Nanovaccines: A Revolutionary Paradigm in Immunization

Gurpreet Kaur , Ashita Pawaiya , Damandeep Kaur , Sumit Pasricha , Priyanka Rani ,

doi:10.5281/zenodo.15189996

Review Paper | Open Access
Volume 03 | Issue 04 | Article Id IJPS/250304122

Nanovaccines: A Revolutionary Paradigm in Immunization
Gurpreet Kaur * Ashita Pawaiya Damandeep Kaur Sumit Pasricha Priyanka Rani
Rayat Bahra Institute of Pharmacy, Hoshiarpur.

Abstract

Vaccination enormously contributes to maintain global health. Resistance for infectious diseases is growing quickly during treatment. Vaccines alone are not able to give enough strong and long-lasting protection against infections. To overcome this nanovaccines are developed. Nanoparticle (NP)-based delivery vehicles, such as dendrimers, liposomes, micelles, virosomes, nanogels, and microemulsions, offer numerous advantages over traditional vaccine adjuvants. The nanovaccines (50–250 nm in size) are considered most efficient in terms of tissue targeting, staying in the bloodstream for a long time. Nanovaccines are proved to in improving antigen presentation, targeted delivery, stimulating body’s innate immune system, and a strong T-cell response which helps in fighting against infectious diseases and cancers. Also,nanovaccines are very helpful for making cancer treatments that use immunotherapy. So, this review highlights the various types of NPs used in the new paradigm in viral vaccinology for infectious diseases and a brief comparison of conventional vaccines and nanovaccines. It focuses on the current NP-based vaccines, their potential as adjuvants, their potential in inducing innate and humoral immunity and the ways they can be delivered to cells. It also provides an overview that in future nanovaccines can be modified in order to attach more antigens and to get maximized therapeutic effect.

Keywords

Vaccine, Nanotechnology, Targeted Delivery, Immunity, Nanocarrier.

Introduction

The preparation of pathogen containing either disabled or killed form of virus or a part of the pathogen's structure is called vaccine. It which helps in promoting the formation of antibodies or cellular immunity against the pathogen when administered¹.An idea of vaccination has changed over ages and this has led to a wide variety of vaccinations. Vaccinations include live viruses in attenuated form, inactivated pathogens, inactivated toxins, or pathogen parts like sub-unit and conjugate vaccines can all be included². As far as public health vaccination offers a reliable line of defense against infectious disorders by delivering specific agents, known as Antigens, into the body³which initiates the immune response and produce adaptive immunity.

Nanovaccines

Nanovaccines made of nanoparticles, are an emerging class of vaccines. In nanovaccines, carry vaccine proteins are carried to the body very small particles that mimic the structures of pathogens and boost the immune system. Nanovaccines contain already determined antigen which is attached to a nanomaterial and an adjuvant and this antigen is responsible for making the immune system to react². Nanovaccines surface may contain number of antigen epitopes. Nanovaccines induce both humoral and cell-mediated immune responses which makes them more effective than traditional vaccinations. COVID-19, HIV, Merkel Cell Polyomavirus, influenza A virus, and a lot of other vaccines are made with nanoparticles.

Advantages Of Nanovaccines⁴

Nanovaccines offer several advantages over conventional vaccines.

a) Nanovaccines provide site-specific targeting which help in minimizing the potential aftereffects.

b) Nanovaccines are able to activate of the immune cells and ultimately, immune-stimulatory response even if administered in small amount.

c) Nanovaccines have potential to protect the antigen from protease degradation thus, increasing the amount of antigen available for initiating immune response.

d) Soluble antigens are less effective at eliciting protective immunity because of their inability to be endocytosed by cells, so nanovaccines help in improving antigen immunogenicity by providing targeted antigen delivery to Antigen Presenting Cells (APCs).

e) Nanovaccines have potential to distribute and release of the antigens to the site of administration in precisely controlled manner which in turn diminish the need for booster doses.

f) Nanovaccines contain Toll-like receptor (TLR) ligands and agonists as immune-stimulatory chemicals which improve adjuvanticity substantially.

g) Nanovaccines help in loading antigens onto major histocompatibility complex (MHC), therefore improving cross-presentation.

h) Nanovaccines provide controllable drug release rates.

i) Nanovaccines offer better stability as compared to conventional vaccines.

j) Nanovaccines can easily enter the cellular mechanism by endocytosis process because of the similarity in size to numerous cellular components and thus, they can elicit a long-lasting and durable response.

