Prelude

Without immunizations, infectious diseases harm humans in several ways. Because vaccines successfully exploit the human immune system to battle infections, they represent an unmatched milestone in medical history. A "variolation" in the 10th century AD is where vaccines first appeared. Dr. Edward Jenner, known as "the father of vaccines," conducted experiments in 1798 to test his theory that people who were given compounds derived from cowpox lesions could develop immunity to smallpox.

This work laid the groundwork for the creation of the modern vaccine. The two primary ways by which modern vaccinations work are to promote active immunity against infections and to confer passive immunity via pre-existing antibodies or cells.

More lives have been saved by vaccination than by any other type of medical treatment over the course of human history, and it has been crucial to public health and safety.

The coronavirus disease 2019 (COVID-19) pandemic, which has a devastating influence on society and the economy around the world, can be fought with vaccinations, which are the most effective and efficient medical treatment available.

However, it has been challenging to develop vaccines to protect against numerous deadly pathogens for which there are no efficient vaccines, including the human immunodeficiency virus (HIV), tuberculosis (TB), and malaria. This has led to high disease mortality rates in communities with limited resources. The challenges in developing innovative vaccines are a result of the pathogen and human co-evolutionary histories, such as viral variety. Moreover, the activation of autoimmunity is advantageous for other disorders, including cancer. The perfect fusion of humoral and cellular immunity, the sequential activation of immunological components, and immune tolerance or poor reactivity are some of the additional obstacles that the new era of vaccine production must face.

The burgeoning fields of material and biological research may offer cutting-edge methods for creating customized vaccines. Nanotechnology techniques are in a special position to overcome the difficulties of vaccination and mine further application potentials in cancer treatment as one of the most attractive and promising choices. Vaccine nanotechnologies have a variety of properties due to their tailored structures, modular compositions, and controlled length scales, including multivalent target delivery to lymphoid tissues and specific immune cells, multistage stimulating control release of immune components, engagement of important immune pathways, and ideal iterative design systems.

It is important to note that the Pfizer/BioNTech and Moderna mRNA COVID-19 vaccines' successful use has underlined the importance of nanotechnology in the creation of new vaccines.

A vaccine is a preparation of a pathogen—such as a weakened or killed bacteria, virus, or part of its structural makeup—that, when administered, prompts the formation of antibodies or cellular immunity against the pathogen but is unable to result in a serious infection.

A suspending fluid (such as sterile water, saline, or fluids containing protein), preservatives and stabilizers (such as albumin, phenols, and glycine), and adjuvants or enhancers that aid increase the vaccine's efficiency are chemicals that are frequently used in the manufacture of vaccinations

The best method of eradicating diseases to date is vaccination. In order to save humanity, a vaccine must be developed right away due to the rapidly spreading drug resistance against infectious diseases and chemotherapy-related toxicities in cancer. However, subunit vaccinations alone are unable to produce a powerful enough and persistent protective immunity against lethal diseases. Traditional vaccination adjuvants have some drawbacks, but nanoparticle (NP)-based delivery vehicles like microemulsions, liposomes, virosomes, nanogels, micelles, and dendrimers provide intriguing solutions. To better tackle infectious diseases and malignancies, nanovaccines can enhance targeted delivery, antigen presentation, stimulation of the body's innate immunity, strong T cell response, and safety. Additionally, nanovaccines can be very helpful in developing potent cancer immunotherapeutic formulations..

Nanoparticles

The creation and fabrication of materials and hardware at the atomic scale between 1 and 100 nanometers is the subject of the applied science known as nanotechnology.

Any particle with a diameter of under 100 nanometers is considered a nanoparticle. In order to deliver effective immunization through better targeting and by inducing an antibody response at the cellular level, the development of nanocarrier-based vaccines has begun to get a lot of attention.

Dendrimers, polymeric NPs, metallic NPs, magnetic NPs, and quantum dots are examples of nanoparticles (NPs) that have shown promise as adjuvants in cancer treatment and vaccines for infectious diseases. Effective vaccine delivery systems that can shield the encapsulated antigen from the hostile in vivo environment and maintain a prolonged release have been developed with the aid of nanotechnology.

