Organic NPs are made of organic molecules that can be found in nature or made in a lab. Organic NPs can be found in nature in many different forms, such as emulsions, lipid bodies, milk protein aggregates, and even more complicated structures like viruses. Most organic materials are biodegradable, nontoxic, and compatible with living things, while most inorganic materials are more stable, have smaller particles, can be tuned to specific needs, have high antigen loadings, are more permeable, and have a controlled release profile. Gregoriadis [12] said that many different organic NPs have been used as platforms for vaccines because they are biocompatible, biodegrade, and don’t cause much harm in general. Purely organic NP platforms have many advantages over other existing NP platforms, such as the ability of antigens and adjuvants to self-assemble in physiologically mild conditions and the ability to accommodate a wide range of compositions, sizes, surface modifications, and modalities [13]. There are recent changes to the organic NP vaccine delivery platform, such as virus-like particles (VLPs) and liposomes, which are polymeric NPs (PNPs).

Most of the time, inorganic NPs have been used in cancer as contrast agents for imaging or for photothermal therapy. In preclinical settings, there has recently been a lot of interest in making inorganic NPs into vaccines. Most inorganic materials have smaller particles, better stability, controlled tunability, better permeability, high drug loadings, and a controlled release profile [73]. This makes them perfect for delivering antigens as a vaccine [13]. Most of these newer generations are made with an inorganic core and an organic shell, making them hybrid inorganic nanomaterials. These inorganic NPs are now being used in vaccines as both carriers and boosters (Table 1).

Self-assembling NP vaccines with the receptor-binding domain (RBD) of SARS-CoV-2 were made (Figure 1H and Table 1). The vaccine candidate elicited strong humoral and T-cell responses and protected rhesus monkeys from infection by 2 105 CCID50 SARS-CoV-2 with short-term shedding and only minor pathological damage. Protein complexes that have been cleverly assembled can be used to produce vaccines [69]. Protein complexes of the size and form of a little virus are synthesized from scratch [5]. All the advantages of current protein nanovaccines are present in these nanoassemblies, with the added bonus of greater control over antigen shape and dosing thanks to their in-house fabrication [69]. One application of this science is in SAPNs. Proteins arrange themselves into complex three-dimensional structures in water (Figure 1H) [6]. In malaria, influenza, and toxoplasmosis animal models, SAPNs have been demonstrated to be immunogenic and protective [7, 8].

In the 1950s, a protein extracted from the tobacco mosaic virus (TMV) was found to form rod-shaped particles that looked like the original TMV but didn’t have any genetic material [45]. This was one of the first examples of a self-associating protein particle. Later, in the 1970s, the hepatitis B virus surface antigen (HBsAg) was separated from infected human serum [45]. For example, almost all living things make ferritin, which is a protein whose main job is to store iron inside cells. Ferritin is made up of 24 subunits, each of which is a bundle of four alpha-helices. These subunits come together on their own to form a quaternary structure with octahedral symmetry. Several high-resolution structures of ferritin have been found, and they show that Helicobacter pylori ferritin is made up of 24 identical protomers. In animals, however, there are both light and heavy chains of ferritin, which can form particles of 24 subunits on their own or in different proportions.

Ferritin, which is made by most living things, is an interesting self-assembling NP-based vaccine platform for infectious diseases [84]. Ferritin is made up of 24 alpha helix subunits with 3-fold axis symmetry. These subunits come together on their own to form NPs that are more stable thermally and chemically [85]. The shape of ferritin NPs makes it possible for trimeric antigens to be shown in a good way, which increases the chance that they will protect against different subtypes of influenza virus.

Nanovaccines that are meant to cause humoral immune responses to put a lot of focus on exposing Env. Different candidates have gone after either the precursor protein gp160, one or more of the processed sections of Env (gp140, gp120, or gp41), or certain parts of Env, like the variable loops or membrane-proximal external regions (MPERs) [84–88]. By putting Env or one of its many subunits on NPs, many of the factors that are thought to be important for HIV-1 immunogen formation can be incorporated into the design, which could lead to better responses. NP immunogens can also carry Env trimers, just like natural Env trimers do. Stabilized envelope glycoprotein (Env) (SOSIP trimers) are native-like structures made from gp140 and disulfide bridges that lock the structure into a native-like prefusion conformation. These structures were used to build a lot of Env [88–92]. In addition to being on the surface of NPs [86, 87, 93–95], these proteins can cause functional responses in animals that have been immunized [86, 87, 93]. Also, nanovaccines can be made to show the Env protein or its parts in a shape similar to their natural form without adding more disulfide bridges [84, 96].

