The next frontier in vaccine design: blending immune correlates of protection into rational vaccine design

A single residue switch mediates the broad neutralization of Rotaviruses

Broadly neutralizing antibodies (bNAbs) could offer escape-tolerant and lasting protection against viral infections and therefore guide development of broad-spectrum vaccines. The increasing challenge posed by viral evolution and immune evasion intensifies the importance of the discovery of bNAbs and their underlying neutralization mechanism. Here, focusing on the pivotal viral protein VP4 of rotavirus (RV), we identify a potent bNAb, 7H13, exhibiting broad-spectrum neutralization across diverse RV genotypes and demonstrating strong prevention of virus infection in female mice. A combination of time-resolved cryo-electron microscopy (cryo-EM) and in situ cryo-electron tomography (cryo-ET) analysis reveals a counterintuitive dynamic process of virus inactivation, in which 7H13 asymmetrically binds to a conserved epitope in the capsid-proximal aspect of VP4, triggers a conformational switch in a critical residue-F418-thereby disrupts the meta-stable conformation of VP4 essential for normal viral infection. Structure-guided mutagenesis corroborates the essential role of the 7H13 heavy chain I54 in activating F418 switch and destabilizing VP4. These findings define an atypical NAbs' neutralization mechanism and reveal a potential type of virus vulnerable site for universal vaccine and therapeutics design.

Establishing an immune correlate of protection for Nipah virus in nonhuman primates

The limited but recurrent outbreaks of the zoonotic Nipah virus (NiV) infection in humans, its high fatality rate, and the potential virus transmission from human to human make NiV a concerning threat with pandemic potential. There are no licensed vaccines to prevent infection and disease. A recombinant Hendra virus soluble G glycoprotein vaccine (HeV-sG-V) candidate was recently tested in a Phase I clinical trial. Because NiV outbreaks are sporadic, and with a few cases, licensing will likely require an alternate regulatory licensing pathway. Therefore, determining a reliable vaccine correlate of protection (CoP) will be critical. We assessed the immune responses elicited by HeV-sG-V in African Green monkeys and its relationship with protection from a NiV challenge. Data revealed values of specific binding and neutralizing antibody titers that predicted survival and allowed us to establish a mechanistic CoP for NiV Bangladesh and Malaysia strains.

Immune correlates of protection as a game changer in tuberculosis vaccine development

The absence of validated correlates of protection (CoPs) hampers the rational design and clinical development of new tuberculosis vaccines. In this review, we provide an overview of the potential CoPs in tuberculosis vaccine research. Major hindrances and potential opportunities are then discussed. Based on recent progress, it is reasonable to anticipate that success in the ongoing efforts to identify CoPs would be a game-changer in tuberculosis vaccine development.

Transforming vaccinology

The COVID-19 pandemic placed the field of vaccinology squarely at the center of global consciousness, emphasizing the vital role of vaccines as transformative public health tools. The impact of vaccines was recently acknowledged by the award of the 2023 Nobel Prize in Physiology or Medicine to Katalin Kariko and Drew Weissman for their seminal contributions to the development of mRNA vaccines. Here, we provide a historic perspective on the key innovations that led to the development of some 27 licensed vaccines over the past two centuries and recent advances that promise to transform vaccines in the future. Technological revolutions such as reverse vaccinology, synthetic biology, and structure-based design transformed decades of vaccine failures into successful vaccines against meningococcus B and respiratory syncytial virus (RSV). Likewise, the speed and flexibility of mRNA vaccines profoundly altered vaccine development, and the advancement of novel adjuvants promises to revolutionize our ability to tune immunity. Here, we highlight exciting new advances in the field of systems immunology that are transforming our mechanistic understanding of the human immune response to vaccines and how to predict and manipulate them. Additionally, we discuss major immunological challenges such as learning how to stimulate durable protective immune response in humans.

Facilitating the development of urgently required combination vaccines

The essence of a vaccine lies in its ability to elicit a set of immune responses specifically directed at a particular pathogen. Accordingly, vaccines were historically designed, developed, registered, recommended, procured, and administered as monopathogen formulations. Nonetheless, the control and elimination of an astonishing number of diseases was realised only after several once-separate vaccines were provided as combinations. Unfortunately, the current superabundance of recommended and pipeline vaccines is now at odds with the number of acceptable vaccine administrations and feasible health-care visits for vaccine recipients and health-care providers. Yet, few new combinations are in development because, in addition to the scientific and manufacturing hurdles intrinsic to coformulation, developers face a gauntlet of regulatory, policy, and commercialisation obstacles in a milieu still largely designed for monopathogen vaccines. We argue here that national policy makers and public health agencies should prospectively identify and advocate for the development of new multipathogen combination vaccines, and suggest ways to accelerate the regulatory pathways to licensure of combinations and other concrete, innovative steps to mitigate current obstacles.

