Comprehensive Characterization of Humoral Correlates of Human Immunodeficiency Virus 1 Superinfection Acquisition in High-risk Kenyan Women

Overview of Neutralizing Antibodies and Their Potential in COVID-19

The antibody response to respiratory syndrome coronavirus 2 (SARS-CoV-2) has been a major focus of COVID-19 research due to its clinical relevance and importance in vaccine and therapeutic development. Neutralizing antibody (NAb) evaluations are useful for the determination of individual or herd immunity against SARS-CoV-2, vaccine efficacy, and humoral protective response longevity, as well as supporting donor selection criteria for convalescent plasma therapy. In the current manuscript, we review the essential concepts of NAbs, examining their concept, mechanisms of action, production, and the techniques used for their detection; as well as presenting an overview of the clinical use of antibodies in COVID-19.

Recent insights into Fc-mediated effector responses to HIV-1

PURPOSE OF REVIEW

Recent work defining Fc-mediated effector functions for both viral control and protection against infection is summarized and considered along with new strategies to drive robust Fc-mediated responses.

RECENT FINDINGS

In new human and nonhuman primate (NHP) vaccine trials as well as studies of natural infection, Fc-mediated effector responses have sometimes been observed to correlate with decreased risk of infection or with better clinical outcomes, suggesting a potential role for these responses in HIV-1 prevention and therapy. Recent highlights include use of antibody-dependent cellular cytotoxicity-sensitizing CD4-induced mimetic compounds, novel V1V2 immunogens, passive transfer studies, and vaccine regimens that successfully elicited Fc-mediated responses and were reported to decrease risk of infection in challenge studies in NHPs. Lastly, detailed studies of IgG3 forms of HIV-specific antibodies have reported that both neutralizing and Fc-mediated responses can be increased relative to the more prevalent IgG1 subclass.

SUMMARY

Successful harmonization of neutralizing and Fc-mediated responses may make key contributions to the goal of reducing HIV-1 infection via active and passive vaccination. New studies continue to highlight the importance of Fc-mediated antibody responses as correlates of decreased risk of infection and suggest enhanced phagocytosis is a potential mechanism of reduced risk of infection associated with human IgG3 responses. Results from recent studies may help guide the rational design of therapies and vaccines that aim to specifically leverage antibody effector function.

A diverse collection of B cells responded to HIV infection in infant BG505

Increasing evidence suggests infants develop unique neutralizing antibody (nAb) responses to HIV compared to adults. Here, we dissected the nAb response of an infant whose virus is in clinical trials as a vaccine immunogen, with a goal of characterizing the broad responses in the infant to this antigen. We isolated 73 nAbs from infant BG505 and identified a large number of clonal families. Twenty-six antibodies neutralized tier 2 viruses-in some cases, viruses from the same clade as BG505, and in others, a different clade, although none showed notable breadth. Several nAbs demonstrated antibody-dependent cellular cytotoxicity activity and targeted the V3 loop. These findings suggest an impressive polyclonal response to HIV infection in infant BG505, adding to the growing evidence that the nAb response to HIV in infants is polyclonal-a desirable vaccine response to a rapidly evolving virus like HIV.

Maternal Envelope gp41 Ectodomain-Specific Antibodies Are Associated With Increased Mother-to-Child Transmission of Human Immunodeficiency Virus-1

Mother-to-child transmission of human immunodeficiency virus (HIV) occurs in the setting of maternal and passively acquired antibodies, providing a unique window into immune correlates of HIV risk. We compared plasma antibody binding to HIV antigens between 51 nontransmitting mother-infant pairs and 21 transmitting mother-infant pairs. Plasma antibody binding to a variety of gp41 ectodomain-containing antigens was associated with increased odds of transmission. Understanding the reasons why gp41 ectodomain-targeting antibodies are associated with transmission risk will be important in determining whether they can directly enhance infection or whether their presence reflects a redirecting of the humoral response away from targeting more protective epitopes.

