1. INTRODUCTION
Since Edward Jenner’s pioneering use of cowpox virus in 1796 to immunize against smallpox, vaccination has remained a cornerstone of disease prevention and worldwide public health endeavours [1]. To date, vaccines against over 30 infectious diseases have received a license in a global perspective, with more than 70 different types of formulations currently in clinical application [2]. Despite these achievements, the development of effective vaccines against complex pathogens and non-infectious diseases is highly demanding in the current scenario and remains a significant challenge. Prominent instances include the continued inability to develop an effective vaccine against malaria, tuberculosis, and human immunodeficiency virus [3–5]. Moreover, the conventional forms of vaccines, such as inactivated, toxoid, or recombinant protein-based approaches, often exhibit inadequate immunogenic responses, necessitating multiple booster doses along with the use of potent adjuvants. It has been seen that the live-attenuated vaccines can induce robust immunogenic responses, but they are associated with safety issues, particularly in immunocompromised individuals. Furthermore, the need for cold chain logistics for several vaccines is an enormous challenge in resource-constrained settings and can present substantial hurdles to the optimum use of vaccines [6,7].
Recent advances in the field of nanotechnology offer transformative solutions to many of the above limitations. Nanoparticles (NPs), generally between 10 and 100 nm in diameter but up to 1,000 nm in certain applications, can be engineered to possess tunable physicochemical properties like size, morphology, surface charge, and functionalization. These are the primary determinants of a number of biological functions, including lymphatic drainage, cellular uptake, endosomal escape, and immune cell targeting [8]. A broad array of nanocarriers, such as liposomes, dendrimers, micelles, carbon-based structures like fullerenes and nanotubes, and metallic NPs, have been investigated for vaccine delivery applications. Depending on their structural organization and chemical composition, these carriers can function as either delivery carriers or intrinsic immune potentiators [8,9].
In the context of vaccination, NPs play two important roles. On the one hand, they serve as carriers for passive or active immunization by protecting antigens from degradation, enhancing uptake by antigen-presenting cells (APCs), and enabling the co-delivery of molecular adjuvants Figure 1 [8–10]. On the other hand, some nanomaterials have an inherent immunostimulatory nature, which allows them to function as a self-adjuvanting platform that can stimulate pattern recognition receptors (PRRs) such as toll-like receptors (TLRs) and cyclic good manufacturing practice (GMP)-AMP synthase-stimulator of interferon genes (STINGs) pathways [11,12]. Numerous nanovaccine preparations, particularly those intended as preventive measures against infectious agents, have either received regulatory approval for human use or are in advanced stages of clinical evaluation, while therapeutic nanovaccines are concurrently being explored for potential applications in cancer, Alzheimer’s disease, hypertension, and addiction disorders [13].
 | Figure 1. Mechanism of nanovaccine-mediated antigen-specific immune response activation for tumour immunotherapy. Following subcutaneous or intradermal administration, nanovaccines carrying TAAs (Antigen 1, 2, 3) and adjuvants are taken up by local antigen-presenting cells (APCs), including immature DCs, at the injection site. These APCs transport the nanovaccine payload to the draining LNs via afferent lymphatic vessels. Within the LNs, immature DCs undergo maturation and present processed antigens on MHC molecules to naïve T cells, accompanied by co-stimulatory signals (e.g., CD80/CD86-CD28 interaction). This antigen cross-presentation results in the activation and proliferation of antigen-specific effector T cells and memory T cells. Subsequently, these activated T cells migrate to tumour sites, infiltrate the TME, and mediate antigen-specific tumour lysis, contributing to effective cancer immunotherapy. [Click here to view] |
Cancer progression is often associated with the induction of complex immunosuppressive mechanisms that enable tumour cells to evade host immune surveillance. These mechanisms include the overexpression of inhibitory immune checkpoints, recruitment of regulatory T cells (Tregs), accumulation of myeloid-derived suppressor cells, and secretion of immunosuppressive cytokines within the tumour microenvironment (TME) [14,15]. Moreover, solid tumours can be targeted by modulating HIF-1α signaling through the inhibition of 2-oxoglutarate-dependent dioxygenases, which play a critical role in the stabilization and transcriptional activity of HIF-1α under hypoxic conditions [16–18]. The primary goal of cancer immunotherapy is twofold: to eliminate tumour cells and to reprogram the immune system to adopt a tumour-eradicating phenotype.
Cancer immunotherapy has advanced significantly over the past few decades, incorporating strategies such as high-dose interleukin-2 therapy [16,19], immune checkpoint blockade (ICB) targeting PD-1/PD-L1 and CTLA-4, and adoptive cell transfer, including chimeric antigen receptor T cell therapy [20–22]. Although these strategies have been very successful, especially in haematological malignancies, their success in curing solid tumours is still limited by aspects such as inadequate immune infiltration, antigenic heterogeneity, and an immunosuppressive TME. Against this backdrop, cancer vaccines have again emerged as promising immunotherapeutic regimens, either as monotherapy or as synergistic components in combination therapy. In contrast to traditional prophylactic vaccines, therapeutic cancer vaccines are required to break self-tolerance mechanisms associated with tumour antigens. Conventional methods involving attenuated tumour cells, tumour lysates, or whole-cell vaccines have shown suboptimal efficacy due to inefficient antigen presentation and inadequate immune activation [23,24]. Conversely, synthetic subunit vaccines with well-characterized tumour-associated antigens (TAAs) or neoantigens provide enhanced and improved safety profiles and scalability [25,26]. Nevertheless, their clinical success has been compromised by poor immunogenicity, fast antigen degradation, poor lymphoid targeting, and inadequate induction of cytotoxic T lymphocyte (CTL) responses.
