Polymeric Nanoparticles for Precision Tumor Immunotherapy: Rational Design Strategies and Spatiotemporal Immune Activation

Abstract

Malignant tumors remain one of the most serious challenges to global health. Although chemotherapy and targeted therapy are available treatment options, their effectiveness is often limited by the complexity of the tumor microenvironment (TME). In recent years, immunotherapy has demonstrated significant potential in harnessing the immune system to combat cancer. Polymeric nanoparticles (PNPs) have emerged as versatile platforms for cancer immunotherapy, offering favorable biocompatibility, tunable size, and surface functionalization for targeted delivery. In this review, we critically evaluate PNP design strategies, emphasizing stimuli-responsive release mechanisms that enable spatiotemporally controlled drug delivery within the TME, thereby enhancing efficacy and minimizing systemic toxicity. We further highlight PNP-enabled synergistic therapies, including photodynamic, chemodynamic, and sonodynamic therapies, that induce immunogenic cell death (ICD) and potentiate antitumor immunity, as well as PNP-based vaccines (RNA, peptide, and in situ) that activate dendritic cells (DCs) and cytotoxic T lymphocytes (CTLs). Nevertheless, the clinical translation of PNP-based therapies is constrained by multiple factors, including manufacturing scalability, emulsifier-related toxicity, rapid RES clearance, inherent immunogenicity, and the heterogeneity of the TME. By bridging material engineering with immunological barriers and translational challenges, this review provides a critical framework for designing next-generation PNP immunotherapies toward personalized cancer treatment.

Introduction

Malignant tumors pose a serious threat to global health, resulting in a substantial disease burden.¹ According to the Global Burden of Disease (GBD) 2023, an estimated 18.5 million new cancer cases worldwide in 2023 (95% uncertainty interval (UL): 16.4–20.7), with 10.4 million deaths (9.65–10.9).² Cancer is now the second leading cause of death globally, ranking only behind cardiovascular disease. Despite the clinical efficacy of surgery, radiotherapy, and chemotherapy, these therapies remain limited by drug resistance and poor targeting.³ As research progresses, it is clearly verified that immunosuppression is a key feature of the tumor microenvironment (TME), which is driven by various immunosuppressive cells, signaling molecules and intercellular interactions.⁴ For example, tumor cells upregulate the expression of programmed cell death protein 1 (PD-1) and cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) to trigger immune evasion.⁵ Increased immunosuppressive factors (eg, interleukin-10 (IL-10), transforming growth factor-β (TGF-β)) and decreased major histocompatibility complex (MHC) molecules and interferons-γ (IFN-γ) enable tumor cells to evade immune surveillance and drive T cell exhaustion.⁶ Further, the interaction between cancer-associated fibroblast (CAFs) and immune cells also influence immunosuppressive effect. For example, CAFs can secrete chemokines, including (C-X-C motif) ligand (CXCL) 12 (CXCL12), IL-6, and TGF-β, which hinder both the recruitment and cytotoxic function of CD8⁺ T cells.^7,8 CAFs drive extracellular signal regulated kinase 5 (ERK5) expression and phosphorylation, leading to programmed death ligand-1 (PD-L1) protein synthesis.⁹ A deeper understanding of the complexity of TME enables immunotherapies to modulate anti-tumor immunity, making cancer treatment more precise and effective.

To overcome the challenges posed by immune suppression, studies have focused on immune checkpoint inhibitors (ICIs) and specific tumor antigens, utilizing combinations of cancer vaccines, antibodies, and immunostimulants to reverse the immunosuppressive state.^10,11 It has been found that combining cancer immunotherapy with traditional treatments significantly improves the long-term survival of cancer patients.¹² However, due to the complexity of the TME, tumors would develop drug resistance and off-target adverse reactions, which influence the effect of immunotherapy.^13,14 Furthermore, the dense extracellular matrix and elevated intratumoral pressure hinder effective drug delivery to the tumor site.¹⁵ Notably, ICI therapy faces significant challenges in effectiveness, safety, and side effects, including autoimmune reactions and cytokine release syndrome (CRS).^16,17 The manufacturing complexity and high cost of advanced immunotherapies, particularly chimeric antigen receptor-T (CAR-T) cell products, pose substantial barriers to their widespread clinical adoption.¹⁸ Thus, rational strategies aimed at modulating the tumor microenvironment (TME) are needed to boost immune responses, minimize side effects, and convert immunologically cold tumors into hot ones.

Advanced nanotechnology, particularly nanoparticles (NPs) with unique physical and chemical properties such as nanoscale dimensions and functionalized surfaces, has transformed applications in the biomedical field.^19,20 Currently, various nanocarrier systems-including liposomes, inorganic nanoparticles, dendrimers, and exosomes-are being explored for cancer therapy. However, each system presents distinct limitations: liposomes suffer from insufficient stability and precision; inorganic nanoparticles (such as gold and silicon) are often non-degradable, raising long-term toxicity concerns; dendrimers involve complex synthesis and are difficult to scale up; and exosomes face substantial challenges in isolation, purification, and standardization.²¹ In contrast, polymeric nanoparticles (PNPs) have emerged as highly promising drug delivery platforms, owing to their biodegradability, biocompatibility, and capacity for controlled and targeted therapeutic release.²² Specifically, the chemical composition and structure of PNPs are pivotal in immune regulation. By allowing precise engineering, such as the introduction of specific chemical groups to modulate interactions with cellular membranes, immune receptors, and intracellular signaling, PNPs can be customized to orchestrate antitumor immune responses.²³ The surface of PNPs can be functionalized with targeting ligands to engage specific receptors, enabling precise immune modulation while minimizing off-target effects.^24,25 Furthermore, key physical properties (such as size, shape, and surface charge) of PNPs critically influence their biodistribution and cellular activation efficiency in vivo.²⁶ Thus, engineered PNPs enable precise spatiotemporal and cell-specific delivery of immunologically active factors, thus synchronizing and amplifying the immune response (Figure 1).

Figure 1.

Schematic overview of the immunosuppressive tumor microenvironment, immunotherapeutic strategies, and PNP‑mediated delivery systems.

Although PNPs can improve drug delivery efficiency and reduce side effects, there are still several limitations and challenges. For instance, the inherent complexity of the TME may compromise the immunomodulatory efficacy of PNPs. The use of emulsifiers such as poly (vinyl alcohol) (PVA) in PNP preparation may contribute to toxicity.²⁷ Moreover, the RES can mediate nonspecific clearance of PNPs, thereby reducing their targeting efficiency.²⁸ Additionally, complex synthesis protocols and batch-to-batch variability may hinder large-scale production and regulatory approval.²⁹ Preclinical studies of PNP-based nanoplatforms have shown considerable promise. However, successful clinical translation remains limited, with only a handful of Food and Drug Administration (FDA)-approved products, including leuprolide acetate (PLGA-based leuprolide acetate) and pegaspargase (Oncaspar), which illustrates the gap between discovery and clinical application.^30,31 In this review, we systematically summarized recent progress of PNPs in cancer immunotherapy, discussed the challenges, and explored future directions, providing insights for further research in this field.

Engineered PNPs: Tailoring Properties and Surface Functionality

Types of PNPs Derived from Natural and Synthetic Polymers

Currently, various natural and synthetic polymers are widely employed in the development of nanoplatforms. Commonly used materials include natural polymers, such as chitosan, alginate, collagen, hyaluronic acid (HA), and albumin. The synthetic polymers include poly (ε-caprolactone) (PCL), poly (lactic acid) (PLA), poly (lactic-co-glycolic acid) (PLGA), and Poly (2-Dimethylamino-Ethylmethacrylate) (PDMAEMA).^32,33 Natural biopolymers offer high biocompatibility, biodegradability, and bioactive components. Alginate, an anionic hydrophilic polymer, has abundant hydroxyl and carboxyl (-COOH) groups for functional modification.^34,35 HA and chitosan are widely utilized polysaccharides in nano-drug delivery systems due to their low toxicity and high biodegradability. Chitosan possesses cationic properties, allowing it to complex with negatively charged macromolecules such as nucleic acids through electrostatic binding. A novel chitosan-based polymeric micelle exhibited pH-responsive drug release and actively targeted lymph nodes, thereby enhancing anti-tumor immune responses.^36,37 HA-modified macrophage-mediated system M@C-HA/ICG enhanced tumor-specific accumulation and retention, activated macrophages to release pro-inflammatory factors, and thereby augmented therapy.³⁸

Synthetic polymers are chemically engineered materials designed with customizable properties, such as mechanical strength, thermal stability, and programmable degradability.³⁹ For example, PCL is an ideal material for sustained drug delivery due to its excellent mechanical properties and biocompatible degradation. PCL-based NPs enable prolonged release in cancer therapy by slowly hydrolyzing into non-toxic caproic acid.^40,41 PLA is a chiral polymer existing as two enantiomers: poly (L-lactic acid) and poly (D-lactic acid). The D-form typically degrades faster via hydrolysis of its ester bonds, leading to accelerated drug release.⁴² The PLGA is a copolymer of polyglycolic acid (PGA) and PLA. The combination of high stability, low toxicity, and tunable degradation makes PLGA suitable for NP-based encapsulation of small molecule drugs.⁴³ PDMAEMA is synthesized from dimethylaminoethyl methacrylate, with its ethylamino groups conferring pH-responsive protonation in acidic environments.^44,45 Its cationic property enables nucleic acid complexation, making PDMAEMA a versatile carrier for targeted immunomodulator and gene therapy delivery.