Table 1: Advantages and Disadvantages of Nanovaccines

Advantages

Dose required is low and thus producing low side effects
Protecting and stabilizing antigens in the extracellular or intracellular environment
Antigen immunogenicity is improved.
Enhanced immune response and reducing the need for booster doses.
Precisely controlled antigen release and targeting antigens to APCs.
Other immune-stimulatory molecules can be incorporated as necessary.
Better stability.
Long-lasting response.

Disadvantages

Difficulty with bulk production.

Short shelf life.

Obtaining uniform size is not possible.

Requirements for Nanovaccines⁴

In order to employ nanovaccines for enhancing immune responses, several conditions must be fulfilled.

i) The most crucial requirements for Nanovaccines are safety, minimal reacto-genicity and production of selective and sustained immune response which will result in improved memory responses. This response is the outcome of controlled release from nanovaccines.

ii) MHC class I molecules must do cross-presentation on Dendritic Cells (DCs).

iii) Cost effective and bulk production should be feasible.

Properties of Nanovaccines⁵:

i) Nanovaccines possess the size-dependent properties which have crucial role in bio-distribution and immune-modulation within the body. For Example, nano-sized particles of size 146 nm generated a stronger response in mice as compared to 64-nm-sized particles.

ii) Because of their nano size, it is easier for them to easily penetrate cells and distribute.

iii) Nanovaccines trigger the production of antibodies when nano-sized particles and their conjugates are considered as foreign substances by B-cells. So, formation of antibodies is affected by composition of nanovaccines, surface coating, absorption, and processing by immune system cells.

iv) Another crucial factor that determines efficacy and effectiveness of vaccination is an adjuvanticity of nanovaccines. The studies reveal that nanovaccines stimulate the Antigen-Presenting Cells (APC) to enhance the uptake of antigens.

v) Nanovaccines specifically target immune cells or organs. Targeting can be done by adding ligands or antibodies to the nanocarrier surface, particular receptors on immune cells can be bound. Targeting of vaccine helps in boosting the effectiveness of the vaccination and reducing the side effects.

Composition of Nanovaccines:

Nanovaccines consist of three main components:

(1) Antigens,

(2) Adjuvants,

(3) Nano carriers.

Antigens and Adjuvants:

The source of antigens can be from natural tumor antigens, synthetic peptides, mRNA, and DNA encoding tumor antigens. Adjuvants are added to enhance the immunogenicity of vaccine antigens, the without compromising vaccine safety. Adjuvants are able to produce a more robust immune response in combination with a specific antigen. Thus, nanoparticles can deliver either antigens or adjuvants to the targeted cells at predetermined rates³. In conventional vaccines, antigens and adjuvants are separate components, which sometimes lead to wastage of adjuvants, reduced vaccine immunogenicity, and an increased risk of adverse immune reactions. Nanoparticle-based delivery vehicles can facilitate the co-delivery of antigens and adjuvants as a whole, which significantly enhances the efficacy, safety of vaccines and achieve targeted delivery of vaccine.

Nanocarriers:

Nanocarriers are promising component of nanovaccine that can carry single or multiple therapeutic agents, thus increasing the solubility, stabilizing therapeutic activity in vivo, enhancing the aim to deliver the drug at desired site, and reducing drug- related side effects. However, some carriers possess adjuvant properties, which aid in activating the immune system and enhancing immune responses, thereby improving the efficacy of vaccines. Liposomes, polymer nanocarriers, inorganic nanocarriers, and exosomes nanocarriers are among the commonly used nanocarriers.

Mode of action of Nanovaccines⁶:

The nanovaccine can be coated with specific ligands or antigens such as Fc receptor, C-type lectin receptor, and anti-DEC-205 which actively get attached to the Dendritic Cells (DCs) receptors. The addition of immune-stimulatory molecules are to nanoparticles could increase the immunogenicity and improve the targeted delivery of antigens. The most prominent immune-stimulatory chemicals are mannose, β-Glucans, chitosan, glycolipids, and saponins. Another important consideration is the stability of the antigen in the vaccine formulation because modern antigens are vulnerable to enzymatic, pH, and temperature degradation, especially peptides, proteins, and nucleic acids. These are degraded before their presentation to antigen-presenting cells (APCs). There is need to develop as delivery systems which provide them protection against these degrading agents and antigen can be delivered to (APCs) efficiently. The mode of action of nanovaccines involves a series of steps that enhance antigen delivery, its processing, immune system activation, and long-term protection. Here's a breakdown:

1. Targeted Delivery & Uptake

The purpose of nanovaccines is to transport adjuvants and antigens to immune cells. They are engineered in such a way that they can be efficiently up taken by antigen-presenting cells (APCs), such as dendritic cells and macrophages, by process phagocytosis or endocytosis.