To address these challenges, nanotechnology is increasingly being employed in the design and development of cancer nanovaccines-nanoscale delivery systems engineered to improve pharmacokinetics, biodistribution, and immune activation. Nano-vaccines allow for effective transportation to secondary lymphoid organs, such as lymph nodes (LNs), overcome physiological barriers, safeguard encapsulated antigens and adjuvants from enzymatic degradation, and enable controlled intracellular release within APCs [26–28]. Importantly, nanovaccines are capable of facilitating cytosolic antigen delivery, which enhances major histocompatibility complex class I (MHC-I) presentation and promotes robust activation of CD8+ T cells. These systems can be designed for in vivo administration to stimulate endogenous phagocytic cells [e.g., dendritic cells (DCs)] or for ex vivo loading of immune cells, followed by reinfusion, a strategy increasingly employed in personalized immunotherapy [29]. This review provides a comprehensive overview of nanovaccine development in the context of cancer immunotherapy. Emphasis is placed on precision nanovaccine platforms, modulation of the TME, and insights from current clinical trials, highlighting their transformative role in the future of oncological treatment given their multifaceted potential.
While many existing reviews broadly cover nanovaccine applications in immunotherapy, this manuscript offers a uniquely focused perspective by synthesizing emerging insights into LN-targeted delivery, molecular vaccine engineering, and intracellular antigen trafficking-particularly within the scope of precision cancer immunotherapy. Rather than reiterating platform overviews, this review underscores the synergistic relationship between physicochemical nanoparticle design (e.g., size, charge, and surface functionalization) and immunological outcomes such as T-cell priming and antigen cross-presentation. Furthermore, it brings attention to novel and underexplored strategies, including albumin-mediated in vivo nanovaccine formation, sHDL nanodisc-based antigen delivery, and nanocarrier-enabled mRNA vaccines. This review aims to offer a strategic framework for the rational design of next-generation nanovaccines with enhanced efficacy in cancer immunotherapy through integrating current experimental advancements with translational challenges.
2. MECHANISMS OF ANTIGEN DELIVERY AND IMMUNE TARGETING
Nanotechnology represents one of the most promising uses in drug delivery. It is essential to target the appropriate location with an antigen during the immune response, just after the vaccination. In contrast to other drug delivery methods targeting particular cell types, antigen vaccine logistics involves spatiotemporal interactions among many cells, including APCs, B cells, different T cells, macrophages, and neutrophils. Additionally, the abovementioned connections are more likely to occur in a particular tissue or region, thus complicating antigen delivery. Consequently, several innovative strategies have been implemented in nanovaccine design, including overcoming biological barriers, enhancing LN trafficking, regulating antigen release, targeting antigen-presenting cells, and facilitating cross-presentation [30,31].
Prolonged antigen persistence or less unnecessary antigen degradation may enhance immune response, as shown by several studies. Consequently, researchers have focused on the linkage or encapsulation of antigens inside NPs to enhance antigen retention at injection sites, lymphoid organs, and APCs. The substantial presence of immune cells in LNs makes LN administration extremely desirable for its structural characteristics and for sustaining neural stimulation antigen in the milieu. Researchers have to alter multiple physical features of NPs, including charge, shape, size, and adaptability, to enhance LN targeted delivery techniques. Presently, APCs could only produce a tiny amount of antigen to the LNs at the injection site; in terms of improving LN delivery systems, researchers must tweak innumerable physical attributes of NPs, including charge, shape, size, and versatility. LNs have been shown to effectively drain NPs smaller than 100 nm, indicating that nanoparticle size must be carefully optimized to enhance LN-targeted delivery. Owing to the negatively charged and porous structure of the mucin glycopolymer framework, the size and surface characteristics of NPs play a crucial role in determining their mucosal transport efficiency.
NPs smaller than the epithelial barrier and below the cationic threshold (typically under 200 nm) exhibit enhanced potential for mucosal penetration. Once antigens are delivered to their target tissues, effective internalization, processing, and presentation by APCs are essential to elicit a strong immune response. To optimize this process, researchers strategically modify the physicochemical properties of NPs, such as size, shape, and surface charge, to improve antigen uptake by APCs and enhance immunogenicity. In particular, DCs show preferential uptake of NPs within the 20–200 nm range. Furthermore, functionalizing NPs with specialized ligands, such as C-type lectin receptor-targeting moieties, can facilitate selective delivery to DC subsets. Additionally, multivalent antigen designs have been shown to improve antigen recognition and stimulate B cells another key subset of APCs, thereby further strengthening the immune response [31,32].
3. KEY COMPONENTS OF CANCER NANOVACCINES
To produce optimum antitumour immunity, both adjuvant and antigen are required. Antigen-specific immune responses are potentiated by adjuvants, which produce powerful innate and adaptive immunity. While soluble subunit antigens are only modestly immunogenic on their own, adjuvant treatment in combination with subunit antigen can drastically increase immunogenicity.
