STAT6: Multidimensional analysis from hematopoietic immune regulation to pathogenesis mechanisms and therapeutic targets in hematologic malignancies

The IL-4/STAT6 signaling pathway plays a central regulatory role in B cell proliferation, differentiation, and humoral immune responses. Research indicates that this pathway drives B cell expansion and maturation, and determines their fate as either activated B cells or plasma blasts (PB) by regulating the differential response of precursor B cells to IL-4. Following early IL-4 stimulation, STAT6 signaling typically downregulates or even disappears, prompting B cells to initiate the plasma blastic differentiation programme. However, when the levels of IL-4 remain persistently high, sustained STAT6 activation paradoxically inhibits differentiation and leads to B cells remaining in an activated state19, indicating that IL-4 has a counter-regulatory effect on B cell differentiation. Concurrently, gain-of-function mutations in STAT6 further amplify IL-4-driven lymphocyte proliferation, leading to a significant increase in B cell numbers and promoting IgE class switching. This ultimately results in elevated systemic IgE levels20,21.

At the molecular level, BCL6 induces somatic hypermutation and B-cell receptor (BCR)-mediated degradation of BCL6. However, the IL-4/STAT6 signaling pathway can directly induce the BCL6 transcription, hindering its degradation and enhancing its stability. This further increases the magnitude and duration of the GC response22 by enhancing the function of the B cell immune response in vivo. Therefore, this study demonstrates that STAT6 plays a crucial role in integrating B-cell fate determination and functional regulation.

STAT6 plays a critical regulatory role in CD4 + T helper cell differentiation, particularly in determining the fate of Th2 cells. CD4 + T cells can differentiate into distinct subsets, including Th1, Th2, Th17, and Th22 cells. Studies indicate that SARS-CoV-2 infection activates STAT6 signaling pathways in both the cytoplasm and nucleus of lung cells, thereby promoting Th2 cell polarization and contributing to cytokine storm formation. This ultimately leads to an imbalance in Th1/Th2 immune responses3. Interestingly, there were no significant differences in the Th17 and Th22 cell subsets of patients with STAT6 gene mutations compared to healthy individuals, which further highlights the specific role of STAT6 in Th2 differentiation.

In terms of the regulatory mechanisms of STAT6 activation, TNF receptor-associated factor 3(TRAF3) enhances IL-4-mediated STAT6 activation in CD4-T cells23. Conversely, the protein tyrosine phosphatase Protein tyrosine phosphatase non-receptor type 1 (PTP1B) acts as a negative regulator by directly binding to the IL-4 receptor complex and interfering with JAK1-mediated STAT6 phosphorylation. This suppresses the upregulation of the GATA binding protein 3(GATA3) transcription factor and Th2 cell polarization23. Taken together, these findings establish STAT6 as a key mediator of Th2 cell differentiation.

The STAT6 signaling pathway also plays a significant role in T cell responses during the clinical treatment of hematologic malignancies. Bone marrow transplantation (BMT) is the most commonly used treatment for hematological malignancies and can induce a graft-versus-tumor (GVT) effect mediated by the donor T cells in the transplant. However, BMT can also induce graft-versus-host disease (GVHD). Our previous reports have demonstrated that IL-4 can induce the secretion of Th2 cytokines (including IL-4, IL-10, and TGF-β) via activation of the STAT6 signaling pathway, forming a positive feedback regulatory loop. The established Th2-polarized state can enhance the GVT effect, and simultaneously diminish the GVHD response by suppressing the production of pro-inflammatory factors and vascular endothelial growth factor (VEGF) 24. This provides new approaches to preventing tumor recurrence post-transplantation and reducing GVHD-related damage.

Macrophages are a crucial component of the innate immune system and exhibit high functional heterogeneity and plasticity25. In the tumor microenvironment, human peripheral blood mononuclear cells can differentiate into macrophages and polarize into either the pro-inflammatory M1 phenotype or the anti-inflammatory M2 phenotype. Studies indicate that STAT6 plays a central regulatory role in M2 polarization of tumor-associated macrophages (TAMs)26. Protein blot analysis reveals that STAT6 phosphorylation significantly increases the expression of M2 macrophage gene markers27. The process is primarily driven by the IL-4/STAT6 signaling pathway, which encourages macrophages to differentiate into the M2 phenotype, characterized by anti-inflammatory and tissue-repairing properties.

