Novel vaccine technologies for the 21st century

Novel approaches to vaccine development include structure-based immunogen design, gene-based vaccine platforms and formulation of recombinant antigens with potent adjuvants. These technologies are producing encouraging results in the development of vaccines for globally important diseases such as tuberculosis, influenza and respiratory syncytial virus. Here we highlight the most important developments in these areas over the past 18 months.

New approaches to vaccine development have generated exciting results over the past 18 months. Focusing on respiratory syncytial virus infection, influenza and tuberculosis, Fauci and Mascola discuss the impact of structure-based vaccine design, gene-based vaccine platforms and advances in adjuvant development.

The atomic level structure of the viral surface fusion protein of respiratory syncytial virus provided key insights that enabled the production of a stabilized subunit vaccine candidate that elicited robust immunogenicity in a phase I study. Technical advances in mRNA vaccines have led to improved intracellular stability and antigen expression, leading to robust and durable immune responses. mRNA candidate vaccines encoding full length haemagglutinin from two pandemic influenzas strains were safe and immunogenic in phase I studies. A tuberculosis (TB) subunit recombinant fusion protein (M72) formulated with a potent adjuvant (ASO1E) was effective at preventing activation of pulmonary TB in latently infected adults. Bacillus Calmette–Guérin (BCG) revaccination of uninfected adolescents provided protection against Mycobacterium tuberculosis infection.

The Extended Impact of Human Immunodeficiency Virus/AIDS Research

Human immunodeficiency virus (HIV) is one of the most extensively studied viruses in history, and numerous extraordinary scientific advances, including an in-depth understanding of viral biology, pathogenesis, and life-saving antiretroviral therapies, have resulted from investments in HIV/AIDS research. While the substantial investments in HIV/AIDS research are validated solely on these advances, the collateral broader scientific progress resulting from the support of HIV/AIDS research over the past 30 years is extraordinary as well. The positive impact has ranged from innovations in basic immunology and structural biology to treatments for immune-mediated diseases and cancer and has had an enormous effect on the research and public and global health communities well beyond the field of HIV/AIDS. This article highlights a few select examples of the unanticipated and substantial positive spin-offs of HIV/AIDS research on other scientific areas.

Integrin α4β7 expression on peripheral blood CD4+ T cells predicts HIV acquisition and disease progression outcomes

The gastrointestinal (GI) mucosa is central to HIV pathogenesis, and the integrin α₄β₇ promotes the homing of immune cells to this site, including those that serve as viral targets. Data from simian immunodeficiency virus (SIV) animal models suggest that α₄β₇ blockade provides prophylactic and therapeutic benefits. We show that pre-HIV infection frequencies of α₄β₇⁺ peripheral blood CD4⁺ T cells, independent of other T cell phenotypes and genital inflammation, were associated with increased rates of HIV acquisition in South African women. A similar acquisition effect was observed in a Kenyan cohort and in nonhuman primates (NHPs) after intravaginal SIV challenge. This association was stronger when infection was caused by HIV strains containing V2 envelope motifs with a preference for α₄β₇ binding. In addition, pre-HIV α₄β₇⁺ CD4⁺ T cells predicted a higher set-point viral load and a greater than twofold increased rate of CD4⁺ T cell decline. These results were confirmed in SIV-infected NHPs. Increased frequencies of pre-HIV α₄β₇⁺ CD4⁺ T cells were also associated with higher postinfection expression of lipopolysaccharide binding protein, a microbial translocation marker, suggestive of more extensive gut damage. CD4⁺ T cells expressing α₄β₇ were rapidly depleted very early in HIV infection, particularly from the GI mucosa, and were not restored by early antiretroviral therapy. This study provides a link between α₄β₇ expression and HIV clinical outcomes in humans, in line with observations made in NHPs. Given the availability of a clinically approved anti-α₄β₇ monoclonal antibody for treatment of inflammatory bowel disease, these data support further evaluation of targeting α₄β₇ integrin as a clinical intervention during HIV infection.

A Universal Influenza Vaccine: The Strategic Plan for the National Institute of Allergy and Infectious Diseases

A priority for the National Institute of Allergy and Infectious Diseases is development of a universal influenza vaccine providing durable protection against multiple influenza strains. NIAID will use this strategic plan as a foundation for future investments in influenza research.

An open-label phase 1 clinical trial of the anti-α4β7 monoclonal antibody vedolizumab in HIV-infected individuals