Physicochemical Characterizations of PNPs

To adapt to the complex TME, PNPs must be engineered in size, shape, surface charge, composition, etc (Figure 2). NP size is a key determinant of their interactions with both tumor and immune cells, directly affecting their biological fate through cellular uptake and biodistribution.^46,47 Optimal diameter enables prolonged circulation, effective tumor penetration, high cellular uptake, and evasion of hepatic and immune clearance. Typically, PNPs are characterized by having at least one structural dimension within the 100–500 nm scale. Those with diameters below 200 nm can enter cells via various endocytic pathways, including receptor-mediated endocytosis, membrane fusion-mediated uptake, and phagocytosis. In contrast, particles larger than 200 nm are primarily internalized through phagocytosis, especially by macrophages.⁴⁸ NP shape also affects internalization (phagocytosis vs endocytosis), with spherical and oblate ellipsoids showing higher phagocytic uptake than prolate ellipsoids or non-spherical shapes, due to curvature differences.^49–51 Further, surface charge of PNPs (negative to positive) is tunable via surfactants (eg, Tween, poly (ethylene-alt-maleic anhydride) (PEMA), and PVA).^52,53 The surface charge of PNPs critically influences biological interactions by influencing protein adsorption and cellular uptake.⁵⁴ Positively charged PNPs enter via clathrin-mediated endocytosis but can cause membrane damage, calcium influx, and cytotoxicity, posing acute toxicity risks.^55,56 Neutral or negatively charged PNPs utilize caveolin-mediated endocytosis, correlating with lower toxicity and favorable immunomodulation.⁵⁷ Consequently, precise control over PNPs’ surface charge is crucial for achieving targeted therapeutic outcomes.

Figure 2.

The physical and chemical properties of PNPs and condition-responsive design strategies.

Surface Modification and Delivering Strategies of PNPs

NPs can deliver drugs through strategies such as cell-specific targeting, intracellular transport, and organelle-specific delivery, effectively addressing the limitations of traditional drug delivery systems.^58,59 The evolution of PNPs has progressed through distinct generations. Initially, the first-generation PNPs focused on drug encapsulation and sustained release. Subsequently, the second-generation systems incorporated stimuli-responsive properties (eg, to pH, temperature, or light) to enhance targeted delivery. The third-generation nanocarriers exhibit multifunctionality, integrating features like active targeting and controlled multi-drug release.⁶⁰ PNPs exhibit variable drug delivery capabilities, with drugs being encapsulated within the core of NPs, embedded in the polymer matrix, chemically conjugated to the polymer, or attached to the NP surface (Figure 2).

Surface Modification of PNPs

Surface modification of PNPs is achieved via physical adsorption (van der Waals, hydrogen bonds, hydrophobic interactions, ionic bonding) or chemical covalent conjugation via functional groups (-NH₂, -COOH, hydroxyl (-OH)).^61,62 Physical adsorption relies on charge/polarity interactions; for example, chitosan’s cationic amino groups (-NH₃⁺) electrostatically adsorbs anti-HER2 antibodies onto doxorubicin (DOX)-loaded PLGA NPs.⁶³ Covalent conjugation forms stable bonds through bioreceptor immobilization, linker attachment, or functional group anchoring.⁶⁴ For example, amino-poly(ethylene glycol) (PEG)-azide conjugation to carboxylated polystyrene for enhanced stability. Further, dopamine and chitosan also offer versatile platforms for covalent surface functionalization.⁶⁵

Another approach exploits functional groups (eg, R-NH₂, R-COOH) on NP surfaces for covalent modification. For instance, silicon NPs are functionalized with amino silanes; gold NPs are modified with thiol/amine linkers; and carbon NPs are oxidized to introduce -COOH, -OH, and carbonyl (=C–O).^66,67 Various macromolecules, including cyclodextrin (CD), PAAM, poly (N-isopropylacrylamide) (NIPAAm), and polyacrylic acid (PAA) can be incorporated into PNPs to enhance properties: NIPAAm/PAA confer temperature/pH responsiveness, while CD prolongs circulation.⁶⁸ Varying ligand-polymer contact time regulates PNP thickness, enabling distinct NP properties. Thus, both physical adsorption and active functional group introduction are essential for multifunctional nanoplatforms.

Stimuli-Responsive Factors of PNPs

Incorporating responsive elements into PNPs allows for precise regulation of nanostructures in response to specific stimuli, enhancing the efficacy and safety of drug delivery systems (Table 1).

Table 1.

Stimuli-Responsive Factors of PNPs

Stimuli Type	Mechanism and Materials	Triggering Condition	Reference
pH-Responsive	Acid-labile bonds: Schiff bases, hydrazones, tertiary amines, acetals/ketals; charge-reversal polymers (such as tertiary amine-containing polymers)	Tumor acidity (~pH 6.5) due to lactate accumulation	[69–72]
Enzyme-Responsive	Enzyme-cleavable peptide linkers: MMP-cleavable sequences (MP9), cathepsin B-cleavable GFLG, caspase-cleavable DEVD	Tumor-overexpressed enzymes (MMP-2, cathepsin B, caspase) with high substrate specificity	[73–75]
Redox-Responsive	Redox-sensitive bonds: disulfide (-S-S-), diselenide (Se-Se-)	Elevated ROS (·OH, 1O2, H2O2) and GSH in tumor cells; redox imbalance	[76,77]
Light-Responsive	PS generating ROS upon NIR excitation	NIR laser irradiation	[78–81]
Temperature-Responsive	Thermosensitive hydrogels with LCST behavior	Localized heating at target site	[82,83]

Abbreviations: PS, Photosensitizers; LCST, lower critical solution temperature; NIR, Near-infrared.

pH-Responsive Polymers

Tumor acidity (pH ~6.5) from lactate is exploited by pH-responsive carriers with acid-labile bonds (Schiff bases, hydrazones, tertiary amines, acetals/ketals).^84,85 For example, schiff-base methoxy poly (ethylene glycol)-b-poly (L-lactide) (mPEG-b-PLA) micelles release R837 to upregulate MHC II under acidic conditions.^69,70 A hydrazone‑linked polymer, poly(methacrylic acid‑co‑histidine/doxorubicin/biotin) (HBD), was designed for the co-delivery of doxorubicin (DOX) and imiquimod (IMQ).⁷¹ In acidic TME, tertiary amine polymers undergo charge reversal from negative to positive, causing chain repulsion, polymer dissociation, and release of encapsulated lipophilic drugs for therapeutic action.⁸⁶ A pH-responsive nanogel with acid-labile acetal/ketal cross-linkers (such as 2,2-bis (aminoethoxy) propane) and with Toll-like receptor 7/8 (TLR 7/8) agonists releases drugs under acidic conditions, driving T-cell immunity and degrading into safe excretable products.⁷²

Enzyme-Responsive Polymers

Tumor-overexpressed enzymes (matrix metalloproteinases (MMPs), cathepsin B, caspase) with high substrate specificity enable enzyme-responsive controlled-release systems for targeted delivery. For example, PEG-MP9-aPDL1, a rigid α-helical, protease-resistant, and cytotoxic peptide-polymer conjugate, could be cleaved by MMP-2, leading to favorable pharmacokinetics and ICD induction.⁷³ Another cathepsin B-responsive PEG-lysine dendrimer-gemcitabine conjugate uses GFLG linker for TME-specific accelerated release.⁷⁴ Further, caspases cleave cysteine-aspartate residues to induce cell death, making them promising targets for therapeutic drug development. For example, a micelle co-loading DOX prodrug (DEVD-S-DOX) and photosensitizer (PS) releases active DOX upon caspase-3 cleavage of the aspartic acid-glutamic acid-valine-aspartic acid (DEVD) during apoptosis.⁷⁵

Redox-Responsive Polymers

Tumor cells are characterized by elevated levels of ROS (such as ·OH, singlet oxygen (¹O₂), H₂O₂) and antioxidants like glutathione (GSH). By exploiting the redox imbalance in tumors, redox-responsive NPs have been developed to effectively deliver anticancer drugs as well as minimize off-target toxicity.^87,88 For example, disulfide bonds are reduced by GSH to thiols and oxidized by ROS to sulfoxides/sulfones, enhancing hydrophilicity for targeted release. NLG919 conjugated to PSSN10 via disulfide linkages enables tumor-specific delivery.⁷⁶ Diselenide bonds, with high reduction sensitivity, are also ideal for constructing redox-responsive PNPs to achieve precise and efficient drug release. Messenger RNA (mRNA)-poly (β-amino ester)s (PBAEs) NPs with diselenide bonds exhibit moderate positive charge, optimal size, redox reactivity, and efficient endosomal escape.⁷⁷

Light-Responsive Polymers

PDT has attracted clinical interest for its non-invasiveness and safety.⁸⁹ For example, antibody-photosensitizer (PS) conjugates generate ROS upon near-infrared (NIR) excitation, thereby selectively killing tumor cells and synergistically enhancing PDT with immunotherapy through the induction of immunogenic cell death (ICD).^78,79 Another hypoxia-responsive PNP prodrug co-delivers 5,10,5,20-tetrakis (4-aminophenyl)-porphine (TAPP) and chloramphenicol (CB). Upon laser exposure, TAPP produces ¹O₂ for PDT and creates local hypoxia, promoting CB release and achieving synergistic killing.⁸⁰ Polythiophene based PNPs offer high photostability, low toxicity, and enable two photon imaging and PDT.⁸¹ In summary, stimuli-responsive PNPs constitute a versatile platform for targeted drug delivery, allowing for the controlled release of therapeutics upon exposure to defined biological or physicochemical stimuli.