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.

Vaccine Design Informed by Virus-Induced Immunity

When an individual is exposed to a viral pathogen for the first time, the adaptive immune system is naive and cannot prevent virus replication. The consequence may be severe disease. At the same time, the host may rapidly generate a pathogen-specific immune response that will prevent disease if the virus is encountered again. Parvovirus B19 provides one such example. Children with sickle cell disease can experience life-threatening transient aplastic crisis when first exposed to parvovirus B19, but an effective immune response confers lifelong protection. We briefly examine the induction and benefits of virus-induced immunity. We focus on three human viruses for which there are no licensed vaccines (respiratory syncytial virus, human immunodeficiency virus type 1, and parvovirus B19) and consider how virus-induced immunity may inform successful vaccine design.

Characterization of the Neutralizing Antibody Response in a Case of Genetically Linked HIV Superinfection

This report describes the identification of a genetically confirmed linked heterosexual human immunodeficiency virus (HIV) superinfection (HIV-SI) in a woman with chronic HIV infection who acquired a second strain of the virus from her husband. Serum neutralizing antibody (NAb) responses against their homologous and heterologous viruses, including the superinfecting strain, in the woman and her husband were examined before and after onset of HIV-SI. The woman displayed a moderately potent and broad anti-HIV NAb response prior to superinfection but did not possess NAb activity against the superinfecting strain. This case highlights the unique potential of linked HIV-SI studies to examine natural protection from HIV infection.

Reduced frequency of HIV superinfection in a high-risk cohort in Zambia

Rates of HIV-1 superinfection, re-infection with a genetically distinct virus despite HIV-1 specific immune responses, vary in different risk populations. We previously found the rates of superinfection were similar to primary HIV infection (PHI) in a Zambian heterosexual transmission cohort. Here, we conduct a similar analysis of 47 HIV-positive Zambians from an acute infection cohort with more frequent follow-up, all infected by non-spousal partners. We identified only one case of superinfection in the first two years, significantly fewer than in our previous study, which was likely due to increased counseling during acute infection and an overall population-wide decline in factors associated with HIV transmission. The predominant virus detected after superinfection was a recombinant of the transmitted founder (TF) and the superinfecting strain. The superinfected individual mounted a neutralizing antibody response to the primary TF virus, which remained TF-specific over time and even after superinfection, did not neutralize the superinfecting variant.

Monkeying Around: Using Non-human Primate Models to Study NK Cell Biology in HIV Infections

Natural killer (NK) cells are the major innate effectors primed to eliminate virus-infected and tumor or neoplastic cells. Recent studies also suggest nuances in phenotypic and functional characteristics among NK cell subsets may further permit execution of regulatory and adaptive roles. Animal models, particularly non-human primate (NHP) models, are critical for characterizing NK cell biology in disease and under homeostatic conditions. In HIV infection, NK cells mediate multiple antiviral functions via upregulation of activating receptors, inflammatory cytokine secretion, and antibody dependent cell cytotoxicity through antibody Fc-FcR interaction and others. However, HIV infection can also reciprocally modulate NK cells directly or indirectly, leading to impaired/ineffective NK cell responses. In this review, we will describe multiple aspects of NK cell biology in HIV/SIV infections and their association with viral control and disease progression, and how NHP models were critical in detailing each finding. Further, we will discuss the effect of NK cell depletion in SIV-infected NHP and the characteristics of newly described memory NK cells in NHP models and different mouse strains. Overall, we propose that the role of NK cells in controlling viral infections remains incompletely understood and that NHP models are indispensable in order to efficiently address these deficits.

Limited anti-HIV neutralizing antibody breadth and potency before and after HIV superinfection in Danish men who have sex with men

BACKGROUND

The role of the anti-HIV neutralizing antibody response in protecting against HIV superinfection, and changes in neutralizing antibody potency and breadth after HIV superinfection have not been fully elucidated. This study examined the rate of HIV superinfection in men who have sex with men (MSM) also diagnosed with syphilis in Denmark, and the anti-HIV neutralizing antibody response in men who became superinfected.

