Nanomaterial-based delivery vehicles for therapeutic cancer vaccine development

mRNA-based therapeutic strategies for cancer treatment

In the rapidly evolving landscape of medical research, the emergence of RNA-based therapeutics is paradigm shifting. It is mainly driven by the molecular adaptability and capacity to provide precision in targeting. The coronavirus disease 2019 pandemic crisis underscored the effectiveness of the mRNA therapeutic development platform and brought it to the forefront of RNA-based interventions. These RNA-based therapeutic approaches can reshape gene expression, manipulate cellular functions, and correct the aberrant molecular processes underlying various diseases. The new technologies hold the potential to engineer and deliver tailored therapeutic agents to tackle genetic disorders, cancers, and infectious diseases in a highly personalized and precisely tuned manner. The review discusses the most recent advancements in the field of mRNA therapeutics for cancer treatment, with a focus on the features of the most utilized RNA-based therapeutic interventions, current pre-clinical and clinical developments, and the remaining challenges in delivery strategies, effectiveness, and safety considerations.

Nanomedicine for T-Cell Mediated Immunotherapy

T-cell immunotherapy offers outstanding advantages in the treatment of various diseases, and with the selection of appropriate targets, efficient disease treatment can be achieved. T-cell immunotherapy has made great progress, but clinical results show that only a small proportion of patients can benefit from T-cell immunotherapy. The extensive mechanistic work outlines a blueprint for using T cells as a new option for immunotherapy, but also presents new challenges, including the balance between different fractions of T cells, the inherent T-cell suppression patterns in the disease microenvironment, the acquired loss of targets, and the decline of T-cell viability. The diversity, flexibility, and intelligence of nanomedicines give them great potential for enhancing T-cell immunotherapy. Here, how T-cell immunotherapy strategies can be adapted with different nanomaterials to enhance therapeutic efficacy is discussed. For two different pathological states, immunosuppression and immune activation, recent advances in nanomedicines for T-cell immunotherapy in diseases such as cancers, rheumatoid arthritis, systemic lupus erythematosus, ulcerative colitis, and diabetes are summarized. With a focus on T-cell immunotherapy, this review highlights the outstanding advantages of nanomedicines in disease treatment, and helps advance one's understanding of the use of nanotechnology to enhance T-cell immunotherapy.

Engineered Cell Membrane-Coated Nanoparticles: New Strategies in Glioma Targeted Therapy and Immune Modulation

Gliomas, the most prevalent primary brain tumors, pose considerable challenges due to their heterogeneity, intricate tumor microenvironment (TME), and blood-brain barrier (BBB), which restrict the effectiveness of traditional treatments like surgery and chemotherapy. This review provides an overview of engineered cell membrane technologies in glioma therapy, with a specific emphasis on targeted drug delivery and modulation of the immune microenvironment. This study investigates the progress in engineered cell membranes, encompassing physical, chemical, and genetic alterations, to improve drug delivery across the BBB and effectively target gliomas. The examination focuses on the interaction of engineered cell membrane-coated nanoparticles (ECM-NPs) with the TME in gliomas, emphasizing their potential to modulate glioma cell behavior and TME to enhance therapeutic efficacy. The review further explores the involvement of ECM-NPs in immunomodulation techniques, highlighting their impact on immune reactions. While facing obstacles related to membrane stability and manufacturing scalability, the review outlines forthcoming research directions focused on enhancing membrane performance. This review underscores the promise of ECM-NPs in surpassing conventional therapeutic constraints, proposing novel approaches for efficacious glioma treatment.

Bacteria-derived nanovesicles enhance tumour vaccination by trained immunity

Trained immunity enhances the responsiveness of immune cells to subsequent infections or vaccinations. Here we demonstrate that pre-vaccination with bacteria-derived outer-membrane vesicles, which contain large amounts of pathogen-associated molecular patterns, can be used to potentiate, and enhance, tumour vaccination by trained immunity. Intraperitoneal administration of these outer-membrane vesicles to mice activates inflammasome signalling pathways and induces interleukin-1β secretion. The elevated interleukin-1β increases the generation of antigen-presenting cell progenitors. This results in increased immune response when tumour antigens are delivered, and increases tumour-antigen-specific T-cell activation. This trained immunity increased protection from tumour challenge in two distinct cancer models.

