altered and inefficient anti-HIV antibody response and premature death of memory B cells. The underlying molecular mechanisms of this dysfunction remain poorly defined. Herein, we have used a unique transcriptional approach to identify these molecular defects. We consequently determined the transcriptional profiles of LN GC-Tfh cells following their interactions with LN GC-B cells from HIV-infected and HIV-uninfected individuals, rather than analyzing resting ex-vivo GC-Tfh cells. We observed that proliferating GC-Tfh cells from HIV-infected subjects were transcriptionally different than their HIV-uninfected counterparts, and displayed a significant downregulation of immune- and GC-Tfh-associated pathways and genes. Our results strongly demonstrated that MAF (coding for the transcription factor c-Maf) and its upstream signaling pathway mediators (IL6R and STAT3) were significantly downregulated in HIV-infected subjects, which could contribute to the impaired GC-Tfh and GC-B cell functions reported during infection. We further showed that c-Maf function was associated with the adenosine pathway and that the signaling upstream c-Maf could be partially restored by adenosine deaminase -1 (ADA-1) supplementation. Overall, we identified a novel mechanism that contributes to GC-Tfh cell impairment during HIV infection. Understanding how GC-Tfh cell function is altered in HIV is crucial and could provide critical information about the mechanisms leading to the development and maintenance of effective anti-HIV antibodies.

Human immunodeficiency virus (HIV) remains a worldwide burden despite available treatments. The virus induces dysregulations in major immune cells and organs including lymph nodes. Germinal center T follicular helper (GC-Tfh) cells are immune cells which induce specific anti-HIV antibodies by helping GC-B cells. In chronic HIV, the interaction between these two cell types is defective, leading to modified and inefficient anti-HIV antibody responses. In this study, we examined the underlying mechanisms of this dysfunction. We observed that proliferating GC-Tfh cells from HIV-infected individuals, displayed distinctive gene expression than those from -uninfected subjects, following GC-B cell interaction. Furthermore, GC-Tfh cells from HIV patients showed a reduction in important immune-related pathway and gene expression. A number of essential GC-Tfh cell genes, such as MAF and its associated genes (IL6R and STAT3), were particularly attenuated in HIV, contributing to the impaired cells function. Moreover, we found an association between MAF function and the key enzyme adenosine deaminase-1 (ADA-1), where supplementation with ADA-1 partially restored the dysfunctional signaling in GC-Tfh cells during chronic infection. Understanding how GC-Tfh cells are altered in HIV is critical to elucidate the mechanisms leading to effective anti-HIV antibodies.

Can Broadly Neutralizing HIV-1 Antibodies Help Achieve an ART-Free Remission?

Many broadly neutralizing antibodies (bnAbs) targeting the HIV-1 envelope glycoprotein are being assessed in clinical trials as strategies for HIV-1 prevention, treatment, and antiretroviral-free remission. BnAbs can neutralize HIV-1 and target infected cells for elimination. Concerns about HIV-1 resistance to single bnAbs have led to studies of bnAb combinations with non-overlapping resistance profiles. This review focuses on the potential for bnAbs to induce HIV-1 remission, either alone or in combination with latency reversing agents, therapeutic vaccines or other novel therapeutics. Key topics include preliminary activity of bnAbs in preclinical models and in human studies of HIV-1 remission, clinical trial designs, and antibody design strategies to optimize pharmacokinetics, coverage of rebound-competent virus, and enhancement of cellular immune functions.

Adeno-Associated Viral Vector Mediated Expression of Broadly- Neutralizing Antibodies Against HIV-Hitting a Fast-Moving Target

The vast genetic variability of HIV has impeded efforts towards a cure for HIV. Lifelong administration of combined antiretroviral therapy (cART) is highly effective against HIV and has markedly increased the life expectancy of HIV infected individuals. However, the long-term usage of cART is associated with co-morbidities and the emergence of multidrug-resistant escape mutants necessitating the development of alternative approaches to combat HIV/AIDS. In the past decade, the development of single-cell antibody cloning methods has facilitated the characterization of a diverse array of highly potent neutralizing antibodies against a broad range of HIV strains. Although the passive transfer of these broadly neutralizing antibodies (bnAbs) in both animal models and humans has been shown to elicit significant antiviral effects, long term virologic suppression requires repeated administration of these antibodies. Adeno-associated virus (AAV) mediated antibody gene transfer provides a long-term expression of these antibodies from a single administration of the recombinant vector. Therefore, this vectored approach holds promises in the treatment and prevention of a chronic disease like HIV infection. Here, we provide an overview of HIV genetic diversity, AAV vectorology, and anti-HIV bnAbs and summarize the promises and challenges of the application of AAV in the delivery of bnAbs for HIV prevention and therapy.

Identification of a CD4-binding site-directed antibody with ADCC activity from a chronic HIV-1B'-infected Chinese donor

Antibody-dependent cell-mediated cytotoxicity (ADCC) plays an important role in controlling HIV-1 invasion and replication in vivo. Isolation and identification of monoclonal antibodies (mAbs) with ADCC activity help design effective vaccines and develop novel treatment strategies. In this study, we first identified a broad neutralizer who had been infected with an HIV-1B' strain for over 10 years. Next, through probe-specific single-B-cell sorting and PCR amplification, we obtained genes for variable regions of the heavy chain (VHs) and light chain (VLs) of six antibodies and ligated them into expression vectors. After antibody expression and ELISA screening, we obtained a CD4-binding site-directed antibody (451-B4), whose VH and VL originated from the IGHV1-24 and IGLV1-40 germlines, respectively. Although 451-B4 neutralized only the SF162 tier 1 pseudovirus and 398F1 tier 2 pseudovirus, it could mediate comparable ADCC activity to a broadly neutralizing antibody, VRC01. The 451-B4 antibody will be a useful candidate for developing an ADCC-based treatment strategy against HIV-1 replication or latent infection in vivo.