In recent years, significant progress has been made in developing inhibitors that target the regulation of STAT6 and macrophage polarization. The phosphopeptide mimic 37 (PM37) targets explicitly the SH2 domain of STAT6, effectively blocking and reversing the expression of M2 polarization markers28. In tumor cell-M2 macrophage co-culture systems, PM37 sensitizes tumor cells to radiation therapy, providing a new strategy to overcome tumor radioresistance. Peroxisome Proliferator-Activated Receptor γ (PPARγ) is a kind of nuclear hormone receptor found in cells that can activate oxidized fatty acids. The IL-4/STAT6 signaling pathway enhances the DNA-binding activity of PPARγ and regulates the lipid metabolism and inflammatory response of PPARγ target cells (macrophages and dendritic cells(DCs)) by expanding the range and intensity of regulated genes29.

Further preclinical studies reveal that the Bruton’s tyrosine kinase inhibitor Zanubrutinib can reprogram macrophages from the M1 phenotype to the M2 phenotype by modulating the STAT6 signaling pathway, thereby maintaining immune homeostasis30. Concurrently, exosome-based targeted therapeutic strategies demonstrate promising applications. As they are released by cells, exosomes serve as ideal drug delivery vehicles. Research utilizing engineered exosomes to deliver STAT6 antisense oligonucleotides (ASOs) has successfully induced TAMs to reprogram from the M2 phenotype to the pro-inflammatory M1 phenotype, thereby reshaping the tumor microenvironment31. These studies provide novel insights and approaches for developing STAT6-targeted tumor immunotherapy.

Acute lymphoblastic leukemia (ALL) is a highly aggressive malignancy that originates in lymphoid progenitor cells and predominantly affects children and the elderly32. In the specific genetic subtype of Philadelphia chromosome-positive ALL (Ph + ALL), the characteristic Breakpoint cluster region-Abelson murine leukemia viral oncogene homolog fusion gene/protein (BCR-ABL) fusion protein exhibits two major subtypes: P210 and P190. Research indicates that abnormal STAT6 activation is particularly pronounced in the P190 subtype. This involves Jak2-phosphorylated STAT6 binding to the c-MYC gene promoter as a transcription factor, thereby driving disease progression in Ph+ ALL 33. Comparative cytokine levels in patient cells revealed no significant differences between P190 and P210 cells. This suggests that classical cytokine pathways do not mediate elevated Phosphorylated STAT6 (p-STAT6) in P190 cells, but rather depend on Jak2 pathway activation34.

Furthermore, studies confirm that the BCR-ABL kinase regulates STAT6 activation. When p-STAT6 is inhibited, ALL cells undergo cycle rearrangement, which manifests as G2/M phase arrest and a significant decrease in the proportion of S phase cells, accompanied by an increase in apoptosis rates. Analysis of clinical samples also revealed that patients with significantly reduced STAT6 levels at diagnosis exhibited higher rates of leukemic cell apoptosis upon relapse35. Collectively, these findings suggest that STAT6 is a key molecule in the mediation of malignant proliferation and poor prognosis in Ph + ALL. Furthermore, they indicate that targeted inhibition of p-STAT6 could be an effective strategy for suppressing P190 cell proliferation.

In B-cell precursor acute lymphoblastic leukemia (BCP-ALL), the expression of the IL-13/STAT6 signaling pathway greatly upregulates cytidine deaminase Activation-induced cytidine deaminase (AID, encoded by the AICDA gene) in germinal center B cells and helper T cells36, which are associated with higher clonal mutation burdens and poorer clinical outcomes, This suggests an extensive pathogenic role for STAT6 in ALL subtypes.

HL is a lymphoid malignancy with unique pathological features, accounting for 15–25% of all lymphomas37. The expression status of STAT6 is used as a reference in the empirical classification of cHL. STAT6 positivity typically indicates the mixed cellularity subtype or lymphocyte-rich subtype, whereas STAT6 negativity is more commonly observed in nodular lymphocyte-predominant HL 38. In cHL, Hodgkin/Reed–Sternberg (HRS) cells express high levels of JAK2¹¹, components of the IL-13 signaling pathway, phosphatase of regenerating liver-3 (PRL-3) 39, and lymphotoxin α (LTA)40, among other factors. Approximately 85% of HRS cells can harbor this cytokine network, which can phosphorylate STAT6 and then promote tumor cell survival and migration41. Consequently, p-STAT6 detection is valuable for distinguishing cHL from certain non-Hodgkin lymphomas.

