Tregs play a pivotal role in shaping the immunosuppressive TME and are closely linked to tumor progression, metastasis, treatment response and clinical outcomes in LUAD (47). Tumor-associated Treg populations can be categorized into tumor-resident Tregs, tissue-resident Tregs and circulating-derived Treg subsets, each exhibiting distinct functional characteristics within the TME (51). Accumulating evidence indicates that Treg infiltration is typically increased in LUAD tissues, metastatic lymph nodes and peripheral blood and is associated with advanced disease stages, tumor recurrence and metastatic progression (52,53). Compared with normal lung tissues and peripheral blood, LUAD tumors demonstrate markedly higher Treg accumulation, suggesting that Treg recruitment and expansion contribute to the establishment of an immunosuppressive niche that facilitates tumor growth (54).

The association between Treg infiltration and clinical outcome has been extensively investigated, with most studies supporting an unfavorable prognostic association, particularly when Tregs are enriched within the tumor. Increased intratumoral Treg abundance has been associated with shorter OS and DFS, although the strength of this association varies according to tumor stage, Treg phenotype, tissue compartment and detection method (55). Xiong et al (55), for example, identified a close relationship between hypoxia-associated prognostic signatures and immune-cell infiltration, including Treg accumulation, suggesting that Treg-associated immune remodeling may contribute to adverse clinical outcomes. Xiao et al (56) provided more direct evidence linking a Treg-regulatory factor with patient survival by showing that Galectin-9 is upregulated in LUAD, suppresses CD8⁺ T-cell cytotoxicity, promotes Treg expansion and is associated with increased Treg infiltration and poor survival. Importantly, the latter findings support a biologically plausible link between Treg accumulation and unfavorable outcome rather than merely describing a statistical correlation.

However, the prognostic role of Tregs should not be interpreted as uniformly detrimental in all LUAD patients. Tregs comprise functionally heterogeneous populations and their prognostic significance may depend on their phenotype, localization and interaction with other immune-cell populations. Spatial immune profiling has shown that the relative distribution of conventional CD4+ T cells, inducible Tregs, natural Tregs and CD8+ T cells can independently predict DFS, emphasizing that the composition and spatial organization of the T-cell compartment may provide more prognostic information than total Treg abundance alone (57). Thus, current evidence supports Treg infiltration as an important component of the LUAD prognostic landscape, but does not establish a simple linear relationship in which increasing Treg numbers invariably predict poor outcome.

Beyond the direct assessment of Treg abundance, several studies have investigated tumor-associated molecules and cellular interactions that may influence Treg infiltration and thereby contribute to LUAD prognosis. These studies provide complementary evidence, but their ability to establish Tregs as the principal determinant of outcome varies considerably.

At the molecular level, GPD1L expression is reduced in LUAD and negatively correlates with Treg infiltration, while low GPD1L expression is associated with tumor progression and poor prognosis (58). Similarly, Zinc Finger CCCH-Type Containing 12D (ZC3H12D), a tumor suppressor involved in the regulation of inflammatory transcripts, is downregulated in LUAD and associated with shorter OS. Single-cell RNA sequencing further showed that ZC3H12D is highly expressed in immune-cell populations, including Tregs, suggesting a potential role in shaping the immune microenvironment (59-61). By contrast, SKA3 and TUBA1C are overexpressed in LUAD and associated with poor survival, together with increased infiltration of immunosuppressive populations including Tregs (61-63). Collectively, these findings support the existence of a Treg-associated molecular phenotype linked to unfavorable prognosis. Nevertheless, because these studies primarily establish associations among gene expression, Treg infiltration and survival, they do not by themselves demonstrate that altered Treg function is the causal mechanism through which these genes determine patient outcome.

The relationship between Tregs and the broader TME provides stronger biological context for these associations. The leukocyte-associated immunoglobulin-like receptor (LAIR) family functions as a collagen receptor and mediates interactions between immune cells and the extracellular matrix (64). LAIR2 expression is particularly enriched in FoxP3-expressing Tregs and the CD4+LAIR2+ Treg signature has prognostic significance in LUAD patients (65). Similarly, EPHA5 mutations are associated with increased CD8+ T-cell and M1 macrophage infiltration, reduced recruitment of immunosuppressive Tregs and prolonged survival in patients receiving immunotherapy (66). These findings suggest that the prognostic relevance of Tregs may depend not only on their absolute abundance but also on the balance between immunosuppressive and antitumor immune populations.

