Human Vaccines

Emerging Technologies in Design and Development

Kayvon Modjarrad, Wayne C. Koff

• Publisher: Academic Press
• Year: 2016
• Print ISBN: 9780128023020
• eBook ISBN: 9780128025420
• Topic: Medizin
• Subtopic: Immunologie

Human Vaccines: Emerging Technologies in Design and Development discusses the advances in molecular biology, biophysics, and informatics—among other disciplines—that have provided scientists with the tools to create new vaccines against emerging and re-emerging pathogens. For example, the virus-like particle technologies that led to licensing of highly efficacious HPV vaccines have only come into full realization in the last 10 years. Their success has, in turn, accelerated the pace with which nanoparticle vaccines are being developed Given the rapidity with which the field is changing and the absence of any text documenting this change, there is a need for a resource that surveys these new vaccine technologies, assesses their potential, and describes their applications. This book provides that resource and complements traditional vaccinology books, but also serves as an excellent standalone for researchers and students with basic knowledge in immunology. - Introduces new topics in vaccine immunology in the context vaccine design and production - Consolidates the growing body of knowledge on new vaccine technologies that have only emerged in the past 2 – 3 decades - Reviews the currently licensed vaccines that have utilized leading-edge technologies and how this has translated into improved efficacy and safety - Provides a broad overview of innovative vaccine technologies, including immunological aspects

Part I

Designing Vaccines From a New Starting Point

Outline

Chapter 1 Broadly Neutralizing Antibodies

Chapter 1

Broadly Neutralizing Antibodies

L. Morris¹ and T.A. Moody², ¹National Institute for Communicable Diseases, Johannesburg, South Africa, ²Duke University, Durham, NC, United States

Abstract

Effective vaccines for a number of human pathogens are lacking. In general, vaccines mimic natural protective immune responses. Thus, the improved ability to harness the native power of the human immune system and isolate pathogen-specific antibodies is helping to fill an important gap in vaccine development. Here we highlight the technological advances that have fast-tracked the discovery of new anti-infective monoclonal antibodies (mAbs). We discuss their role in a reverse vaccinology approach toward facilitating the design of better immunogens. We also review the development of mAbs as biological drugs to both prevent and treat infectious diseases. This chapter will focus mainly on human immunodeficiency virus type 1 and influenza virus but will also discuss other pathogens where significant progress has been made, as in the case of respiratory syncytial virus. These technologies are applicable across different diseases, providing a platform for tackling new or reemerging pathogens, such as Ebola viruses. The emergence and expansion of monoclonal antibody technologies herald a new era in the fight against infectious diseases.

Keywords

Monoclonal antibodies; neutralization; single B cell sorting; B cell culture; high-throughput screening; next-generation sequencing; reverse vaccinology; human immunodeficiency virus; influenza

The antibody response to human pathogens is generally robust, highly specific, long-lasting and, in many cases, able to clear infection. The initial encounter between a naïve B cell receptor (BCR) and a foreign antigen activates B cell clonal lineages that subsequently undergo somatic hypermutation and selection in a process that increases antibody affinity. In most cases, the first detectable antibody response in the plasma is of the IgM class, switching to IgG and IgA classes within several weeks after infection. As most high-affinity antibodies develop, B cells engage CD4⁺ T follicular helper cells in germinal centers and exit as plasmablasts. Intermediate IgM and class-switched memory B cells are also released into circulation at predictable intervals during the process.^1,2 Large quantities of antibodies are produced by short-lived plasmablasts that are found in the circulation during an acute infection. These cells appear in particularly high numbers in response to human immunodeficiency virus type 1 (HIV-1), although the vast majority are not HIV-1-specific because of extensive B cell hyperactivation that is a hallmark of the disease.³ For those infections that are cleared, resolution is associated with a decline in the circulating plasmablast and retention memory B cell pools that are available for recall upon subsequent exposures. Consequently, secondary responses are more rapid, generate higher affinity antibodies and mediate protection against reinfection or at least severe disease.

The BCR is an integral membrane form of the antibody that is specific to each B cell. Antibodies are heterodimeric proteins consisting of heavy and light chains that combine to form a basic “Y” shaped structure. Both surface-bound and secreted antibodies have a compartmentalized construction that includes a region able to recognize antigens. The process of antibody gene rearrangement⁴ results in a large array of antibody binding sites that are further diversified by somatic hypermutation.⁵ Each antibody contains two antigen recognition sites making up each arm of the “Y” shaped structure. These portions—the “fragment antigen binding” or Fab regions—are the primary focus of efforts to isolate and characterize human antibodies. The third major functional and structural component of an antibody is the “fragment constant” or Fc region that defines antibody isotypes and subclasses. It interacts with effector arms of the immune system either by binding receptor molecules (e.g., plasma complement proteins) or by binding cell surface receptors on effector cells (e.g., NK cells). These Fc-mediated effector functions likely play an important role in a number of infections as they enhance the antiviral efficacy of antibodies. Antibody functions can be further manipulated through recombinant engineering of the Fc region, either by mutating amino acid residues, changing glycosylation patterns, or both. This has been a common practice for the development of monoclonal antibodies (mAbs) in clinical use.