Notably, HRS cells in cHL secrete thymic and activation-regulated chemokine (TARC), also known as C-C motif chemokine ligand 17 (CCL17). This factor attracts Th2 cells to the tumor microenvironment. These cells then secrete cytokines such as IL-4, which activate the STAT6 signaling pathway and promote further TARC secretion. This positive feedback loop continuously attracts eosinophils and establishes an immunosuppressive microenvironment, ultimately facilitating immune evasion in HL 42. In exploring therapy options, it was found that the histone deacetylase (HDAC) inhibitor Vorinostat not only downregulates STAT6 mRNA expression and inhibits tumor proliferation, but also directly induces cell cycle arrest and apoptosis in HL cells43.

DLBCL is the most common subtype of NHL, exhibiting high genetic heterogeneity and mutational diversity. The recurrence rate is as high as 40%, with an inferior prognosis and high mortality following relapse2. Among the gene features associated with DLBCL recurrence, the STAT6 D419N mutation is a critical gain-of-function site. This mutation induces the high expression of multiple genes related to cell proliferation and chemotaxis18. This reveals a potential mechanism for sustained signaling pathway activation during DLBCL recurrence: STAT6 activation is driven not by exogenous cytokines such as IL-4, but by the mutation itself within the STAT6 gene in the cell nucleus44.

Further studies revealed that the tumor microenvironment of STAT6-positive patients contained significantly higher proportions of CD4 + T cells than that of STAT6-negative patients. This suggests that STAT6 may recruit helper T cells to the tumor site via chemotaxis in order to modulate antitumor immune responses. As STAT6 mutations are frequently observed in germinal center B-cell-like (GCB) subtypes41, researchers constructed a GCB subtype lymphoma cell line harboring the STAT6 D419N mutation via plasmid construction. Under IL-4 co-culture conditions that simulate STAT6 overexpression, it was found that the STAT6 D419N mutation itself lacks constitutive activity18 and its growth-promoting effects depend on IL-4 stimulation45. Notably, although exogenous IL-4 does not significantly affect the phosphorylation level of STAT6 D419N, the full transactivation function of this mutant protein still requires IL-4 participation46. These seemingly contradictory experimental results collectively indicate that, in DLBCL, the STAT6 D419N mutation is the core intrinsic factor affecting its function, while external cytokine stimulation plays a synergistic regulatory role. In terms of therapy, the epigenetic modulator azacitidine could suppress JAK2-STAT6 signaling activity by inhibiting the hypermethylation of miR-518a-5p. This inhibitor suppressed DLBCL cell proliferation and invasion, promoted apoptosis, and induced cell cycle arrest47, making it an ideal targeted therapeutic agent.

FL, the second most common NHL, is closely associated with the IL-4/IL-4R-activated JAK–STAT6 signaling pathway in its development48. This pathway mediates tumorigenesis in stage I FL patients by modulating BCL2 protein expression through BCL2 translocation49, which ultimately promotes CD23 overexpression. Consequently, CD23 expression serves as an alternative biomarker for STAT6 pathway activation50. In this process, Poly(ADP-ribose) polymerase family member 14(PARP14) acts as a co-activator that binds to STAT6, thereby enhancing the transcriptional activity of this pathway and promoting the regulation of STAT6 by downstream target genes46.

Patients with STAT6 mutations exhibit distinct molecular characteristics compared to those with wild-type STAT6: their STAT6 activation does not depend on tyrosine phosphorylation at the Y641 site9, yet they still show high expression of IL-4-responsive genes51, accompanied by shorter progression-free survival52, reflecting the functional heterogeneity of STAT6 mutations in FL pathogenesis. Further studies have revealed that both IL-4 and BCR signaling activate the mTOR pathway. This process is inhibited by CREB-binding protein (CREBBP) but enhanced by STAT6 53, indicating that STAT6 promotes tumor cell growth via mTOR signaling.