This helps to activate the vaccine's immunostimulatory capabilities. Numerous nanovehicles, including liposomes, nanoparticles, microparticles, dendrimers, and micelles, among others, are examples of this context's gifts from nanotechnology and are widely known for their capacity to safeguard the encapsulated antigen.

Nanovaccines

In contrast to conventional medications, which affect the entire body, nanovaccines are developing as a new type of vaccines that specifically target the spot in the body where the sickness or infection began. Nanovaccines have the possibility of using the immune system to both treat and stop the spread of illnesses and disorders. Because they trigger both a humoral and a cell-mediated immune response, nanovaccines are more effective than traditional vaccines. Since they can be used as nasal drops, they are also more practical to use.

Other vaccinations, such as ones based on DNA, have performed badly in people, especially when it comes to halting the spread of disease, despite doing well in animal models. Thanks to nanovaccines, we now know more about how the body functions and what we can do to treat diseases. Additionally, nanovaccines will be less expensive than traditional vaccination methods.

Researchers have found a method for targeting a particular antigen in the body with nanovaccines. The nanoemulsion is a brand-new way to administer an antigen that is currently utilized in hepatitis B vaccines to stimulate the body's immune system. Researchers created 400-nanometer-sized nanoemulsions containing hepatitis B antigen and calculated the antigen and nanoemulsion's effective doses.

Promising strategies to improve the immune response of Nanovaccines

How to properly elicit an immune response to target antigens is the fundamental idea behind vaccination. A complex network responding to endogenous and foreign danger stimuli, which are involved in different immune cell types and coordinated by innate and adaptive immune responses, underlies this process. Nanomaterials' adaptable structure gives them the ability to augment specific immune responses in nanovaccines. The special drug/antigen delivery capabilities and nano-enabled immunomodulation of nanomedicine primarily help the vaccinations. These methods for triggering the immune response are the main topic of this section.

Delivering antigens to key cells and tissues of the immune system

Drug delivery is one of the most intriguing uses for nanotechnology. Delivering an antigen to the appropriate location in the immune system is crucial when it comes to vaccination. The antigen vaccine delivery method involves the spatiotemporal interactions of numerous cell types, including antigen-presenting cells (APCs), B cells, different T cells, macrophages, and neutrophils, in contrast to other types of medication delivery to specific cell types. Antigen delivery is further complicated by the fact that the interactions mentioned above frequently take place in a particular tissue or area. Therefore, a number of promising techniques have been used to create nanovaccines, including cross-presentation, lymph node (LN) trafficking, controlled antigen release, targeting APCs, and the biological barrier.

The application of multivalency effect in nanovaccine

The immune system can recognize the distinctive repetitive structures that the majority of viruses and bacteria have. The idea of incorporating this repeated antigen structure into vaccine formulation is groundbreaking. In self-assembled polypeptide nanoparticles, multiple antigen attached nanoparticles, and other multivalent assemblies, there is evidence that the multivalency effect induces a greater humoral and cellular immune response. The best news is that nanotechnology has a clear advantage in changing antigen density and orientation, offering excellent platforms for researching the mechanisms behind the multivalency effect and its optimization techniques. Puffer and colleagues discovered that greater Ca2+ signaling in B cells was connected with higher antibody levels being generated by the multivalency of the hapten. Additionally, low-affinity epitopes are even given immunogenicity by multivalent haptens.

Through a variety of processes, including complement activation, in which B cell receptors crosslink via tyrosine-based activation motifs (ITAMs), the multivalency of antigens can be regulated to activate immune cells. The multivalency impact of virus-like particles (VLPs) can improve B cell activation and subsequent immunological responses, despite the fact that the exact mechanism underlying this phenomenon is unknown. Studies on multivalent antigens made from nanomaterials have shown considerable potential in the fight against infectious illnesses.

Delivering nucleic acid for antigen expression in vivo

The COVID-19 pandemic's successful use of mRNA vaccines as a preventative measure has shown the vaccines' untapped potential. The delivery of DNA or RNA molecules, which upregulate the expression of target encoding antigens and elicit a specific, potent immune response in target immune cells, is largely responsible for the effectiveness of nucleic acid-based vaccines. Because they are easy, stable, and affordable to make in large quantities, DNA vaccines were thought to hold tremendous promise for the prevention and treatment of infectious diseases. However, ineffective in vivo distribution of plasmid DNA (pDNA) reduced the efficacy and constrained further preclinical application.