Advancing HIV Broadly Neutralizing Antibodies: From Discovery to the Clinic

Despite substantial progress in confronting the global HIV-1 epidemic since its inception in the 1980s, better approaches for both treatment and prevention will be necessary to end the epidemic and remain a top public health priority. Antiretroviral therapy (ART) has been effective in extending lives, but at a cost of lifelong adherence to treatment. Broadly neutralizing antibodies (bNAbs) are directed to conserved regions of the HIV-1 envelope glycoprotein trimer (Env) and can block infection if present at the time of viral exposure. The therapeutic application of bNAbs holds great promise, and progress is being made toward their development for widespread clinical use. Compared to the current standard of care of small molecule-based ART, bNAbs offer: (1) reduced toxicity; (2) the advantages of extended half-lives that would bypass daily dosing requirements; and (3) the potential to incorporate a wider immune response through Fc signaling. Recent advances in discovery technology can enable system-wide mining of the immunoglobulin repertoire and will continue to accelerate isolation of next generation potent bNAbs. Passive transfer studies in pre-clinical models and clinical trials have demonstrated the utility of bNAbs in blocking or limiting transmission and achieving viral suppression. These studies have helped to define the window of opportunity for optimal intervention to achieve viral clearance, either using bNAbs alone or in combination with ART. None of these advances with bNAbs would be possible without technological advancements and expanding the cohorts of donor participation. Together these elements fueled the remarkable growth in bNAb development. Here, we review the development of bNAbs as therapies for HIV-1, exploring advances in discovery, insights from animal models and early clinical trials, and innovations to optimize their clinical potential through efforts to extend half-life, maximize the contribution of Fc effector functions, preclude escape through multiepitope targeting, and the potential for sustained delivery.

Super LeArner Prediction of NAb Panels (SLAPNAP): A Contain-erized Tool for Predicting Combination Monoclonal Broadly Neu-tralizing Antibody Sensitivity

MOTIVATION

A single monoclonal broadly neutralizing antibody (bnAb) regimen was recently evaluated in two randomized trials for prevention efficacy against HIV-1 infection. Subsequent trials will evaluate combination bnAb regimens (e.g., cocktails, multi-specific antibodies), which demonstrate higher potency and breadth in vitro compared to single bnAbs. Given the large number of potential regimens, methods for down-selecting these regimens into efficacy trials are of great interest.

RESULTS

We developed Super LeArner Prediction of NAb Panels (SLAPNAP), a software tool for training and evaluating machine learning models that predict in vitro neutralization sensitivity of HIV Envelope (Env) pseudoviruses to a given single or combination bnAb regimen, based on Env amino acid sequence features. SLAPNAP also provides measures of variable importance of sequence features. By predicting bnAb coverage of circulating sequences, SLAPNAP can improve ranking of bnAb regimens by their potential prevention efficacy. In addition, SLAPNAP can improve sieve analysis by defining sequence features that impact bnAb prevention efficacy.

AVAILABILITY

SLAPNAP is a freely available docker image that can be downloaded from DockerHub (https://hub.docker.com/r/slapnap/slapnap). Source code and documentation are available at GitHub (respectively, https://github.com/benkeser/slapnap and https://benkeser.github.io/slapnap/).

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Mining HIV controllers for broad and functional antibodies to recognize and eliminate HIV-infected cells

HIV monoclonal antibodies for viral reservoir eradication strategies will likely need to recognize reactivated infected cells and potently drive Fc-mediated innate effector cell activity. We systematically characterize a library of 185 HIV-envelope-specific antibodies derived from 15 spontaneous HIV controllers (HCs) that selectively exhibit robust serum Fc functionality and compared them to broadly neutralizing antibodies (bNAbs) in clinical development. Within the 10 antibodies with the broadest cell-recognition capability, seven originated from HCs and three were bNAbs. V3-loop-targeting antibodies are enriched among the top cell binders, suggesting the V3-loop may be selectively exposed and accessible on the cell surface. Fc functionality is more variable across antibodies, which is likely influenced by distinct binding topology and corresponding Fc accessibility, highlighting not only the importance of target-cell recognition but also the need to optimize for Fc-mediated elimination. Ultimately, our results demonstrate that this comprehensive selection process can identify monoclonal antibodies poised to eliminate infected cells.

Rossignol et al. characterize 185 HIV-envelope-specific antibodies derived from spontaneous HIV controllers, downselecting antibodies based on their ability to broadly recognize infected cells and potently drive Fc-mediated innate effector cell activity. This comprehensive selection process can identify monoclonal antibodies poised to eliminate infected cells for viral reservoir eradication strategies.

Broadly neutralizing antibodies for HIV-1 prevention and therapy

Despite immense progress in our ability to prevent and treat HIV-1 infection, HIV-1 remains an incurable disease and a highly efficacious HIV-1 vaccine is not yet available. Additional tools to prevent and treat HIV-1 are therefore necessary. The identification of potent and broadly neutralizing antibodies (bNAbs) against HIV-1 has revolutionized the field and may prove clinically useful. Significant advances have been made in identifying broader and more potent antibodies, characterizing antibodies in preclinical animal models, engineering antibodies to extend half-life and expand breadth and functionality, and evaluating the efficacy of single bNAbs and bNAb combinations in people with and without HIV-1. Here, we review recent progress in developing bNAbs for the prevention and treatment of HIV-1.