2. Antigen Processing & Presentation

The uptake of nanovaccine by antigen-presenting cells (APCs) causes release of nanovaccines in a controlled manner and is followed by processing and presentation of the antigens on Major Histocompatibility Complex (MHC) molecules and it allows T-cells to recognize the pathogen and start the immune activation.

MHC-I Pathway → Activates CD8+ T cells, leading to cytotoxic responses.

MHC-II Pathway → Activates CD4+ T cells, helping B cell activation.

3. Activation of Immune Responses

CD8+ T Cells → Differentiate into Cytotoxic T Lymphocytes (CTLs), which destroy infected cells.
CD4+ T Cells → Stimulate B cells, enhancing antibody production.
B Cells → Differentiate into plasma cells, secreting antigen-specific antibodies.

4. Induction of Memory Immunity

Some T and B cells develop into memory cells. Thus, providing assurance for a prompt and powerful immune response upon future exposure to the same virus.

5. Immune Modulation & Adjuvant Effect

Nanoparticles have the ability to function as adjuvants, improving immune activation, and they can be engineered to release antigens slowly, offering sustained stimulation.

Figure 1 Schematic Diagram for Cross-Presentation of Exogenous Antigen of Nanovaccine to Dendritic Cells⁴.

How nanovaccines induce immunity⁷:

The use of nanotechnology helps nanovaccines to induce immunity by improving the distribution and presentation of antigens to the immune system. These nanoparticle-based vaccines help in
augmenting primary and secondary immune responses. Nanovaccines achieve this
enhancement through various mechanisms, including activation of innate, cellular, and
humoral immunity.Here's a more detailed breakdown of how they induce immunity:

Activation of innate immunity

Nanovaccines have pathogen-associated molecular patterns (PAMPs) on their surface to interact with immune cells. PAMPs act as ligands for pattern recognition receptors (PRRs) which are abundantly present in these immune cells. Consequently, PAMP-PRR interactions trigger endocytosis, with larger particles being engulfed by macrophages while smaller particles are
engulfed by dendritic cells (DCs). Nanovaccine particles can be modified for enhancing their survival from macrophage degradation and to facilitate their direct delivery to APCs. Moreover, the type of PAMPs present influences cytokine and chemokine secretion by neutrophils and macrophages, which further help in activation and maturation of APCs, thereby initiating strong cellular and humoral immune responses.

Activation of cellular immunity

Following vaccination, cellular immunity is boosted, resulting in the development of immunological memory and pathogen neutralization. Once activated,dendritic cells after binding to nanovaccine particles migrate to the lymphatic organs to start this process. Through MHC class I receptors, activated DCs present antigens to CD8+ CTLs, triggering potent cell-mediated immune responses and the apoptotic destruction of target cells. Additionally, activated DCs use the MHC-II receptor to deliver antigens to CD4+ T-helper helper (Th) cells. The cells released cytokines are used to classify them into Th1 and Th2 subsets. The Th1 fraction mostly generates pro-inflammatory cytokines, which promote the growth of CTLs and strengthen cell-mediated immunity. In humoral immunity, the Th2 cell subset secretes a different class of cytokines that stimulate the generation of B-cells. The total preventive or therapeutic potential of a proposed nanovaccine is greatly influenced by the delicate balance between Th1/Th2 activity. In certain situations, nanovaccines may work by inhibiting T-regulatory (Treg) cells, which inherently prevent the body's effector T cells from activating and proliferating.