Temperature-Responsive Polymers

Temperature-responsive drug delivery exploits localized heating at the target site to trigger release. A representative example is the poly (D, L-lactic acid)-polyethylene glycol-poly (D, L-lactic acid) (PLEL) hydrogel, designed for co-delivery of cyclophosphamide (CTX) and cytosine-phosphate-guanine (CpG) in tumor immunotherapy. This system not only stimulated cytotoxic T lymphocytes (CTLs) responses but also induced durable immune memory, thereby preventing tumor recurrence and metastasis.⁸² Further, a PEG-PCL-PLA-PCL-PEG thermosensitive hydrogel has been engineered to elicit antigen-specific immune responses that persist for up to 49 days.⁸³

Delivering Strategies and Advantages of PNPs

A range of nanoplatforms are currently being explored for cancer immunotherapy, each with its own strengths and weaknesses. For example, liposomes are the most clinically established platform, benefiting from their amphiphilic structure and PEGylation for prolonged circulation, but they are hindered by physical instability, complement activation, and accelerated clearance upon repeat dosing.^90,91 Micelles, formed by self-assembly of amphiphilic polymers, offer improved stability over surfactant-based micelles and enable hydrophobic drug loading.⁹² However, their limited loading capacity and tendency for structural dissociation restrict their application in sustained-release formulations.⁹³ Further, exosomes, as natural extracellular vesicles, possess low immunogenicity, good tissue penetrability, and intrinsic targeting.⁹⁴ However, their clinical adoption is constrained by low isolation yields, batch-to-batch inconsistency, and lack of standardized production protocols.⁹⁵ PNPs are characterized by biodegradability, biocompatibility, low toxicity, and a broad drug-loading capacity, making them ideal for therapeutic drug delivery. PNPs offer superior stability and controlled release compared with liposomes; better biocompatibility and surface tunability than metal nanoparticles, thereby minimizing cytotoxicity and immunogenicity; and greater scalability and multifunctionality relative to dendrimers.^96,97 Furthermore, a wide range of agents, including small molecules, biomolecules, proteins, and vaccines, can be loaded into PNPs and administered via multiple routes, such as oral, intravenous, or topical delivery.⁹⁸ These characteristics not only enhance the efficiency of drug delivery and therapeutic outcomes but also reduce side effects.

PNPs modulate antitumor immunity by transforming the TME from immunosuppressive to immunoreactive phenotype through multiple mechanisms. For example, ligand-functionalized or size-optimized PNPs can induce ICD of tumor cells, releasing antigens to prime immune responses.⁹⁹ PNP-based vaccines efficiently co-deliver TAAs and adjuvants to antigen-presenting cells (APCs), minimizing systemic exposure. Furthermore, PNPs act as intrinsic adjuvants by sustaining antigen release, prolonging bioavailability, and enhancing antigen presentation.^100,101 In conclusion, leveraging the properties of PNPs alongside rational delivery design enables effective immune response.

PNPs in Immunomodulation: Mechanisms and Therapeutic Applications

PNP-Mediated in situ ICD Induction and Exogenous Antigen Presentation Strategies

In recent years, tumor vaccines have demonstrated significant application value in modulating the tumor immune microenvironment. However, the effective presentation of TAAs and tumor lysates is often limited by rapid in vivo clearance and insufficient uptake by APCs. Through surface modification and rational design, PNPs can not only induce in situ tumor ICD, leading to the release of tumor antigens and subsequent activation of antitumor immune responses. In situ ICD induction leverages endogenous tumor antigens, thereby circumventing the challenges associated with preparing TAAs or tumor‑specific antigens (TSAs) and enabling personalized cancer therapy.¹⁰² Current strategies for inducing ICD-based immunomodulation include chemodynamic therapy (CDT), PDT, and sonodynamic therapy (SDT), as well as the use of STING pathway agonists to further potentiate immune activation (Figure 3).

Figure 3.

PNP-based strategies for nanomedicine‑assisted immunomodulation: from in situ and mRNA/peptide cancer vaccines to targeting tumor‑infiltrating immune cells, CAR-T and ICIs therapies.

Moreover, PNPs facilitate the precise delivery of antigenic peptides and tumor antigen mRNA to APCs.^103,104 PNPs loaded with immunomodulators, including cytokines (such as IL and IFN) and ICIs (such as PD-1 antibodies), ensure controlled release kinetics and prevent degradation in the bloodstream.^105,106 Furthermore, the combined delivery of immunomodulators with tumor antigens or cancer vaccines activates the immune system through immunomodulators while presenting antigens, thereby enhancing immune response efficiency.^23,107 Simultaneously, this approach minimizes exposure to other tissues, significantly reducing systemic toxicity (Table 2).

Table 2.

Summary of PNP-Based Cancer Vaccines in Tumor Immunotherapy

Strategy	Type of PNPs	Tumor Model	Immune Strategy	Reference
CDT-induced ICD	PEI/CpG/CAD	Melanoma	CAD cleavage within endosomes releases DOX, releases DAMPs; CpG synergistically promotes DC maturation.	[108]
	DR-SIP micelle	BC	ROS‑triggered depolymerization releases DOX, promotes DAMPs release, and DC maturation.	[109]
	PLGA@Icaritin	GC	Induce GC cells to produce ROS, release DAMPs, and induce ICD. Enhance CD4⁺/CD8⁺ T cell infiltration and increase IFN-γ and TNF-α secretion.	[110]
	Poly(fluorescein) aggregates	BC	Activate the BiP-PERK-CHOP signaling pathway to promote the release of DAMPs and enhance the antitumor immune response.	[111]
PDT-induced ICD	MDK-Nb-PCP	PDAC	Photochemical activation generates ROS, inducing tumor cell apoptosis and ICD to reverse immunosuppression; combination with anti-PD-1 prolongs the survival period.	[112]
	WP1066-loaded COP (TVW)	HCC	VK3 blocks glycolysis to alleviate tumor hypoxia and enhance PDT efficacy; WP1066 downregulates STAT3 and PD-L1 expression to inhibit immune escape.	[113]
	NP2	BC	Generate ROS under 808 nm laser irradiation, induce ICD; downregulate MMP expression, inhibiting tumor invasion and metastasis.	[114]
	NP-PDT@Reg	Osteosarcoma	Generate ROS under 808 nm laser irradiation, trigger ICD; Reg reprograms TAMs from M2 to M1 polarization.	[115]
	Polymer@Gef-YAP-siRNA NPs	NSCLC	Gefitinib blocks the EGFR signaling pathway, YAP-siRNA inhibits EGFR bypass signaling pathways activation, and induces tumor cell apoptosis through PDT.	[116]
SDT-induced ICD	GdNPs/Ce6-Ric	BC	Generate ROS under ultrasound, inducing tumor cell apoptosis and releasing tumor antigens; Downregulate the HDAC6/p-STAT3/PD-L1 pathway, increase NK cell and cytotoxic T cell infiltration, and reduce Tregs. Inhibit TGFβ-induced EMT and reduces lung metastasis.	[117]
	EIPS	Melanoma	CatB-responsive release of DPTIP inhibits tumor exosome generation, while ultrasound-induced ICD suppresses 4T1 lung metastasis and establishes long-lasting immune memory.	[118]
	MnPPs	BC	Light/ultrasound dual-response generates ROS, thereby killing tumor cells.	[119]
	SPNH	BC	Ultrasound-mediated SDT effect; generate ROS and heat under 808 nm laser irradiation, achieving synergistic PDT/PTT; inhibits tumor growth and metastasis.	[120]
Stimulate STING Signal Panthway	PSPA	BC	Ultrasound-induced ROS trigger ICD; GSH-responsive release of MSA-2 activates the STING pathway to elevate IFN-β levels, synergistically enhancing antitumor effects with SDT.	[121]
	cGAMP-siPDL1@GalNPs	Melanoma/BC	Triple-Responsive (Light/Redox/pH); activate STING pathway, knock down PD-L1, and induce light-triggered ICD for targeting low-immunogenicity tumors.	[122]
	DPTT-Mn Lipo NPs	BC	PTT induces tumor cell apoptosis and ICD; Mn2⁺ activates the cGAS-STING pathway in macrophages/DCs; combine anti-PD-1 therapy to establish long-lasting immune memory.	[123]
	Mn/OPDMA	HCC/CRC/PDAC	Mn2⁺ enhances the activity of the cGAS-STING pathway, promotes TAM polarization and IFN-β secretion, and prolongs mouse survival.	[124]
PNP-based peptide vaccine	PEG-b-PAsp-g-PBE/TRP2 nanovaccine	Melanoma	ROS/pH dual response promotes DC maturation and MHC I-restricted antigen presentation, activating T cell immune responses.	[125]
	MAN-P micelles	Melanoma	Galactose modification targets APCs, pH-responsive release of antigen peptides; enhance specific T cell responses	[126]
	hr-8-PLGA@Ag/CpG	Melanoma/Cervical cancer	Target the DEC-205 receptor on the surface of cDC1 cells; combine with OVA/gp100/E7 antigens to activate CD8⁺ T cell-mediated antitumor immunity.	[127]
	OVA-CpG Gal/Man-NPs	Lymphomas	Galactose/mannose-modified targeting of DCs; enhance CD4⁺ T cell and IFN-γ levels in spleen, and boost CD8⁺ T cell cytotoxic activity.	[128]
	POx-based nanovaccine	Melanoma/CRC	Chemically conjugate neoantigen peptides to antigen presentation efficiency, activating potent CD8⁺ T cell responses.	[129]
PNP-based mRNA vaccine	R18D NPs	CRC	Through the co-delivery of mRNA, poly(I:C), and CpG, the TLR3/RIG-I pathway is activated to induce type-I IFN secretion and CTL responses.	[130]
	PVES micelles	BC	Vitamin E succinate-modified PEI self-assembles to deliver mRNA; induce potent antibody responses with no significant toxicity.	[131]
	NVs mRNA@LNPs + anti-PD-1 mRNA@LPNPs	PDAC	Pancreatic cancer neoantigen mRNA primes tumor-specific immunity, anti-PD-1 antibody mRNA enables localized checkpoint blockade with minimized systemic toxicity.	[132]
	PHTA-C18	Melanoma	Stabilize mRNA and prolong circulation in vivo, enable efficient delivery to activate CD8⁺ T cell-mediated antitumor immunity.	[133]
	PD18	Melanoma	By delivering mRNA through the lymphatic system, it activates the STING pathway and expands antigen-specific memory CD8⁺ T cells.	[134]
	POctS	Melanoma/PDAC	Deliver mRNA and activate the STING pathway; enabling targeted mRNA release and innate immune stimulation.	[135]

