Cancers of the gastrointestinal (GI) tract consistently track as some of the deadliest forms of malignancy worldwide [1]. In 2021, an estimated 5.3 million new cases of GI cancer and 3.7 million related deaths occurred globally [1]. In the United States, GI cancers account for over 25 % of cancer-related deaths. Among these, colorectal cancer (CRC) had the highest age-standardized incidence rate, followed by pancreatic, liver, gastric, and esophageal cancers [2]. In fact, CRC is the second leading cause of cancer mortality in the United States, followed by pancreatic cancer [3]. In 2025, an estimated 362,200 new GI cancer cases and approximately 174,520 related deaths are expected in the United States, underscoring the significant burden of these malignancies [3]. Clearly, the morbidity and mortality of GI cancers present a substantial burden to the population’s health in the United States and worldwide.

GI cancers include a variety of malignancies that differ in their cellular origin and etiology but often share common risk factors. Most are classified as adenocarcinomas (AC), though squamous cell carcinoma (SCC), neuroendocrine tumors, and stromal tumors may also occur depending on the tumor location. Esophageal cancers are comprised of two primary histological subtypes, AC and SCC [4]. The SCC is the most common subtype globally and is strongly associated with smoking, alcohol use, and environmental factors such as air pollution [4]. In contrast, AC is more prevalent in high-income countries and is linked to obesity and gastroesophageal reflux disease (GERD). Gastric cancer (GC) is often classified by anatomical location: cardia gastric cancer (CGC) occurs near the esophageal-gastric junction, while non-cardia gastric cancer (NCGC) arises in the more distal regions of the stomach. Due to its location, CGC shares risk factors such as obesity and GERD with esophageal AC, whereas the NCGC is primarily associated with Helicobacter pylori (H. pylori) infection [4].

CRCs include colon, rectal, and anal cancers. Colon and rectal cancers are commonly linked to alcohol consumption, red and processed meat intake, obesity, and smoking [4]. Anal cancer is primarily associated with human papillomavirus (HPV) infection, often associated with cervical cancer [4]. Screening through stool-based tests such as guaiac-based fecal occult blood test (gFOBT) and endoscopic procedures has been associated with reduced CRC mortality [4]. Increased colonoscopy screening in Western countries has contributed to declining CRC incidence; however, incidence rates are rising amongst younger adults, raising significant concern amongst health experts [5]. Liver cancer can be categorized as hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC), along with other, rarer subtypes. HCC is the most common type globally and typically arises from underlying conditions such as hepatitis B or C infection, cirrhosis, or alcohol abuse [4]. Pancreatic cancer (PC) risk factors include smoking, type 2 diabetes, obesity, and heavy alcohol use. Additionally, individuals with genetic syndromes such as Lynch syndrome or inherited mutations (e.g., BRCA1 or BRCA2 genes) have an increased risk of developing PC [6].

Men consistently show higher incidence and mortality rates across all GI cancer types [7]. Despite promising advances in screening and early detection, primary prevention through lifestyle modification remains the most practical approach for reducing the global impact of GI cancer [4]. Most GI cancers share modifiable risk factors such as tobacco use, alcohol consumption, and obesity [6]. These factors contribute to chronic inflammation and immune dysfunction, influencing cytokine-driven pathways that shape the tumor environment in GI cancers [8]. Accordingly, this review examines recent discoveries, therapeutic advancements, and persistent challenges in cytokine biology as they relate to immunotherapeutic strategies for GI cancers. Specifically, this review critically discusses the roles of key anti-tumorigenic cytokines [i.e., interleukin (IL)-12, IL-15, IL-2, and interferon (IFN)-γ] in GI cancers’ therapeutic potentials with improved clinical outcomes.

IL-12 is a pro-inflammatory cytokine primarily produced by antigen-presenting cells (APC) such as dendritic cells (DC) and macrophages [9]. As shown in Fig. 1, it exhibits potent anti-tumor and anti-metastatic effects by activating natural killer (NK)-cells and cytotoxic T-lymphocytes, inducing Th1 polarization as well as stimulating interferon-gamma (IFN-γ) production [10]. IL-12 also promotes antibody-dependent cellular cytotoxicity (ADCC) and reprograms myeloid-derived suppressor cells (MDSC) to support anti-tumor immunity [11]. Furthermore, IL-12 disrupts the tumor microenvironment (TME) through multiple mechanisms, including the induction of anti-angiogenic mediators and facilitating the degradation of the surrounding extracellular matrix [11].