Pathogen-associated molecular patterns (PAMPs) have been proposed for use in nanovaccines as part of the initial phase of molecular combination therapies, where they can recognize cell surface receptors on various immune cells and trigger immunological responses. Examples of PAMPs that can be delivered via nanovaccines include cytosine-phosphate-guanosine oligonucleotides [CpG ODN (TLR9 agonist)], monophosphoryl lipid A (TLR4 agonist), R848 (TLR7/8 agonist), and cyclic diguanosine-monophosphate (cdGMP), an agonist of the STING pathway [33]. Figure 2 depicts the method of CpG ODN producing innate and adaptive immune systems, whereas Table 1 lists the different kinds of CpG.
 | Figure 2. Immunostimulatory mechanism of CpG ODNs in nanovaccines. CpG ODNs activate B cells and plasmacytoid dendritic cells (pDCs) via TLR9, leading to the secretion of IgM, proinflammatory cytokines (IL-6, IL-10, and IL-12), and type I interferons (IFN-α/β). This promotes innate immune cell activation and drives adaptive immunity by inducing Th1 cell differentiation, IFN-γ production, plasma cell maturation, and CTL activation, collectively enhancing antigen-specific immune responses. [Click here to view] |
Table 1. Comparison of types A, B, and C CpG ODNs.
| CpG type | Typical sequence | Structural feature | Immunomodulatory activity |
|---|---|---|---|
| Type A | GGGGGACGA TCGTCGGGGG | Poly-G sequence at the 3′ and/or 5′ termini. The CpG flanking location constitutes a palindrome. A backbone partly changed by PS. GC dinucleotides embedded inside the phosphodiester backbone. | Effectively stimulates pDCs to release interferon-alpha. Facilitates antigen-presenting cell maturation. Minimal impact on the activation of β-cells. |
| Type B | TCGTCGTTTT GTCGTTTTGT CGTT | A complete PS linearized backbone. | Significantly promote β-cell proliferation and pDCs maturation. Gently stimulate pDCs to release IFN-α |
| Type C | TCGTCGTTCG AACGACGTTG AT | A complete PS backbone. CpG has palindromic motif. | Robust stimulation pDCs to release IFN-α. Promotes the activation and proliferation of β-cells. |
Nanovaccines play a pivotal role in enhancing cancer immunotherapy by facilitating the targeted delivery of tumour antigens to LNs, where they can efficiently prime T-cell-mediated immune responses. LNs are rich in APCs, such as DCs, which process and present these antigens to naïve T cells, thereby initiating a robust adaptive immune response [34]. Specifically, subunit tumour antigens, representing the minimal immunogenic epitopes of larger tumour-associated proteins, have been employed to elicit targeted T-cell responses with reduced off-target effects. However, these subunit vaccines often exhibit limited immunogenicity due to poor antigen stability and inefficient delivery, making nanovaccine platforms essential for enhancing their therapeutic potential [13,28].
Over the past two decades, TAAs-antigens that are overexpressed or aberrantly expressed in tumour cells have been extensively investigated in both preclinical and clinical settings. Although TAAs have been used to stimulate immune responses, their effectiveness is often compromised due to central tolerance mechanisms, which reduce the pool of TAA-specific T cells during immune development to prevent autoimmunity [24]. Additionally, tumour cells may undergo immunoediting, a process in which immunogenic antigens are selectively lost or downregulated to escape immune surveillance, leading to diminished T-cell responses [35].
To overcome these limitations, personalized cancer immunotherapy has increasingly focused on neoantigens, which are novel, tumour-specific antigens that arise from somatic mutations and are absent in normal tissues. These neoantigens are not subject to central tolerance, making them highly immunogenic and ideal targets for individualized cancer vaccines delivered via nanocarriers [25,26,36]. In this context, the integration of nanotechnology not only enhances antigen delivery and presentation but also supports the co-delivery of adjuvants, leading to a more effective and durable antitumour immune response.
4. NANOMATERIALS FOR LN-TARGETED VACCINE DELIVERY
Nanovaccines enhance vaccine delivery efficiency to LNs by modulating immune responses through interactions with LN-resident lymphocytes. In contrast, subunit vaccines administered intramuscularly or subcutaneously tend to diffuse quickly into peripheral blood vessels, resulting in systemic distribution but limited accumulation in secondary lymphoid organs, thereby reducing therapeutic efficacy. To address this limitation, over 100 federally registered clinical trials have been conducted. Montanide (an adjuvant) is a water-in-oil emulsion that forms depots at the injection site and enhances antigen immunogenicity [37]. The fundamental mechanism through which it performs its efficacy remains unclear and uncertain as well and the material’s therapeutic outcomes have been inadequate and unsatisfactory. According to a recent study, mice administered the Montanide-emulsified short subunit melanoma antigen vaccine experienced T cell apoptosis instead of tumour infiltration because a significant percentage of antigen-specific T cells, which are essential for tumour immunotherapy, were trapped in the vaccine’s intravenous depot. Research has been conducted on nanovaccines for LN-targeted vaccine administration to enhance the therapeutic effectiveness. The pressure differential between the blood and lymphatic vessels facilitates the effective transport of interstitial NPs from the lymphatics to LNs. Among all draining LNs, tumour-draining LNs are especially noteworthy for nanovaccine delivery in tumour immunotherapy [38–47].
Associated with immune regulatory oversight connected by the downstream tumour, tumour-draining LNs are immunosuppressive; however, these LNs can be easily exposed to the entire tumour-specific neoantigen, and can greatly stimulate the immune microenvironment by the administered nanovaccine [48]. LN-targeted nanovaccine delivery efficiency may be influenced by size, electrostatic current, hydrophobicity, and flexibility. NPs under 5nm easily enter the bloodstream; those 5–100nm efficiently reach LNs via lymphatics, while larger particles (\~100nm) are often taken up by migratory interstitial cells [34].