Other studies provide additional evidence that Tregs participate in a multicellular network within the LUAD TME. ILT4 is an immunosuppressive molecule predominantly expressed in myeloid innate cells and has been implicated in tumor proliferation, invasion and metastasis (67). Cancer-associated fibroblasts (CAFs) can cooperate with Tregs to establish an immunosuppressive niche and the coexistence of CAFs and FoxP3+ Tregs is associated with poor clinical outcomes in LUAD (68). In addition, immune regulatory molecules including ILT4, IκB kinase α (IKKα), 5-hydroxytryptamine and GRP94 have been reported to promote Treg recruitment or activation, thereby contributing to immune escape and unfavorable prognosis (69-72).

Among these studies, the findings of Song et al (70) provide particularly important mechanistic support for the functional relevance of Tregs. Loss of IKKα in LUAD cells stimulates the production of Treg-inducing cytokines, thereby enhancing Treg recruitment and expansion within the TME. The resulting increase in Treg accumulation impairs antitumor immune responses and facilitates tumor immune escape. This study indicates that tumor-intrinsic alterations can actively reshape Treg-mediated immunosuppression through tumor-immune-cell communication. Therefore, Tregs may function not simply as a prognostic correlate, but as an intermediary linking tumor-cell alterations to immune suppression and disease progression.

Taken together, these molecular and cellular studies support a model in which Treg-associated prognosis is generated by interactions among tumor-intrinsic factors, stromal cells, immune regulatory molecules and effector immune populations rather than by Treg abundance alone. However, because a number of these studies rely on correlative analyses, their findings should be interpreted as evidence for a Treg-associated prognostic network rather than definitive evidence that Tregs independently determine patient survival. Biomarkers affecting Treg infiltration and LUAD prognosis are illustrated in Fig. 1 and summarized in Table I.

Recent advances in transcriptomic analysis and computational biology have expanded the assessment of Treg-related prognostic features from single biomarkers to multidimensional molecular and immune signatures. Several studies have developed prognostic models incorporating immune infiltration, tumor metabolism, genetic alterations, or immune-related regulatory networks, consistently demonstrating that the composition of the LUAD immune microenvironment contains clinically relevant prognostic information. Shao et al (73) identified an alternative splicing-based prognostic signature associated with B-cell and immune infiltration, while Wang et al (74) developed an immune infiltration-related model that identified immune-cell populations associated with patient survival. Similarly, Li et al (75) established a mitochondrial-related gene signature associated with both immune infiltration and survival, suggesting an interplay between tumor metabolic status and immune regulation, whereas Gao et al (76) developed an immunophenotype-based risk score that effectively stratified patients according to distinct immune characteristics. Liu et al (77) further demonstrated that competing endogenous RNA networks interact with tumor-infiltrating immune cells to form prognostically relevant regulatory networks and Song et al (78) showed that an immune-related risk model incorporating TP53 status could predict both prognosis and immunotherapy response. Wu et al (79) likewise identified multi-gene immune-related signatures associated with prognosis and potential immunotherapy responsiveness. Fig. 2 and Table II show LUAD prognosis, survival and machine learning models derived from The Cancer Genome Atlas (TCGA; https://portal.gdc.cancer.gov/), Gene Expression Omnibus (GEO; https://www.ncbi.nlm.nih.gov/geo/), and Genotype-Tissue Expression (GTEx; https://gtexportal.org/home/) databases.

Taken together, these studies provide relatively consistent evidence that the immune landscape of LUAD, and the molecular programs associated with immune-cell infiltration, has substantial prognostic value. However, most of these models were not specifically designed around Tregs and their predictive performance reflects the combined contribution of multiple immune and tumor-related features. Therefore, they should be interpreted as indirect evidence supporting the prognostic relevance of Treg-associated immune states rather than as evidence that Tregs independently determine patient outcome. Among these studies, the work of Wang et al (80) provides more direct evidence for the clinical relevance of Treg biology, as a Treg-related prognostic nomogram was specifically developed for LUAD, demonstrating that Treg-associated genes can contribute to survival prediction. Nevertheless, even this Treg-focused model supports the prognostic utility of a Treg-associated molecular signature rather than establishing total Treg infiltration as a standalone biomarker. Thus, the current computational literature supports the concept that Treg-related molecular characteristics can improve prognostic risk stratification, but the incremental value of Treg-specific features over broader immune signatures remains to be systematically determined.

