2.1 Influence on the Peptide Epitope Generation

Oxidative stress can increase the peptide epitope generation through various mechanisms, including the induction of genomic instability, dysregulated alternative splicing processes, and alterations in protein posttranslational modifications (PTMs) [21, 28, 29] (Figure 2).

2.2 Effects on Antigen Processing

Oxidative stress impacts antigen processing and presentation by altering the efficiency of proteasome-mediated degradation of intracellular proteins and endosomal degradation of extracellular proteins [70]. All nucleated cells utilize the proteasome system for endogenous antigen processing, enabling MHC I antigen presentation. APCs with phagocytic capacity utilize endosomal pathways for exogenous antigen processing, promoting MHC II antigen presentation [71-73].

2.2.1 Effects on Proteasome-Based Antigen Processing

Antigen processing in nonprofessional cells begins with proteasome-mediated degradation of endogenous misfolded, damaged, or aberrant proteins [74]. The widely distributed and highly adaptable proteasome system is the 26S ubiquitin-proteasome system, composed of a 20S core particle (CP) and a 19S regulatory particle (RP), responsible for ubiquitin/ATP-dependent protein degradation [75-77]. The 19S RP is essential for identifying ubiquitinated proteins, removing their ubiquitin chains, and unfolding them before they are degraded by the 20S CP. The 20S CP, a cylindrical structure comprising α and β subunits, possesses catalytic activity via the β1, β2, and β5 subunits. Under specific conditions, inducible β1i, β2i, and β5i subunits are capable of substituting for the constitutive catalytic subunits, forming the so-called immunoproteasome (IP) [78]. In response to cellular oxidative stress, the IP can associate with 19S and proteasome activator 28α/β (PA28α/β) regulatory factors to form hybrid proteasomes (HP, 19S-20S-PA28α/β), promoting the rapid, ubiquitin-dependent degradation of oxidatively damaged proteins [79, 80]. Furthermore, both standard proteasomes (SP) and IP can generate neo-epitopes composed of two distinct fragments from noncontiguous peptide sequences within the parent antigen. This occurs through a process known as proteasome-catalyzed peptide splicing (PCPS), where proteasomal cleavage products are fused together, forming peptides that serve as MHC I ligands on the cell surface [81, 82]. Constitutively expressed in immune cells, IP is inducible and expressed in nonimmune tissues by type I and/or II interferons (IFNs). Upon IFN-γ stimulation, the IP, with its distinct proteolytic subunits and cap structures, enhances the processing of proteins into HLA-I compatible peptides. The IP exhibits higher cleavage rates than SP, displaying a preference for cleaving hydrophobic and basic amino acids, thus facilitating peptide binding to MHC I. Additionally, the replacement of 19S caps by PA28 in IP accelerates antigen peptide release [83-85]. Upon IFN-γ stimulation, the IP, with its distinct proteolytic subunits and cap structures, enhances the processing of proteins into HLA-I compatible peptides by generating peptides with hydrophobic C-terminal residues, thereby initiating cytotoxic T lymphocytes (CTL) responses against viral and bacterial antigens [83, 86].

Proteasomes are essential for regulating the peptide and antigen repertoire during adaptation to oxidative stress [76]. Normally, proteasomes, particularly the 20S complex, maintain cellular redox balance by identifying and eliminating oxidatively modified or damaged proteins. Exposure to H₂O₂ increases proteasome-mediated degradation by over tenfold, while proteasome inhibitor treatment intensifies oxidative damage, highlighting the critical regulatory function of the proteasome system in maintaining cellular homeostasis [87, 88]. However, elevated oxidative stress disrupts the function of the proteasome system and subsequent protein degradation. Acute H₂O₂ exposure compromises the structural integrity of the 26S proteasome complex, causing 20S core-19S particle dissociation, reducing 26S proteasome proteolytic activity, and leading to ubiquitinated protein accumulation [89] (Figure 3). Additionally, oxidative stress induces modifications of 19S and 20S proteasome subunits, such as 4-hydroxynonenal (4-HNE) modification, S-glutathionylation, and carbonylation [90-92]. The proteolytic function of the 20S proteasome is inhibited by carbonylation or HNE modification [93]. S-glutathionylation, another oxidative modification, enhances proteasome activity at low concentrations and inhibits it at high concentrations. The biphasic effect of S-glutathionylation on cysteine residues potentially acts as a signal transduction mechanism to modulate proteasome activity in response to cellular redox status [90, 94]. These findings suggest that oxidative stress can influence peptide/antigen repertoire regulation by altering proteasomal degradation.

3.1 Modulating Antigen Presentation by Oxidative Stress

Oxidative stress exerts a complex regulatory effect on antigen presentation, influencing MHC expression, pMHC formation and transport, and ultimately, the efficiency and specificity of T cell activation.

3.2 Impact on Costimulatory Molecules

Oxidative stress influences the antigen-specific immune response by modulating the expression and function of key costimulatory and immune checkpoint molecules. A costimulatory signal (e.g., CD28 with CD80/CD86, CD40 with CD40L, 4-1BB with 4-1BBL) is essential for complete T cell activation following priming by the antigen-specific signal [161]. The absence of costimulation results in activation-induced cell death (AICD) and/or energy, leading to immune tolerance [162]. Immune checkpoint pathways, such as those involving cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and programmed cell death protein-1 (PD-1), exert immunosuppressive effects in contrast to the positive immunoregulatory roles of costimulatory signals [163]. Moderate levels of ROS can enhance immune activation through upregulation of costimulatory molecules, whereas excessive oxidative stress promotes immune evasion by upregulating immune checkpoint molecules, indicating a biphasic role of oxidative stress in immune function [164, 165].

Moderate ROS enhances costimulatory molecules (e.g., CD80/CD86), promoting T cell activation. The accumulation of ROS in the bone marrow (BM) after ovariectomy prompts DCs to enhance the production of CD80, a costimulatory molecule that boosts T cell activation [166]. The ability of DCs to stimulate autologous naive CD4⁺ T cells is enhanced during parasite infection due to the upregulation of CD80 surface expression caused by heightened ROS produced by xanthine oxidase [167]. Elevated ROS levels correlate with increased CD80 and CD86 mRNA expression in macrophages in a murine model of heart failure with preserved ejection fraction (HFpEF) [168]. Moreover, ROS coordinate immune monitoring of colon preneoplastic lesions by promoting CD80 expression in colon cancer epithelial cells via the JNK/p38 MAPK–STAT3 pathways [169].

