Broadly neutralizing antibody and the HIV reservoir in acute HIV infection: a strategy toward HIV remission?

Engineering strategies of Anti-HIV antibody therapeutics in clinical development

PURPOSE OF REVIEW

Anti-human immunodeficiency virus (HIV) antibody-based therapeutics offer an alternative treatment option to current antiretroviral drugs. This review aims to provide an overview of the Fc- and Fab-engineering strategies that have been developed to optimize broadly neutralizing antibodies and discuss recent findings from preclinical and clinical studies.

RECENT FINDINGS

Multispecific antibodies, including bispecific and trispecific antibodies, DART molecules, and BiTEs, as well as Fc-optimized antibodies, have emerged as promising therapeutic candidates for the treatment of HIV. These engineered antibodies engage multiple epitopes on the HIV envelope protein and human receptors, resulting in increased potency and breadth of activity. Additionally, Fc-enhanced antibodies have demonstrated extended half-life and improved effector function.

SUMMARY

The development of Fc and Fab-engineered antibodies for the treatment of HIV continues to show promising progress. These novel therapies have the potential to overcome the limitations of current antiretroviral pharmacologic agents by more effectively suppressing viral load and targeting latent reservoirs in individuals living with HIV. Further studies are needed to fully understand the safety and efficacy of these therapies, but the growing body of evidence supports their potential as a new class of therapeutics for the treatment of HIV.

The role of tunneling nanotubes during early stages of HIV infection and reactivation: implications in HIV cure

Tunneling nanotubes (TNTs), also called cytonemes or tumor microtubes, correspond to cellular processes that enable long-range communication. TNTs are plasma membrane extensions that form tubular processes that connect the cytoplasm of two or more cells. TNTs are mostly expressed during the early stages of development and poorly expressed in adulthood. However, in disease conditions such as stroke, cancer, and viral infections such as HIV, TNTs proliferate, but their role is poorly understood. TNTs function has been associated with signaling coordination, organelle sharing, and the transfer of infectious agents such as HIV. Here, we describe the critical role and function of TNTs during HIV infection and reactivation, as well as the use of TNTs for cure strategies.

Evolution and Diversity of Immune Responses during Acute HIV Infection

Understanding the earliest immune responses following HIV infection is critical to inform future vaccines and therapeutics. Here, we review recent prospective human studies in at-risk populations that have provided insight into immune responses during acute infection, including additional relevant data from non-human primate (NHP) studies. We discuss the timing, nature, and function of the diverse immune responses induced, the onset of immune dysfunction, and the effects of early anti-retroviral therapy administration. Treatment at onset of viremia mitigates peripheral T and B cell dysfunction, limits seroconversion, and enhances cellular antiviral immunity despite persistence of infection in lymphoid tissues. We highlight pertinent areas for future investigation, and how application of high-throughput technologies, alongside targeted NHP studies, may elucidate immune response features to target in novel preventions and cures.

The HIV-1 antibody response: a footprint of the viral reservoir in children vertically infected with HIV

Several assays have been developed to measure and characterise the replication-competent HIV-1 reservoir, which constitutes the barrier to cure. To date, the application of these assays to studies in children and in limited-resource settings has been minimal, primarily because of their expense, the large required blood volumes, and labour-intensive technologies. For children vertically infected with HIV-1 who initiated suppressive antiretroviral therapy (ART) regimens in infancy, HIV-1-specific antibody concentrations are associated with viral persistence and could be used to estimate the size of the residual latent reservoir on ART. This strategy could be particularly useful for screening children on suppressive ART for enrolment into therapeutic vaccine trials and other protocols aimed at achieving HIV-1 remission.

Combination therapies currently under investigation in phase I and phase II clinical trials for HIV-1

Introduction: HIV infection is manageable through the use of antiretroviral drugs. However, HIV reservoirs that are constituted early during infection are resistant to treatment. HIV persistence under treatment necessitates life-long treatment and is associated with various co-morbidities. Two significant research avenues are explored through the development of either new antiretroviral drugs or interventions aimed at stimulating the immune system to eradicate HIV reservoirs.Areas covered: This report provides a review of investigational drugs and cell-based interventions against HIV infection that are currently under Phase I or Phase II clinical trials. We report on new antiretroviral drugs, antibodies directed against viral or host targets, reactivating agents, immune modulators and immune checkpoint inhibitors, and cell-based interventions. These new therapies are often tested in combination, including with current antiretroviral drugs.Expert opinion: Islatravir and GS-6207 are promising antiretroviral drugs that are expected to perform well in phase III trials. Whether the host immune system can be activated sufficiently to reduce HIV reservoirs remains unknown. Additional research is needed to identify surrogate markers of success for curative interventions. Given the current safety and efficacy of antiretroviral treatment, risk-benefits should be carefully evaluated before interventions that risk triggering high levels of immune stimulation.