NPs made from organic and inorganic materials are the predominant synthetic NPs investigated for vaccine delivery. Hexagonal nucleic acids, including a gold nanoparticle core and a CpG shell, an agonist of TLR9, were engineered to effectively transport immunomodulatory agents, resulting in decrease of development of tumours. Organic NPs composed of lipids or polymers may be used as vaccine carriers in many manners [49]. An injectable nanovaccine using large (~350 nm) porous silica NPs (PS3) effectively delivers cancer antigens to APCs, forming an antigen depot and inducing strong tumor-specific immune responses, resulting in significant tumor regression in both preventive and therapeutic models [50].
Liposomes containing the potentially effective immunostimulatory adjuvant cdGMP greatly increased the effectiveness of LN-targeted dosage [51]. Transporting free cyclic dinucleotides into LNs is difficult because of their tiny molecular size, hydrophilicity, and vulnerability to nuclease damage. The advancement of cyclic dinucleotides as vaccine adjuvants is benefiting from improved efficiency. Furthermore, the synthesis of a polymer nanoparticle using N-(2-hydroxypropyl) methacrylamide for the delivery of TLR7/8a resulted in a 400-fold increase in efficiency compared to free TLR7/8a, establishing it as a potential nanoplatform for cancer nano vaccine delivery. Scientists have synthesized a DNA inorganic hybrid nanovaccine by amalgamating inorganic compounds reviewed elsewhere [51] with organic scaffolds, incorporating polymeric CpG with non-toxic inorganic elements; the resultant nanovaccine exhibited an extraordinarily high CpG payload, demonstrated resilience to thermal and chemical conformational alterations, and markedly inhibited tumour growth [26].
Natural nanomaterials have a distinct advantage over their synthetic counterparts in terms of biocompatibility with the host body. Researchers demonstrated that both exogenous vaccine and endogenous protein-based nanocomplexes, high-density lipoprotein NPs, and cell membrane cloaking NPs [52] have been demonstrated to spontaneously generate nanomaterials. Exogenous vaccines have been combined with endogenous proteins to form nanocomplexes in vivo. Unlike externally engineered nanocarriers, molecular vaccines designed to align with physiological and pharmacological parameters offer significant advantages, including simpler synthesis, easier quality control, and compliance with GMP standards. This strategy enables the in vivo formation of nanovaccines, effectively merging the practicality of molecular vaccine development with the enhanced delivery and targeting capabilities of nanotechnology. These nanovaccines demonstrate improved LN targeting and increased bioavailability, thereby boosting the efficacy of cancer immunotherapy. Furthermore, macromolecules such as immunoglobulin G and albumin exhibit prolonged in vivo half-lives, often exceeding 20 days in humans, due to recycling from endosomal degradation pathways. Molecular vaccines that bind to endogenous albumin, which naturally functions as a carrier for diverse biomolecules and drugs, represent a promising alternative to conventional exogenous nanovaccines. Owing to albumin’s long circulation time and multiple binding sites, albumin-bound vaccines enhance antigen delivery and immune response. Notably, an albumin-binding lipid-conjugated cancer vaccine has shown superior outcomes in T cell activation and tumour suppression compared to unmodified vaccines [26,53].
5. NANO VACCINES CO-DELIVER ADJUVANT AND MULTI-EPITOPE ANTIGEN
Nanovaccines are used to deliver antigen and activator to APCs, resulting in strong T-cell activation for tumour immunotherapy and efficient antigen cross-presentation. The same APCs may receive adjuvant and antigen via separate or identical nanocarriers NPs can be carefully manipulated to achieve a certain antigen-to-adjuvant ratio. The tumour evolves to prevent the expression of the same antigen on tumour cells as a result of selection pressures from antigen-specific immunity. For tumour immunotherapy to be effective, multiepitope antigens must be administered to elicit a wide range of T-cell responses. Nanovaccines may be used for the programmed delivery of multiepitope antigens. Working with immune checkpoint inhibitors against PD-1 and CTLA-4, sHDL nanodiscs have been developed to codeliver CpG adjuvant and neoantigen. This led to a 31-fold increase in the antigen-specific T-cell response and the complete removal of most established tumours when compared to Montanide (CTLA-4). The aforementioned nanodiscs may carry multiepitope antigens, resulting in a rather wide T-cell antibody response and an increased incidence of complete regression in the therapy of malignant B16F10 murine melanoma [26].
6. INTRACELLULAR DELIVERY OF NANOVACCINES
Numerous inert ingredients of vaccines are made from infections’ “danger signals”, which identify PRRs on APCs and augment the immunogenicity of antigens for cancer immunotherapy. In order to attach to intracellular PRRs and activate downstream signal transduction for effective immunomodulation, these adjuvants must be supplied intracellularly. Nanovaccines closely resemble microbial illnesses, facilitating their entry into antigen-presenting cells more effectively than free molecular vaccines, therefore making them attractive for intracellular adjuvant delivery. A diverse array of nanovaccines has shown the capability of delivering molecular additives intracellularly. CpG may be transported to the endolysosomes of antigen-presenting cells via a nanovaccine, where it is detected by TLR9, initiating the immunostimulatory response. Moreover, nanocarriers can effectively deliver cyclic dinucleotides into the cytosol, enabling these cytosolic agonists to interact with STING and stimulate the synthesis of cytokines, including type I interferon (Fig. 3). Combination intracellular delivery therapy offers numerous advantages, such as multivalent combination therapy dependent on receptors (when an aptamer is affixed to the nanovaccine’s surface), generally superior cellular uptake efficiency of NPs compared to free molecular agents, and adjuvant protection through encapsulation within NPs.