The quest for nanoparticle-powered vaccines in cancer immunotherapy

Despite recent advancements in cancer treatment, this disease still poses a serious threat to public health. Vaccines play an important role in preventing illness by preparing the body's adaptive and innate immune responses to combat diseases. As our understanding of malignancies and their connection to the immune system improves, there has been a growing interest in priming the immune system to fight malignancies more effectively and comprehensively. One promising approach involves utilizing nanoparticle systems for antigen delivery, which has been shown to potentiate immune responses as vaccines and/or adjuvants. In this review, we comprehensively summarized the immunological mechanisms of cancer vaccines while focusing specifically on the recent applications of various types of nanoparticles in the field of cancer immunotherapy. By exploring these recent breakthroughs, we hope to identify significant challenges and obstacles in making nanoparticle-based vaccines and adjuvants feasible for clinical application. This review serves to assess recent breakthroughs in nanoparticle-based cancer vaccinations and shed light on their prospects and potential barriers. By doing so, we aim to inspire future immunotherapies for cancer that harness the potential of nanotechnology to deliver more effective and targeted treatments.

Cancer vaccines in the clinic

Vaccines are an important tool in the rapidly evolving repertoire of immunotherapies in oncology. Although cancer vaccines have been investigated for over 30 years, very few have achieved meaningful clinical success. However, recent advances in areas such antigen identification, formulation development and manufacturing, combination therapy regimens, and indication and patient selection hold promise to reinvigorate the field. Here, we provide a timely update on the clinical status of cancer vaccines. We identify and critically analyze 360 active trials of cancer vaccines according to delivery vehicle, antigen type, indication, and other metrics, as well as highlight eight globally approved products. Finally, we discuss current limitations and future applications for clinical translation of cancer vaccines.

Anticancer activity of thymoquinone against breast cancer cells: Mechanisms of action and delivery approaches

The rising incidence of breast cancer has been a significant source of concern in the medical community. Regarding the adverse effects and consequences of current treatments, cancers' health, and socio-economical aspects have become more complicated, leaving research aimed at improved or new treatments on top priority. Medicinal herbs contain multitarget compounds that can control cancer development and advancement. Owing to Nigella Sativa's elements, it can treat many disorders. Thymoquinone (TQ) is a natural chemical derived from the black seeds of Nigella sativa Linn proved to have anti-cancer and anti-inflammatory properties. TQ interferes in a broad spectrum of tumorigenic procedures and inhibits carcinogenesis, malignant development, invasion, migration, and angiogenesis owing to its multitargeting ability. It effectively facilitates miR-34a up-regulation, regulates the p53-dependent pathway, and suppresses Rac1 expression. TQ promotes apoptosis and controls the expression of pro- and anti-apoptotic genes. It has also been shown to diminish the phosphorylation of NF-B and IKK and decrease the metastasis and ERK1/2 and PI3K activity. We discuss TQ's cytotoxic effects for breast cancer treatment with a deep look at the relevant stimulatory or inhibitory signaling pathways. This review discusses the various forms of polymeric and non-polymeric nanocarriers (NC) and the encapsulation of TQ for increasing oral bioavailability and enhanced in vitro and in vivo efficacy of TQ-combined treatment with different chemotherapeutic agents against various breast cancer cell lines. This study can be useful to a broad scientific community, comprising pharmaceutical and biological scientists, as well as clinical investigators.

Preclinical and clinical trials of oncolytic vaccinia virus in cancer immunotherapy: a comprehensive review

Oncolytic virotherapy has emerged as a promising treatment for human cancers owing to an ability to elicit curative effects via systemic administration. Tumor cells often create an unfavorable immunosuppressive microenvironment that degrade viral structures and impede viral replication; however, recent studies have established that viruses altered via genetic modifications can serve as effective oncolytic agents to combat hostile tumor environments. Specifically, oncolytic vaccinia virus (OVV) has gained popularity owing to its safety, potential for systemic delivery, and large gene insertion capacity. This review highlights current research on the use of engineered mutated viruses and gene-armed OVVs to reverse the tumor microenvironment and enhance antitumor activity in vitro and in vivo, and provides an overview of ongoing clinical trials and combination therapies. In addition, we discuss the potential benefits and drawbacks of OVV as a cancer therapy, and explore different perspectives in this field.