Virus Evolution and Neutralization Sensitivity in an HIV-1 Subtype B' Infected Plasma Donor with Broadly Neutralizing Activity

We sought to analyze the evolutionary characteristics and neutralization sensitivity of viruses in a human immunodeficiency virus type 1 (HIV-1) subtype B′ infected plasma donor with broadly neutralizing activity, which may provide information for new broadly neutralizing antibodies (bNAbs) isolation and immunogen design. A total of 83 full-length envelope genes were obtained by single-genome amplification (SGA) from the patient’s plasma at three consecutive time points (2005, 2006, and 2008) spanning four years. In addition, 28 Env-pseudotyped viruses were constructed and their neutralization sensitivity to autologous plasma and several representative bNAbs were measured. Phylogenetic analysis showed that these env sequences formed two evolutionary clusters (Cluster I and II). Cluster I viruses vanished in 2006 and then appeared as recombinants two years later. In Cluster II viruses, the V1 length and N-glycosylation sites increased over the four years of the study period. Most viruses were sensitive to concurrent and subsequent autologous plasma, and to bNAbs, including 10E8, PGT121, VRC01, and 12A21, but all viruses were resistant to PGT135. Overall, 90% of Cluster I viruses were resistant to 2G12, while 94% of Cluster II viruses were sensitive to 2G12. We confirmed that HIV-1 continued to evolve even in the presence of bNAbs, and two virus clusters in this donor adopted different escape mechanisms under the same humoral immune pressure.

Long-acting injectable HIV therapies: the next frontier: Republication

PURPOSE OF REVIEW

There has been significant development of long-acting injectable therapy for the management of HIV in recent years that has the potential to revolutionise HIV care as we know it. This review summarises the data and outlines the potential challenges in the field of long-acting antiretroviral therapy (ART).

RECENT FINDINGS

In recent years, monthly and two monthly long-acting injectable ART in the form of cabotegravir and rilpivirine has shown safety and efficacy in large-scale phase 3 randomised control trials. Also, agents with novel mechanisms of action, such as Lenacapavir, have been tested in early-phase studies and are currently being tested in phase 2-3 clinical trials; if successful, this may allow six-monthly dosing schedules.

SUMMARY

However, despite evidence that suggests that these therapies are efficacious and acceptable to patients, the challenge of integrating these agents into our current healthcare infrastructure and making these novel agents cost-effective and available to the populations most likely to benefit remains. The next frontier for long-acting therapy will be to introduce these agents in a real-world setting ensuring that the groups most in need of long-acting therapy are not left behind.

The Role of Tissue Resident Memory CD4 T Cells in Herpes Simplex Viral and HIV Infection

Tissue-resident memory T cells (TRM) were first described in 2009. While initially the major focus was on CD8⁺ TRM, there has recently been increased interest in defining the phenotype and the role of CD4⁺ TRM in diseases. Circulating CD4⁺ T cells seed CD4⁺ TRM, but there also appears to be an equilibrium between CD4⁺ TRM and blood CD4⁺ T cells. CD4⁺ TRM are more mobile than CD8⁺ TRM, usually localized deeper within the dermis/lamina propria and yet may exhibit synergy with CD8⁺ TRM in disease control. This has been demonstrated in herpes simplex infections in mice. In human recurrent herpes infections, both CD4⁺ and CD8⁺ TRM persisting between lesions may control asymptomatic shedding through interferon-gamma secretion, although this has been more clearly shown for CD8⁺ T cells. The exact role of the CD4⁺/CD8⁺ TRM axis in the trigeminal ganglia and/or cornea in controlling recurrent herpetic keratitis is unknown. In HIV, CD4⁺ TRM have now been shown to be a major target for productive and latent infection in the cervix. In HSV and HIV co-infections, CD4⁺ TRM persisting in the dermis support HIV replication. Further understanding of the role of CD4⁺ TRM and their induction by vaccines may help control sexual transmission by both viruses.

HIV-1 Envelope Glycosylation and the Signal Peptide

The RV144 trial represents the only vaccine trial to demonstrate any protective effect against HIV-1 infection. While the reason(s) for this protection are still being evaluated, it serves as justification for widespread efforts aimed at developing new, more effective HIV-1 vaccines. Advances in our knowledge of HIV-1 immunogens and host antibody responses to these immunogens are crucial to informing vaccine design. While the envelope (Env) protein is the only viral protein present on the surface of virions, it exists in a complex trimeric conformation and is decorated with an array of variable N-linked glycans, making it an important but difficult target for vaccine design. Thus far, efforts to elicit a protective humoral immune response using structural mimics of native Env trimers have been unsuccessful. Notably, the aforementioned N-linked glycans serve as a component of many of the epitopes crucial for the induction of potentially protective broadly neutralizing antibodies (bnAbs). Thus, a greater understanding of Env structural determinants, most critically Env glycosylation, will no doubt be of importance in generating effective immunogens. Recent studies have identified the HIV-1 Env signal peptide (SP) as an important contributor to Env glycosylation. Further investigation into the mechanisms by which the SP directs glycosylation will be important, both in the context of understanding HIV-1 biology and in order to inform HIV-1 vaccine design.