NPs could be used to fix the problem that there aren’t enough Env molecules on the surface of the virus. Different nanovaccines can be made with different symmetries and shapes that make it easier to show off Env or a specific part of Env. Antigens can also be put at a distance of 5–10 nm, which is the best distance for activating B cells [97–99]. This change allows for better cross-linking of the B-cell receptor, which leads to better immune responses. With this change, you can make antibodies that have higher titers than recombinant proteins or even the HIV-1 virus itself.

Nanovaccine research for HIV-1-specific antibodies focuses on nabs [100]. VLPs from HIV-1 have been attempted. These vaccinations can induce Tier-2 neutralizing antibodies (NAbs), but they have many of the same issues as the HIV-1 virus, including low Env presentation, unstable and incomplete spikes, and longer spike intervals [101, 102]. Other attempts to make fusion VLPs by combining HIV-1 group specific antigen (Gag) or capsid proteins from other viruses with HIV-1 proteins like gp160, gp120, trimeric gp140, third hypervariable loop (V3 loop), first and second hypervariable regions (V1V2 loop), and CD4 binding site yielded mixed results, with only a few making NAbs in animal models [103–112]. Animals administered a Gag-VLP with MPER made few gp41-specific antibodies to inhibit the virus. However, animal models responded less to gp41 on non-eVLPs from other viruses [113, 114].

Ferritin NPs are naturally occurring iron-binding nanocages consisting of 24 monomers that self-assemble [100, 115]. SOSIP on ferritin NPs is more immunogenic than soluble SOSIP, although it didn’t aid neutralization significantly [92, 116, 117]. SOSIP’s design or the ferritin nanovaccine’s eight timers may explain this [100]. Sixty Aquifex aeolicus lumazine synthase monomers form a NP with 20 trimers [118]. The Env outer domain (eOD) of gp120 was attached to these particles to activate VRC01-type broadly NAb (bNAb) germ-line progenitors [119]. After vaccination, transgenic mice produced broad-NAbs. This candidate is awaiting Phase I clinical trials [100, 120].

Liposomes, like protein NPs, help create NAbs [121]. Most nanovaccine research has focused on how to deliver peptides or proteins to the host immune system to make them immunogenic [100]. Antibodies targeting gp41’s MPER are a priority. Infected patients have bNAbs that bind to the protein and viral Env [122–124]. Liposomes coated with the entire gp41 subunit or MPER peptides increased antibody titers. This may cause weak to moderate neutralization and cross-reactivity [85, 125, 126]. Virosomes delivered gp41 as part of a mucosal vaccination technique that caused NAbs to develop in the vagina of vaccinated nonhuman primates (NHPs) and protected most animals when challenged [127]. Most Phase I trial participants had mucosal antibodies [128].

Liposomes deliver Env trimers. SOSIPs on liposomes have been attempted in several articles [86, 129]. As expected, the liposomal virus rendered it immunogenic and harder to fight [86, 129]. Liposome-based nanovaccines were created to circumvent the glycan barrier [129]. Changes in glycans and a prime-boost technique focused the immune response on the CD4 binding site. Cross- NAbs and a bNAb that bound to a novel glycan/protein epitope resulted [129].

mRNA vaccines in lipid NPs are a promising area of vaccine research [130]. Two research examined HIV-1-neutralizing antibody production using Env-coding mRNA vaccines [131, 132]. In the first investigation, rabbits and NHPs made NAbs, and NHPs made tier 2 NAbs [131]. These results were expanded to show that nucleoside-modified mRNA generated NAbs that lasted at least 41 weeks to a protein-based immunogen with the identical sequence [132].