For instance, the likelihood of pDNA interacting with APCs is decreased by the tendency of conventional DNA vaccines to disseminate quickly after injection. Additionally, the inherent risk of conventional viral transmission brought comparatively safe nonviral vectors into prominence. Nanomaterials stand out among the prospective nonviral vectors because of their unique delivery advantages; the requirement to effectively deliver innovative mRNA-based vaccines drove the development of nanomedicine in vaccine creation. As was indicated before, it is possible to program nanoparticles with specific LN and APC targeting capabilities, which may also be applicable to nucleic acid-based vaccines.

Nucleic acids are more vulnerable to endonuclease destruction than protein/peptide antigens. Additionally, a significant barrier to clinical translation is the nonspecific immune reaction to foreign nucleic acids. Researchers must therefore take into account an encapsulating component when developing nucleic acid nano delivery systems in order to shield the nucleic acids from endonuclease enzymes.

Nucleic acid-based vaccines have long been attractive prospects for cancer treatment in addition to the treatment of infectious diseases. The tumor microenvironment's immunosuppression, however, necessitates the use of many pathways in vaccine design in order to sufficiently elicit an immune response against the tumor.

Nucleic acid molecules were found to take role in tumor immunomodulation as well. For instance, siRNA can prevent PD-L1 expression to reduce tumor growth, and some nucleic acids can act as immune adjuvants.

Additionally, nucleic acids can serve as the carriers for vaccines. A DNA nanodevice with a tubular structure created by Liu and colleagues loads molecular adjuvants and antigen peptides to elicit a potent anticancer immune response.

Administration strategies

Currently, the parenteral method, which is invasive and has low compliance, is used to deliver the majority of vaccines. For both cancer treatment and infectious disease prevention, the development of nanomedicine has opened up a variety of vaccine administration possibilities, including postoperative, intradermal/subcutaneous, intranasal, inhalation, and oral administration.

Postoperative administration

The current standard of care for treating solid tumors is surgery. However, tumor recurrence is still difficult to prevent because there is a chance that leftover tumor cells will cause a rapid return and spread. Nanomedicine techniques are being developed for post-operative tumor medication delivery and immunotherapy.

A thermoresponsive, curcumin-loaded, polymer nanoparticles-assembled hydrogel with an antigenic peptide and CpG-ODN was created to improve the effectiveness of postoperative T-cell immunity. This tactic can cause ICD, which strengthens the immune system's ability to fight tumors. This immunotherapy method encouraged CTL infiltration while preventing pulmonary metastasis and local recurrence. Another study developed an implanted 3D porous scaffold to eliminate myeloid-derived suppressor cells and deliver entire tumor lysates with nanogel-based adjuvants to encourage CTLs. The immunosuppressive environment was altered by this immune niche technique, which also inhibited postoperative tumor recurrence and metastasis.

Intradermal/subcutaneous administration

For DNA vaccines, intradermal/subcutaneous delivery is a typical method of immunization. APCs that are present in the skin's dermis and epidermis are the focus of vaccination. Intradermal/subcutaneous delivery has been used extensively for preventive vaccination since the skin is painless.

This administration method has recently been investigated for anticancer therapy. Subcutaneous vaccinations with VLPs conjugated to human EGFR 2 epitopes have been shown to increase HER2-specific antibody titers against HER2 positive cancers. Versatile microneedle devices have also been investigated for tumor and infectious disease vaccination for advanced intradermal injection. For topical and intratumoral immunotherapy against melanoma, a transdermal vaccination may be used. Magnesium (Mg) microparticles and cowpea mosaic virus nanoparticles were delivered propulsively by autonomous active microneedles, which significantly slowed the growth of the tumor and improved antitumor immunity.

The delivery of vaccines can also use microneedles that dissolve. P47 and CpG, two Plasmodium falciparum surface proteins, were put into microneedles and demonstrated strong TLR9 signaling activation for malaria vaccination. Recently, a microneedle patch with a vaccine core and PLGA shell was created for the vaccine's long-lasting and timed burst release. Without further immunization, this tactic can be employed for both preventive and therapeutic objectives.