An important limitation is that most existing models are derived from bulk transcriptomic datasets, in which Treg-associated signals may be confounded by other immune-cell populations, tumor purity, or differences in Treg abundance and phenotype. Moreover, the predictive performance of these models does not necessarily establish a biological or causal role for Tregs in determining survival. Future studies should therefore integrate Treg-specific single-cell and spatial features with clinical variables and longitudinal treatment information to determine whether specific tumor-promoting Treg subsets can provide more robust and reproducible prognostic information than bulk Treg-related signatures.

Overall, the available evidence supports several relatively robust conclusions. First, Tregs are consistently enriched in the LUAD TME and are associated with an immunosuppressive immune contexture (47,52-54). Second, a substantial proportion of clinical and molecular studies associate increased Treg infiltration or Treg-related signatures with advanced disease and unfavorable survival outcomes (55,56,58-65). Third, mechanistic studies such as the IKKα study provide biological support for the concept that tumor cells can actively promote Treg recruitment and expansion, thereby linking Treg accumulation to immune suppression and tumor progression (70). Finally, computational studies indicate that Treg-associated molecular characteristics can contribute to prognostic risk stratification and may have potential value in predicting immunotherapy response (73-78).

Nevertheless, the current evidence does not justify concluding that Treg infiltration alone is a universally applicable or independent prognostic biomarker for LUAD. The prognostic effect may differ according to Treg subset, spatial localization, disease stage, detection methodology and the relative abundance of other immune populations. Furthermore, a number of molecular and machine-learning studies demonstrate associations rather than causality and their predictive performance may reflect the combined effects of multiple biological processes rather than Treg biology alone. Importantly, even when high Treg infiltration is associated with poor survival, this does not necessarily establish that Tregs are the primary drivers of tumor progression; Treg accumulation may also reflect an already established immunosuppressive or tumor-promoting microenvironment.

Therefore, the most appropriate interpretation of the current literature is that Treg infiltration and Treg-associated molecular signatures represent promising components of a multidimensional prognostic framework for LUAD, rather than definitive standalone biomarkers. Future studies should determine whether specific tumor-promoting Treg subsets, rather than total Treg abundance, provide stronger and more reproducible prognostic information. Integrating single-cell sequencing, spatial transcriptomics, longitudinal clinical sampling and functional validation may help distinguish Tregs that actively drive tumor progression from those that primarily reflect the existing immune state of the tumor.

A primary mechanism through which Tregs facilitate immune escape is the expression of inhibitory receptors and immunosuppressive molecules that directly impair effector immune responses. Tregs are known to highly express immune checkpoint molecules such as CTLA-4, PD-1, TIGIT and LAG-3, which suppress the activation and cytotoxic functions of CD8⁺ T cells and NK cells, thereby enabling tumor cells to evade immune surveillance (81). Among these molecules, CTLA-4 expressed by Tregs competitively binds to CD80/CD86 on antigen-presenting cells, reducing costimulatory signaling and limiting T cell activation. Studies indicate that blocking CTLA-4 signaling can diminish Treg-mediated immunosuppression and enhance antitumor immune responses, underscoring the significance of Treg-associated checkpoint regulation in cancer immunotherapy (82). In LUAD, tumor cells can further amplify Treg-mediated immune suppression by inducing immunoregulatory molecules. Tumor-derived factors, for example, promote Treg recruitment and activation through the CCL22/CCR4 axis, resulting in increased Treg accumulation at the tumor site and suppression of CD8⁺ T cell-mediated tumor killing (83,84). Additionally, tumor-associated immune checkpoint molecules and soluble immunosuppressive mediators contribute to sustaining Treg suppressive activity, facilitating immune escape (83,84).