Human clinical investigations have only connected non-NAbs to protection (RV144, the Army-led Thai HIV vaccine efficacy trial). Despite the fact that most studies investigating the generation of humoral responses in response to a nanovaccine have focused on NAbs, it is the non-NAbs that have been demonstrated to correlate with protection. Antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), antibody-dependent cell-mediated virus inhibition (ADCVI), and antibody-dependent complement activation (ADCA) all result from the Fc portion of the manufactured antibody binding to the Fc receptor on effector cells. ADCC was observed in those who had a lower susceptibility to the RV144 virus. It’s likely that the significance of these reactions was underestimated or under-researched due to the complexity and inconsistency of the assays utilized for quantification [133, 134]. Some antibodies defy easy categorization as neutralizing or non-neutralizing. Instead, they can pursue multiple potential solutions simultaneously [135–139]. In the passive transfer of previously discovered neutralizing monoclonal antibodies (mAbs) into NHP models, non-neutralizing responses have been linked to 25–45% of the antiviral activity [140–142]. This demonstrates how critical it is for the advancement of vaccinations.

When investigating the potential for a nanovaccine to have an effect other than neutralization, one of the earliest experiments focused on a VLP containing various fragments of gp41 [113]. In contrast to VLPs without the HR2 region, those containing it were able to activate ADCC [113]. In a second prime-boost vaccine research, VLPs were utilized in conjunction with two DNA injections and two Gag-VLP injections. Mice that received these injections displayed both ADCC and ADCIV activity [143]. Animals that had been injected with a SAPN depicting the V1V2 loop of Env displayed ADCP activity in another investigation [96]. Vaginal ADCC-inducing antibodies were produced after a mucosal vaccination in NHPs [57]. After receiving LNPs-encased mRNA vaccinations, both rabbits and nonhuman primates developed antibodies with the potential to trigger ADCC [131]. Additionally, mRNA analysis revealed that vaccinated NHPs produce antibodies with the potential to induce ADCC and ADCP activity [132].

Nanovaccines and cell-based immunity VLPs were used in some of the earliest attempts to create vaccinations that would elicit CD4+ or CD8+ responses [144]. Making Gag NPs, with or without additional antigens like Env, was a major focus of the earliest studies. Cytotoxic T lymphocytes (CTL), T helper (Th) cells, and antibody titers were all found to increase, however, the exact amounts varied between trials and between related antigens [107, 109, 110]. More plans were devised to boost these figures. In the first strategy, CD40 ligand (CD40L) was included in the Gag-VLP to bind to CD40 and activate DCs, hence increasing the virus’ immunogenicity [145, 146] When mice were administered VLPs containing CD40L, their CD4+ and CD8+ cell responses to p24 were significantly higher than when mice were given VLPs alone [145]. NHPs exhibited enhanced cellular and humoral immune responses after receiving a simian HIV (SHIV) Gag-VLP including Env and CD40L as a vaccine [147]. Similar VLPs including Env and CD40L were employed in a simian immunodeficiency virus (SIV) challenge model. Anti-Env antibodies, CD4+ and CD8+ responses rose after vaccination, although infection was still transmitted. Mice that were administered SHIV Gag-VLP along with CD40L showed significantly reduced viremia [147].

The primary function of VLPs in T-cell-based vaccines has been to serve as the “boost” component of the “prime-boost” strategy [17, 148–151]. One experiment used a DNA prime together with a Gag-VLP displaying reverse transcriptase or a Tat: Nef fusion protein. VLP was more effective than two DNA-only vaccines at boosting CD4+ and CD8+ responses [151]. The CD4+ and CD8+ immunological responses of mice were enhanced when they were first given two doses of a DNA vaccination, and then two doses of a Gag-VLP vaccine [17, 143]. The CD4+ and CD8+ responses of mice immunized with DNA were lower than those of mice immunized with a VLP displaying gp120 and a rMVA (recombinant modified vaccinia Ankara viruses) vector, as demonstrated in another research [148]. This demonstrates the critical role of prime-boost in the formation of effective immune responses against HIV-1 [148].

Making a nanovaccine effective enough to minimise sickness and death worldwide has been and continues to be a primary objective of the scientific community. Various approaches have been tried to determine which immunogen could be most effective. This conversation has been more challenging due to several factors, including the vast diversity of viruses, the lack of information about which immune response is most crucial for preventing infection or eliminating the virus, and the absence of a reliable animal model that accurately mimics HIV-1 infection. Using what we’ve learned over the previous almost 40 years, we’ve developed strategies that may result in a more robust immune response, such as native-like trimers, mosaic sequences, and prime-boost vaccine schedules.