Vaccination induces maturation in a mouse model of diverse unmutated VRC01-class precursors to HIV-neutralizing antibodies with >50% breadth

Vaccine elicitation of broadly neutralizing antibodies (bnAbs) is a key HIV-research goal. The VRC01 class of bnAbs targets the CD4-binding site on the HIV-envelope trimer and requires extensive somatic hypermutation (SHM) to neutralize effectively. Despite substantial progress, vaccine-induced VRC01-class antibodies starting from unmutated precursors have exhibited limited neutralization breadth, particularly against viruses bearing glycan on loop D residue N276 (glycan276), present on most circulating strains. Here, using sequential immunization of immunoglobulin (Ig)-humanized mice expressing diverse unmutated VRC01-class antibody precursors, we elicited serum responses capable of neutralizing viruses bearing glycan276 and isolated multiple lineages of VRC01-class bnAbs, including two with >50% breadth on a 208-strain panel. Crystal structures of representative bnAbs revealed the same mode of recognition as known VRC01-class bnAbs. Structure-function studies further pinpointed key mutations and correlated their induction with specific immunizations. VRC01-class bnAbs can thus be matured by sequential immunization from unmutated ancestors to >50% breadth, and we delineate immunogens and regimens inducing key SHM.

COVID-19 antibody development fueled by HIV-1 broadly neutralizing antibody research

PURPOSE OF REVIEW

The coronavirus disease 2019 (COVID-19) pandemic has caught the world unprepared, with no prevention or treatment strategies in place. In addition to the efforts to develop an effective vaccine, alternative approaches are essential to control this pandemic, which will most likely require multiple readily available solutions. Among them, monoclonal anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies have been isolated by multiple laboratories in record time facilitated by techniques that were first pioneered for HIV-1 antibody discovery. Here, we summarize how lessons learned from anti-HIV-1 antibody discovery have provided fundamental knowledge for the rapid development of anti-SARS-CoV-2 antibodies.

RECENT FINDINGS

Research laboratories that successfully identified potent broadly neutralizing antibodies against HIV-1 have harnessed their antibody discovery techniques to isolate novel potent anti-SARS-CoV-2 antibodies, which have efficacy in animal models. These antibodies represent promising clinical candidates for treatment or prevention of COVID-19.

SUMMARY

Passive transfer of antibodies is a promising approach when the elicitation of protective immune responses is difficult, as in the case of HIV-1 infection. Antibodies can also play a significant role in post-exposure prophylaxis, in high-risk populations that may not mount robust immune responses after vaccination, and in therapy. We provide a review of the recent approaches used for anti-SARS-CoV-2 antibody discovery and upcoming challenges in the field.

Lactobacilli Expressing Broadly Neutralizing Nanobodies against HIV-1 as Potential Vectors for HIV-1 Prophylaxis?

In the absence of an active prophylactic vaccine against HIV-1, passively administered, broadly neutralizing antibodies (bnAbs) identified in some chronically infected persons were shown to prevent HIV-1 infection in animal models. However, passive administration of bnAbs may not be suited to prevent sexual HIV-1 transmission in high-risk cohorts, as a continuous high level of active bnAbs may be difficult to achieve at the primary site of sexual transmission, the human vagina with its acidic pH. Therefore, we used Lactobacillus, a natural commensal in the healthy vaginal microbiome, to express bn nanobodies (VHH) against HIV-1 that we reported previously. After demonstrating that recombinant VHHA6 expressed in E. coli was able to protect humanized mice from mucosal infection by HIV-1Bal, we expressed VHHA6 in a soluble or in a cell-wall-anchored form in Lactobacillus rhamnosus DSM14870. This strain is already clinically applied for treatment of bacterial vaginosis. Both forms of VHHA6 neutralized a set of primary epidemiologically relevant HIV-1 strains in vitro. Furthermore, VHHA6 was still active at an acidic pH. Thus, lactobacilli expressing bn VHH potentially represent an attractive vector for the passive immunization of women in cohorts at high risk of HIV-1 transmission.

Autologous IgG antibodies block outgrowth of a substantial but variable fraction of viruses in the latent reservoir for HIV-1

In untreated HIV-1 infection, rapid viral evolution allows escape from immune responses. Viral replication can be blocked by antiretroviral therapy. However, HIV-1 persists in a latent reservoir in resting CD4⁺ T cells, and rebound viremia occurs following treatment interruption. The reservoir, which is maintained in part by clonal expansion, can be measured using quantitative viral outgrowth assays (QVOAs) in which latency is reversed with T cell activation to allow viral outgrowth. Recent studies have shown that viruses detected in QVOAs prior to treatment interruption often differ from rebound viruses. We hypothesized that autologous neutralizing antibodies directed at the HIV-1 envelope (Env) protein might block outgrowth of some reservoir viruses. We modified the QVOA to reflect pressure from low concentrations of autologous antibodies and showed that outgrowth of a substantial but variable fraction of reservoir viruses is blocked by autologous contemporaneous immunoglobulin G (IgG). A reduction in outgrowth of >80% was seen in 6 of 15 individuals. This effect was due to direct neutralization. We established a phylogenetic relationship between rebound viruses and viruses growing out in vitro in the presence of autologous antibodies. Some large infected cell clones detected by QVOA carried neutralization-sensitive viruses, providing a cogent explanation for differences between rebound virus and viruses detected in standard QVOAs. Measurement of the frequency of reservoir viruses capable of outgrowth in the presence of autologous IgG might allow more accurate prediction of time to viral rebound. Ultimately, therapeutic immunization targeting the subset of variants resistant to autologous IgG might contribute to a functional cure.