Despite the substantial clinical benefits of antiretroviral therapy (ART), complete eradication of HIV has not been possible. The gastrointestinal tract and associated lymphoid tissues may play an important role in the pathogenesis of HIV infection. The integrin α₄β₇ facilitates homing of T lymphocytes to the gut by binding to the mucosal addressin cell adhesion molecule-1 (MAdCAM-1) expressed on venules in gut-associated lymphoid tissue. CD4⁺ T cells with increased expression of α₄β₇ are susceptible to HIV infection and may be key players in subsequent virus dissemination. Data from nonhuman primate models infected with simian immunodeficiency virus (SIV) have suggested that blockade of the α₄β₇/MAdCAM-1 interaction may be effective at preventing SIV infection and may have beneficial effects in animals with established viral infection. To explore whether these findings could be reproduced in HIV-infected individuals after interruption of ART, we conducted an open-label phase 1 clinical trial of vedolizumab, a monoclonal antibody against α₄β₇ integrin. Vedolizumab infusions in 20 HIV-infected individuals were well tolerated with no serious adverse events related to the study drug. After interruption of ART, the median time to meeting protocol criteria to restart therapy was 13 weeks. The median duration of plasma viremia of <400 copies/ml was 5.4 weeks. Only a single subject in the trial experienced prolonged suppression of plasma viremia after interruption of ART. These results suggest that blockade of α₄β₇ may not be an effective strategy for inducing virological remission in HIV-infected individuals after ART interruption.

Opioids and Infectious Diseases: A Converging Public Health Crisis

A converging public health crisis is emerging because the opioid epidemic is fueling a surge in infectious diseases, such as human immunodeficiency virus infection with or without AIDS, the viral hepatitides, infective endocarditis, and skin and soft-tissue infections. An integrated strategy is needed to tailor preventive and therapeutic approaches toward infectious diseases in people who misuse and/or are addicted to opioids and to concurrently address the underlying predisposing factor for the infections-opioid use disorder. This commentary highlights the unique and complementary roles that the infectious diseases and substance use disorder communities can play in addressing this crisis of dual public health concerns.

Impact of Treatment Interruption on HIV Reservoirs and Lymphocyte Subsets in Individuals Who Initiated Antiretroviral Therapy During the Early Phase of Infection

Therapeutic strategies for achieving sustained virologic remission are being explored in human immunodeficiency virus (HIV)-infected individuals who began antiretroviral therapy (ART) during the early phase of infection. In the evaluation of such therapies, clinical protocols should include analytical treatment interruption (ATI); however, the immunologic and virologic impact of ATI in individuals who initiated ART early has not been fully delineated. We demonstrate that ATI causes neither expansion of HIV reservoirs nor immunologic abnormalities following reinitiation of ART. Our findings support the use of ATI to determine whether sustained virologic remission has been achieved in clinical trials of individuals who initiated ART early during HIV infection.

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

VRC01 protects macaques from vaginal SHIV infection after a single high-dose challenge. Infusion of a simianized anti-α4β7 mAb (Rh-α4β7) just prior to, and during repeated vaginal exposures to SIVmac251 partially protected macaques from vaginal SIV infection and rescued CD4+ T cells. To investigate the impact of combining VRC01 and Rh-α4β7 on SHIV infection, 3 groups of macaques were treated with a suboptimal dosing of VRC01 alone or in combination with Rh-α4β7 or with control antibodies prior to the initiation of weekly vaginal exposures to a high dose (1000 TCID50) of SHIVAD8-EO. The combination Rh-α4β7-VRC01 significantly delayed SHIVAD8-EO vaginal infection. Following infection, VRC01-Rh-α4β7-treated macaques maintained higher CD4+ T cell counts and exhibited lower rectal SIV-DNA loads compared to controls. Interestingly, VRC01-Rh-α4β7-treated macaques had fewer IL-17-producing cells in the blood and the gut during the acute phase of infection. Moreover, higher T cell responses to the V2-loop of the SHIVAD8-EO envelope in the VRC01-Rh-α4β7 group inversely correlated with set point viremia. The combination of suboptimal amounts of VRC01 and Rh-α4β7 delayed infection, altered antiviral immune responses and minimized CD4+ T cell loss. Further exploration of the effect of combining bNAbs with Rh-α4β7 on SIV/HIV infection and antiviral immune responses is warranted and may lead to novel preventive and therapeutic strategies.

Improvement of antibody functionality by structure-guided paratope engraftment

Broadly neutralizing antibodies (bNAbs) represent a promising alternative to antiretroviral drugs for HIV-1 prevention and treatment. Selected antibodies to the CD4-binding site bolster envelope trimer binding via quaternary contacts. Here, we rationally engraft a new paratope, i.e., the extended heavy-chain framework region 3 (FR3) loop of VRC03, which mediates quaternary interaction, onto several potent bNAbs, enabling them to reach an adjacent gp120 protomer. The interactive quaternary surface is delineated by solving the crystal structure of two FR3 loop-chimeric antibodies. Chimerization enhances the neutralizing activity of several potent bNAbs against a majority of global HIV-1 strains. Compared to unmodified antibodies, chimeric antibodies display lower autoreactivity and prolonged in vivo half-life in huFcRn mice and rhesus macaques. Thus, paratope engraftment may be used to expand the epitope repertory of natural antibodies, improving their functionality for disease prevention and treatment.

Quaternary contacts mediated by an extended heavy-chain framework region 3 (FR3) have been shown to improve binding to HIV envelope and virus neutralization for a few antibodies. Here, Liu et al. engraft such an FR3 loop onto several potent broadly neutralizing antibodies, resulting in improved neutralization activity and pharmacokinetics.