In the context of GI cancers, particularly CRC, IL-12-induced IFN-γ signaling has demonstrated notable clinical relevance. Polarization of the T helper cells (Th1) response by IFN-γ has been correlated with prolonged survival in CRC patients [10]. Additionally, elevated IFN-γ serum levels have been associated with the absence of nodal metastases in CRC patients, highlighting its role in tumor suppression [10]. IL-12 itself has also demonstrated potential relevance in CRC, with some studies reporting elevated IL-12p40 levels across all CRC patients, with the highest concentrations observed in stage I disease [10]. This finding aligns with data showing increased NK-cell and Th1 infiltration during the early stages of CRC, supporting the hypothesis that IL-12 contributes to early antitumor immune responses [10]. However, other studies have failed to observe elevated IL-12 in CRC patients regardless of stage, possibly reflecting a shift in the TME toward Th2 dominance [10]. These discrepancies suggest that while IL-12 may serve as a valuable prognostic indicator of early immune engagement, its inconsistent expression limits its broader clinical utility as a diagnostic biomarker. For example, in gastric adenocarcinoma, serum IL-12 levels did not differ significantly between patients and healthy controls, further suggesting that IL-12 is not a reliable standalone marker for GI cancer detection [12].

While IL-12 has limited diagnostic potential, its expression and immunomodulatory roles have shown prognostic relevance in certain GI cancers. For instance, Nakayama et al. [13] found that low pre-operative serum IL-12 levels in patients with GC or CRC were associated with advanced tumor stage. Talukdar et al. [14] reported that IL-12 expression in esophageal SCC revealed no significant difference in tissue and serum compared to healthy controls (p = 0.064 and p = 0.689, respectively), indicating limited diagnostic utility. However, altered IL-12 expression was significantly associated with patient survival (p < 0.05), suggesting its relevance in esophageal SCC progression [14]. In a subcutaneous xenograft model of gastric cancer (HGC-27 cells) in athymic mice, Dellalibera-Joviliano et al. [15] demonstrated that IL-12 treatment significantly reduced tumor growth and modulated molecular pathways linked to metastasis. Specifically, IL-12 upregulated microRNA (miR-203), which suppressed expression of calcium/calmodulin-dependent serine protein kinase (CASK), a gene implicated in tumor progression [15]. The authors proposed that miR-203 and CASK, as downstream targets of IL-12 signaling, could serve as diagnostic and prognostic biomarkers in GC [15]. These findings also underscore IL-12's therapeutic potential in GI malignancies.

IL-12 shows substantial promise as an anti-tumoral immunotherapy for GI malignancies. Nonetheless, systemic administration of IL-12 has shown toxic inflammatory responses and even lethal side effects in some instances, requiring alternative methods of IL-12 delivery [11]. To address these challenges, researchers have explored innovative approaches to retain IL-12's anti-tumor efficacy while minimizing its systemic toxicity. Lai et al. [11] demonstrated that delivering IL-12 mRNA via lipid nanoparticles suppressed tumorigenesis in a MYC-driven murine model of HCC. The nanoparticle-mediated delivery of IL-12 has also been shown to enhance cytotoxic activity against human HCC cells [9]. When delivered via an oncolytic adenovirus, modified IL-12 improved survival in mouse models of pancreatic cancer [9].

While these innovations to IL-12 delivery have improved its safety profile, studies evaluating IL-12 as a monotherapy in GI cancer have demonstrated both efficacy and limitations. In a transgenic mouse model of HCC, Zabala et al. [16] used a doxycycline-regulated plasmid to induce liver-specific IL-12 expression. This treatment led to tumor regression or stabilization in 40 % of mice—a significant finding given the resistance of multifocal HCC to conventional therapies. However, long-term IL-12 expression increased IL-10 levels and activated suppressor T-cells, limiting the anti-tumor effect in the remaining 60 % of mice [16]. Combining IL-12 with agents that block regulatory T-cells (Tregs) of IL-10 may improve its therapeutic efficacy.