Divergent antibody recognition profiles are generated by protective mRNA vaccines against Marburg and Ravn viruses

The first-ever recent Marburg virus (MARV) outbreak in Ghana, West Africa and Equatorial Guinea has refocused efforts towards the development of therapeutics since no vaccine or treatment has been approved. mRNA vaccines were proven successful in a pandemic-response to severe acute respiratory syndrome coronavirus-2, making it an appealing vaccine platform to target highly pathogenic emerging viruses. Here, 1-methyl-pseudouridine-modified mRNA vaccines formulated in lipid nanoparticles (LNP) were developed against MARV and the closely-related Ravn virus (RAVV), which were based on sequences of the glycoproteins (GP) of the two viruses. Vaccination of guinea pigs with both vaccines elicited robust binding and neutralizing antibodies and conferred complete protection against virus replication, disease and death. The study characterized antibody responses to identify disparities in the binding and functional profiles between the two viruses and regions in GP that are broadly reactive. For the first time, the glycan cap is highlighted as an immunoreactive site for marburgviruses, inducing both binding and neutralizing antibody responses that are dependent on the virus. Profiling the antibody responses against the two viruses provided an insight into how antigenic differences may affect the response towards conserved GP regions which would otherwise be predicted to be cross-reactive and has implications for the future design of broadly protective vaccines. The results support the use of mRNA-LNPs against pathogens of high consequence.

Correlates of immune protection against human rotaviruses: natural infection and vaccination

Species A rotaviruses are the leading viral cause of acute gastroenteritis in children under 5 years of age worldwide. Despite progress in the characterization of the pathogenesis and immunology of rotavirus-induced gastroenteritis, correlates of protection (CoPs) in the course of either natural infection or vaccine-induced immunity are not fully understood. There are numerous factors such as serological responses (IgA and IgG), the presence of maternal antibodies (Abs) in breast milk, changes in the intestinal microbiome, and rotavirus structural and non-structural proteins that contribute to the outcome of the CoP. Indeed, while an intestinal IgA response and its surrogate, the serum IgA level, are suggested as the principal CoPs for oral rotavirus vaccines, the IgG level is more likely to be a CoP for parenteral non-replicating rotavirus vaccines. Integrating clinical and immunological data will be instrumental in improving rotavirus vaccine efficacy, especially in low- and middle-income countries, where vaccine efficacy is significantly lower than in high-income countries. Further knowledge on CoPs against rotavirus disease will be helpful for next-generation vaccine development. Herein, available data and literature on interacting components and proposed CoPs against human rotavirus disease are reviewed, and limitations and gaps in our knowledge in this area are discussed.

Vaccine development against tuberculosis before and after Covid-19

Coronavirus disease (Covid-19) has not only shaped awareness of the impact of infectious diseases on global health. It has also provided instructive lessons for better prevention strategies against new and current infectious diseases of major importance. Tuberculosis (TB) is a major current health threat caused by Mycobacterium tuberculosis (Mtb) which has claimed more lives than any other pathogen over the last few centuries. Hence, better intervention measures, notably novel vaccines, are urgently needed to accomplish the goal of the World Health Organization to end TB by 2030. This article describes how the research and development of TB vaccines can benefit from recent developments in the Covid-19 vaccine pipeline from research to clinical development and outlines how the field of TB research can pursue its own approaches. It begins with a brief discussion of major vaccine platforms in general terms followed by a short description of the most widely applied Covid-19 vaccines. Next, different vaccination regimes and particular hurdles for TB vaccine research and development are described. This specifically considers the complex immune mechanisms underlying protection and pathology in TB which involve innate as well as acquired immune mechanisms and strongly depend on fine tuning the response. A brief description of the TB vaccine candidates that have entered clinical trials follows. Finally, it discusses how experiences from Covid-19 vaccine research, development, and rollout can and have been applied to the TB vaccine pipeline, emphasizing similarities and dissimilarities.

Knife's edge: Balancing immunogenicity and reactogenicity in mRNA vaccines

Since the discovery of messenger RNA (mRNA), there have been tremendous efforts to wield them in the development of therapeutics and vaccines. During the COVID-19 pandemic, two mRNA vaccines were developed and approved in record-breaking time, revolutionizing the vaccine development landscape. Although first-generation COVID-19 mRNA vaccines have demonstrated over 90% efficacy, alongside strong immunogenicity in humoral and cell-mediated immune responses, their durability has lagged compared to long-lived vaccines, such as the yellow fever vaccine. Although worldwide vaccination campaigns have saved lives estimated in the tens of millions, side effects, ranging from mild reactogenicity to rare severe diseases, have been reported. This review provides an overview and mechanistic insights into immune responses and adverse effects documented primarily for COVID-19 mRNA vaccines. Furthermore, we discuss the perspectives of this promising vaccine platform and the challenges in balancing immunogenicity and adverse effects.

Omicron-specific mRNA vaccine induced cross-protective immunity against ancestral SARS-CoV-2 infection with low neutralizing antibodies

The major challenge in COVID-19 vaccine effectiveness is immune escape by SARS-CoV-2 variants. To overcome this, an Omicron-specific messenger RNA (mRNA) vaccine was designed. The extracellular domain of the spike of the Omicron variant was fused with a modified GCN4 trimerization domain with low immunogenicity (TSomi). After immunization with TSomi mRNA in hamsters, animals were challenged with SARS-CoV-2 virus. The raised nonneutralizing antibodies or cytokine secretion responses can recognize both Wuhan S and Omicron S. However, the raised antibodies neutralized SARS-CoV-2 Omicron virus infection but failed to generate Wuhan virus neutralizing antibodies. Surprisingly, TSomi mRNA immunization protected animals from Wuhan virus challenge. These data indicated that non-neutralizing antibodies or cellular immunity may play a more important role in vaccine-induced protection than previously believed. Next-generation COVID-19 vaccines using the Omicron S antigen may provide sufficient protection against ancestral or current SARS-CoV-2 variants.