Abbreviations: BC, Breast cancer; PDAC, Pancreatic adenocarcinoma; CRC, Colorectal carcinoma; HCC, Hepatocellular carcinoma; NSCLC, non-small cell lung carcinoma; GC: Gastric cancer.

Induce ICD to Release Endogenous Antigens

PNP-Based CDT Therapy

During cancer treatment, chemotherapeutic agents such as paclitaxel (PTX), oxaliplatin, and DOX induce apoptosis or necrosis in tumor cells. This process not only releases tumor antigens but also triggers ICD, leading to the exposure of damage-associated molecular patterns (DAMPs) that stimulate pro-inflammatory immune responses.^136,137 For example, pH-sensitive cis-aconityl-DOX (CAD) and unmethylated CpG were co-encapsulated in a polycationic polyethylenimine (PEI) carrier to form the PEI/CpG/CAD nanocomplex.¹⁰⁸ CAD was cleaved in endosomes to release DOX, which killed tumor cells and induced DAMP release. Importantly, tumor fragments serve as antigen sources and synergize with CpG adjuvants to promote DC maturation, thereby triggering a comprehensive antitumor immune response. Another ROS-responsive self-immolative polymer (R-SIP) micelle loaded with DOX (DR-SIP) rapidly depolymerized in high-ROS environments, releasing DOX.¹⁰⁹ This release induced ER stress-related cell death via eIF2α phosphorylation and calreticulin overexpression. Simultaneously, DR-SIP triggered the release of DAMPs from dying tumor cells, leading to DC maturation. Additionally, nanocarriers that induce mitochondrial DNA release or activate specific signaling pathways can promote DAMP release, thereby activating antitumor immune responses. For example, PLGA NPs loaded with icaritin (PLGA@Icaritin) generated substantial ROS in gastric cancer (GC) cells, reducing mitochondrial membrane potential and releasing oxidized mitochondrial DNA.¹¹⁰ The oxidized DNA acted as a trigger, promoting DAMP release and subsequently inducing ICD. Notably, PLGA@Icaritin promoted infiltration of CD4⁺ and CD8⁺ T cells into tumors and stimulated secretion of IFN-γ, TNF-α, and IL-1, thereby activating antitumor immunity. Furthermore, leveraging tumor-specific aggregation, L-cysteine synergistically delivers 2-cyanobenzothiazole (CBT) into tumor cells, inducing a condensation reaction that forms poly(fluorescein) aggregates.¹¹¹ Importantly, these aggregates activate the BiP-PERK-CHOP signaling pathway, promoting DAMP release and thereby enhancing the antitumor immune response. Therefore, chemotherapy often fails to induce antitumor immunity effectively; however, nanomedicines activate immune responses by inducing CDT-mediated tumor killing and promoting DAMP release, thereby inducing more powerful antitumor immunity.

PNP-Based PDT Therapy

PDT employs PSs to generate ROS upon light irradiation, which induces endoplasmic reticulum (ER) stress, disrupts mitochondrial and plasma membranes, and triggers tumor cell apoptosis.^138,139 The release of DAMPs from dying cells promotes ICD and stimulates a systemic anti-tumor immune response. For example, Qu et al¹¹² designed a novel photo-responsive semiconducting PNP (MDK-Nb-PCP) that efficiently targeted the TME. Upon photo activation, it generated substantial ROS locally, inducing tumor cell apoptosis and ICD to reverse immunosuppression. When combined with PD-1 checkpoint blockade, MDK-Nb-PCP significantly prolonged survival in mice. A pH-sensitive covalent organic photosensitizer (COP) was constructed by combining a porphyrin photosensitizer with the pyruvate kinase inhibitor vitamin K3 (VK3). The signal transducer and activator of transcription 3 (STAT3) inhibitor WP1066 was further encapsulated within this COP to form the WP1066-loaded COP (TVW).¹¹³ Experimental results showed that VK3 reduced oxygen consumption by blocking glycolysis, alleviated tumor hypoxia, and enhanced PDT via ROS generation. Meanwhile, WP1066 downregulated STAT3 and PD‑L1 expression, inhibiting immune escape and amplifying antitumor activity. The synthesis of NIR-activated photosensitive polymers represents a significant advancement, as their ability to achieve targeted delivery enhances the precision and efficacy of PDT. For example, a near-infrared (NIR)-activatable photosensitizing polymer (NP1) was synthesized from AIE-OH (M1), 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride (M2), and 2,2’-(propane-2,2-diylbis(sulfanediyl)) bis(ethan-1-ol) (M3). Then, the side chain of NP1 was grafted with the anti-metastatic ruthenium complex NAMI-A to yield NP2.¹¹⁴ Under 808 nm light, NP2 generated ROS to kill tumor cells and induce ICD. Moreover, NP2 downregulated matrix metalloproteinase (MMP) expression, suppressed tumor cell invasion and migration, and inhibited liver and lung metastases. A synthetic NIR-II biodegradable pseudo‑conjugated PNP (NP-PDT@Reg) co-delivered the vascular normalizer regorafenib (Reg) to alleviate tumor hypoxia.¹¹⁵ Under NIR-II light, it generated ROS to induce ICD and activate antitumor immunity. Furthermore, Reg reprogrammed tumor-associated macrophages (TAMs) from M2 to M1 phenotype, thereby reversing the immunosuppressive TME. Combining functional small interfering RNA (siRNA) with PDT synergistically enhances the efficacy of ICIs.¹¹⁶ Therefore, PDT-based tumor vaccines achieve a multimodal therapeutic approach that integrates pharmacologic, genetic, and photodynamic modalities.