The literature supports using IL-12 as an adjuvant in combination therapies across multiple GI cancers. In a murine model of ductal PC, a typically non-immunogenic tumor, the use of an adenoviral vector encoding IL-12 combined with B7.1 led to a prolonged immune response and mediated complete regression in 80 % of the treated animals [17]. Similarly, IL-12 in combination with doxorubicin, decorin, or oncolytic adenovirus expressing suicide genes also resulted in improved anti-tumor immune response in murine colon cancer [11]. Additionally, Deplanque et al. [18] showed that combining IL-12 with radiation therapy in mouse models of colon cancer helped overcome radiation-induced immune suppression by restoring Th1 responses. The above noted facts are summarized in Table 1 based on the key literatures support.

In a physiological sense, the IL-15 cytokine modulates both the innate and adaptive immune systems with a key role in NK cell regulation [19]. The role of IL-15 in relation to the development and progression of GI cancers is well-documented in the existing literature. A study by Cheng et al. [20] utilized syngeneic mice to model metastatic HCC and compare those with enhanced IL-15 signaling versus those with baseline levels. The Hyper-IL-15 mice demonstrated increased IL-12 and IFN-γ levels as well as increased expression of tumor-specific CD8 + T-cells. The purported role of IL-15 in preventing HCC is consistent with its suspected role in other cancer models. Bergamaschi et al. [21] examined the anti-tumorigenic properties of IL-15 in a more generalized sense. The authors found that IL-15 expression is related to an enhanced ability of T-cells to enter tumor cells and thus formulate a more significant anti-tumor response. Additionally, an increased amount of CXCR3 + NK-cells was found to be circulating when increased IL-15 expression was induced in the mouse tumor models [Fig. 2].

As part of the mucosal layer of the intestines, IL-15 is also implicated in various inflammatory diseases of the GI tract, including celiac disease, inflammatory bowel disease (IBD), and tropical sprue [22], [23]. As such, Bahri et al. [24] sought to characterize the interplay of IL-15’s role in inflammation-induced cancer pathologies. In a model of inflammation-associated colon carcinogenesis in mutant and wild-type mice, it was found that when IL-15 was absent, there was a significant upregulation in IL-1β, IL-22, IL-23, Cxcl5, and Spp1 cytokines, which have been identified as key inflammatory mediators in the pathogenesis of colon cancer progression [Fig. 2]. Additionally, the deletion of IL-15 resulted in increased apoptosis with no change in cell proliferation, suggesting that IL-15 has a significant role in the repair of inflammation-plagued colon cells. Increased IL-15 and IL-15Rα expression, in the setting of aerobic exercise as the causative agent, has demonstrated significant anti-tumor effects in PC as well [25]. A significant barrier to treating solid malignancies of the GI tract, such as colorectal and pancreatic cancer, remains the identification of specific antigens that can be targeted with immunologic treatment. Van den Eynde et al. [26] identified CD70 as a major target of interest on tumor cells of both CRC and pancreatic cancer patients. Additionally, it was found that IL-15 heavily influenced the ability of CD70 + NK cells to eliminate CD70 + tumor cells and CD70 + cancer-associated fibroblasts (CAFs) [Fig. 2]. Thus, it is possible that part of the utility of the anti-tumorigenic effects of IL-15 may rely on its significant relationship with identifying the CD70 ligand. While the antitumor properties of IL-15 in GI cancers are apparent, there is conflicting research that also supports a tumor-promoting role of IL-15 [27].

Apparent in its physiological mechanism, there lies great utility in its abilities as a therapeutic agent against many subtypes of GI cancers. Van Audenaerde et al. [28] discussed a trial of IL-15 combined with a CD40 agonist as a potential therapeutic for pancreatic ductal adenocarcinoma (PDAC). Their results demonstrated enhanced infiltration of tumors by both T cells and NK cells, a massive reduction in tumor growth with increased survival of mice, and a significant increase in the overall efficiency of their tumor-specific immune response. Similar to non-human trials experimenting with IL-15 agonism as a therapy for pancreatic cancer, early results of human trials have demonstrated comparably promising results. The QUILT-88 trial (NCT04390399) is focused on introducing N-803, an IL-15 cytokine fusion protein that acts as a “superagonist,” to standard chemoradiation therapy in treating pancreatic cancer. Recently published phase 2 results of the trial demonstrated enhanced median overall survival (n = 65, 6.3 months vs. 3 months in previous trials), few side effects, and no deaths related to treatment [29]. As investigations into its therapeutic value continue, the exact mechanistic role of IL-15 in relation to GI cancers will be further characterized, but the available literature analyzed is summarized in Table 2.