MATERIALS AND METHODS

MSM enrolled in the Danish HIV cohort who acquired syphilis were examined longitudinally for HIV superinfection using a validated next-generation sequencing assay. HIV superinfection cases were matched 3:1 to controls, and neutralizing antibody responses before (cases/controls) and after (cases) HIV superinfection were determined using a 20-pseudovirus panel.

RESULTS

Four cases of HIV superinfection were identified from 95 MSM screened for a rate of HIV superinfection of 1.56/100 pys (95% CI = 0.43-4.01). Prior to HIV superinfection neutralizing antibody responses were low in breadth and potency, and did not differ between cases and controls (p = 1.0). In cases, neutralizing antibody responses increased modestly after HIV superinfection.

CONCLUSIONS

These data support the theory that the natural neutralizing antibody response to HIV infection may not be the controlling factor in protecting against a subsequent HIV challenge.

Broadly neutralizing antibodies: What is needed to move from a rare event in HIV-1 infection to vaccine efficacy?

The elicitation of broadly neutralizing antibodies (bnAbs) is considered crucial for an effective, preventive HIV-1 vaccine. Led by the discovery of a new generation of potent bnAbs, the field has significantly advanced over the past decade. There is a wealth of knowledge about the development of bnAbs in natural infection, their specificity, potency, breadth and function. Yet, devising immunogens and vaccination regimens that evoke bnAb responses has not been successful. Where are the roadblocks in their development? What can we learn from natural infection, where bnAb induction is possible but rare? Herein, we will reflect on key discoveries and discuss open questions that may bear crucial insights needed to move towards creating effective bnAb vaccines.

Multi-Envelope HIV-1 Vaccine Development: Two Targeted Immune Pathways, One Desired Protective Outcome

In 2016, there were more than 30 million individuals living with HIV-1, ∼1.8 million new HIV-1 infections, and ∼1 million HIV-1-related deaths according to UNAIDS ( unaids.org ). Hence, a preventive HIV-1 vaccine remains a global priority. The variant envelopes of HIV-1 present a significant obstacle to vaccine development and the vaccine field has realized that immunization with a single HIV-1 envelope protein will not be sufficient to generate broadly neutralizing antibodies. Here we describe two nonmutually exclusive, targeted pathways with which a multi-envelope HIV-1 vaccine may generate protective immune responses against variant HIV-1. Pathways include (i) the induction of a polyclonal immune response, comprising a plethora of antibodies with subset-reactive and cross-reactive specificities, together able to neutralize diverse HIV-1 (termed Poly-nAb in this report) and (ii) the induction of one or a few monoclonal antibodies, each with a broadly neutralizing specificity (bnAb). With each pathway in mind, we describe challenges and strategies that may ultimately support HIV-1 vaccine success.

Immunological and virological characteristics of human immunodeficiency virus type 1 superinfection: implications in vaccine design

Superinfection is frequently detected among individuals infected by human immunodeficiency virus type I (HIV-1). Superinfection occurs at similar frequencies at acute and chronic infection stages but less frequently than primary infection. This observation indicates that the immune responses elicited by natural HIV-1 infection may play a role in curb of superinfection; however, these responses are not sufficiently strong to completely prevent superinfection. Thus, a successful HIV-1 vaccine likely needs to induce more potent and broader immune responses than those elicited by primary infection. On the other hand, potent and broad neutralization responses are more often detected after superinfection than during monoinfection. This suggests that broadly neutralizing antibodies are more likely induced by sequential immunization of multiple different immunogens than with only one form of envelope glycoprotein immunogens. Understanding why the protection from superinfection by immunity induced by primary infection is insufficient and if superinfection can lead to cross-reactive immune responses will be highly informative for HIV-1 vaccine design.