Beyond immune checkpoint pathways, metabolic reprogramming within the TME plays a key role in maintaining Treg function and promoting immune escape. Tumor cells commonly generate a metabolically unfavorable environment characterized by glucose depletion, heightened lactate accumulation, hypoxia and altered amino acid metabolism. Tregs exhibit significant metabolic adaptability, allowing them to survive under these challenging conditions while maintaining suppressive activity as effector T cells become functionally exhausted (85). Glucose competition is a critical metabolic mechanism regulating Treg-mediated immune suppression. Activated Tregs efficiently utilize available metabolic substrates and resist metabolic stress, while glucose deprivation impairs effector T cell proliferation and cytokine production, conferring a selective advantage to Tregs in the TME (85). Furthermore, metabolic pathways related to lipid metabolism, mitochondrial activity and oxidative phosphorylation contribute to Treg stability and functional maintenance. Consequently, alterations in tumor metabolism may indirectly enhance Treg-mediated immune suppression and promote immune escape in LUAD (86). Glutamine (Gln) metabolism plays a vital role in LUAD. Liu et al (87) constructed a risk model for LUAD using Cox regression and Lasso regression analysis based on genes associated with Gln metabolism, categorizing patients into low-risk and high-risk groups. The low-risk group was characterized by low Gln metabolism, a survival advantage, a 'hot' immunophenotype and benefits from immunotherapy. Among immune cells, tumor-infiltrating T cells exhibited the most active levels of Gln metabolism, particularly highlighting CD8 T cell depletion and Treg suppression. These findings suggest that targeting the metabolic function of Tregs may present a promising strategy for restoring antitumor immunity.

Treg-mediated immune escape is a complex process that relies on extensive interactions between Tregs and various cellular components within the TME. Tumor cells, tumor-associated macrophages (TAMs), CAFs and other immune populations work together to regulate Treg recruitment, expansion and suppressive function. Currently, advancements in single-cell technology have markedly contributed to the analysis of TME-infiltrating Tregs and their roles in immune escape. For instance, by utilizing scRNA-seq to identify molecular subtypes and homologous immune metabolism characteristics of LUAD immune cell marker genes, researchers developed the LID-score model. Patients with low LID scores demonstrate higher survival rates due to abundant immune cell infiltration, immune activation and low genetic variation. However, elevated levels of Tregs in the immune microenvironment can lead to immune cell dysfunction, promoting tumor immune escape and reducing responsiveness to immunotherapy (88). Furthermore, fibroblast growth factor 11 (FGF11) has been observed to accelerate tumor proliferation in various cancer types. Notably, FGF11 gene expression is negatively correlated with most immune cell populations, particularly with characteristic genes of functional T cells such as Tregs and resting Tregs. This suggests that FGF11 could emerge as a new biomarker in LUAD patients, as it may enhance tumor cell immune escape by promoting T-cell depletion within the TME, leading to poorer prognoses (89). Chemokines also play a critical role in tumor immunotherapy, with studies showing that CCL28 secreted by LUAD can induce Treg infiltration, further supporting immune escape (90). Animal studies have demonstrated that CCR2 knockout mice exhibit fewer CD4⁺ T cells and Tregs in tumors, alongside increased infiltration of CD8 T cells producing IFN-γ and granzyme B (91). Additionally, TNF-α-dependent inflammation related to LUAD has been shown to upregulate MHC-II in alveolar type II cells via CXCR-2, promoting Treg expansion (92).

With the advancement of transcriptomic sequencing and bioinformatics, there is growing interest in Treg-associated molecular signatures as potential biomarkers for immune escape and treatment response. Various studies have identified immune-related gene signatures linked with Treg infiltration, tumor progression and LUAD prognosis (93-95). These findings suggest that Treg-related characteristics may reflect tumor immune status and hold predictive value for immunotherapy.

Nonetheless, Treg-targeted therapeutic strategies pose challenges. While the depletion or functional inhibition of Tregs may enhance antitumor immunity, systemic elimination may induce autoimmune toxicity due to Tregs' critical role in maintaining immune homeostasis. Therefore, selectively targeting tumor-associated Tregs or their specific suppressive pathways is seen as a more promising therapeutic approach (96-98).

In summary, Tregs facilitate immune escape in LUAD through a multifaceted regulatory network involving inhibitory molecules, metabolic adaptations and interactions with other TME components. Tregs influence tumor characteristics through cytokines and ligands, activating multiple signaling pathways. Additionally, tumor cells recruit Tregs via chemokines, cytokines and metabolic regulations to enhance immune escape. Thus, understanding the functional heterogeneity of tumor-associated Tregs and identifying tumor-specific regulatory mechanisms are critical for developing targeted immunotherapeutic strategies. Biomarkers that promote immune escape in LUAD are illustrated in Fig. 3 and summarized in Table III.