 | Figure 3. Sources, adjuvants, antigens, and advantages of nanovaccines [57] . [Click here to view] |
Intracellular antigen delivery is essential for eliciting strong, antigen-specific T-cell responses in cancer immunotherapy. In contrast to adjuvants, antigens rarely bind directly to receptors on APCs and generally necessitate internalization and subsequent intracellular processing. Following uptake, antigens undergo degradation by proteolytic systems and are subsequently transported to compartments where they associate with MHC molecules for presentation, with the exception of minimal epitope subunit antigens. Antigen-MHC complexes are presented to CD8+ or CD4+ T cells through MHC class I or II pathways, respectively. The MHC I pathway involves the processing of cytosolic non-self or altered proteins by the proteasome, their transport into the endoplasmic reticulum via Transporter Associated with antigen Processing, and subsequent loading onto MHC I, which is expressed on all nucleated cells and platelets. These complexes are subsequently presented APCs to activate CD8+ T cells, facilitating the recognition and destruction of infected or malignant cells. In the MHC II pathway, APCs internalize extracellular antigens, process them within endocytic compartments, and present them through MHC II molecules to CD4+ T cells, thereby addressing extracellular threats [54,55]. In contrast to extracellular soluble antigens, antigens on extracellular micro/NPs or microorganisms engulfed by APCs undergo cross-presentation, wherein internalized antigens are processed intracellularly, loaded onto MHC I, and presented to CD8+ T lymphocytes. Consequently, nanovaccines have been thoroughly investigated for antigen delivery, cross-presentation, and the induction of CD8+ T-cell responses, all of which are essential for cancer immunotherapy [55,56].
6.1. mRNA vaccines delivered by nanovaccines
In the cytosol, the translation of mRNA into protein confers many benefits of antigen-encoding in vitro transcribed mRNA vaccines over peptide antigens, DNA vaccines, and viral vaccines, such as less immunogenicity, a lower risk of latent viral infection, and a vigorous T-cell response. To elicit an effective immune response, antigen-encoding mRNA must be delivered to DCs, the specialized antigen-presenting cells. The intricate procedure of ex vivo transfecting DCs with mRNA and then reinjection of these cells into the body limits its widespread practical use; nonetheless, both safety and effectiveness have been demonstrated in human clinical trials, and many products have been marketed. Therefore, in vivo delivery of mRNA to DCs is essential for practical mRNA-based immunisation, but it is fraught with difficulties. To begin with, unaltered mRNA is vulnerable to nucleases found throughout the body.
Secondly, the anionic nature (negative charge) of mRNA, similar to that of other nucleic acids, inhibits its cellular absorption. For ingested mRNA to be translated into antigens, it must first leave the endosome and enter the cytosol. The delivery of naked mRNA intranodally elicits an anticancer T-cell response; nevertheless, its efficacy is rather low, and the process is too complex for practical use. Conversely, nanotechnology offers specific benefits for addressing the challenges associated with mRNA vaccine delivery. Nanovaccines, including mRNA may protect mRNA from RNase degradation while promoting DC uptake; NPs can also be engineered to evade endosomal entrapment via the proton sponge effect. In murine models and human melanoma patients, mRNA lipoplex (RNALPX) was synthesized by amalgamating liposomes with neoantigen-based mRNA. Intravenous administration of RNALPX facilitated efficient mRNA dissemination to lymphoid DCs, subsequently eliciting robust neoantigen-specific T-cell responses. Genome engineering may generate a singular mRNA that encodes many cancer-specific neoantigen epitopes, leading to diverse anticancer T-cell responses upon intracellular neoantigen translation [36,58].
6.2. NPs as a tool for vaccine delivery
Traditional vaccinations are incapable of regulating the dosage and precise administration of the vaccine, leading to indiscriminate dissemination throughout the body. This results in disparate medication doses being administered to cells according to their location. Conversely, nanoparticle (NP)-based drug delivery technologies mitigate this challenge by enabling precise regulation of vaccination distribution. NPs are crucial to the advancement of next-generation vaccines, especially in facilitating controlled release and targeted delivery to specified regions. NPs have two main targeting mechanisms: active and passive. Active targeting entails the functionalization of NPs with targeting molecules (e.g., receptor ligands) that direct them to certain cell surfaces, while passive targeting depends on non-functionalized NPs. Nanovaccine particles may be coated with antibodies to selectively attach to DC receptors, enabling tailored administration [59].
Superparamagnetic iron oxide NPs are extensively used in vaccine administration owing to their distinctive characteristics. These NPs, with diameters between 1 and 30 nm, may be subjected to a magnetic field without residual effects, making them suitable for magnetic targeting. Their ferromagnetic properties, meticulous regulation of pore size distribution, capacity to transport various molecules by surface functionalization, economical manufacture, and robust immunological compatibility are significant advantages in this domain [60]. The accountability of NPs substantiates their use in vaccines administered by unconventional techniques, such as inhalation, topical, or ocular routes, and for the amalgamation of a single particle with several antigens to provide protection against diverse illnesses [61].