In addition to acting directly on tumor cells, STAT6 plays an active role in remodeling the FL tumor microenvironment (TME). For instance, it recruits CD4 + T cells to infiltrate tumor regions by upregulating the CCL17 chemokine, modulates redox homeostasis and protein disulfide bond formation via Quiescin sulfhydryl oxidase 1 (QSOX1), and influences apoptosis through Nuclear factor, interleukin 3 regulated (NFIL3). In summary, STAT6 mutations play a central role in FL pathogenesis and promote the disease process by multidimensionally regulating the tumor microenvironment.

PMBL is a distinct subtype of DLBCL characterized by unique clinical and pathological features. Its molecular hallmarks primarily involve the abnormal expression of STAT6 and BCL6 54. In PMBL patients, the incidence of STAT6 mutations is relatively low, ranging from approximately 33% to 36%⁴⁴. The disease is characterized by an earlier age of onset and a male predominance.

At the molecular level, PMBL patients commonly exhibit high JAK2 expression 11, with 91% of cases accompanied by Suppressor of cytokine signaling 1(SOCS1) gene mutations44. These SOCS1 mutations primarily disrupt normal negative feedback regulation through somatic hypermutation, leading to sustained phosphorylation and activation of STAT6. Interestingly, unlike in FL, CD23 expression in PMBL patients shows no significant correlation with STAT6 mutation status (p = 0.13) 55.

STAT6 gene mutations primarily occur in the exons encoding the DNA-binding domain. Approximately 35% of PMBL patients exhibit substitution mutations, predominantly at the D419 site56,57. These mutations predominantly occur at T: A base pairs within the DBD and SH2 domains58, primarily affecting aspartic acid (Asp) residues, followed by glutamic acid (Glu) residues8. Analysis of the large-scale population genome database (gnomAD) revealed that the mutation rate of STAT6 in the general population is close to zero and that all identified STAT6 mutations have high Combined Annotation-Dependent Depletion (CADD) scores (> 20 points). Collectively, this evidence supports the idea that both germline and somatic gain-of-function variants in STAT6 independently contribute to the pathogenesis of PMBL.

However, recent studies have demonstrated that STAT6 activation can also be induced by mutations. This finding highlights the distinct nature of PMBL in the regulation of STAT6 signaling compared to other lymphoma subtypes. More importantly, recent studies have reported that the region encoding the STAT6 DNA-binding domain is a major hotspot for recurrent mutations in PMBL59, with this molecule playing a central role in PMBL pathogenesis.

PTCL constitutes a group of T-lymphocyte malignancies characterized by significant heterogeneity60. The presence of Hodgkin/Reed-Sternberg (HRS)-like cells in the tumor microenvironment often complicates differential diagnosis with other cells that are morphologically similar to HRS cells in cHL. To solve this problem, the study analyzed the molecular characteristics of HRS cells in PTCL and cHL. The study found that HRS-like cells in PTCL exhibited significantly lower expression levels of STAT6 (P < 0.001) and p-STAT6 (P < 0.001), a difference which was statistically significant61. This indicates that the expression status of STAT6 holds important clinical value in differentiating between the two conditions.

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Furthermore, studies demonstrate that high activation of the JAK1/2-STAT6 signaling pathway correlates positively with favorable progression-free survival (PFS) in patients with T-lymphoblastic lymphoma (T-LBL), the second most common childhood NHL. Therefore, the activity level of the JAK1/2-STAT6 pathway can be used to predict the prognosis of patients with T-LBL, providing a basis for the precise treatment of this disease.

The most common clinical subtypes of CTCL, Sezary syndrome (SS) and mycosis fungoides (MF), exhibit a close association between their pathogenesis and abnormal activation of the STAT6 signaling pathway. Research indicates that SS/MF tumor cells can produce high levels of cytokines, such as IL-13 and IL-19, via autocrine mechanisms, thereby inducing sustained activation of STAT6. Pharmacological inhibition of STAT6 expression greatly downregulates related signaling pathways, including those involved in cell cycle progression, DNA repair, and Th2 cytokine production. This results in tumor cell cycle arrest at the G1/G2 phase and effectively suppresses the proliferative activity of malignant lymphocytes62.