PNP-Based SDT Therapy

SDT is one of the non-invasive treatments with deep tissue penetration (>8 cm). It employs ultrasound to activate sonosensitizers, generating ROS that eliminate tumor cells.^140,141 For example, TME-responsive NPs (GdNPs), co-loaded with the sonosensitizer chlorin e6 (Ce6) and the histone deacetylase 6 (HDAC6) inhibitor Ricolinostat (Ric).¹¹⁷ Upon ultrasound stimulation, GdNPs/Ce6-Ric generated ROS to induce cancer cell apoptosis and release TAAs, which promoted an immunogenic TME, increasing natural killer (NK) and cytotoxic T cells while decreasing regulatory T cells (Tregs). Mechanically, this synergistic regulation is amplified through downregulation of the HDAC6/p-STAT3/PD-L1 pathway. By inhibiting α‑tubulin deacetylation, GdNPs/Ce6‑Ric blocked TGFβ-induced epithelial-mesenchymal transition (EMT), thereby significantly suppressing lung metastasis. DPTIP is a potent inhibitor of neutral sphingomyelinase-2 (nSMase2), a key regulator of exosome biogenesis.¹¹⁸ Building on this, researchers designed an exosome-inhibiting polymeric sonosensitizer (EIPS) featuring a semiconducting polymer (SP) backbone, PEG side chains, a Cathepsin B (CatB)-cleavable substrate, a self-destruct linker, and a DPTIP unit.¹⁴² Experimental results showed that EIPS selectively inhibited tumor exosome generation by releasing DPTIP in response to tumor-overexpressed CatB. Under ultrasound, EIPS induces ICD, achieving efficient tumor killing, suppressing 4T1 lung metastasis, and establishing long-term immune memory. The synergistic combination of PDT and SDT significantly inhibited tumor growth. A multifunctional integrated Mn‑protoporphyrin IX (MnPPs) coordination polymer was developed to serve as a dual photo- and sonosensitizer.¹¹⁹ Under light or ultrasound stimulation, MnPPs generated ROS within tumor cells, leading to effective tumor elimination. Another radioactive hybrid semiconductor polymer NP (SPN_H) was prepared via nanocoprecipitation of two semiconductor polymers and labeled with iodine-131 to enhance imaging.¹²⁰ SPN_H exhibited excellent SDT effect, while under 808 nm laser irradiation, it generated ¹O₂ and released heat, exhibiting combined PDT and photothermal effects. SPN_H effectively inhibited tumor growth and suppressed metastasis through the concurrent application of photodynamic, photothermal, and sonodynamic therapies.

Combination of in situ Vaccines and STING Agonists for Enhanced Cancer Immunotherapy

The TME of “cold” tumors is immunosuppressive, lacking robust antitumor immune responses and pro-inflammatory immune cells.^143,144 The activation of the STING pathway is a key mechanism to overcome and convert “cold” tumors to “hot”.¹⁴⁵ Mechanistically, the cyclic guanosine monophosphate (cAMP) synthase (cGAS) binds cytosolic double-stranded DNA to catalyze cyclic guanosine monophosphate adenosine (cGAMP) synthesis, which activates STING and subsequently induces type-I IFN expression, thereby promoting downstream antitumor immunity.¹⁴⁶

PNPs enable the co-delivery of immunostimulants and sonosensitizers, allowing for precise spatiotemporal regulation in ultrasonic immunotherapy to achieve synergistic anticancer effects. A novel polymeric STING pro-agonist (PSPA) was composed of a GSH-activated linker that conjugated a semiconductor polymer sonosensitizer to the STING agonist MSA-2, making it dually activatable by ultrasound and high GSH.¹²¹ Under ultrasound irradiation, PSPA generated ROS to induce ICD, while GSH-triggered MSA-2 release activated the STING pathway, elevating IFN-β levels and synergizing with SDT for enhanced antitumor efficacy. Zhao et al¹²² developed multifunctional triblock PNP (cGAMP-siPDL1@GalNPs) containing PS with cationic/thiol side chains to conjugate the STING agonist cGAMP and PD-L1-targeting siRNA (siPDL1). By targeting galactose receptors, cGAMP‑siPDL1@GalNPs achieve efficient intracellular delivery, enabling cargo release via a photo-, redox-, and pH‑responsive mechanism. Mechanically, cGAMP‑siPDL1@GalNPs enhance antitumor immunity by activating the STING pathway, suppress immune escape via PD-L1 knockdown, and induce ICD under laser irradiation, thereby achieving potent therapy against low-immunogenicity tumors and inhibiting distant metastasis.

Further, manganese ions (Mn²⁺) also play important roles in activating the STING pathway. For example, PTT mediated by semiconductor polymer nanoparticles (DPTT-Mn Lipo NPs) effectively induced tumor cell apoptosis and triggered ICD.¹²³ For example, Mn²⁺ activated the cGAS-STING pathway in immune cells such as macrophages and DCs within the TME, thereby remodeling the immunosuppressive status of TME. Notably, combining DPTT-Mn Lipo NP-based photothermal therapy with checkpoint blockade therapies (such as anti-PD-1 treatment) not only effectively eradicates tumors but also induces long-lasting immune memory. Another Mn²⁺based PNPs was developed by combining Mn²⁺ with poly[2-(N-oxide-N, N-dimethylamino) ethyl methacrylate] (OPDMA), enabling endoplasmic reticulum (ER) targeting.¹²⁴ Mn/OPDMA selectively accumulated in the ER of TAMs, potently enhancing cGAS‑STING pathway activity. This enhanced signaling promoted TAM polarization and IFN-β secretion, thereby remodeling the tumor immune microenvironment and ultimately prolonging survival in mice. Therefore, STING-activating PNPs promote M1 macrophage polarization, enhance T-cell infiltration, facilitate dendritic cell maturation, and modulate type-I IFN secretion, ultimately inhibiting tumor growth.

Exogenous Tumor Vaccines: Targeted Delivery of Antigens

PNP-Based Peptide Vaccines

Peptide-based vaccines achieve antigen presentation by carrying immunogenic TAA peptide fragments. Utilizing PNPs nanoparticles to deliver antigen peptides offers significant advantages in safety, specificity, and reproducibility, thereby demonstrating unique application potential.^147,148 Using nanocarriers to protect these peptides, enhance antigen presentation, activate innate immune cells, and modulate inflammatory responses would boost anti-tumor immune efficacy. PNPs enable the targeted and conditional release of peptide vaccines. For example, Wang et al¹²⁵ developed a TRP2 nanovaccine modified with phenylboronic ester (PBE). Specifically, it consisted of the TRP2 peptide antigen (SVYDFFVWL) and a diblock copolymer PEG-b-PAsp. Experimentally, PEG-b-PAsp-g-PBE/TRP2 nanovaccine exhibited a high negative charge and excellent ROS/pH responsiveness, which promoted DC maturation and enhanced MHC I-restricted antigen presentation. This activation stimulated potent T-cell immune responses, leading to significant antitumor efficacy. A mannose-grafted polymer with self-assembly properties was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Peptide antigens were linked to pH-sensitive hydrophobic segments on the polymer through reversible disulfide bonds, enabling pH-responsive antigen release (named MAN-P).¹²⁶ Experimental results demonstrated that MAN-P nanovaccine promoted the accumulation of vaccine components in inguinal lymph nodes and facilitated their uptake by APCs. Biological experiments demonstrated that this mannosyl-modified micelle formulation activated DCs, enhanced the responsiveness of specific T cells, and strengthened antitumor efficacy.

Further, PNP-based peptide vaccines enable effective antigen presentation, thereby activating CD8⁺ T cells. For example, a peptide segment that binds the endocytic receptor DEC-205 on cDC1 cells was optimized to yield the hydrolytically stable fragment hr-8. This fragment was conjugated to antigen- and CpG-loaded PLGA NPs, developing hr‑8‑PLGA@Ag/CpG.¹²⁷ The hr‑8‑PLGA@Ag/CpG promoted DC maturation and enhanced cross-presentation. When combined with exogenous OVA or endogenous gp100/E7 antigens, boosted CD8⁺ T cell-mediated antitumor immunity. ChouA et al¹²⁸ designed a type of galactose- or mannose-modified poly(lactic-co-glycolic acid) NP that achieved targeted activation of DCs by loading SIINFEKL antigen peptides and the immunological adjuvant CpG oligonucleotide (designated OVA-CpG Gal-NPs and OVA-CpG Man-NPs). Experimental results demonstrated that OVA-CpG Gal/Man-NPs significantly enhanced antigen uptake and accumulated in the spleen, increased levels of CD4⁺ T cells and IFN-γ in the spleen, and enhanced the tumor-killing activity of CD8⁺ T cells. Another novel poly(2-oxazoline)s (POx)-based nanovaccine platform could chemically conjugate diverse neoantigen peptides, enhancing their accumulation and lymph node penetration.¹²⁹ This PNP-based nanovaccine improved antigen presentation efficiency, leading to potent CD8⁺ T-cell responses and significant antitumor efficacy. Overall, PNPs can protect encapsulated peptide antigens from enzymatic degradation, enhance their cellular uptake capacity, and promote their accumulation within the lymphatic nodes. By adjusting the size, particle shape, and surface properties of the PNPs, the efficacy of peptide vaccines can be optimized, thereby enhancing antigen uptake by DCs and their immunostimulatory capacity.