Broadly Neutralizing Antibodies for HIV Prevention

In the last decade, over a dozen potent broadly neutralizing antibodies (bnAbs) to several HIV envelope protein epitopes have been identified, and their in vitro neutralization profiles have been defined. Many have demonstrated prevention efficacy in preclinical trials and favorable safety and pharmacokinetic profiles in early human clinical trials. The first human prevention efficacy trials using 10 sequential, every-two-month administrations of a single anti-HIV bnAb are anticipated to conclude in 2020. Combinations of complementary bnAbs and multi-specific bnAbs exhibit improved breadth and potency over most individual antibodies and are entering advanced clinical development. Genetic engineering of the Fc regions has markedly improved bnAb half-life, increased mucosal tissue concentrations of antibodies (especially in the genital tract), and enhanced immunomodulatory and Fc effector functionality, all of which improve antibodies' preventative and therapeutic potential. Human-derived monoclonal antibodies are likely to enter the realm of primary care prevention and therapy for viral infections in the near future.

Glycoengineering of AAV-delivered monoclonal antibodies yields increased ADCC activity

The absence of fucose on asparagine-297 of the human immunoglobulin G (IgG) heavy chain has been shown to enhance antibody-dependent cellular cytotoxicity (ADCC) activity by 10- to 100-fold compared to fucosylated antibody. Our lab is studying the use of adeno-associated virus (AAV) as a vector for the delivery of HIV-specific antibodies for therapeutic purposes. Since the antibody is produced by vector-transduced cells in vivo, current techniques of glycoengineering cannot be utilized. In order to achieve similar enhancement of ADCC with AAV-delivered antibodies, short hairpin RNAs (shRNAs) that target fucosyltransferase-8 (FUT8), were designed, tested, and cloned into AAV vectors used to deliver HIV-specific broadly neutralizing antibodies (bNAbs). Antibodies produced by our glycoengineered-AAV (GE-AAV) vectors were analyzed for fucose content and ADCC. GE-AAV constructs were able to achieve over 80% knockdown of FUT8. Results were confirmed by lectin western blot for α1-6 fucose, which revealed almost a complete absence of fucose on GE-AAV-produced antibodies. GE-AAV-produced antibodies revealed >10-fold enhancement of ADCC, while showing identical neutralization and gp140 trimer binding compared to their fucosylated counterparts. ADCC was enhanced 40- to 60-fold when combined with key Fc mutations known to enhance binding to FcγRIIIA. Our findings define a powerful approach for supercharging AAV-delivered anti-HIV antibodies.

HIV-1 infection of CD4 T cells impairs antigen-specific B cell function

Failures to produce neutralizing antibodies upon HIV‐1 infection result in part from B‐cell dysfunction due to unspecific B‐cell activation. How HIV‐1 affects antigen‐specific B‐cell functions remains elusive. Using an adoptive transfer mouse model and ex vivo HIV infection of human tonsil tissue, we found that expression of the HIV‐1 pathogenesis factor NEF in CD4 T cells undermines their helper function and impairs cognate B‐cell functions including mounting of efficient specific IgG responses. NEF interfered with T cell help via a specific protein interaction motif that prevents polarized cytokine secretion at the T‐cell–B‐cell immune synapse. This interference reduced B‐cell activation and proliferation and thus disrupted germinal center formation and affinity maturation. These results identify NEF as a key component for HIV‐mediated dysfunction of antigen‐specific B cells. Therapeutic targeting of the identified molecular surface in NEF will facilitate host control of HIV infection.

Removal of variable domain N-linked glycosylation as a means to improve the homogeneity of HIV-1 broadly neutralizing antibodies

Broadly neutralizing antibodies are showing promise in the treatment and prevention of HIV-1, with several now being evaluated clinically. Some lead clinical candidates, including antibodies CAP256-VRC26.25, N6, PGT121, and VRC07-523, have one or more N-linked glycosylation sequons in their variable domains (Fvs) from somatic hypermutation, and these glycans increase chemical heterogeneity, complicating the manufacture of these antibodies as products. Here we propose a general method to remove Fv glycans and use this method to develop engineered versions of these four antibodies with Fv glycans removed. When germline residues were introduced to remove each glycan, antibody properties between wild type and mutant were not significantly altered for CAP256-VRC26.25 and PGT121; however, germline mutants for N6 and VRC07-523 showed increased polyreactivity, which is known to correlate with unfavorable in vivo pharmacokinetics. To reduce polyreactivity induced by removal of Fv glycan, we mutated aromatic residues and arginines structurally proximal to the removed glycan and identified Fv glycan-removed variants with low polyreactivity for N6 and VRC07-523. Two such variants, N6-N72_LCQ-R18_LCD and VRC07-523-N72_LCQ-R24_LCD, showed thermostability, neutralization potency and breadth, and half-life in humanized FcRn mice that were similar to their wild-type Fv-glycosylated counterparts. The removal of Fv glycan and reduction of chemical heterogeneity were confirmed by liquid chromatography-mass spectrometry. With reduced heterogeneity, the Fv-glycan-removed variants developed here may have utility as products for treating or preventing infection by HIV-1.

Major Scientific Hurdles in HIV Vaccine Development: Historical Perspective and Future Directions

Following the discovery of HIV as a causative agent of AIDS, the expectation was to rapidly develop a vaccine; but thirty years later, we still do not have a licensed vaccine. Progress has been hindered by the extensive genetic variability of HIV and our limited understanding of immune responses required to protect against HIV acquisition. Nonetheless, valuable knowledge accrued from numerous basic and translational science research studies and vaccine trials has provided insight into the structural biology of the virus, immunogen design and novel vaccine delivery systems that will likely constitute an effective vaccine. Furthermore, stakeholders now appreciate the daunting scientific challenges of developing an effective HIV vaccine, hence the increased advocacy for collaborative efforts among academic research scientists, governments, pharmaceutical industry, philanthropy, and regulatory entities. In this review, we highlight the history of HIV vaccine development efforts, highlighting major challenges and future directions.