Oxidative stress also modulates the expression of immune checkpoint molecules, including PD-L1, which interacts with PD-1 to suppress immune activation [170, 171]. Increased ROS production due to KRAS-G12V activation promotes PD-L1 expression through fibroblast growth factor receptor 1 (FGFR1) pathway, promoting cancer evasion of the immune surveillance [172]. Enhanced PD-L1 expression in tumor-associated macrophages (TAMs) has been consistently observed following exposure to various ROS inducers, such as buthionine sulfoximine and paclitaxel [173]. Multiple mechanisms underlying ROS-mediated PD-L1 regulation have been reported [174], including iron-mediated oxidative stress-induced c-Myc activation in lung cancer [175], ROS-mediated activation of the JAK/STAT3 pathway [176], accelerating expression of the transcription factor NRF2 [170], and nuclear factor κB (NF-κB) signaling activation [173]. Furthermore, solute carrier family 7 member 11 (SLC7A11) inhibition-induced ROS upregulation promotes PD-L1 expression in melanoma cells via the IRF4/EGR1 pathway. The increased PD-L1 were transported by exosome to drive M2 macrophage polarization, resulting anti-PD-1/PD-L1 therapy resistance [177]. ROS regulates PD-L1 protein levels; for example, IL-17A-induced ROS production increases Nrf2 and p62 expression, thus inhibiting autophagic PD-L1 degradation [178]. Therefore, modulating ROS levels offers a potential novel approach to overcoming PD-L1-mediated immunosuppression and enhancing antigen-specific immune responses.

Moderate ROS levels boost T cell activation by increasing costimulatory molecules (like CD80/CD86). However, high ROS levels increase immune checkpoint molecules (like PD-L1), suppressing the immune response and promoting immune evasion. Therefore, controlled ROS induction may enhance antigen-specific signaling and overcome resistance to checkpoint inhibitors such as anti-PD-1.

3.3 Influence on Antigen-Specific Response of Immune Cells

Oxidative stress significantly influences the function of antigen-specific immune cells, including B cells and T cells. By influencing the activation and differentiation of immune cells, oxidative stress affect the efficacy of the immune system in monitoring and combating pathogens and diseased cells.

3.3.1 Antigen-Specific T Cells

The local concentration of ROS rises quickly during T-cell activation as a byproduct of oxidative metabolism due to the increased need for energy metabolism [179]. The engagement of pMHC complex on APC with TCRs initiates T cell activation, driving adaptive immune responses. Upon antigenic stimulation, quiescent naive T cells undergo metabolic reprogramming to meet the heightened energy demands of activation. Glycolysis, amino acid metabolism and fatty acid synthesis were upregulated to promote cell proliferation and cytokine secretion in effector CD8⁺ T cells, whereas the tricarboxylic acid cycle (TCA) and fatty acid oxidation (FAO) were essential for the lifespan maintenance of memory CD8⁺ T cells [180]. CD4⁺ T-cell development primarily relies on aerobic glycolysis as its main energy source, whereas FAO is the primary energy source for regulatory T (Treg) metabolism. The overactivation of these metabolic pathways is accompanied by the production of ROS, which serve as messenger to initiate the proliferation, activation, and effector functions of antigen-specific T cells.

The cellular redox state is crucial for the antigen-specific response of T cells. The stimulation of CD28 and CD3 receptors, which collaborate with the TCR to activate T cells, induces the generation of mitochondrial ROS by CD3-initiated calcium signaling. The mitochondrial ROS is necessary for the activation of nuclear factor of activated T cells (NFAT) and subsequent expression of IL-2, thereby facilitating the antigen-specific expansion of T cells in vivo [181]. Following TCR and CD28 costimulation, the production of ROS leads to the stabilization and elevation of SUMO-specific protease 3 (SENP3). The accumulation of SENP3 facilitates the deSUMOylation of BTB and CNC homology 1, basic leucine zipper transcription factor 2 (BACH2), which in turn preserved the stability and functionality of Treg cells [182]. Similarly, TCR stimulation-induced ROS promote the cytosolic translocation of SUMO-specific peptidase 7 (SENP7), which mediates the deSUMOylation and degradation of phosphatase and tensin homolog (PTEN), thereby maintaining the metabolic status and antitumor function of CD8⁺ T cells [183]. Conversely, oxidative stress due to elevated ROS production promotes T cell exhaustion and terminal differentiation, which can be hampered by the neutralization of ROS. Oxidative stress work in tandem with endosome recycling to reorganize the TCR signaling complex at the cell surface [184, 185]. Chronic oxidative stress, driven by diminished antioxidant glutathione (GSH) levels, causes the membrane displacement of linker for activation of T cells (LAT), a key adapter protein in the TCR-mediated signaling pathways. This disruption of TCR-mediated signaling due to a conformational change in redox-sensitive cysteine residues of LAT ultimately reduces T lymphocyte responsiveness [186]. Extracellular/microenvironmental redox state can also determine the activity of T cells. Adoptively transferred T cells, following chronic activation and expansion, exhibit increased vulnerability to cell death within oxidative TMEs [187]. Survival within these oxidative TMEs requires enhanced antioxidant capacity and elevated levels of reduced thiol groups (–SH) on T cell membranes, facilitated by reduced thioredoxin (Trx) and CD4 molecules [188, 189]. Therefore, central memory-like (TCM) T cells demonstrate superior survival compared to effector memory-like (TEM) cells in oxidative TMEs, attributable to their superior antioxidant capacity and higher surface thiol levels. Enhancing surface thiol levels through treatments like N-acetylcysteine (NAC) or rapamycin extends in vivo lifespan and improves tumor suppression in TCR-transduced CD8⁺ T cells [190]. Importantly, the surface redox status of T cells is primarily dictated by the local oxidative environment rather than by intracellular redox regulation systems. Reducing extracellular ROS improves T cell responsiveness and mitigates immunosuppressive cell death by increasing surface thiol groups [191]. Additionally, hypoxia, prevalent in the TME across various cancer types, intensifies T cell exhaustion through impaired mitochondrial function and consequent ROS accumulation [192]. The persistent production of ROS in the mitochondria under low oxygen conditions is enough to induce a state of exhaustion in CD8⁺ T lymphocytes. This is partially achieved by increasing the levels of phosphotyrosine signaling and the nuclear location of NFAT, a known transcriptional circuit associated with T cell exhaustion [193]. Therefore, modulating oxidative stress factor could offer a viable approach for regulating T cell function (Figure 4) [183].

In summary, both intracellular and extracellular redox conditions are critical determinants of T cell activity and function, suggesting avenues for targeted therapeutic intervention.

3.3.2 Antigen-Specific B Cells

Maintaining redox balance is crucial for the survival, antibody secretion, and immune homeostasis of antigen-specific B cells. B cell activation occurs through two primary pathways: T-dependent (TD) antigen stimulation via the B cell receptor (BCR), and T-independent (TI) antigen stimulation via the BCR or TLRs. Following activation, once activated, B cells differentiate into plasma cells (also known as plasmacytes or effector cells), memory B cells, and cytokine-secreting cells. Plasma cells mediate humoral immunity through antibody production, contributing to complement-dependent cytolysis and bactericidal activity, as well as antibody-dependent cell-mediated cytotoxicity (ADCC) via Fc receptor engagement on effector cells such as macrophages and natural killer (NK) cells. Memory B cells, characterized by extended lifespans, retain immunological memory of the initiating antigen, facilitating enhanced secondary immune responses upon subsequent antigen exposure [194-196].