Activation of humoral immunity

Nanovaccines can induce strong Th2 cytokine responses that stimulate B cells in the lymph nodes and spleen. B cells recognize soluble antigens and undergo proliferation in the germinal center. Activated B cells become either antibody-secreting plasma cells producing soluble antibodies or memory cells providing immunity for future encounters with the same antigen. Due to the short lifespan of plasma cells, antibody titers gradually decrease over time. Memory cells that are kept in the bone marrow or lymphatic organs become active and offer defense against reinfection with the same antigen. Memory B cells proliferate quickly and change into cells that secrete antibodies, mostly IgG antibodies that fight the antigen. Likewise, memory T cells, such as CD4+ and CD8+ cells, enhance humoral and cellular immune responses by helping to produce more cytokine and chemokine signals. However, memory B and T cells may not be able to produce adequate protection if the antigen (epitope) undergoes major structural alterations. Even though the initial vaccination can offer about 90% protection, the residual 10% may still have negative consequences, requiring booster shots to reach 100% protection.

Figure 2: Activation of cellular and humoral immune responses by nanovaccines

Types of Nanovaccines

Nanovaccines are the vaccines of today’s age which are designed for enhancing the immune response by providing delivery of antigens in a controlled and targeted manner. Nanovaccines are classified on the basis of various parameters such as composition, type of construction, shape, and their mode of action against desired diseases. Nanovaccines employ nano sized particles, which are of size range from 1 to 100 nanometers and help to carry the vaccine components to specific cells in the body⁸.

i) Organic NPs⁹

Organic NPs are made of organic molecules of natural or synthetic origin. Most organic materials used are preferred because they are biodegradable, nontoxic, and biocompatible. These organic NPs offer advantages such as antigens' and adjuvants' potential to self-fabricate under physiologically favorable circumstances and their versatility in accommodating a broad range of sizes, compositions, surface modifications, and modalities. This organic NP vaccine delivery platform can be easily modified, such as virus-like particles (VLPs) and liposomes, which are polymeric NPs (PNPs).

a) Virus-like particles (VLPs) are a type of nanoparticle that closely mimic the structure of viruses but are non-infectious in nature due to lack of genetic material. VLPs vaccines have antigens on their surface, which stimulate an immune response without causing disease. Various examples of VLP-based vaccines including human papillomavirus (HPV),hepatitis B, influenza, norovirus, and coronavirus.

VLP vaccines have several advantages over traditional vaccines, which include:

*Safety: VLP vaccines are non-infectious because they do not contain genetic material which makes them safe for use in humans,

*Efficacy: Due to the antigens are present in highly structured and repetitive manner replicating the natural structure of viruses, VLP vaccinations elicit a potent and sustained immune response.

*Versatility; VLPs can be modified to display multiple antigens on their surface, which can help in enhancing the immune response and providing protection against multiple strains or types of viruses.

*Stability: VLP vaccines are stable at a wide range of temperatures, thus facilitating storage and distribution.

Figure 3: Schematic representation of Virus-like particle

b) Polymeric Nanoparticles (PNPs)⁶

Polymeric nanoparticles are that type of vaccine delivery system where antigens and adjuvants are encapsulated in a biocompatible and biodegradable polymer matrix. PNPs are divided into two main categories: natural PNPs and synthetic PNPs. Polymers are derived from biological sources in natural PNPs such as proteins, polysaccharides, and lipids, while in synthetic PNPs synthetic polymers are used for encapsulation. Natural polymers are more preferred over synthetic polymers as they are biodegradable, nontoxic, biocompatible and less likely to cause adverse reactions or long-term toxicity. Poly (lactic-co-glycolic acid) (PLGA), polyethyleneimine (PEI), and polypropylene sulphide (PPS) are examples of synthetic polymeric NPs that are used to make vaccines.Examples of natural polymeric NPs used in vaccine development include chitosan, alginate, and silk fibroin. But on the other hand, highly effective vaccine delivery systems can be created by carefully controlling the size, shape, and surface characteristics of synthetic PNPs. Nevertheless, they could be more hazardous and have a larger chance of causing immunological responses.

Advantages of PNPs over conventional vaccine delivery methods:

Enhanced antigen storage,
Protection against deterioration,
Controlled antigen and adjuvant release,
Capacity to target certain cells or tissues.

Figure 4: Schematic representation of Polymeric Nanoparticles

c) Liposomes⁹:

Liposomes are a special type of organic NPs which are made up of biodegradable phospholipids which get self-assembled into a lipid bilayer on contact with water. This lipid bilayer on the surface of a particle makes the particle more stable. That’s why liposomes are mostly impermeable like salts and macromolecules. Liposomes have ability to hold both hydrophobic and hydrophilic molecules, like antigenic proteins and peptides, in their lipid bilayer and aqueous core, respectively. Liposomes can protect the vaccine against degradation. Moreover, liposomes are able to carry single or multiple hydrophilic and lipophilic antigens and provide controlled release of antigens. Liposomes also show enhanced cellular uptake and improved antigen- specific immune response.