PNP-Based mRNA Vaccine

MRNA carries genetic information transcribed from DNA and, after processing within the nucleus, is transported out of the nucleus into the cytoplasm to serve as a template for protein synthesis.^149,150 In recent years, mRNA vaccines have demonstrated several key advantages: the mRNAs only need to reach the cytoplasm to be translated into the target antigen by ribosomes, enabling rapid and high-level protein expression; furthermore, they do not integrate into the host genome, thereby eliminating the risk of insertional mutagenesis.¹⁵¹ DCs process exogenous proteins/peptides in endosomes/lysosomes into peptides that bind MHC II molecules. These complexes are presented on the cell surface to activate CD4⁺ helper T cells. Endogenous antigens are processed by the proteasome and loaded onto MHC I molecules to activate CTLs.¹⁵² This dual capacity of DCs to simultaneously activate helper T cells and CTLs makes mRNA cancer vaccines encoding antigens for both MHC pathways one of the most promising platforms in cancer immunotherapy.

PNPs serve as effective mRNA carriers, combining low side effects with excellent biocompatibility. For example, the biodegradability of Poly(beta-amino ester)s (PBAE)s and their ability to spontaneously self‑assemble with nucleic acids enable efficient mRNA encapsulation. Based on this, R18D NPs were designed to co-deliver mRNA, the TLR3 agonist poly(I:C), and the TLR9 agonist CpG.¹³⁰ Experimental studies showed that R18D activated TLR3 and RIG‑I, inducing type-I IFN secretion and cytotoxic CTL activation, while minimizing systemic side effects. A novel vitamin E succinate modified polyethyleneimine copolymer (PVES) was used to develop self-assembled polymeric micelles for mRNA delivery. PVES induced strong antibody responses without any apparent toxicity, indicating its potential as a safe and effective mRNA delivery vehicle.¹³¹ Further, dual mRNA delivery strategies demonstrate potential value in enhancing cancer immunotherapy efficacy. For instance, lipid-polymer hybrid NPs (LPNPs) were used to deliver mRNA encoding anti-PD-1 antibodies directly to tumors, enabling high expression of anti-PD-1 protein. In addition, RNA sequencing was used to identify pancreatic cancer neoantigens, based on which an NV-LNP-mRNA vaccine was developed.¹³² This vaccine activated the tumor-specific immune response, thereby reducing the systemic toxicity associated with broad immune checkpoint inhibition.

PNP-based mRNA vaccines can further enhance their efficacy by activating the STING signaling pathway, thereby triggering potent antitumor immunity. For example, researchers synthesized a block copolymer, “PHTA”, composed of ortho-hydroxy tertiary amine (HTA) repeating units.¹³³ This carrier simultaneously stabilized mRNA, enhanced NP integrity, and prolonged circulation time in vivo. PHTA-C18 successfully delivered mRNA within the body, thereby inducing a powerful CD8⁺ T cell-mediated antitumor immune response. Further, a multivalent stimulator polymer (PD) capable of activating IFN genes was synthesized from tertiary amine units linked to biodegradable alkyl chains.¹³⁴ PD18, containing 18 tertiary amines, was combined with lipids and mRNA to form lipid-like NPs (PD LNPs). PD18 effectively transported mRNA within the lymphatic system and induced robust immune responses via the STING pathway, thereby expanding antigen-specific memory CD8⁺ T cells. Another novel mRNA delivery vector POctS combined high-efficiency mRNA delivery with intrinsic STING-pathway activation.¹³⁵ POctS enabled targeted mRNA release and innate immune stimulation. Based on the immune-infiltrated properties of tumors, an ovalbumin (OMV)-mRNA/POctS vaccine was effective against melanoma, while a mixed lineage kinase domain-like protein (MLKL)-mRNA/POctS construct functioned as an in-situ vaccine for pancreatic cancer, demonstrating its versatility across immunologically distinct tumors.

Overall, compared to traditional protein or peptide-based cancer vaccines, mRNA vaccines demonstrate distinct advantages: they can be customized to individual requirements while meeting the demands of commercial-scale production. Furthermore, their stability can be enhanced through engineering modifications without compromising immunogenicity, thereby inducing complementary innate and adaptive immune responses (Table 2).

PNPs Target Immune Infiltrating Cells

The immunosuppressive TME within solid tumors severely restricts immune cell function, leading to rapid impairment of their capabilities.¹⁵³ Cancer immunotherapy offers the potential to reverse the immunosuppressive effects of TME.

PNPs can precisely target immune cells and promote immune cell-mediated antitumor responses through controllable spatiotemporal immune modulation mechanisms (Table 3). For instance, polylactic-polyhydroxyacetic acid (PLHA) nanoparticles can trigger transcriptional activation processes in NK cells and pan-T cells. Notably, in cytokine-deficient environments, PLHA enhances the antitumor function of NK cells. Conversely, silica-based gadolinium (Si-Gd) NPs can suppress T-cell activation capacity and their response to antigen stimulation.¹⁵⁴ Research has shown that nanoparticles can encapsulate IL-12 for tumor-targeted accumulation, reducing systemic side effects. Building on this, a polymer-based “immune fiber” was developed to target NK cells.¹⁵⁵ It co-delivered anti-CD16 antibodies and IL-12 to achieve synergistic NK cell activation. Experimental results confirmed that “immune fiber” promoted TNF-α and IFN-γ secretion and upregulated activation markers, including CD25, CD69, and the degranulation marker CD107a. Further, a novel micropatch composed of a PLGA copolymer with a diameter of 4–8 micrometers, whose surface is modified with NK cell receptor-targeting antibodies, enables sustained, targeted activation of NK cells, which is referred to as “microparticle as a cell-mediated effector” (MACE).¹⁵⁶ NK cells could bind to MACE and realize transendothelial migration and exhibit antitumor activity. Furthermore, MACE-modified NK cells can activate T cells, macrophages, and DCs. In vivo experiments demonstrate that MACE-modified NK cells exhibit superior antitumor efficacy compared to unmodified NK cells.

Table 3.

Target Tumor-Infiltrating Immune Cells, and PNPs-Based ICIs and CAR-T Therapies

Strategy	Type of PNPs	Tumor Model	Immunomodulatory Effects	Reference
Target NK cells	Si-Gd NPs	CML	Promoting the internalization and activation of primary NK cells and pan-T cells	[154]
	Polymer-based “immune fiber”	IFN-γ-sensitive tumors	Co-delivery of anti-CD16 antibody and IL-12 synergistically activates NK cells; promote TNF-α/IFN-γ secretion; upregulate CD25, CD69, and CD107a.	[155]
	MACE	Melanoma	Target and activate NK cells; promote NK cell transendothelial migration; activate T cells, macrophages, and DCs	[156]
Target TAMs	Glycocalyx-mimetic NP	BC	Maintain the pro-inflammatory phenotype of macrophages; Reshape the TME and enhance T cell responses	[157]
	Res:ID20:80 micelles	BC	Promote TAMs M2→M1 polarization, reduce MDSCs and Tregs; combine radiotherapy alleviates immunosuppression.	[158]
	PLGA@BBI608	HCC	Delivery napabucasin, inhibit STAT3/FAO pathway in TAMs, promote M2→M1 polarization; enhance T cell-mediated antitumor immunity	[159]
Target DCs	SPN-R848	Melanoma/BC	pH-responsive; enhance tumor penetration and lymph node transport; reprogram TAMs and activates DCs.	[160]
	aDCM@PLGA/RAPA	Glioma	DC membrane coating crosses the BBB; promote DC maturation, activate tumor-infiltrating T cells and NK cells.	[161]
PNP-based ICIs therapies	aNP@IR780	CRC	Load IR780 with PD-L1 antagonist peptides; integrate photothermal therapy, tumor vaccine effects, and PD-1/PD-L1 pathway blockade; induce ICD.	[162]
	P-PDL1-CP	Prostate cancer	Acid activation; disrupt lysosomal function to block autophagy and upregulate MHC I; synergize with anti-PD-L1 antibodies to promote T cell/DC maturation and induce immune memory.	[163]
	ANGel	BC	Enhance ICI efficacy and reprogram TME gene expression; Protein A-modified nanogel conjugate with CTLA-4/PD-1 bispecific aptamers.	[164]
	BNP/CMCS nanogel	OC	Injectable hydrogel co-loaded with paclitaxel and anti-PD-1 antibody; inhibit OC peritoneal metastasis.	[165]
PNP-based CAR-T therapies	HA-Mn-CAP Gel	Melanoma	Release Mn2⁺ to alleviate tumor hypoxia; Upregulate NKG2D ligand expression to enhance NKG2D-CAR-T therapeutic efficacy.	[166]
	Cr@PD	HCC/BC	NIR-mediated PTT “heats” the immunosuppressive TME; release Cr3+ to upregulate the chemokine CXCL13/CCL3, enhance CAR-T cell infiltration.	[167]
	pDNA@SNPG1/800	HCC	Deliver EGFRvIII-specific CAR-encoding plasmids to achieve transient CAR expression in T cells; target, recognize, and eliminate EGFRvIII-positive tumor cells.	[168]

Abbreviations: BC, Breast cancer; CRC, Colorectal carcinoma; HCC, Hepatocellular carcinoma; CML, Chronic myeloid leukemia; OC, ovarian cancer.