Physiological levels of ROS are crucial for B cell activation and proliferation by enhancing BCR signaling. Ligation of the BCR in splenic B cells initiates biphasic ROS production: an initial, short-lived burst generated by NOX2, followed by a sustained increase mediated by NOX3 or mitochondrial sources. This later phase of ROS generation is vital for enhancing BCR signaling and facilitating B cell activation and growth [197, 198]. When B cells are exposed to H₂O₂, the redox factor APE/Ref- [1] rapidly translocate to the nucleus, increasing the DNA-binding activity of Pax5a, a transcription factor that regulates early B cell development and maturation [199]. Investigations into MHC II-mediated activation of resting B cells have highlighted the role of ROS in pro-survival signaling pathways, such as RAS/ERK/AP-1, PI3K/AKT/mTOR, ERK/JNK/P38 MAPK, and PKC/NF-κB [200, 201]. Conversely, oxidative stress induced by antigens can lead to apoptosis in regulatory B cells (Bregs) [202]. Treatment with hydrogen peroxide activates spleen tyrosine kinase (Syk), which can trigger pro-survival Akt pathways, inhibiting caspase-9 and offering protection against apoptosis induced by oxidative stress. In contrast, activation of PLC-γ2 through Syk promotes apoptosis in response to oxidative stress. The interplay between these proapoptotic and pro-survival pathways ultimately determines the fate of B cells under different levels of oxidative stress [203].

The differentiation of B cells is significantly influenced by the homeostatic levels of ROS. Redox alterations have been shown to play a role in the physiological activation and terminal differentiation of B cells in peripheral tissues [204]. A modest increase in ROS levels, induced by 1 μM CpGC, enhances the frequency of IL-10⁺ Breg cells [205]. ROS may also facilitate the differentiation of B cells into plasma cells and boost antibody production. In mice experiencing chronic oxidative stress, those lacking the antioxidant protein Tumor Protein 53-Induced Nuclear Protein 1 (TP53INP1) demonstrate an increase in plasma cell generation and greater antibody secretion [206]. Conversely, under conditions of pathological severe oxidative stress, the activation and differentiation of B lymphocytes are often suppressed [207]. Higher ROS concentrations significantly decrease the frequencies of IL-10⁺ Breg cells, without affecting the overall frequencies of transitional (CD24^hiCD38^hi), mature (CD24^intCD38^int), memory (CD24⁺CD38^lo) B cells, or plasmablasts (CD24^lo/−CD38^hi Blimp1⁺). Reducing ROS levels to “physiological” ranges through the action of Trx, an antioxidant enzyme, promotes the induction of Breg cells while suppressing effector B cells. The inactivation of Trx in B cells leads to mitochondrial outer membrane depolarization and elevated ROS levels, which impair IL-10 expression and suppressive functionality, resulting in an increase in B cells that produce pro-inflammatory cytokines. Trx deficiency contributes to Breg cell dysfunction in patients with SLE, while exogenous stimulation with Trx can restore Breg cells and mitochondrial membrane polarization in SLE to levels typical of healthy B cells [205].

Oxidative stress influences the antibody synthesis and storage functions of plasma cells, thereby impacting the humoral immune response. In a group of patients with non-alcoholic fatty liver disease (NAFLD), there was an observed increase in IgG antibody levels targeting oxidative damage molecules, referred to as oxidative stress-derived epitopes (OSE) [208]. Notably, the elevated levels of anti-OSE antibodies in these patients were positively associated with liver inflammation, suggesting an antibody-mediated response to oxidative stress linked to disease progression [209]. Treatment with Ginsenoside Rb1, an antioxidant compound, significantly alleviated immune damage caused by deoxynivalenol (DON) in mice, as indicated by a substantial rise in serum levels of IgA, IgG, and IgM [210, 211].

In general, physiological ROS produced by mitochondria or NOXs can boost the function and activity of APCs, whereas pathophysiological oxidative stress tends to suppress the antigen-specific immune response (Figure 5). Gaining a thorough understanding of how oxidative stress affects the antigen-specific immune responses of T cells and B cells could have important implications for the development of new immunotherapeutic strategies.

4.1 Oxidative Stress in Cancer: Dual Immune Activation and Suppression

The redox balance within cancer cells and the TME profoundly influences antitumor immune responses. ROS can enhance antitumor immunity through three mechanisms: promoting antigen generation, activating antigen presentation pathways, and stimulating immune cell functions. Oxidative stress-induced DNA damage and protein oxidative modifications produce TSAs or neoantigens, which activate T cells to recognize and attack tumors. At moderate levels, ROS enhance the antigen presentation activity of APCs—such as DCs and macrophages, and boost the antitumor activity of T cells and B cells, strengthening the cancer-immune cycle. However, excessive ROS inhibits antitumor immunity by causing dysfunction in antigen presentation, immune cell exhaustion and apoptosis, and the formation of an immunosuppressive microenvironment.

Physiologic ROS levels promote antitumor immunity by enhancing the cross-presentation capacity of DCs. DCs internalize tumor-derived microparticles (T-MPs) into lysosomes, where increased NOX2 leads to elevated ROS production and pH. This higher pH facilitates the generation and presentation of tumor antigenic peptides to CD8⁺ T cells. Simultaneously, elevated ROS levels upregulate CD80 and CD86 expression through lysosomal Ca²⁺ pathways and downstream transcription factor EB (TFEB), providing costimulatory signals that enhance T cell activation [212]. As a metabolic regulator, oxidative stress promotes STING-mediated DC antitumor immune responses. DC-generated ROS facilitates the interaction between SENP3 and interferon-induced protein 204 (IFI204), leading to IFI204 deSUMOylation. This activates the stimulator of interferon genes (STING) pathway, amplifying the type I interferon response and strengthening DCs' ability to present antigens and activate T cells [213]. Unlike conventional DC1s, plasmacytoid DCs (pDCs) rely on mitochondrial ROS (mtROS) rather than NOX2 for cross-presentation. Studies using mCAT transgenic mice, which express human catalase in mitochondria, show that reduced mtROS in pDCs significantly impairs CD8⁺ T cell responses, highlighting mtROS's critical role in pDC cross-presentation [95]. The ROS-responsive factor Nrf2 plays a key role in CD8⁺ T and chimeric antigen receptor (CAR) T cell antitumor responses within the ROS-rich tumor microenvironment. T cells lacking Nrf2 show enhanced antitumor responses due to ROS resistance and sustained effector functions. In human CAR-T cells, Nrf2 knockdown improves intratumoral survival and function in solid tumor xenograft models, effectively controlling tumor growth. Consequently, tumor growth in Nrf2^−/− mice is significantly suppressed and can be reversed by T cell depletion [214]. However, NRF2 in cancer cells inhibits MHC-I complex expression and NK cell-activating ligands. This reduced antigen presentation enables cancer cells to evade immune surveillance and progress to malignant tumors [215].