Intranasal, Inhalation & Oral administration

An significant route for the treatment of infectious respiratory disorders is intranasal administration. Nasal immunization with nanovaccines holds promise for the treatment of cancers as well as the prevention of diseases that primarily attack diseased respiratory tracts, including TB. For the intranasal delivery of antigen for TB vaccination, chitosan nanoparticles are water-soluble platforms that can be investigated. Following intranasal delivery, thiolated OVA conjugated to N-trimethylaminoethylmethacrylate chitosan demonstrated increased cellular uptake, deep cervical lymph nodes transport efficiency, and immunological responses.

Another effective immunization method for lung infectious illnesses like TB is inhalation delivery. Inhalation compositions can benefit from the usage of synthetic nanoparticles.

Imiquimod, a TLR-7 agonist, and a fusion antigen protein have been formed into polymeric nanocapsules with an oily core and a polymer shell for pulmonary delivery. This polymeric nanocapsule vaccination produced potent immunological reactions. The discovery of biomimetic nanotechnology provided methods for creating respiratory droplets-inspired nanovaccines. In a recent work, a bionic-virus nanovaccine was created using liposomes as the capsid structure and the receptor binding domains as the "spike" to replicate the shape of SARS-CoV-2. Strong mucosal immunity was established by this inhalable nanovaccine, which can also be employed to treat other infectious respiratory illnesses.

A non-invasive approach with great compliance is oral administration. For administration, vaccination, safety, and storage, oral vaccines are the best formulations. As TB vaccinations that can be taken orally, several nanocarriers have been created. DNA vaccines contained in liposomes can effectively stimulate the immune system to fight TB. HIV envelope cDNA may also be transported through VLP, and it does so with improved stomach stability. After oral administration, this tactic causes a high antigen concentration throughout the intestinal lumen. As another illustration, even in an acidic environment, polyethyleneimine-coated SPIONs carrying malarial DNA demonstrated strong DNA binding and transfection efficiency.

Type of nanomaterial-based vaccines

Nanomaterials based on lipids, proteins, polymers, inorganic nanocarriers, and bio-inspired nanoparticles have all recently been investigated for use in vaccine development. Different types of nanocarriers exhibit different physicochemical profiles and in vivo behaviors, which have an impact on vaccination.

Self-assembled protein nanoparticles

Excellent biocompatibility and biodegradability can be found in natural nanomaterials. For the delivery of antigens, a variety of protein nanoparticle types derived from natural source proteins have been used. Promising prospects for nanovaccines include self-assembled protein nanoparticles. Ferritin family proteins, pyruvate dehydrogenase (E2), and virus-like particles (VLPs) are typical examples of self-assembled protein nanoparticles that have potential for use in the creation of nanovaccines.

VLPs, which are viral protein-based self-assembled complexes, are intended to be secure and highly effective delivery systems for antigen delivery devoid of genetic material and replication capacity. Because they are self-adjuvants and can be detected immunologically due to the virus size and repeated surface shape, VLPs have advantageous immunological features. APCs can efficiently pick up VLPs from polydispersed systems and trigger immunological reactions. Antibodies can attach themselves to VLPs with great density either chemically or genetically. Since VLPs-based vaccinations are currently on the market, such as Cervarix® and Gardasil® against the human papillomavirus virus (HPV) and Sci-B-VacTM against the hepatitis virus, they have led to effective immunization programs.

Polymeric nanoparticles

Colloidal systems made up of polymeric nanoparticles range in size from 10 to 1000 nm. Polymeric nanoparticles can be injected into the core and coupled to the surface and have good immunogenicity and stability for effective antigen encapsulation and presentation. Polymeric nanoparticles, albeit typically solid, can have controlled sizes and act as adjuvants103. Polymeric nanoparticles can increase the phagocytosis or endocytosis efficacy of antigen absorption by APCs.