In immunosuppressive microenvironments, macrophages exhibit high plasticity, shifting from M1-like to M2-like states. To counteract this plasticity, a glycocalyx-mimetic NP was developed, consisting of (oligo)mannoside-modified glycopolymers conjugated to iron oxide.¹⁵⁷ These hybrid glycocalyx-inspired NPs enable primary macrophages to sustain a pro-inflammatory phenotype. The synergistic action of the two signals enhanced macrophage immune activity, remodeled the TME, and amplified T-cell responses, yielding stronger antitumor effects in vitro and in vivo. The combination of PNPs with small-molecule drugs significantly enhances tumor treatment efficacy. For example, researchers employed poly(2-oxazoline) block copolymer micelle nanoparticles (Res:ID20:80) to co-deliver a small-molecule agonist of TLR7/8 and a PI3Kδ inhibitor into the TME.¹⁵⁸ This combination polarized macrophages toward an M1 phenotype, reduced myeloid‑derived suppressor cell accumulation and tissue‑resident Treg numbers, and enhanced adaptive T‑ and B‑cell responses. When combined with radiotherapy, Res:ID20:80 alleviated immunosuppression in the TME, thereby promoting tumor regression. Another PLGA NPs loaded with the STAT3 inhibitor BBI608 (Napabucasin) enhanced passive targeting, improved drug bioavailability, and potentiate anti-HCC activity while reducing toxicity.¹⁵⁹ These nanoparticles inhibit the STAT3/fatty acid oxidation (FAO) signaling pathway in TAMs, promoting their polarization from M2 to M1 phenotype, which remodeled the tumor immune microenvironment and enhanced T cell-mediated antitumor responses.

Additionally, PNPs not only facilitate the M2-to-M1 polarization of TAMs but also activate DCs in lymph nodes, thereby promoting the activation of CTLs. Tong et al¹⁶⁰ designed a pH-responsive, size-tunable NP (SPN-R848) through self-assembly of a resiquimod (R848)-conjugated PAMAM derivative. In acidic TME, SPN-R848 decomposed into 8 nm components, enhancing permeability and transport to lymph nodes. Furthermore, they reprogrammed M2 to M1 macrophages and activated DCs, which in turn promoted CTLs activation and thereby inhibited tumor growth. A nanocarrier coated with activated mature DC membranes and loaded with rapamycin (RAPA) in a PLGA core, which was named as aDCM@PLGA/RAPA, effectively crossed the blood-brain barrier (BBB) and modulated the TME.¹⁶¹ Further studies proved it significantly inhibited glioma growth and promoted dendritic cell maturation, which in turn activated tumor-infiltrating T cells and natural killer cells through direct and indirect mechanisms to activate an antitumor immune response. Therefore, PNPs can help modulate the tumor immunosuppressive microenvironment, including targeting natural killer cells to recover their antitumor killing capacity, reversing M2-type to M1-type macrophages, and activating DCs to enhance the antitumor capabilities of CTLs. Furthermore, the combination of PNPs with immunotherapy overcomes limitations of conventional cancer treatments by enhancing the delivery efficiency and efficacy of immunotherapeutic agents, thereby improving patient outcomes (Figure 3).

PNP-Based ICIs Therapies

Currently, ICIs, such as PD-1/PD-L1 and CTLA-4 blocking antibodies, hold tremendous promise in cancer therapy. Nevertheless, only a minority of patients respond well to PD-1/PD-L1 blocking antibodies due to the inherently immunosuppressive nature of the TME.^169,170 NPs loaded with ICIs achieve tumor targeting and conditional release, producing synergistic antitumor effects (Table 3). For example, a novel PNP composed of PEG-PLGA loaded with IR780 and PD-L1 antagonist peptides (aNP@IR780).¹⁶² The aNP@IR780 integrated photothermal therapy, antitumor vaccine effects, and PD-1/PD-L1 signaling pathway blockade into a system, significantly enhancing antitumor efficacy. Furthermore, aNP@IR780 induced strong antitumor immune responses by triggering ICD. One novel acid-activatable PNP, termed P-PDL1-CP, consisted of the poly(2-diisopropylaminoethyl methacrylate) (PDPA) core coated with anti-PD-L1 antibodies and long-chain PEG.¹⁶³ P-PDL1-CP disrupted lysosomal function, thereby blocking autophagy and increasing MHC‑I expression on cancer cells, which enhanced their susceptibility to TNF-α and CTL attack. Furthermore, P-PDL1-CP synergized with anti-PD-L1 antibodies to promote the maturation of tumor-infiltrating T cells and DCs, elevate TNF-α and IFN-γ levels, and induced anti-tumor immune memory, collectively inhibiting prostate cancer growth.

PNP-based hydrogels provide binding sites for ICIs, stabilize drug properties, promote uniform drug distribution, and ensure controlled release of therapeutic agents. An antibody-conjugated nanogel (named ANGel) was developed, composed of an N-isopropylacrylamide-co-acrylic acid copolymer and protein A for antibody binding. ANGel was further conjugated with a bispecific aptamer targeting CTLA-4 and PD-1 antibodies.¹⁶⁴ The combination of ICIs with ANGel enhanced anticancer efficacy beyond monotherapy and significantly reshaped tumor and TME-related gene expression profiles, thereby suggesting a broader mechanism of action. An injectable BNP/CMCS nanogel is formed via a Schiff-base bond between the amino groups of carboxymethyl chitosan (CMCS) and the aldehyde groups on bioadhesive nanoparticles (BNPs).¹⁶⁵ BNP/CMCS nanogel could co-load paclitaxel and anti-PD-1 antibodies, which allowed for sustained release over 7 days and significantly inhibited peritoneal metastasis in ovarian cancer (OC). Although ICIs exhibit high specificity and affinity for target cells, challenges remain in terms of targeting efficiency and bioavailability. Utilizing PNPs to anchor ICIs, thereby achieving synergistic effects, is crucial for maintaining their biological activity and enhancing the efficacy of immunotherapy.

PNP-Based CAR-T Cell Therapies

CAR-T cell therapy, as an innovative immunotherapy, modifies a patient’s T cells to express CAR proteins on their surface, thereby granting them the ability to recognize and eliminate cancer cells.¹⁷¹ While this therapy still faces challenges in solid tumor treatment, such as antigen selection, tolerability, and safety, PNPs demonstrate new possibilities in CRT-T therapy (Table 3).

To enhance tumor treatment efficacy, novel strategies aim to pre-treat tumors by boosting target ligand expression and optimizing the TME before CAR-T cell administration. One novel example is the HA-Mn-CAP Gel, a hyaluronic acid-based nanogel that targets CD44 and TRPV1 receptors.¹⁶⁶ At the tumor site, HA-Mn-CAP Ge releases Mn²⁺ to alleviate hypoxia and upregulate specific CAR-T target ligands. In vitro, the nanogel significantly increased expression of NKG2D ligands (MICA/B, ULBP2/5/6) on tumor cells. When combined with NKG2D-CAR-T therapy, HA-Mn-CAP Gel markedly enhanced tumor suppression. Zou et al¹⁶⁷ developed a biodegradable dopamine-based nanocarrier (Cr@PD) to synergize photothermal therapy with CAR-T cell treatment. Under NIR irradiation, Cr@PD “warms” immunologically TME. In immunodeficient mice receiving B7-H3 CAR-T cells, Cr@PD significantly suppressed tumor growth and elevated serum cytokines (IL-2, IFN-γ, TNF-α). Moreover, the primary degradation product, trivalent chromium (Cr³⁺) ions, upregulated chemokines such as CXCL13 and CCL3, thereby enhancing CAR-T cell infiltration. PNPs conjugate with CAR-encoding plasmids confer T cells with specific antigen-recognition capabilities. For example, an adamantane-grafted PAMAM dendrimer (Ad-PAMAM) and CD-grafted branched PEI (CD-PEI) were combined to form self-assembling NPs (pDNA@SNP^G1/800). The pDNA@SNP^G1/800 platform delivered plasmids encoding EGFRvIII-specific CARs (pEGFRvIII-CAR), yielding pEGFRvIII-CAR@SNP^G1/800, which enabled transient CAR expression in transfected cells and conferred specific recognition and binding to EGFRvIII-positive tumor cells.¹⁶⁸ The combination of NPs with CAR-T cells represents a promising strategy for treating solid tumors. By adjusting PNPs’ composition and their engagement with CAR-T cells, this approach enables precise modulation of the TME, thereby enhancing therapeutic efficacy (Figure 3).