Figure 5: Schematic Representation of Liposomes

ii) Lipid nanoparticles (LNPs)⁶:

LNPs consist of a lipid bilayer that surrounds an aqueous core.LNP can be encapsulated to protect nucleic acids, such as mRNA or DNA, from degradation and thus enables a longer-lasting immune response. LNPs possess the ability to target particular cells, such as immune cells or liver cells, is one benefit of them. Lipid-based nanoparticles are the most preferred drug delivery system because they are biocompatible, self-assembled, have a substantial drug capacity, provide enhanced drug availability, are inexpensive, easy to create and release can be controlled. However, LNPs possess some potential limitations. LNPs can induce immune responses and cause inflammation, which can limit their effectiveness. Moreover, manufacturing of LNPs can be difficult and expensive on a large scale.

Figure 6: Schematic representation of Lipid Nanoparticles

iii) Inorganic Nanoparticles¹⁰:

Inorganic NPs find their benefits for vaccine distribution due to their hard structure and predictable fabrication; however, they are predominantly non-biodegradable. The main inorganic NPs are carbon, silica,calcium phosphate, aluminum-based, gold and magnetic nanoparticles. Size and shape of an inorganic nanoparticle affects vaccine delivery. It is easy to synthesize Gold nanoparticles (AuNPs) are easily into a variety of shapes (spherical, rods, cubic, etc.) which can induce humoral and cellular responses. Examples of gold nanoparticles are DNA vaccine adjuvants for human immunodeficiency virus (HIV) or as carriers for antigens from viruses, such as influenza and foot-and-mouth disease. Nanotubes and Mesoporous spheres are synthesized from Carbon nano-particles (CNTs) and are able to enhance the IgG response. Carbon nanoparticles get conjugated to multiple copies of protein and peptide antigens. Silica-based nanoparticles are considered another promising nano-carrier in vaccine delivery because of their ability to target a selective tumor and real-time imaging. The structural properties of nanoparticles can be changed to modify their interaction with cells while their synthesization. Calcium phosphate nanoparticles are another type of inorganic nanoparticle which is formed on mixing calcium chloride, dibasic sodium phosphate, and sodium citrate under certain conditions. They are nontoxic and show excellent biocompatibility and can be formed in size range between 50 and 100 nm. They are useful as adjuvants for DNA vaccines and mucosal immunity.

Figure 7: Schematic representation of Gold Nanoparticles

Iron Oxide Nanoparticles Due to their distinct magnetic characteristics, iron oxide nanoparticles function exceptionally well and offer a great deal of promise for usage in biological applications including targeted medication administration and magnetic resonance imaging. Iron oxide nanoparticles can be used as immune adjuvants to improve antigen processing or as a delivery mechanism to transfer antigens to the immune system. Magnetic nanoparticles can be coated with single layer ligands, polymers, mixtures of polymers and biomolecules (phospholipids and carbohydrates), or inorganic materials (silica and gold) to stop them from oxidizing and aggregating after manufacture. In addition to stabilizing nanoparticles in solution, these coatings help different biological ligands—such as proteins, antibodies, transferrin, and folate—bind to the surface of the nanoparticles, which is necessary for medicinal applications. These ligands can be chemically connected to magnetic nanoparticles coated with polymers, giving them the ability to target. Iron oxide nanoparticles can therefore be used in nanovaccines.