Additionally, STAT6 stimulates Th2 cells to generate IL-4 and IL-13, These cytokines then direct the polarization of TAMs towards the M2 phenotype. This alters their unique gene expression patterns, fosters the development of an immunosuppressive microenvironment, and increases tumor invasiveness. Notably, STAT6 also recruits additional immunosuppressive cells to the tumor microenvironment by regulating the expression of chemokines such as CCL17, CCL13, and CCL8 63. At the same time, STAT6 induces the expression of systemic and local immunosuppressive factors, such as TGF-β, thereby enhancing the immunosuppressive functions of TAMs64. These mechanisms collectively induce an immunosuppressive state in CTCL and provide an experimental basis for inhibiting the STAT signaling pathway in advanced cutaneous T-cell lymphoma.

Breast implant–associated anaplastic large cell lymphoma (BIA-ALCL) is a CD30-positive, ALK-negative peripheral T-cell lymphoma. Immunohistochemical studies reveal that approximately 90% of BIA-ALCL cases express IL-13 65. This cytokine can mediate the downstream STAT6 signaling pathway and promote the survival and proliferation of tumor cells. Subsequent experiments also found that CD30-targeted therapy can significantly reduce the expression of IL-13 in BIA-ALCL and inhibit the growth of tumor cells. Additionally, experimental studies suggest that the STAT6-specific inhibitor AS1517499 can reduce the survival rate of BIA-ALCL cell lines by up to 80% 66. These results indicate that the STAT6 signaling pathway plays a significant role in the pathogenesis process of BIA-ALCL and provides a basis for the use of STAT6 inhibitors in the treatment of this disease. (Fig. 3).

Figure Legends: Figure 3 was created with BioRender.com. Schematic illustration of signal transducer and activator of transcription 6 (STAT6) signaling pathways across multiple cell types and pathological conditions. Center: Domain structure of STAT6 protein featuring phosphorylation sites (P). B cell compartment (upper left): Canonical IL-4/STAT6 signaling through JAK1 sustains baseline immunosurveillance, regulating B cell differentiation, immunoglobulin class switching, and normal lymphopoiesis. Sustained IL-4/STAT6 activation leads to B cell activation, BCL6 upregulation, and IgE hyperreactivity, resulting in differentiation arrest and humoral imbalance. Viral infection (left) : Viral infection activates STAT6 via the non-canonical STING-TBK1-MAVS axis, independent of JAK1, modulating chemokine expression (CCL2/CCL20/CCL26) to direct immune cell trafficking. T cell compartment (upper right): IL-4/STAT6 signaling promotes CD4 + T cell differentiation toward Th2 predominance, facilitated by TRAF3 and GATA3. This Th2 bias favors graft-versus-tumor (GVT) effects while mitigating graft-versus-host disease (GVHD) in bone marrow transplantation settings. M2 macrophage compartment (right): IL-4/STAT6 signaling drives M2 polarization through PPARγ DNA binding enhancement, resulting in altered lipid metabolism and inflammatory gene regulation compared to homeostatic M1-M2 balanced phenotypes. Follicular lymphoma (FL) (lower right): Wild-type STAT6 maintains baseline BCL2 and CD23 expression. PARP14 serves as a STAT6 coactivator, promoting BCL2 and CD23 overexpression, which initiates stage I tumor formation and serves as a STAT6 activation surrogate marker. CREBBP negatively regulates this pathway. Diffuse large B-cell lymphoma (DLBCL) (bottom): Wild-type STAT6 shows baseline expression with unaltered T cell distribution, whereas D419N-mutated STAT6 exhibits IL-4-dependent potentiation, enriched CD4 + T cell infiltration via chemotaxis, and enhanced expression of pro-proliferative and pro-migratory genes. Classical Hodgkin lymphoma (cHL) (lower left): In physiological lymphoid tissue, STAT6 undergoes transient activation with normal immune function. In Hodgkin/Reed-Sternberg (HRS) cells, constitutive JAK2 activation drives persistent STAT6 phosphorylation, establishing a positive feedback loop involving TARC secretion and CCR4 + Th2 cell recruitment. This results in sustained eosinophil recruitment, immunosuppressive microenvironment formation, immune evasion, and tumor survival. Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph + ALL) (left): Normal BCP-ALL shows transient, regulatable STAT6 phosphorylation. The P190 BCR-ABL subtype exhibits JAK2-mediated persistent STAT6 hyperphosphorylation, promoting c-MYC transcription, cell cycle arrest at G2/M phase, S-phase reduction, suppressed apoptosis, and hyperproliferation.