Effects of gp120 Inner Domain (ID2) Immunogen Doses on Elicitation of Anti-HIV-1 Functional Fc-Effector Response to C1/C2 (Cluster A) Epitopes in Mice

Fc-mediated effector functions of antibodies, including antibody-dependent cytotoxicity (ADCC), have been shown to contribute to vaccine-induced protection from HIV-1 infection, especially those directed against non-neutralizing, CD4 inducible (CD4i) epitopes within the gp120 constant 1 and 2 regions (C1/C2 or Cluster A epitopes). However, recent passive immunization studies have not been able to definitively confirm roles for these antibodies in HIV-1 prevention mostly due to the complications of cross-species Fc–FcR interactions and suboptimal dosing strategies. Here, we use our stabilized gp120 Inner domain (ID2) immunogen that displays the Cluster A epitopes within a minimal structural unit of HIV-1 Env to investigate an immunization protocol that induces a fine-tuned antibody repertoire capable of an effective Fc-effector response. This includes the generation of isotypes and the enhanced antibody specificity known to be vital for maximal Fc-effector activities, while minimizing the induction of isotypes know to be detrimental for these functions. Although our studies were done in in BALB/c mice we conclude that when optimally titrated for the species of interest, ID2 with GLA-SE adjuvant will elicit high titers of antibodies targeting the Cluster A region with potent Fc-mediated effector functions, making it a valuable immunogen candidate for testing an exclusive role of non-neutralizing antibody response in HIV-1 protection in vaccine settings.

Early exposure to broadly neutralizing antibodies may trigger a dynamical switch from progressive disease to lasting control of SHIV infection

Antiretroviral therapy (ART) for HIV-1 infection is life-long. Stopping therapy typically leads to the reignition of infection and progressive disease. In a major breakthrough, recent studies have shown that early initiation of ART can lead to sustained post-treatment control of viremia, raising hopes of long-term HIV-1 remission. ART, however, elicits post-treatment control in a small fraction of individuals treated. Strikingly, passive immunization with broadly neutralizing antibodies (bNAbs) of HIV-1 early in infection was found recently to elicit long-term control in a majority of SHIV-infected macaques, suggesting that HIV-1 remission may be more widely achievable. The mechanisms underlying the control elicited by bNAb therapy, however, remain unclear. Untreated infection typically leads to progressive disease. We hypothesized that viremic control represents an alternative but rarely realized outcome of the infection and that early bNAb therapy triggers a dynamical switch to this outcome. To test this hypothesis, we constructed a model of viral dynamics with bNAb therapy and applied it to analyse clinical data. The model fit quantitatively the complex longitudinal viral load data from macaques that achieved lasting control. The model predicted, consistently with our hypothesis, that the underlying system exhibited bistability, indicating two potential outcomes of infection. The first had high viremia, weak cytotoxic effector responses, and high effector exhaustion, marking progressive disease. The second had low viremia, strong effector responses, and low effector exhaustion, indicating lasting viremic control. Further, model predictions suggest that early bNAb therapy elicited lasting control via pleiotropic effects. bNAb therapy lowers viremia, which would also limit immune exhaustion. Simultaneously, it can improve effector stimulation via cross-presentation. Consequently, viremia may resurge post-therapy, but would encounter a primed effector population and eventually get controlled. ART suppresses viremia but does not enhance effector stimulation, explaining its limited ability to elicit post-treatment control relative to bNAb therapy.

In a remarkable advance in HIV cure research, a recent study showed that 3 weekly doses of HIV-1 broadly neutralizing antibodies (bNAbs) soon after infection kept viral levels controlled for years in most macaques treated. If translated to humans, this bNAb therapy may elicit a functional cure, or long-term remission, of HIV-1 infection, eliminating the need for life-long antiretroviral therapy (ART). How early bNAb therapy works remains unknown. Here, we elucidate the mechanism using mathematical modeling and analysis of in vivo data. We predict that early bNAb therapy suppresses viremia, which reduces exhaustion of cytotoxic effector cells, and enhances antigen uptake and effector stimulation. Collectively, these effects drive infection to lasting control. Model predictions based on these effects fit in vivo data quantitatively. ART controls viremia but does not improve effector stimulation, explaining its weaker ability to induce lasting control post-treatment. Our findings may help improve strategies for achieving functional cure of HIV-1 infection.

Engineering monoclonal antibody-based contraception and multipurpose prevention technologies†

Sexually transmitted infections are highly prevalent, and over 40% of pregnancies are unplanned. We are producing new antibody-based multipurpose prevention technology products to address these problems and fill an unmet need in female reproductive health. We used a Nicotiana platform to manufacture monoclonal antibodies against two prevalent sexually transmitted pathogens, HIV-1 and HSV-2, and incorporated them into a vaginal film (MB66) for preclinical and Phase 1 clinical testing. These tests are now complete and indicate that MB66 is effective and safe in women. We are now developing an antisperm monoclonal antibody to add contraceptive efficacy to this product. The antisperm antibody, H6-3C4, originally isolated by Shinzo Isojima from the blood of an infertile woman, recognizes a carbohydrate epitope on CD52g, a glycosylphosphatidylinositol-anchored glycoprotein found in abundance on the surface of human sperm. We engineered the antibody for production in Nicotiana; the new antibody which we call "human contraception antibody," effectively agglutinates sperm at concentrations >10 μg/ml and maintains activity under a variety of physiological conditions. We are currently seeking regulatory approval for a Phase 1 clinical trial, which will include safety and "proof of principle" efficacy endpoints. Concurrently, we are working with new antibody production platforms to bring the costs down, innovative antibody designs that may produce more effective second-generation antibodies, and delivery systems to provide extended protection.