The oxidative stress within the TME fosters an immunosuppressive milieu that facilitates immune evasion and resistance to immunotherapy. Tumor cell metabolic activity and dysregulated antioxidant defenses contribute to a ROS-rich TME. High ROS levels inhibit antigen processing, blocking antigen cross-presentation, and the effectiveness of CD8⁺ T cells. Ethanol-induced oxidative stress impairs antigen-processing enzymes, such as 20S and 26S proteasomes, limiting antigenic peptide processing [216]. In an ovarian cancer model, DCs produce oxidized lipids upon ROS activation, which block the antigen cross-presentation by sequestering partner HSP70 and preventing the translocation of pMHC complexes to the surface of mouse cells, thereby inhibiting the occurrence of immune responses [151]. Specifically, peroxynitrite (PNT), a highly reactive oxidant synthesized by myeloid cells within the TME, hinders the proteasome activity of tumor cells. This impaired antigen processing reduces the presentation of PNT modified peptides (PNT-S peptides) on MHC I molecules, characterized by increased peptide dissociation rates. Consequently, CD8⁺ T cell antitumor responses are diminished, negatively impacting immunotherapy efficacy [217, 218]. Oxidative stress, particularly under nutrient restriction, promotes CAR T cell exhaustion and apoptosis. Decreasing levels of ROS by isocitrate dehydrogenase 2 (IDH2) ablation or NAC, a cell-permeable antioxidant, mitigate CAR T cell exhaustion and apoptosis, improve the anticancer effect of CAR T cells [219]. T cell–targeting fusogenic liposomes equipped with 2,2,6,6-tetramethylpiperidine, which protected T cells from oxidation-induced activity loss and efficiently inhibited tumor growth in multiple mouse tumor models [191]. Finally, ROS promotes the polarization of macrophages toward an M2 phenotype, which drives tumor progression in colorectal cancer through increased angiogenesis, tissue remodeling, and immune tolerance [220, 221].

The ability to modulate redox balance offers a promising strategy for cancer therapy. A deeper understanding of how oxidative stress and immune regulation interact will be essential for developing more effective cancer immunotherapies.

4.2 Oxidative Stress in Infection-Related Cancers: Immune Defense and Oncogenesis

Oxidative stress plays a complex and multifaceted role in infectious diseases caused by pathogenic microorganisms such as bacteria, viruses, fungi, or parasites. The ROS generated by phagocytes during respiratory bursts via NOXs are crucial for pathogen killing and aid the host antigen-specific immune response by enhancing antigen processing and presentation. Furthermore, ROS triggered by bacterial lipopolysaccharides (LPS), such as those from Escherichia coli (E. coli) and Salmonella, enhances antigen presentation and pathogen clearance [222-224]. This occurs because oxidative molecules (like H₂O₂) promote maturation of APCs, increasing expression of MHC II and costimulatory molecules (CD80, CD86) via NF-κB signaling [225]. This enhanced immune response is observed in both Gram-negative bacterial infections and Mycobacterium tuberculosis, where ROS production activates macrophages and upregulates costimulatory molecules (CD80, CD86, and CD40), improving antigen presentation to T cells and facilitating pathogen elimination. The increased expression of MHC molecules and costimulatory molecules, particularly CD40, on APCs strengthens T cell interactions and improves antigen presentation efficiency [70, 226, 227]. Similarly, ROS are essential for effective antiviral immunity, especially against respiratory viruses like influenza A and SARS-CoV-2. These viral infections trigger a respiratory burst, increasing ROS levels and activating CD4⁺ and CD8⁺ T cells through direct interactions or cytokine signaling [228-230]. This ROS-dependent T cell activation is demonstrated by reduced T cell expansion following treatment with the antioxidant Mn(III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP) [231].

Oxidative stress-mediated immune evasion plays a crucial role in viral-induced cancer development. This is particularly evident in cancers like hepatocellular carcinoma (HCC) and cervical cancer. In HCC, Hepatitis B virus (HBV) infection elevates ROS levels, which silences the SOCS3 gene and activates the IL-6/STAT3 pathway, promoting cancer development [232]. Additionally, HBV-related HCC patients with low antioxidant levels show poorer prognosis [233]. In cervical cancer, human papillomavirus (HPV) 16/18 E7 protein generates ROS, which modifies lactate dehydrogenase A (LDHA) and increases nuclear α-hydroxybutyrate (α-HB). This α-HB protects cancer cells from oxidative damage through Wnt signaling pathway activation via epigenetic modifications [234]. Excessive oxidative stress in hepatitis C virus (HCV) infected cells disrupts immune responses by impairing proteasomal function, reducing MHC I presentation, and altering APC function. This hinders pathogen clearance and can worsen disease severity. In HCV-positive hepatocytes exposed to ethanol, oxidative stress disrupts proteasomal composition, compromising viral antigen processing. This leads to reduced presentation of viral peptides on the cell surface by pMHC-I [235]. While CTLs typically target hepatocytes, the limited antigen peptides from impaired proteasomal activity reduce CTL recognition, potentially allowing HCV to persist in hepatocytes [236]. HPV-related cancers provide another example of oxidative stress disrupting immune responses. HPV-induced ROS accumulation facilitates HPV16 DNA integration into human keratinocytes, promoting cancer development [237, 238]. Oxidative stress weakens NK cell cytotoxicity by reducing perforin and granzyme B expression, diminishing their ability to eliminate HPV-infected cells [239]. Furthermore, ROS-induced DC dysfunction reduces HPV antigen presentation efficiency and creates a Th1/Th2 immune imbalance that favors Th2-type responses (primarily IL-4 and IL-10), suppressing cellular immune responses [240].

Collectively, ROS play a crucial role in pathogen clearance by enhancing APC maturation and antigen presentation. However, in viral-related cancers, virus-induced ROS contributes to immune evasion through multiple mechanisms: it impairs antigen processing and presentation, reduces NK cell activity, and disrupts the Th1/Th2 balance. These findings suggest that modulating redox balance could improve cancer immunotherapy outcomes.

4.3 Oxidative Stress in Autoimmune Disorders: From Epitope Spreading to Immune Tolerance Breakdown

Autoimmune diseases are characterized by the immune system's inappropriate and excessive attacks on the body's own cells. These responses typically involve abnormal presentation of self-antigens, loss of immune tolerance, and the production of autoantibodies or autoreactive T cells that target self-antigens, resulting in detrimental effects on healthy tissues. Under normal physiological conditions, self-tolerance is preserved by removing self-reactive lymphocytes in the thymus during immune development and by inducing energy in self-reactive T cells in the peripheral tissues. When this self-tolerance is disrupted, the immune response can generalize and extend to various epitopes derived from the whole complex containing the original antigenic epitopes or other structural/functional proteins, causing these epitopes to be unrecognized as self by the immune system. The aberrant presentation of these self-antigens leads to the development of systemic autoimmune diseases such as SLE, RA, and autoimmune hemolytic anemia, as well as tissue-specific autoimmune diseases, including diabetes mellitus, ulcerative colitis, Graves' disease, and myasthenia gravis. Oxidative stress-mediated oxidative PTMs cause the formation of neoepitopes and gives rise to autoantibodies in autoimmune disease, providing new insights for uncovering the mechanisms underlying these disorders.