6.3. The use of NPs as an adjuvant
In response to the injected antigens, chemical or biochemical additives nonspecifically stimulate the immune system. The following are examples of these additives: cytokines, bacterial derivatives, derivatized polysaccharides, oil emulsions, saponins, nonionic block copolymers, immune-stimulating complexes, liposomes, and NPs. Effective strategies for optimizing nanoscale adjuvanticity and delivery are listed in Table 2. The most frequently employed and authorized adjuvants in vaccines are aluminum-based compounds (alum). However, they are subject to a number of constraints, including the necessity of refrigeration, the inability to elicit the Th1 (cellular immune) response, and the potential for hypersensitivity reactions at the injection site. Additionally, they have low efficacy with peptide vaccines. These challenges underscore the necessity of the development of adjuvants that can effectively resolve them [62].
Table 2. Examples of nanovaccine complexes with their corresponding compounds and adjuvant properties.
| Nanovaccine complex | Compound/Adjuvant properties |
|---|---|
| Self-adjuvating moieties | Self-adjuvant polymeric and hydrophobic amino acids conjugated with antibodies that reduce bacterial load. |
| Trimethyl chitosan, whether used independently or in conjunction with poly (anionic amino acid), has the potential to significantly increase serum antibody levels and improve opsonin-mediated cytotoxicity of nanovaccines. | |
| Biomimetic NPs incorporating receptor phospholipids and nucleotide agonists elicit robust immune responses, presenting a safe, straightforward, and efficient approach to anti-tumour immunotherapy. | |
| Biodegradable polymeric NPs | PLGA and PLA-PEG are copolymers composed of PLA and PEG, supplemented with adjuvant derivatives, which facilitate release during matrix degradation and extend biodegradation duration. |
| A ROS-activated antigen delivery system using three-armed PLGA connected to PEG through peroxalate ester (3s-PLGA-PO-PEG) and PEI as a cationic adjuvant (PPO NPs). | |
| Chitosan derivatives improve mucoadhesiveness, thereby promoting both systemic and local immune responses following nasal vaccination. | |
| Liposome-mRNAs | Antigen immunogenicity can be modified by incorporating lipid moieties into peptide epitopes. |
| IgM modulates recognition of antigen-presenting cells by activation of complement and acts self-adjuvant. | |
| carrier composed of non-encoding RNA associated with mtamine naked I-methylpseudouridine having modified mRNA and small-molecule TLR2 and TLR7 agonists | |
| Lipid-PLGA NPs | Hybrid NPs containing hyaluronic acid (HA) and a cationic lipid and poly(lactide-co-glycolide) acid (PLGA) |
| Nanoemulsion | In vivo, nanoemulsion formed by self-assembly of hyper-branched poly (ethyleneimine) shows superior adjuvant activity compared to traditional and non-cationic adjuvants. |
NPs have been proven in numerous trials to have same, if not more, immune system activation capacity as aluminum-based additives. Even though the actual mechanism underpinning NPs’ adjuvanticity capabilities is uncertain, several theories have been offered. NPs can easily mimic the process of a natural infection by functioning like a virus or bacteria due to their structure and size. Antigen presentation units can start picking up these particles, allowing an immune response to be activated. NPs, which are believed to interact with CD8+ DCs, are considered to activate cellular immune responses. Their size ranges from 1 to 100 nm. The capacity of NPs to migrate from subcutaneous tissue to LNs is a critical characteristic. At this site, the antigen is transported to immune cells, thereby activating the adaptive immune system. Additionally, research indicates that the use of NPs in immunization significantly increases antibody production in comparison to vaccines that do not contain NPs [63].
6.4. Benefits of nanovaccines
Unlike conventional vaccines, which target the entire body, nanovaccines focus on specific regions where infections or maladies can originate. The solubility of hydrophobic compounds is improved by nanoparticle systems, which facilitates transdermal delivery. They also stabilize and protect antigens, including proteins, nucleic acids, and peptides, from degradation, thereby reducing vaccine dosages. Additionally, antigens are protected from gastrointestinal degradation by particle systems in mucosal immunity. These systems have the potential to modulate immune responses and act as controlled repositories for antigens [64]. These particles may have a long-term impact by retaining the antigen at the injection site, progressively releasing it, and extending its availability to immune cells. NPs show better depot effect in comparison to microparticles [65].
Due to the NP’s size mimic to the cellular component, they can enter into cell via endocytosis mechanism. Nanovaccine decorated with antibodies may recognize target cell-specific receptors, allowing for targeted delivery. NPs promote or facilitate antigen absorption and uptake by APCs. Cationic NPs are easily absorbed by macrophages and DCs, which have opposite charges on their membrane surfaces, due to their positive charge. Nanovaccines may circumvent the MHC class 1 barrier, stimulating both the humoral and cellular immune responses, hence enhancing their efficacy compared to conventional vaccinations. They may also access LNs independently of peripheral DCs [66]. Moreover, nanovaccines facilitate administration by direct nasal spray and are more economical than traditional immunization techniques [67]. Table 3 lists the primary cancer immunotherapeutics authorized by the US FDA [68].
Table 3. FDA-approved cancer immunotherapeutic.
| Commercial name | Targets and types | Target disease | Approval date |
|---|---|---|---|
| Ipilimumab | CTLA-4 (mAb) | Advanced melanoma | March-2011 |
| Pembrolizumab | PD-L1 (mAb) | Advanced melanoma and non-small cell lung cancer | September-2014 |
| Nivolumab | Unresectable or metastatic melanoma and non-small cell lung cancer | December-2014 | |
| Atezolizumab | Locally advanced or metastatic bladder cancer Merkel cell carcinoma Urothelial carcinoma and non-small cell lung cancer | October-2016 | |
| Avelumab | May-2017 | ||
| Durvalumab | December-2017 |
7. CLINICAL-STAGE NANOVACCINES: PROGRESS AND CHALLENGES
In recent years, the translation of nanovaccines from the bench to the bedside has gained momentum, with several candidates advancing into clinical trials. These trials reflect both the promise and complexity of nanovaccine development.