Figure 8: Schematic representation of Iron Oxide Nanoparticles

iv) Emulsion: Emulsion vaccines employ an oil-in-water emulsion for the delivery of the antigen. An emulsion is typically composed of an oil phase containing an antigen, and water phase contains a surfactant and other adjuvants that enhance the immune response. These vaccines show improved stability and uptake of the vaccine antigen that leads to a stronger and longer-lasting immune
response. Various examples of emulsion vaccines include influenza, hepatitis B, and human papillomavirus (HPV).

v) Exosomes¹¹: Exosome-based vaccine delivery systems are an emerging field of research for the development of vaccines against infectious diseases. Exosomes are small, membrane-bound vesicles released by cells for intercellular communication. They contain various bioactive molecules, including proteins, lipids, and nucleic acids, that can be modified and engineered to deliver therapeutic agents, including vaccine antigens. Exosome membranes can easily bind to target cells and thus increase the bioavailability of the loaded drugs. The phospholipid bilayer structures of exosomes help in enabling stable drug transport, extending drug half-life during delivery, and protecting drugs from enzymatic degradation that’s why exosome-based vaccines can be stored easily if cold storage is not available. Exosome-based vaccine delivery systems are more preferred over traditional vaccine delivery methods because exosomes are biocompatible and biodegradable which makes them safe for use in the human body. Because of their small size they are able to penetrate tissues and cross biological barriers, such as the blood-brain barrier. Moreover, they are immunogenic and are able to stimulate an immune response to the vaccine antigen.

Figure 9: Schematic representation of Exosomes

vi) Dendrimers: Dendrimers are well-defined synthetic globular macromolecules that possess various chemical and biological properties. Chemical properties include the presence of various functional groups on the surface that can be easily accessed for linking the molecules and these surface functional groups can be changed to precisely change the properties. This in turn will help in controlling their interaction with bio-membrane and their bio-distribution. Dendrimers bears adjuvant properties that provide multivalent scaffolds to produce highly defined conjugates with small molecule immune-stimulators and/or antigens.

Figure 10: Schematic representation of Dendrimers

vii) Self-assembling NP⁹:

These vaccines are synthesized from protein complexes. These proteins get themselves arranged into complex three-dimensional structures in water. SANPs possess advantages of self-assemblies and better over antigen shape. One application of this science is in SANPs.

Figure 11: Schematic representation of SANPs

viii) Protein/peptide NPs⁹:

Virus capsid proteins are used to synthesize protein/peptide NP vaccines and these proteins have ability to get self-assembled. They are considered copy of their parent viruses, but they lack any genetic material and are not able to spread disease. These are considered as “viruslike particles” (VLPs) which can be enveloped (eVLP) or not enveloped (non-eVLP),

Figure 12: Schematic representation of Protein/peptide NPs

Table 2. Roles of different types of NPs in vaccine development

Types	Vaccine NPs	Roles in vaccine development	Disease cured
Organic NPs	PNPs	Provides better immunogenicity by modifying surface proteins, biodegradable and targeted antigen delivery	Hepatitis B virus (HBV), malaria,Ebola, and Mycobacterium tuberculosis (M.tb)
	Liposomes	They protect vaccine against degradation, able to carry hydrophilic and lipophilic antigen, control the release of antigen, increased cellular uptake, and improved antigen- specific immune response	HBV, hepatitis A virus (HAV),Human Immunodeficiency Virus(HIV), influenza A viruses (IAVs), and influenza B viruses (IBVs)
	Dendrimers	Also have adjuvant properties and provide small,highly defined conjugates as immune-stimulators and/or antigens	Ebola; hemagglutinin type 1 and neuraminidase type 1-influenza A (H1N1);Toxoplasma gondii
	VLPs	The particles copy their parent pathogen, with high gastrointestinal stability,and possess self-adjuvant properties	Human papillomavirus (HPV),H1N1 IAV, HIV, H5N1 IAV
Inorganic NPs	Gold NPs	Increase immune response, act as both delivery systems and as adjuvants	West Nile virus, foot and mouth disease virus, H1N1 IAV, Streptococcus pneumonia, and Burkholderia mallei
Inorganic NPs	Iron oxides NPs (IONPs)	Activate immune cells, humoral and cellular immune responses and cytokine production	Mycobacterium tuberculosis, malaria, HBV
Self-assembled NPs		Have multiple binding sites, improved antigen stability and immunogenicity	EBV, malaria
Protein/peptide NPs		Have multiple binding sites, improved antigen stability and immunogenicity	HIV, influenza, and malaria

Table 3: Advantages and disadvantages of different nanoparticles in vaccine delivery