Oxidative stress results in a loss of tolerance and epitope spreading within antigen-specific autoimmune responses. This epitope spreading can lead to the diversification and amplification of autoimmunity in an individual. Several studies on the immunization of non-autoimmune mice with self-peptides suggest that the wide range of B and T cell responses seen in SLE could stem from a single protein or even a particular cryptic self-epitope. A notable example is the modified Ro RNP complex, composed of a 60-kDa protein noncovalently associated with human cytoplasmic RNA, which is targeted by antibodies in 25%–40% of lupus patients. The modification of the lupus-associated 60 kDa Ro protein by HNE, a common reactive lipid oxidation product, significantly enhance its antigenicity and promoting epitope spreading to nuclear antigens such as La, double-stranded DNA, and snRNP [45, 241]. Another instance of oxidative PTMs leading to the breakdown of immune tolerance involves the complement component 1, q subcomponent (C1q), which features a collagen-like domain. Antibodies against C1q are recognized as clinically valuable for diagnosing nephritis in SLE. Recently, it has been shown that the oxidative modification of C1q enhances its antigenicity in an animal model and when analyzing serum from SLE patients [242]. Additionally, NOX-derived intracellular ROS in macrophages play a critical role in antigen presentation related to autoimmune diseases. The single-nucleotide polymorphism (SNP) rs201802880 in the human neutrophil cytosolic factor 1 (NCF1) gene, which encodes an essential component of the inducible NOX2 complex, is associated with autoimmune diseases like SLE [243]. A deficiency in NCF4 leads to reduced intracellular ROS production, impairing macrophages' ability to process and present antigenic peptides. Specifically, macrophages lacking NCF4 are unable to effectively oxidize and cross-link cysteine-containing antigenic peptides (such as GPI [244-258]), making these peptides more prone to processing and presentation to T cells. This autoantigen presentation subsequently activates autoreactive T cells and triggers arthritis [259, 260]. These findings indicate that oxidative stress plays a vital role in antigen-specific autoimmune responses by regulating immune tolerance and promoting epitope spreading.

Increased levels of free radicals can induce modifications to biomolecules, resulting in the production of neo-epitopes that sustain antigen-driven autoimmune responses. For example, the conversion of aspartic acid to isoaspartate derivatives or arginine to citrulline leads to the generation of autoantibodies in RA models. These autoantibodies often cross-react with native antigens, perpetuating the autoimmune response [261]. Similarly, isoaspartyl modifications of the lupus autoantigen Sm snRNP enhance lupus autoimmunity by increasing interaction with autoantibodies in SLE patients [262]. Furthermore, oxidative modifications of amino acids by reactive nitrogen species (RNS) and ROS increase the antigenicity of both DNA and immunoglobulin G (IgG), leading to the production of autoantibodies with higher affinity ligands [263]. Elevated levels of autoantibodies against oxidized low-density lipoprotein (LDL) have been observed in both SLE and RA patients compared to healthy controls. Additionally, RA patients with cardiovascular complications show increased autoantibodies targeting nitrated LDL, which is more easily taken up by macrophages than native or oxidized LDL. The clearance of oxidized or nitrated LDL via scavenger receptors, such as CD36 on macrophages, may contribute to the higher incidence of cardiovascular issues commonly seen in RA patients [264]. In addition to its effect on modified proteins, oxidative stress also influences the production of autoantibodies against other macromolecules, like DNA. Oxidized DNA antigens are more easily recognized by antibodies present in the serum of SLE patients compared to native DNA [265].

Oxidative stress also contributes to the autoimmune-mediated destruction and dysfunction of pancreatic β-cells in insulin-dependent diabetes mellitus. The autoimmune etiology of T1D is well-defined, with CD4⁺ and CD8⁺ T cells capable of recognizing various β-cell-derived antigenic epitopes, like oxPTM-insulin [266]. In individuals with diabetes, hyperglycemia and insulin resistance lead to oxidative stress, resulting from both elevated ROS production and a weakened antioxidant defense system [267]. Oxidative processes lead to specific modifications to insulins, resulting in the generation of oxPTM-insulin neoantigenic peptides with a higher ability to elicit T cell responses [56]. In addition to nonenzymatic processes implicated in neoepitope generation, oxidative stress also leads to enzymatic modifications of specific residues, thereby increasing the immunogenicity of β-cell peptides [268]. Oxidative or cytokine stress enhances the activity of tissue transglutaminase 2 (TTG2) in β-cells, which results in the production of deamidated neoepitopes. Deamidated neoepitopes from insulin, zinc transporter 8 (ZnT8), insulinoma-associated antigen 2 (IA-2), and glutamic acid decarboxylase 65 (GAD65) are more efficiently presented by disease-susceptible HLA-DQ proteins in APCs [268-270].

In conclusion, abnormal antigen presentation triggered by oxidative stress may play a key role in the development of autoimmune diseases. Further research is needed to clarify the exact causal relationship between these two processes.

5.1 Covalent Modification Induces Neoantigen Generation and Immune Responses

Covalent drugs can induce covalent modifications in abnormal proteins, leading to the production of neoantigens and enhancing T cell immune responses. One of the antigens presented by MHC is a relatively unique hapten that possesses immune reactivity but lacks immunogenicity, such as polysaccharides, lipids, and certain drugs. However, a hapten can transform into a complete antigen when it binds to a carrier protein. This hapten-protein complex is recognized as a foreign entity and is presented by MHC on APCs. Following this principle, numerous covalent drugs have been developed to modify specific “undruggable” proteins, facilitating their presentation to T cells and B cells and triggering an adaptive immune response.

The notable example of covalent drugs is targeting the KRAS mutation, a prevalent genetic alteration in the initial identified oncogene RAS in humans. The G12C mutation is a common genetic alteration in the KRAS gene, where the amino acid glycine is substituted with cysteine. This mutation is known to contribute to the development of tumors [271, 272]. Targeted covalent inhibitors (TCI), like ARS1620, permanently alter the mutant cysteine in KRAS-G12C and produce changed peptides that can be processed and displayed on the cell surface by MHC I. This leads to the creation of novel hapten epitopes, which stimulate T cell responses and activate cytotoxic T cells [273-275]. Similar covalent inhibitors like sotorasib (AMG510) [276], adagrasib (MRTX849) [277-279], JNJ-74699157 [280], LY3499446 [281], have been proven to react with cysteine residue and drive tumor regression. Building on this principle, a novel class of molecules can target mutated tumor suppressor proteins, covalently modifying hotspot residues to generate neoantigens and elicit specific immune responses such as p53 Y220C and p53 R273C [282, 283]. In recent times, many covalent drugs have been developed for the treatment of cancer or HCV [284, 285]. By incorporating a bio-reactive amino acid-fluorosulfate-l-tyrosine (FSY) into human PD-1, the resulting covalent PD-1 (FSY) significantly augments antitumor activity in mice [286].