Natural polymeric nanoparticles like chitosan and dextran as well as manufactured polymeric nanomaterials like PLA and PLGA are both helpful for the creation of nanovaccines. Natural polymeric nanoparticles are highly biocompatible, soluble in water, and cost-effective. For instance, the natural polymer chitosan, which is often generated from chitin, is a linear cationic polysaccharide that can be utilized to administer vaccines. Chitosan is a viable choice for gene delivery and coating other polymeric nanoparticles to increase adhesion and immunogenicity because of its cationic charge and bioadhesive qualities. Moreover, by adding functional groups, chitosan can be modified according to purpose.

Synthetic polymeric nanoparticles typically have higher repeatability than natural polymers and are easier to manage in terms of molecular weight compositions and degradation rates. For instance, PLGA nanoparticles are extremely biodegradable and have adjustable characteristics. A polymeric micelle made of PLGA and PEG can self-assemble to deliver hydrophobic peptide antigens and improve T cell responses.

Lipid-based nanoparticles

Lipid nanoparticles (LNPs) are nanoscale lipid vesicles created by self-assembling amphipathic phospholipid molecules. With minimal toxicity, great biocompatibility, and controlled release characteristics, LNPs are attractive nanocarriers for delivering nucleic acids.

LNPs are essential ingredients in both mRNA medicines and vaccinations. LNPs contain critical characteristics that may have an impact on the effectiveness of immune activation, including adjustable size, shape, and charge. LNP modification can produce the best immune reactions. LNPs can deliver numerous antigens and adjuvants simultaneously when used as nanovaccines. Additionally, LNPs' membrane surfaces can show antigen with improved natural conformation representation.

LNPs have demonstrated excellent potential for the creation of nanovaccines in a variety of preclinical and clinical applications. As was already established, lipid nanoparticles are essential for effectively delivering mRNA vaccines by shielding them from nuclease. Recently, LNPs (mRNA-1273 and BNT162b2) have been successfully translated for the delivery of mRNA against COVID-19. According to a recent assessment, numerous other LNP-mRNA formulations are currently undergoing clinical trials for the prevention and treatment of serious dangers to human health, including as cancer, viral infections, and genetic illnesses. LNPs can be made of cationic lipids, ionizable lipids, and other lipid types. Additionally, lipids can be functionalized through modifications like PEGlyation, which increases the versatility and potency of LNPs for vaccine production.

Inorganic nanomaterials

Metals and oxides, non-metal oxides, and inorganic salts are examples of inorganic materials frequently employed in nanomedicine. Low biodegradability despite structural stability characterizes inorganic materials. Many inorganic nanoformulations naturally behave as adjuvants. However, to increase their biocompatibility for use in nanovaccines, inorganic nanomaterials must have their physicochemical qualities altered. Gold, iron, and silica nanoparticles are among the most popular inorganic materials for antigen delivery.

Positively charged and spherical gold nanoparticles (GNPs) are present. GNPs have a high antigen loading capacity, minimal immunogenicity, and good biocompatibility. The toxicity of GNPs varies with their size, but they also have a strong affinity for sulfhydryl groups, which can be used in surface engineering to couple with cysteine residues to create polypeptide antigens with better pharmacokinetic and safety profiles. Additionally, GNPs have inherent immunostimulatory activities that promote the generation of inflammatory cytokines. As a result, GNPs can be employed to stimulate immunological responses in addition to acting as an antigen transporter. Additionally strong options for carrier materials for nanovaccines are silica nanoparticles. According to recent research, silicon particles can have variable porosity by manipulating their shape and pore size, which increases their effective load capacity for various adjuvants and antigens. Their porous silicon particle structure allows different active biomolecules to fill the pores or directly wrap around the surface, improving the targeting and uptake of the nano-vaccine. To deliver antigens and adjuvants, silica nanoparticles have been employed to target lymph nodes and aggregate in APCs.

Biomimetic nanomaterials

For the development of nanovaccines, biomimetic nanomaterials are emerging due to their efficient and complicated biofunctions. Nanomaterials that mimic biological processes can effectively interact with living things or transfer substances to a desired spot. High biocompatibility, prolonged circulation, and distinctive antigenic characteristics of bioinspired nanoparticles have also been generated for the creation of efficient vaccination formulations.