mRNA Delivery Platform Based on Bacterial Outer Membrane Vesicles for Tumor Vaccine

The rapid display and delivery method for customized tumor mRNA vaccines is limited. Herein, bacteria-derived outer membrane vesicles (OMVs) are employed as an mRNA delivery platform by surface engineering of an RNA-binding protein, L7Ae. OMV-L7Ae can rapidly adsorb boxC/D sequence-labeled mRNA antigens through L7Ae-boxC/D binding and deliver them into HEK-293T and dendritic cells. This platform provides an mRNA delivery technology distinct from lipid nanoparticles (LNPs) for personalized mRNA tumor vaccination and with a Plug-and-Display strategy suitable for rapid preparation of the personalized mRNA tumor vaccine against varied tumor antigens. Key features OMVs are employed as an mRNA delivery platform through L7Ae-boxC/D binding.

Production of a promising modular proteinaceous self-assembled delivery system for vaccination

Recently, there have been enormous advances in nano-delivery materials, especially safer and more biocompatible protein-based nanoparticles. Generally, proteinaceous nanoparticles (such as ferritin and virus-like particles) are self-assembled from some natural protein monomers. However, to ensure their capability of assembly, it is difficult to upgrade the protein structure through major modifications. Here, we have developed an efficient orthogonal modular proteinaceous self-assembly delivery system that could load antigens with an attractive coupling strategy. In brief, we constructed a nanocarrier by fusing two orthogonal domains-a pentameric cholera toxin B subunit and a trimer forming peptide-and an engineered streptavidin monomer for binding biotinylated antigens. After successfully preparing the nanoparticles, the receptor-binding domain of SARS-CoV-2 spike protein and influenza virus haemagglutination antigen are used as model antigens for further evaluation. We found that the biotinylated antigen is able to bind to the nanoparticles with high affinity and achieve efficient lymph node drainage when loaded on the nanoparticles. Then, T cells are greatly activated and the formation of germinal centers is observed. Experiments of two mouse models demonstrate the strong antibody responses and prophylactic effects of these nanovaccines. Thus, we establish a proof-of-concept for the delivery system with the potential to load diverse antigen cargos to generate high-performance nanovaccines, thereby offering an attractive platform technology for nanovaccine preparation.

Targeting the tumor microenvironment: Potential strategy for cancer therapeutics

Cellular and stromal components including tumor cells, immune cells, mesenchymal cells, cancer-linked fibroblasts, and extracellular matrix, constituent tumor microenvironment (TME). TME plays a crucial role in reprogramming tumor initiation, uncontrolled proliferation, invasion and metastasis as well as response to therapeutic modalities. In recent years targeting the TME has developed as a potential strategy for treatment of cancer because of its life-threatening functions in restricting tumor development and modulating responses to standard-of-care medicines. Cold atmospheric plasma, oncolytic viral therapy, bacterial therapy, nano-vaccine, and repurposed pharmaceuticals with combination therapy, antiangiogenic drugs, and immunotherapies are among the most effective therapies directed by TME that have either been clinically authorized or are currently being studied. This article discusses above-mentioned therapies in light of targeting TME. We also cover problems related to the TME-targeted therapies, as well as future insights and practical uses in this rapidly growing field.

Co-Delivery of the Human NY-ESO-1 Tumor-Associated Antigen and Alpha-GalactosylCeramide by Filamentous Bacteriophages Strongly Enhances the Expansion of Tumor-Specific CD8+ T Cells

Tumor-associated antigens (TAAs) represent attractive targets in the development of anti-cancer vaccines. The filamentous bacteriophage is a safe and versatile delivery nanosystem, and recombinant bacteriophages expressing TAA-derived peptides at a high density on the viral coat proteins improve TAA immunogenicity, triggering effective in vivo anti-tumor responses. To enhance the efficacy of the bacteriophage as an anti-tumor vaccine, we designed and generated phage particles expressing a CD8+ peptide derived from the human cancer germline antigen NY-ESO-1 decorated with the immunologically active lipid alpha-GalactosylCeramide (α-GalCer), a potent activator of invariant natural killer T (iNKT) cells. The immune response to phage expressing the human TAA NY-ESO-1 and delivering α-GalCer, namely fdNY-ESO-1/α-GalCer, was analyzed either in vitro or in vivo, using an HLA-A2 transgenic mouse model (HHK). By using NY-ESO-1-specific TCR-engineered T cells and iNKT hybridoma cells, we observed the efficacy of the fdNY-ESO-1/α-GalCer co-delivery strategy at inducing activation of both the cell subsets. Moreover, in vivo administration of fdNY-ESO-1 decorated with α-GalCer lipid in the absence of adjuvants strongly enhances the expansion of NY-ESO-1-specific CD8+ T cells in HHK mice. In conclusion, the filamentous bacteriophage delivering TAA-derived peptides and the α-GalCer lipid may represent a novel and promising anti-tumor vaccination strategy.