Furthermore, the direct covalent interaction between drugs and HLA can alter the peptide repertoire presented by HLA, thereby inducing T cell proliferation. It has been demonstrated that abacavir, covalently bound to amino acids, binds to HLA-B*57:01 and triggers a hypersensitivity reaction [287, 288]. Therefore, haptens that selectively modify mutant oncoproteins, rather than merely acting as pharmacological inhibitors, could considerably broaden the spectrum of tumor-specific neoantigens available for therapeutic targeting. By selectively covalently modifying specific amino acid residues on receptors or enzymes, these drugs offer enhanced biochemical potency and selectivity [289]. These tumor-specific PTMs involve the covalent alkylation of mutated cysteine residues on oncoproteins by drugs, creating novel neoantigens that immunotherapy can effectively target and providing a promising solution for drug resistance.

5.2 Reactive Oxygen Species Formation and Elimination in Immune Response

The generation of ROS such as superoxide anion (•O₂⁻), hydrogen peroxide (H₂O₂), hydroxyl radical (•OH), and singlet oxygen (¹O₂) in immune cells occurs through various pathways [290]. NOXs, especially within macrophages and neutrophils, are pivotal enzymes that convert oxygen into superoxide anion, the primary form of ROS [291]. Mitochondria also generate ROS (•O₂⁻ and H₂O₂) during electron transport [292]; however, mitochondrial dysfunctions, like mtDNA mutations and reduced membrane potential, can lead to increased ROS production [293]. Moreover, other enzymes, including cyclooxygenases (COXs), lipoxygenases (LOXs), and xanthine oxidase, further contribute to ROS generation [294]. To combat ROS, cells employ antioxidant enzymes such as superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx), along with antioxidants like GSH and vitamins C and E [295]. Given their short lifespan (Table 1), ROS play crucial roles in signaling and metabolism. Balanced levels of ROS are essential for normal immune functions, acting as second messengers in TCR signaling, which regulates T cell activation and differentiation, stimulates the release of inflammatory cytokines (e.g., IL-6, TNF-α), and modulates autophagy [298]. Conversely, excessive ROS can lead to cellular damage and dysfunction, such as T cell apoptosis through the upregulation of Fas and downregulation of Bcl2 [299]. Therefore, maintaining ROS homeostasis is vital for health. Because of the dual nature of ROS, both antioxidant and pro-oxidant approaches are being actively pursued in drug development for various diseases related to oxidative stress.

Specific inhibitors targeting ROS sources, including NOX inhibitors and mtROS inhibitors, improve the antigen-specific immune response in TME. NOX inhibitors, such as GKT137831, effectively prevent hypertensive cardiac remodeling in mice [300], reduce oxidative stress and proteinuria in T1D mouse models [301]. In in vivo experiments, GKT137831 reduced the levels of cancer-associated fibroblasts (CAFs), and the accumulation of CD8⁺ T cells at the tumor edge was no longer apparent, while the infiltration of CD8⁺ T cells into the tumor significantly increased. Therefore, targeting CAFs specifically with GKT137831 can reshape the immune microenvironment [302]. NOS31, a selective NOX1 inhibitor derived from Streptomyces, inhibits NOX1 activity and cell growth in multiple cancer cell lines, including gastric and colorectal cancers [303]. Other NOX inhibitors, including GKT136901, VAS2870, APX-115, CPP11G, and CPP11H, have shown promising clinical efficacy by indirectly reducing ROS production [304-306]. NOX inhibitors may mitigate oxidative stress within the tumor microenvironment and rejuvenate the functionality of immune cells by diminishing the production of ROS [307]. Furthermore, NOX inhibitors facilitate the polarization towards the M1 phenotype by reducing ROS levels, thereby enhancing antigen presentation and the secretion of inflammatory cytokines [308]. Mitoquinone, a ubiquinone derivative with selective mtROS-scavenging activity, inhibits lipid peroxidation and prevents apoptosis induced by oxidative stress [309]. Lipid peroxidation is a chain reaction triggered by oxygen free radicals attacking cell membrane lipids, which can lead to biomembrane damage. Oxidized lipids induce maturation phenotype characteristics in DCs, upregulating CD86 while suppressing phagocytic activity, thereby reducing the phagocytic efficiency and antigen-processing capacity of APCs. The antioxidant effects of mitoxantrone can mitigate such damage [310].

It is important to note that once cells progress to a precancerous state, antioxidants are no longer sufficient to halt cancer development, and apoptosis-inducing agents are required. In the regulation of cell fate, ROS levels exhibit a threshold effect. When redox balance is disrupted, the accumulation of ROS can damage biomolecules and promote malignant transformation. Elevated levels of ROS beyond this threshold can induce cancer cell death [311]. Therefore, employing pro-oxidant strategies to enhance ROS generation in cancer cells or to weaken their antioxidant defenses can disrupt the oxidative balance in tumor cells. This, in turn, activates various cell death pathways, including apoptosis, necrosis, and autophagy, ultimately restraining cancer progression [312]. One widely used small molecule drug in clinical practice, Elesclomol (formerly STA-4783), has been shown to elevate intracellular ROS levels, selectively inducing apoptosis in melanoma cells (NCT00879866) [313]. As a metal chelator, Elesclomol forms a stable complex with copper ions (Cu²⁺) and participates in the Fenton reaction within cells, leading to the generation of ·O₂⁻ and H₂O₂. This oxidative stress disrupts the balance of Bcl-2 family proteins, promoting the activation of proapoptotic proteins such as Bax, which increases mitochondrial membrane permeability and selectively induces apoptosis in melanoma cells [314]. During the process of apoptosis, cells release tumor-associated antigens (TAAs) and damage-associated molecular patterns (DAMPs), such as HSP. These antigens and DAMPs can be taken up by APCs, thereby initiating an immune response [310]. A research team developed a ROS-sensitive polymer (PHPM) that co-encapsulates Elesclomol (ES) and Cu to form nanoparticles (NP@ESCu). The combination of ES and Cu works synergistically to induce ROS and copper-mediated cell death, effectively killing bladder cancer cells. Additionally, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that protein processing in the endoplasmic reticulum, antigen processing, and presentation are activated in cells treated with NP@ESCu, inducing a significant immune response [315]. Nitrovin (difurazone), an antibacterial nitrofuran drug, can induce paraptosis-like cell death in glioblastoma multiforme cells independent of caspase activation by targeting thioredoxin reductase 1 (TrxR1), accompanied by ROS generation and endoplasmic reticulum stress activation. This confirms the cytotoxic effects of Nitrovin on cancer cells [316]. ROS and ER stress may enhance the efficiency of antigen presentation by upregulating the expression of MHC molecules through the activation of NF-κB signaling pathway [317]. In fact, anthracycline-based anticancer drugs, such as doxorubicin, can chelate intracellular iron, leading to the accumulation of •OH and ultimately resulting in cell death [318]. These drugs are effective against breast cancer and various solid tumors [319]. This process not only directly kills tumor cells but may also enhance its anticancer effects by activating the immune response. Specifically, anthracycline drugs can induce immunogenic cell death and the release of DAMPs in tumor cells, which in turn helps to trigger tumor-specific CD8⁺ T cell infiltration through cross-presentation by DCs [320]. Cisplatin, by cross-linking DNA purine bases and disrupting DNA repair mechanisms in cancer cells, damages mitochondrial DNA (mtDNA) and causes ETC injury, thereby inducing oxidative stress to target cancer cells [321]. mtDNA stress is involved in cytoplasmic antiviral signaling, enhancing the expression of a subset of interferon-stimulated genes, and plays an important role in antiviral signaling and type I interferon responses during infection [322]. Detailed information regarding some drugs that regulate ROS levels and have entered clinical trials or are in the clinical phase has been summarized in Table 2.