Long-Term Persistence of Anti-HIV Broadly Neutralizing Antibody-Secreting Hematopoietic Cells in Humanized Mice

Broadly neutralizing antibodies (bNAbs) are among the most promising strategies to achieve long-term control of HIV-1 in the absence of combination antiretroviral therapy. Passive administration of such antibodies in patients efficiently decreases HIV-1 viremia, but is limited by the serum half-life of the protein. Here, we investigated whether antibody-secreting hematopoietic cells could overcome this problem. We genetically modified human CD34⁺ hematopoietic stem and progenitor cells (HSPCs) to secrete bNAbs and transplanted them into immunodeficient mice. We found that the gene-modified cells engraft and stably secrete antibodies in the peripheral blood of the animals for the 9 months of the study. Antibodies were predominantly expressed by human HSPC-derived T- and B cells. Importantly, we found that secreted PGT128 was able to delay HIV-1 viremia in vivo and also prevent a decline in CD4⁺ cells. Gene-modified cells were maintained in bone marrow and were also detected in spleen, thymus, lymph nodes, and gut-associated lymphoid tissue. These data indicate that the bNAb secretion from HSPC-derived cells in mice is functional and can affect viral infection and CD4⁺ cell maintenance. This study paves the way for potential applications to other diseases requiring long-lasting protein or antibody delivery.

HIV Entry and Its Inhibition by Bifunctional Antiviral Proteins

HIV entry is a highly specific and time-sensitive process that can be divided into receptor binding, coreceptor binding, and membrane fusion. Bifunctional antiviral proteins (bAVPs) exploit the multi-step nature of the HIV entry process by binding to two different extracellular targets. They are generated by expressing a fusion protein containing two entry inhibitors with a flexible linker. The resulting fusion proteins exhibit exceptional neutralization potency and broad cross-clade inhibition. In this review, we summarize the HIV entry process and provide an overview of the design, antiviral potency, and methods of delivery of bAVPs. Additionally, we discuss the advantages and limitations of bAVPs for HIV prevention and treatment.

Rational design of a trispecific antibody targeting the HIV-1 Env with elevated anti-viral activity

HIV-1 broadly neutralizing antibodies (bNAbs) are being explored as passively administered therapeutic and preventative agents. However, the extensively diversified HIV-1 envelope glycoproteins (Env) rapidly acquire mutations to evade individual bNAbs in monotherapy regimens. The use of a "single" agent to simultaneously target distinct Env epitopes is desirable to overcome viral diversity. Here, we report the use of tandem single-chain variable fragment (ScFv) domains of two bNAbs, specific for the CD4-binding site and V3 glycan patch, to form anti-HIV-1 bispecific ScFvs (Bi-ScFvs). The optimal Bi-ScFv crosslinks adjacent protomers within one HIV-1 Env spike and has greater neutralization breadth than its parental bNAbs. Furthermore, the combination of this Bi-ScFv with a third bNAb recognizing the Env membrane proximal external region (MPER) results in a trispecific bNAb, which has nearly pan-isolate neutralization breadth and high potency. Thus, multispecific antibodies combining functional moieties of bNAbs could achieve outstanding neutralization capacity with augmented avidity.