Biomaterials-assisted construction of neoantigen vaccines for personalized cancer immunotherapy

INTRODUCTION

Cancer vaccine represents a promising strategy toward personalized immunotherapy, and its therapeutic potency highly relies on the specificity of tumor antigens. Among these extensively studied tumor antigens, neoantigens, a type of short synthetic peptides derived from random somatic mutations, have been shown to be able to elicit tumor-specific antitumor immune response for tumor suppression. However, challenges remain in the efficient and safe delivery of neoantigens to antigen-presenting cells inside lymph nodes for eliciting potent and sustained antitumor immune responses. The rapid advance of biomaterials including various nanomaterials, injectable hydrogels, and macroscopic scaffolds has been found to hold great promises to facilitate the construction of efficient cancer vaccines attributing to their high loading and controllable release capacities.

AREAS COVERED

In this review, we will summarize and discuss the recent advances in the utilization of different types of biomaterials to construct neoantigen-based cancer vaccines, followed by a simple perspective on the future development of such biomaterial-assisted cancer neoantigen vaccination and personalized immunotherapy.

EXPERT OPINION

These latest progresses in biomaterial-assisted cancer vaccinations have shown great promises in boosting substantially potentiated tumor-specific antitumor immunity to suppress tumor growth, thus preventing tumor metastasis and recurrence.

Conserved Candidate Antigens and Nanoparticles to Develop Vaccine against Giardia intestinalis

Giardia intestinalis (Giardia lambia, Giardia duodenalis) infections in humans may be asymptomatic or symptomatic and associated with diarrhea (without blood), abdominal cramps, bloating, flatulence, and weight loss. The protozoan Giardia is the third most common cause of diarrhea and death in children under five, preceded only by rotavirus and by Cryptosporidium parvum and C. hominis infections. Antimicrobial drugs, particularly 5-nitroimidazole (5-NIs), are used to treat giardiasis in humans. Immunologically naive or immunocompromised host are more vulnerable to Giardia infection, whereas a degree of resistance to this protozoan is present in humans living in endemic areas. This suggests that vaccination may be a potential and appropriate means to control this parasitic disease outbreak and protect the human population. This review discusses Giardia antigens related to vaccine development. Additionally, based on the latest development of nanoparticle technology, a combination of methods for future research and development is proposed for the design of the next generation of powerful immunogens and an effective vaccine against Giardia.

Lipid-Based Delivery Systems in Development of Genetic and Subunit Vaccines

Lipidic carriers are composed of natural, synthetic, or physiological lipid/phospholipid materials. The flexibility of lipid-based delivery systems for transferring a variety of molecules such as immunomodulators, antigens, and drugs play a key role in design of effective vaccination and therapeutic strategies against infectious and non-infectious diseases. Genetic and subunit vaccines are two major groups of promising vaccines that have the potential for improving the protective potency against different diseases. These vaccine strategies rely greatly on delivery systems with various functions, including cargo protection, targeted delivery, high bioavailability, controlled release of antigens, selective induction of antigen-specific humoral or cellular immune responses, and low side effects. Lipidic carriers play a key role in local tissue distribution, retention, trafficking, uptake and processing by antigen-presenting cells. Moreover, lipid nanoparticles have successfully achieved to the clinic for the delivery of mRNA. Their broad potential was shown by the recent approval of COVID-19 mRNA vaccines. However, size, charge, architecture, and composition need to be characterized to develop a standard lipidic carrier. Regarding the major roles of lipid-based delivery systems in increasing the efficiency and safety of vaccine strategies against different diseases, this review concentrates on their recent advancements in preclinical and clinical trials.