Historically and prospectively, nanotechnology’s primary contribution to vaccine development has been as a vehicle for administering the vaccine. Nanovaccines have been proven to elicit better immune responses than soluble protein alone in numerous preclinical and clinical testing. Even if this strategy has been applied to HIV-1 research, there is still a long way to go. Modern antigen production methods, such as the native-like SOSIPs and mosaic vaccines, can and have been implemented using a variety of NPs. Depending on the particle's size, shape, or chemical composition, nanotechnology can be used to establish a direct connection with specific types of cells. It is possible to create nanovaccines that transport targeted epitopes in a form mimicking endogenous tissue. Thus, the immune system is freed up to respond more effectively to actual threats by reducing responses that aren’t necessary or helpful. Nanovaccines will play an increasingly important part in their development as technology advances.

Nanovaccines are a broad and complex topic with many subfields. The ideal antigen or immune response cannot be achieved with a single NP. There are a lot of factors to consider while deciding how to manufacture nanovaccines. To think of it as simply attaching an antigen to a pre-existing NP is to miss the point of this dynamic process. Antigen, carrier, adjuvant, and vaccine formulation are all optimized throughout the course of a series of steps. Biophysical tuning of the NP and antigen(s) is required to ensure that the antigen is displayed accurately, that the ideal density and distance are attained, and that the formulation is stable and immune stimulating. A successful nanovaccine formulation is impossible without first resolving all of these concerns. Multiple examples suggest that prime-boost techniques may be the wave of the future for nanovaccines. Because of this, nanovaccines can play a crucial role as either the “prime” or the “boost”. Making antibodies targeting a specific region requires first priming the immune system with a larger antigen, such as a SOSIP on a NP, and then boosting with parts of the antigen, such as the native-like presentation of the V2 loop, on a well-crafted NP. This method can also be used to produce a more effective vaccination against HIV-1 by using boosts from many HIV-1 strains.

It is expected that within the next five years, a significant number of HIV-1 vaccines will be manufactured using nanovaccines. There are still many avenues open for exploring and employing nanovaccine technology, in addition to exploring and employing new antigens and methods of delivering vaccinations. It’s evident that vaccinology has entered a new era with the advent of mRNA vaccines. NPs are essential for administering mRNA vaccines and their use is expected to increase in the next years. Although mRNA vaccines have been demonstrated to be effective against COVID-19, it is unclear how long the responses will last. An enhanced immune response may result from combining an mRNA vaccination with a protein boost supplied by NPs. It’s possible that this trend is being observed in the HIV-1 field, where the ever-evolving virus is met with responses based on a variety of antigens.

Antigen cross-presentation is the process by which DCs put antigens from outside the body on major histocompatibility complex (MHC) class I molecules. This activates CD8+ T cells and helps get rid of tumours. DC-mediated antigen cross-presentation is controlled by a number of things, such as the stage of maturation of DCs, co-stimulatory signals, the microenvironment of T-cells, the way antigens are taken into cells, and adjuvants. Recently, the ability of DCs to cross-present tumour antigens may have led to the success of new cancer immunotherapies. Warrier et al. [152] reported recent changes in making new nanovaccines for strong CD8+ T-cell responses in cancer. In this context, recent studies have been focusing on nanocarriers that have been used as antigen cross-presentation-based cancer immunotherapies.

The first step in a cancer-specific, cellular immune response is to have antigen presented to T cells by the most potent APCs—DCs [153]. One of the hardest components of creating a robust T-cell response is spatial and temporal coordination of antigen cross-presentation in APCs after innate activation. Luo et al. [154] create a simple nanovaccine from an antigen and PC7A, a synthetic PNP. Despite little systemic cytokine response, this nanovaccine induces a robust cytotoxic T-cell immune response. PC7A NP transfers tumour antigens from the cytosol to lymph node-draining APCs. Type I IFN-activated genes activate surface presentation. This impact is caused by the stimulator of IFN genes (STING), not the Toll-like receptors (TLR) or mitochondrial antiviral-signaling (MAVS) pathway [154].