Increasing the Clinical Potential and Applications of Anti-HIV Antibodies

Preclinical and early human clinical studies of broadly neutralizing antibodies (bNAbs) to prevent and treat HIV infection support the clinical utility and potential of bNAbs for prevention, postexposure prophylaxis, and treatment of acute and chronic infection. Observed and potential limitations of bNAbs from these recent studies include the selection of resistant viral populations, immunogenicity resulting in the development of antidrug (Ab) responses, and the potentially toxic elimination of reservoir cells in regeneration-limited tissues. Here, we review opportunities to improve the clinical utility of HIV Abs to address these challenges and further accomplish functional targets for anti-HIV Ab therapy at various stages of exposure/infection. Before exposure, bNAbs' ability to serve as prophylaxis by neutralization may be improved by increasing serum half-life to necessitate less frequent administration, delivering genes for durable in vivo expression, and targeting bNAbs to sites of exposure. After exposure and/or in the setting of acute infection, bNAb use to prevent/reduce viral reservoir establishment and spread may be enhanced by increasing the potency with which autologous adaptive immune responses are stimulated, clearing acutely infected cells, and preventing cell-cell transmission of virus. In the setting of chronic infection, bNAbs may better mediate viral remission or "cure" in combination with antiretroviral therapy and/or latency reversing agents, by targeting additional markers of tissue reservoirs or infected cell types, or by serving as targeting moieties in engineered cell therapy. While the clinical use of HIV Abs has never been closer, remaining studies to precisely define, model, and understand the complex roles and dynamics of HIV Abs and viral evolution in the context of the human immune system and anatomical compartmentalization will be critical to both optimize their clinical use in combination with existing agents and define further strategies with which to enhance their clinical safety and efficacy.

Strategies to target non-T-cell HIV reservoirs

PURPOSE OF REVIEW

A central question for the HIV cure field is to determine new ways to target clinically relevant, latently and actively replicating HIV-infected cells beyond resting memory CD4 T cells, particularly in anatomical areas of low drug penetrability.

RECENT FINDINGS

HIV eradication strategies being positioned for targeting HIV for extinction in the CD4 T-cell compartment may also show promise in non-CD4 T-cells reservoirs. Furthermore, several exciting novel therapeutic approaches specifically focused on HIV clearance from non-CD4 T-cell populations are being developed.

SUMMARY

Although reservoir validity in these non-CD4 T cells continues to remain debated, this review will highlight recent advances and make an argument as to their clinical relevancy as we progress towards an HIV cure.

Human Immunodeficiency Virus Type 1 Monoclonal Antibodies Suppress Acute Simian-Human Immunodeficiency Virus Viremia and Limit Seeding of Cell-Associated Viral Reservoirs

Combination antiretroviral therapy (cART) administered shortly after human immunodeficiency virus type 1 (HIV-1) infection can suppress viremia and limit seeding of the viral reservoir, but lifelong treatment is required for the majority of patients. Highly potent broadly neutralizing HIV-1 monoclonal antibodies (MAbs) can reduce plasma viremia when administered during chronic HIV-1 infection, but the therapeutic potential of these antibodies during acute infection is unknown. We tested the ability of HIV-1 envelope glycoprotein-specific broadly neutralizing MAbs to suppress acute simian-human immunodeficiency virus (SHIV) replication in rhesus macaques. Four groups of macaques were infected with SHIV-SF162P3 and received (i) the CD4-binding-site MAb VRC01; (ii) a combination of a more potent clonal relative of VRC01 (VRC07-523) and a V3 glycan-dependent MAb (PGT121); (iii) daily cART, all on day 10, just prior to expected peak plasma viremia; or (iv) no treatment. Daily cART was initiated 11 days after MAb administration and was continued for 13 weeks in all treated animals. Over a period of 11 days after a single administration, MAb treatment significantly reduced peak viremia, accelerated the decay slope, and reduced total viral replication compared to untreated controls. Proviral DNA in lymph node CD4 T cells was also diminished after treatment with the dual MAb. These data demonstrate the virological effect of potent MAbs and support future clinical trials that investigate HIV-1-neutralizing MAbs as adjunctive therapy with cART during acute HIV-1 infection.

IMPORTANCE

Treatment of chronic HIV-1 infection with potent broadly neutralizing HIV-1 MAbs has been shown to significantly reduce plasma viremia. However, the antiviral effect of MAb treatment during acute HIV-1 infection is unknown. Here, we demonstrate that MAbs targeting the HIV-1 envelope glycoprotein both suppress acute SHIV plasma viremia and limit CD4 T cell-associated viral DNA. These findings provide support for clinical trials of MAbs as adjunctive therapy with antiretroviral therapy during acute HIV-1 infection.