Engineered Bacterial Outer Membrane Vesicles as Controllable Two-Way Adaptors to Activate Macrophage Phagocytosis for Improved Tumor Immunotherapy

The most immune cells infiltrating tumor microenvironment (TME), tumor-associated macrophages (TAMs) closely resemble immunosuppressive M2-polarized macrophages. Moreover, tumor cells exhibit high expression of CD47 "don't eat me" signal, which obstructs macrophage phagocytosis. The precise and efficient activation of TAMs is a promising approach to tumor immunotherapy; however, re-education of macrophages remains a challenge. Bacteria-derived outer membrane vesicles (OMVs) are highly immunogenic nanovesicles that can robustly stimulate macrophages. Here, an OMV-based controllable two-way adaptor is reported, in which a CD47 nanobody (CD47nb) is fused onto OMV surface (OMV-CD47nb), with the outer surface coated with a polyethylene glycol (PEG) layer containing diselenide bonds (PEG/Se) to form PEG/Se@OMV-CD47nb. The PEG/Se layer modification not only mitigates the immunogenicity of OMV-CD47nb, thereby remarkedly increasing the dose that can be administered safely through intravenous injection, but also equips the formulation with radiation-triggered controlled release of OMV-CD47nb. Application of radiation to tumors in mice injected with the nanoformulation results in remodeling of TME. As two-way adaptors, OMV-CD47nb activates TAM phagocytosis of tumor cells via multiple pathways, including induction of M1 polarization and blockade of "don't eat me" signal. Moreover, this activation of TAMs results in the stimulation of T cell-mediated antitumor immunity through effective antigen presentation.

Bacterial outer membrane vesicle-based cancer nanovaccines

Tumor vaccines, a type of personalized tumor immunotherapy, have developed rapidly in recent decades. These vaccines evoke tumor antigen-specific T cells to achieve immune recognition and killing of tumor cells. Because the immunogenicity of tumor antigens alone is insufficient, immune adjuvants and nanocarriers are often required to enhance anti-tumor immune responses. At present, vaccine carrier development often integrates nanocarriers and immune adjuvants. Among them, outer membrane vesicles (OMVs) are receiving increasing attention as a delivery platform for tumor vaccines. OMVs are natural nanovesicles derived from Gram-negative bacteria, which have adjuvant function because they contain pathogen associated molecular patterns. Importantly, OMVs can be functionally modified by genetic engineering of bacteria, thus laying a foundation for applications as a delivery platform for tumor nanovaccines. This review summarizes 5 aspects of recent progress in, and future development of, OMV-based tumor nanovaccines: strain selection, heterogeneity, tumor antigen loading, immunogenicity and safety, and mass production of OMVs.

Nanocarriers based on bacterial membrane materials for cancer vaccine delivery

Here we present a protocol for the construction and use of two types of nanocarrier based on bacterial membrane materials for cancer vaccine delivery. Cancer vaccines induce tumor regression through triggering the specific T-cell responses against tumor neoantigens, a process that can be enhanced by nanocarrier delivery. Inspired by the body's natural immune defenses against bacterial invasion, we have developed two different types of nanocarrier based on bacterial membrane materials, which employ genetically engineered outer-membrane vesicles (OMVs), or hybrid membrane vesicles containing bacterial cytoplasmic membrane, respectively. The OMV-based nanocarriers can rapidly display different tumor antigens through the surface modified Plug-and-Display system, suitable for customized cancer vaccines when the tumor neoantigens can be identified. The hybrid membrane-based nanocarriers are prepared through fusion of the bacterial cytoplasmic membrane and the primary tumor cell membrane from surgically removed tumor tissues, possessing unique advantages as personalized cancer vaccines when the neoantigens are not readily available. Compared with chemically synthesized nanocarriers such as liposomes and polymer without intrinsic adjuvant properties, owing to the large amounts of pathogen-associated molecular patterns, the two nanocarriers can activate the antigen-presenting cells while delivering multiple antigens, thus inducing effective antigen presentation and robust adaptive immune activation. Excluding bacterial culture and tumor tissue collection, the preparation of OMV- and hybrid membrane-based nanocarriers takes ~8 h and 10 h for tumor vaccine construction, respectively. We also detail how to use these nanocarriers to create cancer nanovaccines and evaluate their immunostimulatory and antitumor effects.