5.3 Promoting the Antigen-Presentation Machinery by Redox Regulation

Oxidative stress directly influences the activity and functionality of APCs by either modulating signaling pathways or altering the expression levels of proteins involved in antigen presentation, suggesting that redox regulation could be used as a therapeutic strategy to boost immune response.

A potent antioxidant of itaconate, a potent electrophile capable of alkylating cysteine residues in various target proteins, has been linked to several antigen presentation conditions due to its ability to alleviate oxidative stress by inducing the expression of the transcription factor Nrf2.

The cell-permeable itaconic acid derivative, 4-octyl itaconate (4-OI), acts as an immunomodulator by alleviating pathogenic inflammation and oxidative stress. It achieves this by modifying cysteine residues in target proteins, such as the major antioxidant transcription factor Nrf2 and the critical metabolic regulator glyceraldehyde 3-phosphate dehydrogenase (GAPDH) [361-363]. These compounds also inhibit the JAK1/STAT6 signaling pathway, which leads to reduced succinate dehydrogenase (SDH) activity in macrophages, thereby decreasing ROS production and preventing M2 macrophage polarization [364]. Given in antigen presentation, itaconate and its derivative dimethyl fumarate (DMF) exhibit therapeutic potential for the treatment of autoimmune diseases (such as psoriasis and multiple sclerosis), allergic conditions (such as asthma), and infections (including SARS-CoV-2) [361, 364, 365]. Furthermore, the cross-presentation ability of mesenchymal stem cells (MSCs) treated with the pyrimidinyl-indole derivative UM171a is dependent on mitochondrial ROS production. These treated MSCs show increased MHC I expression and elevated levels of several genes associated with antigen presentation. This increase allows MSCs to effectively cross-present immunogenic peptides derived from exogenous soluble proteins, thereby enhancing T cell responses [366].

Bruton's tyrosine kinase (BTK) is a crucial enzyme in the BCR signaling pathway and is known to be involved in inflammatory and oxidative signaling across various immune cells. When activated, BTK triggers the upregulation of NOX-2 and iNOS, contributing to oxidative stress in immune cells such as DCs, neutrophils, and B cells [367]. This oxidative stress can be alleviated by BTK inhibitors, as indicated by reduced levels of markers such as iNOS, NOX2, lipid peroxides, nitrotyrosine, and protein carbonyls. Inhibition of BTK via BIIB091 has also been found to dampen B cell-mediated antigen presentation to T cells [368]. Therefore, highly selective BTK inhibitors offer safer therapeutic alternatives for cancer patients and autoimmune diseases which exhibits disturbed antigen presentation. Covalent BTK inhibitors (acalabrutinib, ibrutinib, orelabrutinib, zanubrutinib, BGB-8035, tirabrutinib) are clinically validated for various cancers [284, 369, 370]. Furthermore, several other selective BTK inhibitors (evobrutinib, bribrutinib, spebrutinib, remibrutinib, rilzabrutinib, fenebrutinib) are in clinical trials for autoimmune diseases such as SLE, RA, multiple sclerosis (MS), and chronic spontaneous urticaria (CSU) [371-373].

5.4 Nanotechnology-Based Regulation of Antigen Processing and Presentation

Nanoparticle technology is currently attracting much attention due to its potential in redox regulation and promoting antigen presentation [374, 375]. A biomineralized nano-vaccine, NVs^cp, which is made by combining a self-assembled nano-vaccine with calcium peroxide, generates significant amount of ROS in response to the acidic environment of lysosomes. The accumulation of ROS promotes proteasome activity and the cross-antigen presentation by DCs, leading to the activation of tumor-specific Th cells and CTLs for tumor immunotherapy [356]. Incorporating of ROS-inducing all-trans-retinoic acid into pH-sensitive polysaccharide-based nanodelivery systems has been found to boost proteasome activity and significantly enhance ovalbumin (OVA) antigen presentation in mice [375]. Since optimal ROS levels promote DC maturation, ROS induction nanoparticles may also serve as a potential cancer vaccine platform [108]. Nanogel-induced lysosomal rupture directly stimulates ROS production within DCs, further augmenting proteasomal activity and subsequent MHC I antigen presentation. This controlled intracellular ROS elevation facilitates better cross-presentation of antigens, thereby improving the efficacy of cancer vaccines [357]. Furthermore, ROS-responsive nanomaterials modified with hyaluronic acid (HA, a ligand for CD44 receptors) such as PHO NPs, could serve as effective antigen delivery systems that promote DC maturation, antigen uptake, and presentation [185]. The optimal liposomal formulation containing cationic lipids has been shown to induce appropriate ROS levels in APCs, effectively controlling tumor growth [359, 376].

Simultaneously, certain nanomedicines can enhance antigen presentation through oxidative stress-induced antigen release [377-379]. For instance, liposomal nanomedicines encapsulating doxycycline hydrochloride (Doxy) and chlorin e6 (Ce6) generate ROS through dual pathways: Ce6 directly produces ROS upon near-infrared laser irradiation, while Doxy-induced mitochondrial damage synergistically increases ROS production, thereby amplifying photodynamic therapy (PDT)-induced immunogenic cell death (ICD) [360]. Additionally, Doxy enhances antigen presentation by inhibiting autophagy, leading to upregulated MHC I expression on the tumor cell surface [380]. By integrating the photosensitizer AIE with conversion nanoparticles, a robust ROS-dependent immune activation mechanism is achieved, which induces ICD and subsequently releases antigens, thereby facilitating a potent antitumor immune response [381]. Albumin-based NPs combined with indocyanine green, gold nanorods, catalase, and KDEL peptides increase ER stress and oxidative stress, leading to ICD and damaging tumor cells. This approach enhances antigen presentation and stimulates tumor-specific immune responses [382]. Moreover, MPS-PVP, polyvinylpyrrolidone (PVP)-modified two-dimensional manganese thiophosphate (MnPSe3, MPS) nanosheets, promotes antigen release by generating ROS from disrupted biofilms in the infectious microenvironment (IME). The subsequent rebalance of immunosuppressive signals, such as CD206, and costimulatory signals, including CD40 and CD80, enhances APC functionality and antigen presentation, triggering robust antibacterial immunity [383].