Broadly neutralizing antibodies potently inhibit cell-to-cell transmission of semen leukocyte-derived SHIV162P3

BACKGROUND

HIV-1 sexual transmission occurs mostly through infected semen, which contains both free virions and infected leukocytes. Transmission initiated by infected cells has been shown by several in vitro and in vivo studies and a reduced capacity of broadly neutralizing antibodies (bNAbs) to inhibit cell-to-cell transmission has also been reported. However, due to limitations of available experimental models, there is yet no clarity to which extend bNAbs can prevent transmission mediated by semen leukocytes.

METHODS

We developed a novel in vitro assay to measure cell-cell transmission that makes use of splenocytes or CD45+ semen leukocytes collected from acutely SHIV162P3-infected cynomolgus macaques. A panel of 11 bNAbs was used either alone or in combination to assess their inhibitory potential against both cell-free and cell-cell infection.

FINDINGS

Splenocytes and semen leucocytes displayed a similar proportion of CD4+T-cell subsets. Either cell type transferred infection in vitro to target TZM-bl cells and PBMCs. Moreover, infection of macaques was achieved following intravaginal challenge with splenocytes. The anti-N-glycans/V3 loop bNAb 10-1074 was highly efficient against cell-associated transmission mediated by infected spleen cells and its potency was maintained when transmission was mediated by CD45+ semen leukocytes.

INTERPRETATION

These results support the use of bNAbs in preventative or therapeutic studies aiming to block transmission events mediated not only by free viral particles but also by infected cells. Our experimental system could be used to predict in vivo efficacy of bNAbs.

FUNDING

This work was funded by the ANRS and the European Commission.

Influenza virus glycoprotein-reactive human monoclonal antibodies

Influenza continues to be a significant public health challenge. Two glycoproteins on the surface of influenza virus, hemagglutinin and neuraminidase, play a prominent role in the process of influenza virus infection and release. Monoclonal antibodies targeting glycoproteins can effectively prevent the spread of the virus. In this review, we summarized currently reported human monoclonal antibodies targeting glycoproteins of influenza A and B viruses.

Evaluation of HIV-1 neutralizing and binding antibodies in maternal-infant transmission in Thailand

Despite anti-retroviral therapy (ART) interventions for HIV+ pregnant mothers, over 43,000 perinatal infections occur yearly. Understanding risk factors that lead to mother-to-child transmission (MTCT) of HIV are critical. We evaluated maternal and infant plasma binding and neutralizing antibody responses in a drug-naïve, CRF01_AE infected MTCT cohort from Thailand to determine associations with transmission risk. Env V3-specific IgG and neutralizing antibody responses were significantly higher in HIV- infants, as compared to HIV+ infants. In fact, infant plasma neutralizing antibodies significantly associated with non-transmission. Conversely, increased maternal Env V3-specific IgG and neutralizing antibody responses were significantly associated with increased transmission risk, after controlling for maternal viral load. Our results highlight the importance of evaluating both maternal and infant humoral immune responses to better understand mechanisms of protection, as selective placental antibody transport may have a role in MTCT. This study further emphasizes the complex role of Env-specific antibodies in MTCT of CRF01_AE HIV.

Durable protection against repeated penile exposures to simian-human immunodeficiency virus by broadly neutralizing antibodies

Penile acquisition of HIV accounts for most infections among men globally. Nevertheless, candidate HIV interventions for men advance to clinical trials without preclinical efficacy data, due primarily to a paucity of relevant animal models of penile HIV infection. Using our recently developed macaque model, we show that a single subcutaneous administration of broadly neutralizing antibody (bNAb) 10-1074 conferred durable protection against repeated penile exposures to simian-human immunodeficiency virus (SHIV_SF162P3). Macaques co-administered bNAbs 10-1074 and 3BNC117, or 3BNC117 alone, also exhibited significant protection against repeated vaginal SHIV_AD8-EO exposures. Regression modeling estimated that individual plasma bNAb concentrations of 5 μg ml^-1 correlated with ≥99.9% relative reduction in SHIV infection probability via penile (10-1074) or vaginal (10-1074 or 3BNC117) challenge routes. These results demonstrate that comparably large reductions in penile and vaginal SHIV infection risk among macaques were achieved at clinically relevant plasma bNAb concentrations and inform dose selection for the development of bNAbs as long-acting pre-exposure prophylaxis candidates for use by men and women.

HIV-1 antibodies in prevention of transmission

PURPOSE OF REVIEW

To present the data that suggest that antibodies to HIV may prevent HIV-1 infection.

RECENT FINDINGS

Many human monoclonal broadly neutralizing antibodies (bnAbs) have been isolated over the last decade. Numerous experiments of passive immunization in nonhuman primate models have allowed to accumulate strong evidences that bnAbs, opposed to nonneutralizing antibodies, are the best candidates to prevent HIV-1 infection. bnAbs counteract HIV-1 by both blocking the virus at the portal of entry and clearing rapidly viral foci established at distance after dissemination of the virus following infection. Cocktails of bnAbs or modified bi/trispecific antibodies will be necessary to counter the large and evolving antigenic diversity of the HIV-1 species. Two large multicenter phase IIb clinical trials have been initiated. Even if they are not conducted with the most recent and most potent bnAb, the results which are expected in 2022 will inform us on the real potency of bnAbs at preventing HIV-1 acquisition in the real life.

SUMMARY

If these trials demonstrate the efficacy of bnAbs, they will open the trail toward new strategies for preexposure prophylaxis, eventually postexposure prophylaxis and prevention of mother-to-child transmission.