In melanoma, colon cancer, and HPV-E6/E7 tumour models, nanovaccine inhibited tumour growth significantly. In a TC-1 tumour model, combining a PC7A nanovaccine with an anti-PD-1 antibody resulted in 100% survival after 60 days. Rechallenging these tumour-free animals with TC-1 cells completely inhibited tumour growth, implying the formation of long-term anticancer memory [154].

More studies into cancer therapeutic nanovaccines demonstrate that poor delivery to lymphoid organs causes the immune system to respond slowly to tumours. The rapid growth of tumours demands an effective mechanism, which distributes nanovaccines to lymphoid organs to immediately trigger an immune response. Traditional preventive vaccinations usually form a depot at the injection site to gradually trigger a long-lasting immune response. Optimizing nanovaccine size, shape, charge, colloidal stability, and surface ligands can increase lymphoid organ uptake. Dynamic nanovaccines can precisely target lymphoid tissues. Cai et al. [155] announced nanovaccine delivery strategy progress. It discusses future difficulties and plans [155].

Vaccines are good for public health because they keep people from getting sick by getting the body’s adaptive and innate immune systems ready to fight infection. There is growing interest in priming the host immune system for a thorough and focused antitumor response as we understand more about cancer and how it affects the immune system. NP systems have shown promise as ways to effectively deliver antigens as vaccines or boost immune responses as adjuvants. Several studies have attempted to address the critical physiological processes involved in vaccine delivery, current breakthroughs in the use of NP systems for vaccinations, and the issues that must be resolved before NP-based vaccines and adjuvants may be utilized by the general public [156].

Small antigens, like proteins, peptides, or nucleic acids, are used in vaccinations to wake up the immune system and get it to respond in a way that protects against a pathogen. Instead of regular vaccines, scientists are working on nanovaccines right now. Nanovaccines are between 10nm and 500 nm in size, which makes them easy for cells to take up and gives them a better safety profile. But low-level immune responses, such as the removal of redundant pathogens, activate the immune system in a way that isn’t helpful and can be hard for APCs to recognize and take up (APCs). Also, toxicity can be a big problem. Cell-penetrating peptide (CPP)-mediated vaccine delivery systems based on nanotechnology have been proposed to solve these problems. Most of these systems are meant to improve the stability of antigens in vivo and their delivery into immune cells. Antigen delivery systems that include CPPs are very appealing. So, the unique ability of CPPs to translocate makes them an attractive carrier that can deliver cargoes in an efficient way. This makes them useful for delivering drugs, genes, proteins, and DNA/RNA vaccines. CPP-mediated nanovaccines can make it easier for APCs to take in antigen, process it, and show it to the immune system. These are the main steps that start an immune response. This article looks at the different ways CPP-based nanovaccines can be given to people [157].

Viruses, microscopic disease-causing agents, are primarily proteins and nucleic acids. Long-term selection has improved animals’ viral defenses. The immune system can recognize viral proteins and sequence-specific nucleic acids like CpG ODN, single- and double-strand RNA, making virus removal easier. Researchers aimed to develop a cancer-fighting nanovaccine. Immunology inspired this notion. This nanovaccine is mostly made of nucleic acids (CpG ODN), proteins [including tumour-associated antigen and neutravidin (nAvidin) as skeleton materials for building nanovaccines and carriers for loading tumour-associated antigen and CpG ODN], and dye molecules for assembling nAvidin into virus-sized NPs and tracking the vaccine in vitro and in vivo. In vitro, the nanovaccine stimulates DC maturation, antigen cross-presentation, and cytokine production. In vivo, it targets lymph nodes, offers antigens to produce tumour-specific CD8+ T cells, and induces a Th1-biased immune response. Most crucially, this virus-like nanovaccine reduces antigen-expressed tumour growth and helps mice with tumours live longer [158].

Larrouturou [159] says that having a sense of ethics is what makes us openly argue about the moral basis of our findings, turning the scientist back into a concerned citizen. In nanoscience, the idea of conquering complexity at a microscopic scale is sometimes used to scare people. Even if their concerns aren’t valid, scientists have a moral duty to talk about ethics in public. The first step in this argument is to admit that there is a huge gap between what is known about a few nanometric functions and what is known about life as a whole.