One of the most significant successes is BioNTech’s mRNA-based cancer nanovaccine (BNT111), delivered via a liposomal nanoparticle platform, which targets four TAAs (NY-ESO-1, MAGE-A3, MAGE-A4, and TPTE). In a Phase I clinical trial (NCT02410733), BNT111 demonstrated a robust antigen-specific CD8+ T-cell response and partial tumour regression in patients with advanced melanoma [69,70].
Similarly, Moderna’s mRNA-4157/V940, which was developed in collaboration with Merck, combines patient-specific neoantigens with lipid NPs for in vivo delivery. In a recent Phase IIb trial, this nanovaccine showed significant improvement in recurrence-free survival when administered in combination with pembrolizumab in high-risk melanoma patients (NCT03897881) [71,72].
Another promising candidate is DPX-Survivac, a lipid-based nanovaccine targeting the survivin antigen in ovarian cancer. In a Phase II trial (NCT03029403), DPX-Survivac combined with checkpoint inhibitors showed durable disease stabilization and manageable toxicity profiles [73,74].
Despite these advancements, challenges remain. Several trials have reported inconsistent immune responses, partly due to tumour heterogeneity, variability in patient HLA types, and limited lymphoid targeting. For instance, the DC-targeted nanovaccine NCI-4650 (targeting HER2) failed to demonstrate significant benefit in a Phase I trial due to poor in vivo targeting and immunosuppressive TMEs [75,76].
To address these limitations, current strategies focus on multi-epitope loading, co-delivery of adjuvants (e.g., STING or TLR agonists), and TME modulation. Several next-generation nanovaccine trials are now ongoing, including the following:
- Lipo-MERIT (BNT112) in prostate cancer (NCT03890163)
- mRNA-5671 (KRAS vaccine) for solid tumours (NCT03948763)
- PRGN-2012, a gorilla adenovector-based therapeutic vaccine for HPV-associated cancers (NCT04724980)
Collectively, these clinical efforts underline the growing maturity of nanovaccines as a therapeutic class and highlight the importance of rational design, personalized antigen selection, and combinatorial immunotherapy approaches.
8. COMPARISON OF NANOVACCINES WITH OTHER EMERGING IMMUNOTHERAPEUTIC PLATFORMS
In recent years, diverse vaccine delivery platforms have emerged as powerful tools in cancer immunotherapy. While nanovaccines offer controlled release, improved lymphoid targeting, and co-delivery of antigens and adjuvants, other platforms, such as viral vectors, cell-based vaccines, and next-generation adjuvants, also show unique advantages.
Viral vector-based vaccines, such as adenoviral or lentiviral vectors, deliver antigen-encoding genes directly into host cells, leading to robust intracellular antigen expression and MHC-I-mediated CTL responses Table 4. However, pre-existing immunity to viral capsids and concerns about insertional mutagenesis may limit their repeated use or long-term safety [77]. Another viral-based nanovaccine (PLGA@hdCVB3I4T1M), combining heat-deactivated CVB3 and membranes from infected cancer cells, enhances immune activation, reduces tumor immune evasion, and shows potent antitumor effects, especially when combined with oncolytic virotherapy, offering promising clinical potential [78].
Table 4. Summarizes the key features of these immunotherapeutic delivery platforms in comparison with nanovaccines.
| Platform | Delivery mechanism | Advantages | Limitations | Applications |
|---|---|---|---|---|
| Nanovaccines | Nanocarriers for antigen/adjuvant delivery | Controlled release, LN targeting, cold chain-free, co-delivery capability [13,26,27] | Manufacturing complexity, in vivo translation is still limited [26,28] | Cancer, infectious diseases, autoimmune disorders [13,28] |
| Viral vector vaccines | Gene delivery via modified viruses | High transfection efficiency, and strong CTL response [77] | Pre-existing immunity, insertional mutagenesis risk [77] | Cancer, COVID-19, gene therapy [77] |
| Cell-based vaccines | Ex vivo antigen loading in APCs (e.g., DCs) | Personalized, high specificity [79] | High cost, patient-specific, and regulatory hurdles [79] | Cancer (melanoma, glioblastoma) [79] |
| Cancer cell membrane NPs | More potent antitumour response | High cost, patient-specific, and regulatory hurdles | CD8+ cancer cells [81] | |
| Next-gen adjuvants | PRR agonists (e.g., STING, TLRs), cytokines | Potent immune activation, can enhance the efficacy of existing vaccines [12,33] | Systemic toxicity, and instability without carrier [12,33] | Cancer, and viral infections [12,33] |
Cell-based vaccines, particularly DC-based approaches, involve the ex vivo loading of patient-derived DCs with tumour antigens or nucleic acids before reinfusion. These vaccines offer high specificity and individualized therapy but they are costly, labor-intensive, and challenging to scale [79].
Next-generation adjuvants, including STING agonists, TLR ligands, and cytokine mimetics, aim to elicit more targeted immune activation and are often incorporated into nanocarriers to enhance delivery and reduce systemic toxicity [8,12]. A next-generation nanoparticle vaccine platform co-delivers peptide neoantigens with synergistic adjuvants (cGAMP and MPLA), enhancing DC activation, CD8+ T cell response, LN targeting, and improving ICB efficacy for cancer treatment [80].