Novel Strategies for Spinal Cord Regeneration

A spinal cord injury (SCI) is one of the most devastating lesions, as it can damage the continuity and conductivity of the central nervous system, resulting in complex pathophysiology. Encouraged by the advances in nanotechnology, stem cell biology, and materials science, researchers have proposed various interdisciplinary approaches for spinal cord regeneration. In this respect, the present review aims to explore the most recent developments in SCI treatment and spinal cord repair. Specifically, it briefly describes the characteristics of SCIs, followed by an extensive discussion on newly developed nanocarriers (e.g., metal-based, polymer-based, liposomes) for spinal cord delivery, relevant biomolecules (e.g., growth factors, exosomes) for SCI treatment, innovative cell therapies, and novel natural and synthetic biomaterial scaffolds for spinal cord regeneration.

Antigen Capture and Immune Modulation by Bacterial Outer Membrane Vesicles as In Situ Vaccine for Cancer Immunotherapy Post-Photothermal Therapy

Tumor antigens released from tumor cells after local photothermal therapy (PTT) can activate the tumor-specific immune responses, which are critical for eliminating the residual lesions and distant metastases. However, the limited recognition efficiency of released tumor antigens by the immune system and the immunosuppressive microenvironment lead to ineffective antitumor immunity. Here, an in situ multifunctional vaccine based on bacterial outer membrane vesicles (OMVs, 1-MT@OMV-Mal) is developed by surface conjunction of maleimide groups (Mal) and interior loading with inhibitor of indoleamine 2, 3-dioxygenase (IDO), 1-methyl-tryptophan (1-MT). 1-MT@OMV-Mal can bind to the released tumor antigens after PTT, and be efficiently recognized and taken up by dendritic cells. Furthermore, in situ injection of 1-MT@OMV-Mal simultaneously overcomes the immune inhibition of IDO on tumor-infiltrating effector T cells, leading to remarkable inhibition on both primary and distant tumors. Together, a promising in situ vaccine based on OMVs to facilitate immune-mediated tumor clearance after PTT through orchestrating antigen capture and immune modulation is presented.

Bibliometric analysis of the 100 top-cited articles on immunotherapy of urological cancer

Purpose

To highlight the scientific progress in immunotherapy of urological cancer by identifying and analyzing the 100 top-cited (T100) articles from the last 15 years.

Methods

Papers in immunotherapy of urological cancer were identified from Clarivate Web of Science Core Collection database. Data of the T100 articles and papers published in recent 2 years, including citations, topic, year of publication, country of origin, institution and authorship, were extracted and analyzed.

Results

Of the T100 articles, the citation number ranged from 7387 to 183 with a mean of 590.66. The USA led the field with 80 T100 articles and 53097 citations. Pro Sharma P from MD Anderson Cancer Center was at the top of list with 8 T100 articles (3 as first author and 6 as corresponding author). Memorial Sloan Kettering Cancer Center ranked first with 26 T100 articles and 22573 citations, followed by Johns Hopkins University with 21 T100 articles and 25095 citations. Forty-nine T100 articles were related to the renal cancer, followed by prostate cancer (29), bladder cancer (13) and urothelial cancer (13). According to the type of immunotherapy, most T100 articles were related to ICI (55 articles) and vaccine (19 articles).

Conclusions

It is the first bibliometric analysis to identify the T100 articles on immunotherapy of urological cancer. The USA made great contribution in the field of immunotherapy related to urological cancer. Renal, bladder and prostate cancers were the major organs treated by immunotherapy especially by ICIs and vaccines. The multiple aspects of ICIs research in renal and bladder cancer and the neoantigen-based vaccine therapy will be hotspots for future research.

Polymer-Based Nanosystems-A Versatile Delivery Approach

Polymer-based nanoparticles of tailored size, morphology, and surface properties have attracted increasing attention as carriers for drugs, biomolecules, and genes. By protecting the payload from degradation and maintaining sustained and controlled release of the drug, polymeric nanoparticles can reduce drug clearance, increase their cargo's stability and solubility, prolong its half-life, and ensure optimal concentration at the target site. The inherent immunomodulatory properties of specific polymer nanoparticles, coupled with their drug encapsulation ability, have raised particular interest in vaccine delivery. This paper aims to review current and emerging drug delivery applications of both branched and linear, natural, and synthetic polymer nanostructures, focusing on their role in vaccine development.