A straightforward biomimetic design modifies nanoparticles and improves binding to increase targeting for effective administration using natural ligands or peptides like arginylglycylaspartic acid (RGD) and candoxin (CDX) peptides. Additionally, molecularly imprinted polymers can be employed to create biomimetic nanoparticles by imitating antibodies. Individual natural ligands can give nanoparticles specialized activities, but many decorating would be challenging and hardly be able to reproduce biological complexity. Utilizing biomembranes to create membrane-coated nanoparticles for improving biointerfacing is an emerging biomimetic technique. Nanotechnology cell membrane coating has been widely used to enhance nanoparticle circulation, targeted delivery, and imaging. The ability of nanoparticles to blend in with cell membranes may aid in vaccine development by allowing them to target the lesion without being detected by the immune system. For instance, the red blood cell (RBC) membrane can increase the bioavailability of nanoparticles and increase circulation; platelet membranes can target certain pathogens and damaged vasculature; nanoparticles coated with cancer cell membranes have demonstrated autologous targeting to cancer cells; and nanoparticles with immune cell membrane coating can interact with tumor tissues. Intracellular membranes, such as the outer mitochondrial membrane, can also be used for precise targeting and detection in addition to cell membranes. Additionally, biomimetic nanoparticles could be used to create cancer nanovaccines that combat metastasis by a combination of photothermal (PTT) and photodynamic (PDT) therapy.

Nanovaccines for diseases prevention and treatments

Millions of people die each year from diseases like HIV/AIDS, malaria, and TB, underscoring the need for prevention and treatment plans. However, vaccination programs virtually ever result in the population developing a protective immunity. Malaria has a complex life cycle and numerous infection types (sporozoites, merozoites, and gametocytes); people with TB infection may also have HIV and bacteria that are multi-drug resistant. HIV has a highly dynamic genome and unclear immune protection. Despite having different pathogens, these illnesses' vaccine development has certain commonalities, and antigen delivery is still essential for vaccination.

Protein nanoparticles that self-assemble are effective delivery systems for antigens. The first and only malaria vaccine on the market, RTS,S, delivers antigen through VLP. For vaccine purposes, VLP has been shown to exhibit HIV envelope proteins such the V1V2 loop and to produce particular IgG in mice. In order to improve immunogenicity, ferritin nanoparticles have also been used to display HIV envelope trimers on particle surfaces. For HIV immunization, bigger proteins such lumazine synthase and dihydrolipoyl acetyltransferase (E2) are especially helpful. Recently, a two-component protein nanoparticle was created by combining well-folded trimers with self-assembled nanoparticles in order to increase the immunogenicity of HIV envelope (SOSIP) trimers. The role of spacing, antigens, and particle (size, shape, and charge) components in the protective immune responses is being further investigated.

Way forward

The last decades' rapid advancement of nanotechnology opened doors for the creation of vaccines and nanomedicine. Nanovaccines, which have important advantages over conventional vaccinations in terms of delivery effectiveness, dosing regimens, mode of administration, adjuvants, and vaccination effects, use a variety of nanoparticles. In this review, we outlined the main categories of nanomaterials for vaccines and talked about cutting-edge applications, focusing on the global spread of cancer and infectious diseases. In addition to designing nanomaterials, creating novel immunogens is crucial to achieving the desired prophylactic immune response for infectious diseases; meanwhile, when developing cancer nanovaccines, the safety, targeting potential, and effective whole vaccination cascade are crucial for the treatment immune response.

Immunogenicity and toxicity are two significant concerns with regard to the safety of nanovaccine. After delivery, nanoparticles may stimulate the host's immune system. Additionally, during biodegradation, compounds made from nanoparticles may trigger unanticipated, nonspecific immunological reactions. Increased levels of proinflammatory cytokines may cause immunogenicity in cationic and ionizable nanoparticles. The type of nanomaterials and the dose have a direct impact on the cytotoxicity of nanoparticles. It is strongly recommended to include biodegradable components while creating nanovaccines with increased biocompatibility.

In experimental studies, vaccine nanotechnology has demonstrated promising outcomes; further collaborations between the pharmaceutical, immunology, virology, oncology, and nanomaterials industries will support the clinical translation and application of nanovaccines for the treatment of deadly infectious diseases and cancers.

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