Nanovaccines can be used in synergy with these platforms. For instance, nanocarriers are increasingly being employed to deliver mRNA, DNA, or adjuvants within viral or cell-based systems to enhance antigen presentation, reduce off-target effects, and improve stability.
9. LIMITATIONS AND CHALLENGES OF NANOVACCINES IN CANCER IMMUNOTHERAPY
Despite the promising advancements in nanovaccine technologies, several limitations hinder their widespread clinical translation. One of the foremost challenges is the complexity of manufacturing and scalability. The reproducible synthesis of nanocarriers with uniform physicochemical properties, such as size, charge, and surface functionality, is essential for regulatory approval but remains technically demanding and cost-intensive at scale [26,27].
Another significant concern is potential immunotoxicity and long-term safety. Although nanomaterials are often designed to be biocompatible, their interaction with immune cells can trigger unintended immune activation or suppression, leading to off-target effects or immune tolerance. Additionally, some nanoparticle formulations may accumulate in the liver, spleen, or kidneys, raising concerns about systemic toxicity and organ burden following repeated dosing [13,28].
The heterogeneity of the TME presents another barrier. Tumour tissues vary greatly in their vascularization, extracellular matrix density, and immunosuppressive cell populations, which can impede nanovaccine penetration and antigen presentation efficiency. Moreover, the risk of central immune tolerance in the case of TAAs, and the rapid mutation and immunoediting of tumour neoantigens, can reduce vaccine efficacy and demand personalized design strategies [64,65].
Regulatory hurdles further complicate clinical translation. Regulatory agencies require rigorous preclinical and clinical data for nanomedicines, and there is still a lack of standardized protocols for evaluating nanovaccine efficacy, biodistribution, and immunogenicity [13,28]. Finally, the cold-chain requirements and stability issues for certain formulations, especially those involving mRNA or labile proteins, may also limit their accessibility in low-resource settings despite advances in nanoparticle stabilization [7,35]. Therefore, while nanovaccines hold transformative potential in oncology, overcoming these multifaceted challenges will be key to their successful clinical implementation.
10. CONCLUSION
Nanotechnology is increasingly being employed in a variety of medical fields, leading to the creation of nanovaccines. Due to their numerous advantages, nanovaccines have aroused researchers’ curiosity, boosting hopes for the development of more effective and less hazardous vaccines. Furthermore, several studies are being done in order to develop vaccines for cancer, hypertension, and Alzheimer’s medical interventions.
Vaccines provide considerable promise for cancer immunotherapy, used either alone or in conjunction with therapies including chemotherapy, radiation, and surgery. Subunit vaccines, consisting of antigen-containing components, may elicit antigen-specific T-cell responses and are readily amenable to mass production. Nevertheless, their clinical effectiveness has been limited, mostly because of suboptimal delivery. Emerging technologies, such as nanotechnology, provide prospective answers by improving the targeted delivery of subunit vaccinations to secondary lymphoid organs. Nanovaccines may effectively migrate into LNs via lymphatic channels, circumventing quick distribution into the circulation and facilitating extended engagement with immune cells. They may provide tumour antigens, active drugs, and multiepitope antigens, provoking a comprehensive T-cell-mediated anticancer response with low immunological tolerance. Furthermore, nanovaccines are efficiently internalized by APCs and may be designed to release adjuvants and antigens accurately inside designated cytoplasmic compartments to enhance immunotherapy results.
The interplay between nanovaccines and immune cells is essential for vaccine effectiveness. The features of NPs, namely type, size, shape, surface charge, and hydrophobicity, profoundly affect their immunological function, including antigenicity, adjuvanticity, and inflammation. These parameters may be customized based on the method of delivery (injection, oral, and inhalation), targeted immune cells, and affected organs to enhance therapeutic efficacy. Despite nanovaccine research being in its nascent phase, with just a limited number of candidates undergoing exploratory clinical trials, this innovative class of vaccines has significant potential for enhancing cancer immunotherapy.
11. ACKNOWLEDGMENT
The authors are thankful to the management of Chandigarh University, Teerthanker Mahaveer University, and GITAM (Deemed to be University) for their kind support.
12. AUTHOR CONTRIBUTIONS
All authors made substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; took part in drafting the article or revising it critically for important intellectual content; agreed to submit to the current journal; gave final approval of the version to be published; and agree to be accountable for all aspects of the work. All the authors are eligible to be author as per the International Committee of Medical Journal Editors (ICMJE) requirements/guidelines.
13. FINANCIAL SUPPORT
There is no funding to report.
14. CONFLICT OF INTEREST
The authors report no financial or any other conflicts of interest in this work.
15. ETHICAL APPROVALS
This study does not involve experiments on animals or human subjects.
16. DATA AVAILABILITY
All data generated and analyzed are included in this research article.
17. PUBLISHER’S NOTE
All claims expressed in this article are solely those of the authors and do not necessarily represent those of the publisher, the editors and the reviewers. This journal remains neutral with regard to jurisdictional claims in published institutional affiliation.
18. USE OF ARTIFICIAL INTELLIGENCE (AI)-ASSISTED TECHNOLOGY
The authors declare that they have not used artificial intelligence (AI)-tools for writing and editing of the manuscript, and no images were manipulated using AI.
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