The most important antiviral function of an antibody is pathogen neutralization, mediated through the specificity afforded by the Fab portion. Neutralization is a measure of the ability of an antibody to prevent pathogen entry into a cell, and it is thought to occur by a variety of mechanisms that include steric hindrance, target dissociation and promotion of structural inflexibility in the pathogen’s surface proteins. Effective neutralization is dependent on antibodies that target functionally active sites. Those antibodies that recognize highly conserved regions in the pathogen proteins are more likely to be broadly neutralizing and, therefore, most desirable to elicit when designing a vaccine.

The isolation of broadly neutralizing antibodies has been a major focus of efforts to develop vaccines against many pathogens, including HIV, influenza, respiratory syncytial virus (RSV).⁶ In addition to their roles in preventing, reducing and clearing infection, neutralizing antibodies serve as a correlate of protection for most human vaccines.⁷ Thus, studying the targets of protective antibodies could result in improvements to existing vaccines or the development of novel ones. Furthermore, isolation, detailed biochemical characterization, epitope mapping and structural modeling of mAbs could pave the way for the development of vaccines and therapeutics for a range of diseases for which no interventions are currently available.

Identification of Broadly Cross-Reactive Antibodies in Human Donors

The detection of serum antibody responses to a pathogen of interest is generally a good indication of the presence of circulating antigen-specific memory B cells and/or plasmablasts from which the mAbs are isolated. In the case of HIV-1, suitable donors have been identified by screening large volumes of sera for their ability to neutralize viral isolates of multiple subtypes.^8–12 This process has resulted in the isolation of a large number of highly potent, broadly neutralizing antibodies to HIV-1.^13,14 A similar approach has been applied to the isolation of a mAb that cross-reacts with RSV and metapneumovirus. In this example healthy donors with presumed past infection, by one or both of these viruses, were screened for serum activity against both viruses.¹⁵ Broadly neutralizing influenza mAbs have also been isolated and have largely come from studies of pandemic survivors,^16–18 experimental and licensed vaccine recipients^19–21 and experimentally infected volunteers.²⁰ Since antigen-specific antibodies persist in the circulation for many years,²² donor screenings can be performed long after infection, as was the case among 1918 Spanish influenza pandemic survivors.¹⁸

The characterization of antibody specificities responsible for serum neutralizing activity greatly facilitates efforts to isolate mAbs of interest. However, mapping antibody specificity is confounded by the fact that neutralizing antibodies are a minor component of the polyclonal antibody response. Nevertheless, multiple techniques have been developed for this purpose and used successfully. Peptide arrays, for example, screen antibody specificities through the presentation of overlapping peptides. Although they have been used for a number of infections, the general approach is limited by the fact that most broadly neutralizing antibodies recognize conformational epitopes and glycans that are not represented in the arrays.²³ The use of epitope-ablating mutants has also been helpful in mapping neutralizing antibody specificities, particularly those that target glycans on the HIV-1 envelope glycoprotein.^24–26 Depletion of plasma neutralizing activity through protein or peptide adsorption provides additional information for the design of soluble antigens that can bait antibodies of interest.^27,28

The availability of large neutralization datasets has aided in the design of bioinformatic algorithms to predict specificities of serum samples, particularly in the case of HIV-1.^29–31 However, both experimental and computational epitope mapping methods are hampered by the presence of antibodies against multiple or undefined targets; in these cases mAb isolation may be necessary. While many of these technologies have been developed for the study of HIV-1, they have not been limited to this pathogen but applied others, like dengue virus, with great success.³²

Isolation of Monoclonal Antibodies Using B Cell Culture Technologies

The first generalizable technique for isolating monoclonal antibodies was reported in 1975 by Kohler and Milstein.³³ This Nobel-prize winning pair fused an immortalized myeloma cell line (P3-X63Ag8) with mouse splenocytes to generate so-called hybridomas: stable cell-lines that secrete antibodies in culture. This process has led to the development of many mAbs that are still...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Foreword
• Part I: Designing Vaccines From a New Starting Point
• Part II: Pathogen Free Vaccines
• Part III: Immune Monitoring
• Part IV: Advanced Vaccine Development
• Index