Types of Nanoparticle Systems	Advantages	Disadvantages
Virus-like particles (VLP)	Devoid of pathogenic agents Immunomodulator shielding reduces off-target effects Self-adjuvant	Poly dispersed particle size Limited encapsulation Lack of reproducibility
Liposomes	Phospholipids have inherent adjuvant characteristics and is stable in GI fluids when altered Able to absorb both hydrophilic and hydrophobic antigens	Limited antigen loading; Poor stability of GI exposed liposomes; Less stable than polymer particles
Polymeric	It is biodegradable Immunogenicity can be easily improve by surface properties modifications Release of antigens at targeted sites	Premature release of antigens; Low antigen protection; Inadequate protection against antigens
Inorganic nanoparticles	Improved resistance towards adsorbed antigens There is less chance of an early release; Surface modification is simple.	Non-biodegradable Low aqueous solubility
Emulsion	Can take in both hydrophilic and hydrophobic antigens Self-adjuvant	Poor GI stability Premature release of antigens
Lipid nanoparticle	Safe and versatile vehicles for drugs Biodegradable and biocompatible Improved oral drug bioavailability	Low loading efficiency Drug expulsion during storage
Exosomes	Delivery of vaccine to targeted site Modification is possible by transferring active molecules between cells	Methods for quantification are not sensitive enough High cost

Summary:

Research on vaccines has advanced significantly in recent years examining their enormous potential to treat a wide range of illnesses. In particular, nanovaccines have potential of developing less harmful and more effective vaccines due to the strong interactions of nanoparticles with the immune system. Strong antigenicity combined with extended retention and release makes nanovaccines producing memory effector response and both cell-mediated and antibody-mediated antibody responses, and thus reducing the need for repeated booster doses.

Challenges and future prospects:

The production of nanovaccines is limited by the toxicity of nanomedicines, scaling-up procedures, and the absence of regulatory requirements. Because pre-clinical and clinical investigations have demonstrated that nanovaccines causes dose-dependent acute and chronic toxicities with preferential bioaccumulation based on the route of administration, so the use of nanovaccines is controversial. Inorganic nanoparticles, such as metallic nanoparticles, are one of the types of nanoparticles that are inherently hazardous after extended exposure. Another key issue that has been somewhat mitigated by technical advancements is scaling up; nonetheless, scaling up in a sterile environment remains a considerable obstacle. In this era of modern medicine, where aim is to save countless lives. The persistent increase in antibiotic resistance and the lack of effective cancer treatment because of ongoing causative strain changes and disease heterogeneity has led to personalized medicine. Similar to this, vaccines against cancers and bacterial infections could be very beneficial; nevertheless, the existing vaccine's lack of potency and antigenic breadth are its main drawbacks. In order to create biomimetic nanovaccines as personalized medications, researchers have recently turned to biomimetic nanotechnology. These nanovaccines may be naturally multi-antigenic and immunostimulatory. When bacterial outer membrane vesicles (OMVs) are coated onto nanoparticles for anti-virulence immunization, the pathogen is surpassed by employing its own survival strategy and bacterial toxins are delivered and neutralized. This can lessen development of antibiotic resistance and successfully stop bacterial colonization. By altering these biomimetic nanovaccines' outer membrane coating, several nano-toxoid formulations can be created. Although cancer nano-based immunotherapy has advanced, the main obstacle remains the toxicity evaluations of these nanovaccines. It is necessary to evaluate autoimmune adverse effects that result from immune activation triggered by nanovaccines beforehand. Nanovaccines that over-activate antigen-presenting cells may be harmful because they can kill dendritic cells. Finally, the successful implementation of nano-based immunotherapy necessitates strategies to reduce the increasing complexity, manufacturing expense, and commercialization challenge associated with nanovaccine therapy.

Abbreviations

HIV: Human Immunodeficiency Virus

APCs: Antigen Presenting Cells

TLR: Toll-like receptor

MHC: Major Histocompatibility Complex

DCs: Dendritic Cells

mRNA: Messanger Ribonucleic Acid

DNA: Deoxyribonucleic Acid

CTLs: Cytotoxic T Lymphocytes

PAMPs: Pathogen-Associated Molecular Patterns

PRRs:Pattern Recognition Receptors

VLPs:Virus-Like Particles

PNPs:Polymeric NanoParticles

HPV: Human Papilloma Virus

PLGA:Poly lactic-co-glycolic acid

PEI:Polyethyleneimine

PPS: Poly Propylene Sulphide

AuNPs: Gold nanoparticles

CNTs: Carbon nano-particles

OMVs: Outer Membrane Vesicles

IONPs: Iron oxides Nano Particles

SANPs: Self-Assembling Nano Particles

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