Clinical Application of PNPs for Cancer Immunotherapy

The application of PNPs for immunotherapy has demonstrated encouraging preclinical efficacy and is undergoing clinical trials for cancer treatment. For example, nab-paclitaxel, an albumin-bound paclitaxel formulation, employs nanotechnology to conjugate the hydrophobic drug with human serum albumin. This strategy avoids the adverse effects of organic solvents and improves both safety and efficacy.¹⁷² Based on the results of the IMpassion130 clinical trial, the combination of atezolizumab and nab-paclitaxel is indicated for the treatment of locally advanced or metastatic triple-negative breast cancer.¹⁷³ BO-112, a nanocomplex of a TLR3 agonist with PEI, has demonstrated promising clinical activity. In a Phase I trial, BO-112 increased immune-related gene expression in 46% of patients and elevated circulating immune cells in 88%.¹⁷⁴ Another Phase II trial in advanced melanoma combining BO-112 with pembrolizumab (anti-PD-1) reported an objective response rate (ORR) of 25% (3 complete and 7 partial responses), with disease stabilization in 44% of patients, and was well-tolerated.¹⁷⁵

Poly-ICLC is a poly-L-lysine-protected double-stranded RNA (dsRNA) TLR3 agonist that upregulates type I IFN. Poly-ICLC exhibits potent DC targeting capability.¹⁷⁶ In clinical trials, Poly-ICLC demonstrated favorable antitumor efficacy and tolerability when administered as monotherapy, in combination with peptide/protein antigens, or in combination with ICIs. One nanocomplex (named CHP-NY-ESO-1) composed of cholesteryl pullulan (CHP) and NY-ESO-1 antigen protein can present multiple epitopes to both MHC class I and II, inducing immunogenic responses of CD8⁺ and CD4⁺ T cells. In a Phase 1 trial involving patients with advanced or recurrent esophageal cancer, CHP-NY-ESO-1, combined with poly-ICLC, elicited antibody responses in all patients, with higher titers than the vaccine alone. Co-administration of anti-PD-1 antibodies with the CHP-NY-ESO-1/poly-ICLC combination formulation demonstrated the ability to inhibit tumor growth in NY-ESO-1-expressing tumors, exhibiting significant potential in human clinical trials.¹⁷⁷ Another PLGA nanocomposite encapsulating the NKT activator IMM60 and NY-ESO-1 was developed to evaluate the safety, tolerability, and immunomodulatory effects of PRECIOUS-01 in advanced solid tumors.¹⁷⁸ The immunomodulatory properties of PRECIOUS-01 were evaluated by detecting tumor biopsies for CD45RO, CD3, Foxp3, CD8⁺, and CD20⁺ cells and quantifying their immune composition in a phase I clinical trial. Currently, numerous clinical trials exploring PNP-based cancer immunotherapy are continuously advancing, aiming to refine its clinical application, accelerate its clinical translation process, and establish it as a treatment strategy for cancer.

Conclusion and Discussion

Cancer remains a leading cause of mortality globally, and the application of NPs in cancer immunotherapy represents a transformative approach that could significantly enhance treatment efficacy and patient outcomes. Despite the exploration of various nanocarriers (liposomes, inorganic nanoparticles, dendrimers, and exosomes) for cancer therapy, each has inherent drawbacks: liposomes lack stability and targeting accuracy; inorganic nanoparticles pose degradation and toxicity issues; dendrimers are limited by complex synthesis and scalability; and exosomes face hurdles in isolation and standardization. Due to unique properties such as biocompatibility, tunable size, and surface functionality, PNPs have been extensively studied for their potential in drug delivery and therapeutic applications.¹⁷⁹ Notably, modifying their surface with targeting ligands allows selective binding to cancer cells, enhancing the precision of treatment.¹⁸⁰ PNP-based nanoplatforms have achieved smart, stimuli-responsive release in response to TME (such as pH, enzymes, and redox), which not only increases local drug concentration but also reduces systemic toxicity.

Furthermore, integrating PNPs with other therapeutic strategies (such as PDT, CDT, and SDT) significantly induces ICD of tumor cells, thereby enhancing the efficacy of cancer immunotherapy.^179,181 Consequently, the multifaceted properties of PNP enable synergistic delivery of multiple drugs, thereby addressing tumor heterogeneity and drug resistance. Further, PNP-based tumor vaccines have opened new avenues for immunotherapy. For example, employing PNPs for the delivery of RNA or peptide vaccines activates DCs, enhancing the antigen presentation process and thereby boosting the cytotoxic activity of CTLs.¹⁸² Moreover, the multifunctionality of nanocarriers enables the co-delivery of immunomodulators with chemotherapeutics, ICIs, or CAR-T plasmids, thereby generating synergistic effects to improve therapeutic outcomes.

Although PNPs enhance drug delivery efficiency and reduce the side effects of drugs, the safety of PNPs remains one of the key challenges for their clinical application. During the preparation of PNPs, the use of emulsifiers like PVA may introduce toxicity.¹⁸³ Further research is necessary to explore the biocompatibility and stability of PNPs and to prevent adverse reactions. Another critical issue for systemically administered PNPs is the non-specific clearance by the reticuloendothelial system (RES), which significantly reduces the delivery efficiency of PNPs to the target tissues. Conversely, it would increase associated immunogenicity and toxicity, posing a major barrier to their clinical translation. Additionally, the complexity of the TME, including heterogeneous cell populations and immunosuppressive states, warrants further investigation. Although preclinical results are encouraging, clinical translation remains limited, with only a few FDA‑approved products-underscoring the substantial gap between research and clinical application.

In conclusion, the journey of PNPs in cancer immunotherapy is at a pivotal juncture, promising significant advancements but also necessitating careful navigation of the challenges ahead. By fostering interdisciplinary collaborations and focusing on innovative research strategies, the full potential of PNPs can be harnessed, ultimately leading to more effective and personalized cancer treatment options.

Funding Statement

There is no funding to report.

Abbreviations

APCs, antigen-presenting cells; BBB, blood-brain barrier; CAD, cis-aconityl-DOX; CAFs, cancer-associated fibroblast; cAMP, cyclic guanosine monophosphate synthase; CAR-T, chimeric antigen receptor-T; CatB, Cathepsin B; CB, chloramphenicol; CBT, 2-cyanobenzothiazole; CD, cyclodextrin; CDT, chemo-dynamic therapy; Ce6, chlorin e6; cGAMP, cyclic guanosine monophosphate adenosine; cGAS, cyclic guanosine monophosphate synthase; CMCS, carboxymethyl chitosan; -COOH, carboxyl; COP, covalent organic photosensitizer; CpG, cytosine-phosphate-guanine; CRS, cytokine release syndrome; CTLA-4, cytotoxic T-lymphocyte-associated antigen 4; CTLs, cytotoxic T lymphocytes; CTX, cyclophosphamide; CXCL12, (C-X-C motif) ligand 12; DAMPs, damage-associated molecular patterns; DCs, dendritic cells; DEVD, aspartic acid-glutamic acid-valine-aspartic acid; DMXAA, 5,6-dimethylxantheonone-4-acetic acid; DOX, doxorubicin; ECM, extracellular matrix; EIPS, exosome-inhibiting polymeric sonosensitizer; EMT, epithelial-mesenchymal transition; ER, endoplasmic reticulum; ERK5, extracellular signal regulated kinase 5; FDA, Food and Drug Administration; GSH, glutathione; HA, hyaluronic acid; ICD, immunogenic cell death; ICIs, immune checkpoint inhibitors; IFN-γ, interferons-γ; IL, interleukin; IMQ, imiquimod; LNPs, liposomes NPs; LPNPs, lipid-polymer hybrid NPs; MDSCs, myeloid-derived suppressor cells; MHC, major histocompatibility complex; MLKL, mixed lineage kinase domain-like protein; mPEG-b-PLA, poly (ethylene glycol)-b-poly (L-lactide); mRNA, Messenger RNA; -NH₃⁺, amino groups; NIPAAm, poly (N-isopropylacrylamide); NIR, near-infrared; NP, nanoparticles; -OH, hydroxyl; OMV, ovalbumin; ORR, objective response rate; PAA, polyacrylic acid; PBAE, Poly(beta-amino ester); PBAEs, (β-amino ester)s; PCL, poly (ε-caprolactone); PD-1, programmed cell death protein 1; PD-L1, programmed death ligand-1; PDMAEMA, Poly (2-Dimethylamino-Ethylmethacrylate); PDT, photodynamic therapy; PEG, poly(ethylene glycol); PEI, polycationic polyethylenimine; PEMA, poly (ethylene-alt-maleic anhydride); PGA, polyglycolic acid; PLA, poly (lactic acid); PLEL, poly (D, L-lactic acid)-polyethylene glycol-poly (D, L-lactic acid); PLGA, poly (lactic-co-glycolic acid); PLHA, polylactic-polyhydroxyacetic acid; PNPs, polymeric NPs; PS, photosensitizer; PTX, paclitaxel; PVA, poly (vinyl alcohol); RAFT, reversible addition-fragmentation chain transfer; RES, reticuloendothelial system; ROS, reactive oxygen species; SDT, sonodynamic therapy; siRNA, small interfering RNA; SP, semiconducting polymer; STAT3, signal transducer and activator of transcription 3; STING, stimulator of interferon genes; TAAs, tumor-associated antigens; TAMs, tumor-associated macrophages; TAPP, 5,10,5,20-tetrakis (4-aminophenyl)-porphine; TGF-beta, transforming growth factor-beta; TLR 7/8, Toll-like receptor 7/8; TME, tumor microenvironment; Treg, regulatory T; TSAs, tumor-specific antigens; VK3, vitamin K3; =C–O, carbonyl; ¹O₂, singlet oxygen.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare that they have no competing interests in this work.