Neutralizing antibodies for HIV-1 prevention

PURPOSE OF REVIEW

In the absence of a protective vaccine against HIV-1, passive immunization using novel broadly neutralizing antibodies (bNAbs) is an attractive concept for HIV-1 prevention. Here, we summarize the results of preclinical and clinical studies of bNAbs, discuss strategies for optimizing bNAb efficacy and lay out current pathways for the development of bNAbs as prophylaxis.

RECENT FINDINGS

Passive transfer of second-generation bNAbs results inpotent protection against infection in preclinical animal models. Furthermore, multiple bNAbs targeting different epitopes on the HIV-1 envelope trimer are in clinical evaluation and have demonstrated favorable safety profiles and robust antiviral activity in chronically infected individuals. The confirmation that passive immunization with bNAb(s) will prevent HIV-1 acquisition in humans is pending and the focus of ongoing investigations. Given the global diversity of HIV-1, bNAb combinations or multispecific antibodies will most likely be required to produce the necessary breadth for effective protection.

SUMMARY

Encouraging results from preclinical and clinical studies support the development of bNAbs for prevention and a number of antibodies with exceptional breadth and potency are available for clinical evaluation. Further optimization of viral coverage and antibody half-life will accelerate the clinical implementation of bNAbs as a critical tool for HIV-1 prevention strategies.

Glycan-dependent HIV-specific neutralizing antibodies bind to cells of uninfected individuals

A number of highly potent and broadly neutralizing antibodies (bNAbs) against the human immunodeficiency virus (HIV) have recently been shown to prevent transmission of the virus, suppress viral replication, and delay plasma viral rebound following discontinuation of antiretroviral therapy in animal models and infected humans. However, the degree and extent to which such bNAbs interact with primary lymphocytes have not been fully delineated. Here, we show that certain glycan-dependent bNAbs, such as PGT121 and PGT151, bind to B, activated T, and natural killer (NK) cells of HIV-infected and -uninfected individuals. Binding of these bNAbs, particularly PGT121 and PGT151, to activated CD4+ and CD8+ T cells was mediated by complex-type glycans and was abrogated by enzymatic inhibition of N-linked glycosylation. In addition, a short-term incubation of PGT151 and primary NK cells led to degranulation and cellular death. Our data suggest that the propensity of certain bNAbs to bind uninfected/bystander cells has the potential for unexpected outcomes in passive-transfer studies and underscore the importance of antibody screening against primary lymphocytes.

T cell-inducing vaccine durably prevents mucosal SHIV infection even with lower neutralizing antibody titers

Recent efforts toward an HIV vaccine focus on inducing broadly neutralizing antibodies, but eliciting both neutralizing antibodies (nAbs) and cellular responses may be superior. Here, we immunized macaques with an HIV envelope trimer, either alone to induce nAbs, or together with a heterologous viral vector regimen to elicit nAbs and cellular immunity, including CD8+ tissue-resident memory T cells. After ten vaginal challenges with autologous virus, protection was observed in both vaccine groups at 53.3% and 66.7%, respectively. A nAb titer >300 was generally associated with protection but in the heterologous viral vector + nAb group, titers <300 were sufficient. In this group, protection was durable as the animals resisted six more challenges 5 months later. Antigen stimulation of T cells in ex vivo vaginal tissue cultures triggered antiviral responses in myeloid and CD4+ T cells. We propose that cellular immune responses reduce the threshold of nAbs required to confer superior and durable protection.

Vaccines and Broadly Neutralizing Antibodies for HIV-1 Prevention

Development of improved approaches for HIV-1 prevention will likely be required for a durable end to the global AIDS pandemic. Recent advances in preclinical studies and early phase clinical trials offer renewed promise for immunologic strategies for blocking acquisition of HIV-1 infection. Clinical trials are currently underway to evaluate the efficacy of two vaccine candidates and a broadly neutralizing antibody (bNAb) to prevent HIV-1 infection in humans. However, the vast diversity of HIV-1 is a major challenge for both active and passive immunization. Here we review current immunologic strategies for HIV-1 prevention, with a focus on current and next-generation vaccines and bNAbs.

Induction of Transient Virus Replication Facilitates Antigen-Independent Isolation of SIV-Specific Monoclonal Antibodies

Structural characterization of the HIV-1 Envelope (Env) glycoprotein has facilitated the development of Env probes to isolate HIV-specific monoclonal antibodies (mAbs). However, preclinical studies have largely evaluated these virus-specific mAbs against chimeric viruses, which do not naturally infect non-human primates, in contrast to the unconstrained simian immunodeficiency virus (SIV)mac239 clone. Given the paucity of native-like reagents for the isolation of SIV-specific B cells, we examined a method to isolate SIVmac239-specific mAbs without using Env probes. We first activated virus-specific B cells by inducing viral replication after the infusion of a CD8β-depleting mAb or withdrawal of antiretroviral therapy in SIVmac239-infected rhesus macaques. Following the rise in viremia, we observed 2- to 4-fold increases in the number of SIVmac239 Env-reactive plasmablasts in circulation. We then sorted these activated B cells and obtained 206 paired Ab sequences. After expressing 122 mAbs, we identified 14 Env-specific mAbs. While these Env-specific mAbs bound to both the SIVmac239 SOSIP.664 trimer and to infected primary rhesus CD4+ T cells, five also neutralized SIVmac316. Unfortunately, none of these mAbs neutralized SIVmac239. Our data show that this method can be used to isolate virus-specific mAbs without antigenic probes by inducing bursts of contemporary replicating viruses in vivo.