Interestingly, nanoparticle formulations with ROS scavengers regulate antigen-specific immune tolerance, playing a pivotal role in treating autoimmune diseases [384-387]. For instance, lignin-based nanoparticles, synthesized from plant-derived natural products with inherent ROS-scavenging properties, have been conjugated with self-antigens to facilitate antigen presentation to tolerogenic DCs. This approach reinstates immune tolerance by inhibiting autoreactive Th1 and Th17 cells, making it a promising tolerogenic vaccine platform for treating MS [388]. The introduction of cerium oxide nanoparticles, another potent ROS scavenger, can further suppress APC activation and enhance antigen-specific immune tolerance. This approach has been shown to induce a significant recovery in the late chronic phase of experimental autoimmune encephalomyelitis (EAE) in mice [345].

Collectively, redox-active nanomaterials can regulate the generation and clearance of ROS, thus showing potential applications in treating diseases related to antigen-specific immune disorders.

5.5 Improving the Function of Antigen-Specific Immune Cells

Establishing effective antitumor immunity depends on the activation, proliferation, and differentiation of lymphocytes that are specific to the tumor antigen [389]. Most cancer immunotherapies rely on the activation and infiltration of immune cells to generate immune response effects, such as cellular immunotherapy, including CAR-T and engineered T cells [390, 391]. This process largely depends on the interaction between T cells and APCs. However, recent studies have shown that only 10 percent or even fewer tumor-infiltrating CD8⁺ T cells have identifiable cytotoxic effects on tumors [392-394]. One of the challenges of tumor epitope-reactive T cells is oxidative stress in the TME, which causes T cell death [395]. Researchers hypothesize that reducing the oxidative stress by enhancing Trx could sustain the antitumor function of T cells [396, 397]. Trx1-overexpressing T cells from transgenic mice have lower levels of ROS and diminished vulnerability to TCR restimulation or oxidation-induced cell death. These T cells showed a central memory-like phenotype, characterized by decreased glucose uptake and diminished effector functions. Additionally, culturing T cells with recombinant Trx improved their mitochondrial metabolism and tumor control ability [189]. Another method by scavenging ROS to protect T cells from oxidative stress damage is using a nanomaterial delivery system. Researchers have utilized T-cell-targeted liposomes composed of 2,2,6,6-tetramethylpiperidine fused with anti-CD3 F(ab')₂ antibodies (T-Fulips) to regulate the redox state of T cells and control their activity. This liposome protects T cell activity from being lost due to oxidative stress by neutralizing the levels of ROS, thereby maintaining their antigen presentation, recognition, and processing capabilities [191]. Thus, enhancing the antioxidant capacity of antitumor T cells can reshape their immunometabolic phenotype and enhance their tumor control capacity.

Although excessive amounts of ROS can be harmful, moderate levels act as crucial signaling molecules in T-cell activation and differentiation [398]. Studies indicate that appropriate ROS elevation partially activates T lymphocytes [244, 399, 400]. ROS is significant in the activating signaling pathways initiated by the TCR and CD28. Particularly, mitochondrial complex III-derived ROS production is essential for T cell activation by activating NFAT. Activation of NFAT increase the production of IL-2 and leading to antigen-specific T cell activation [181]. T cells isolated from patients on treatment of Venetoclax, a Bcl-2 inhibitor, have shown increased ROS levels in vitro. Studies indicate that Venetoclax, when administered at safe levels, enhances ROS production, leading to improved T-cell efficacy without harming cell survival [181, 401]. Additionally, certain small-molecule drugs can modulate the activity of immune cells. The inhibitory mechanism triggered by carbon monoxide-releasing molecule-2 (CORM-2) involves the suppression of intracellular ROS production, effectively curbing T cell proliferation. This inhibition parallels the effects seen with the antioxidant NAC, ultimately leading to a reduction in autoimmune hepatitis severity [344].

ROS has the ability to modify the functionality of Tregs. Studies have found that SENP3 is rapidly stabilized under the influence of ROS generated by TCR and CD28 stimulation, leading to the desumoylation of BACH2 and thereby maintaining the sustained functionality of Treg cells [182]. These molecular mechanisms underlying the interaction between ROS and Treg cell-mediated tumor immunosuppression indicate that targeting ROS within Treg cells may improve tumor immune tolerance. The fruits of the Berberis genus are a significant source of bioactive compounds, such as chlorogenic acid, catechin, rutin, quercetin, 3-d-galactoside, berberine, and magnoflorine, which can be leveraged in the development of alternative therapeutic strategies to alleviate inflammation and oxidative stress [258, 340-343, 402, 403]. Studies have demonstrated that cells treated with Berberis fruit extracts exhibited a reduction in ROS levels, which can be partly attributed to the activation of the heme oxygenase-1 (HO-1) pathway [404]. Moreover, Berberis fruit extract appears to positively influence adaptive immune cells by controlling concanavalin A-mediated Treg cell proliferation [255, 405]. Additionally, the inhibition of the NF-κB, MAPK inflammatory pathways by Berberis fruit extract further contributed to the mitigation of ROS accumulation and the suppression of the oxidative-inflammatory cycle [403].

Beyond its regulatory effects on DCs and T cells, ROS also plays a crucial role in modulating macrophage activity [406-408]. Melanin nanoparticles (MNPs), derived from the ink of marine organisms like cuttlefish, are incorporated into hydrogels synthesized through the reaction with alginates extracted from seaweed. These MNPs can interact with ROS to generate O₂ while simultaneously scavenging ROS, thereby mitigating oxidative stress-induced damage in cardiomyocytes. This dual action fosters the M1 macrophages to the reparative M2 phenotype [346]. Additionally, high iron loads induce elevated ROS levels, which enhance the activity of p300/CREB-binding protein (p300/CBP) acetyltransferases and promote the acetylation of p53, facilitating the conversion of macrophages towards the M1 phenotype [409]. Moreover, a deficiency in the GTPase family M protein (IRGM) in macrophages inhibits ROS production, and the removal of ROS effectively suppresses IRGM overexpression-induced macrophage apoptosis [410]. The Irg1/itaconate axis enhances macrophage phagocytosis by modulating the Keap1/Nrf2/CD36 molecular mechanism. This process effectively reduces bacterial load and offers therapeutic potential for treating bacterial infectious peritonitis [411]. These the regulatory role of oxidative stress in influencing the functionality of antigen-specific immune cells and suggest a potential therapeutic strategy for antigen-specific immune disorders.