IL-2 is a pro-inflammatory cytokine produced after antigen activation that plays a pivotal role in the immune response [30]. Specifically, IL-2 is a four α-helical bundle cytokine produced primarily by CD4 + T-cells, but also released by CD8 + T-cells, NK-cells, activated DCs, and mast cells in much lower quantities [31]. By stimulating the production of CD4 + , CD8 + T-cells, and NK cells, the body's immune response is enhanced, while also aiding in the development and homeostatic survival of Treg cells [31]. IL-2's ability to enable Tregs to survive can result in immune suppression that helps tumors evade the immune system [32], [33]. The immune system’s ability to fight cancer weakens because many GI tumors create an environment where Tregs outnumber cytotoxic T-cells [32], [34]. The expression of IL-2 and its receptor by certain GI tumor cells enables autocrine signaling, leading to tumor growth and reduced apoptosis resistance [35]. The IL-2 pathway dysfunction diminishes immune surveillance and results in faster tumor progression [30]. IL-2 can also bind to the IL-2 receptor (IL-2R) subunit CD25, which induces a conformational change that recruits CD122 and γ-chain (γc) [36]. This complex can induce gene transcription and activate signaling pathways, including the Janus kinase - signal transducer and activator of transcription (JAK-STAT), phosphatidylinositol 3-kinase (PI3K), and mitogen-activated protein kinase (MAPK) pathways, which signal cells to proliferate, survive, and differentiate, leading to cancer development [36], [37], [38].

In relation to GI cancers, T-cell-mediated immune responses and NK-cells are key in the body's anti-tumor response, as seen in Fig. 2. In gastric cancer, cytotoxic CD8 + T-cells are particularly important because of their tumor-killing capacity with cytotoxic molecules such as granzyme B [39]. In addition, elevated T-cell numbers in the TME of GC have been associated with improved survival. Lee et al. [40] found that more tissue CD3(+) TILs, indicative of pan-T-cell expression, had a positive effect on survival with a hazard ratio (HR) of 0.64 (95 % CI 0.52–0.78) for OCS (overall cancer survival) in patients with GC. In CRC, NK-cells are primary effectors in eliminating CRC cells [41]. The lack of or dysfunction of NK cells in CRC patients limits the antitumor immune response and is associated with lower survival rates [41]. IL-2 activates these crucial anti-tumor immune cells, making it an intriguing marker in managing and treating GI cancers.

IL-2 itself has not been investigated in the literature as a potential diagnostic tool in GI cancers. However, IL-2 and its soluble receptor (sIL-2r) have been implicated as potential prognostic factors for multiple GI cancers. Sakata et al. [42] investigated IL-2R levels in CRC using immunohistochemical (IHC) staining. The authors showed that the pre-operative levels of serum soluble IL-2R in patients with CRC were significantly higher than those of normal controls (p = 0.0065). For samples with either lymph node metastasis or liver metastasis, the preoperative levels of serum soluble IL-2R were also statistically higher than in those without metastasis (p = 0.0258 and p = 0.0223, respectively). The post-operative levels of serum soluble IL-2R were significantly lower than the pre-operative levels (p = 0.009). This makes serum soluble IL-2R a possible parameter for evaluating the stage of a disease, especially when considering whether the patient has lymph node or liver metastasis. Nakata et al. [43] also investigated serum soluble IL-2R in gastric cancer. The authors found no statistically significant difference between serum sIL-2R levels in all patients with gastric cancer and healthy control subjects. However, there was a significantly higher median level of sIL-2R in stage 3/4 gastric cancer patients when compared to stage 1/2 gastric cancer patients and healthy controls.

IL-2 therapy at high doses produces tumor reduction in selected patients, but the treatment remains restricted because of dangerous side effects, including capillary leak syndrome and hypotension [44]. Research into alternative solutions aims to solve these problems. The development of engineered IL-2 variants now focuses on creating versions that enhance cytotoxic immune cell activation while minimizing Treg stimulation, and targeted delivery systems work to confine IL-2 activity to the tumor site for reduced systemic side effects.

Due to its pathophysiologic role in activating antitumor agents, IL-2's feasibility and efficacy have been investigated to determine if it can be used as a potential immunotherapy for multiple cancers. IL-2 is an FDA-approved treatment for renal cell carcinoma and melanoma, but its efficacy for GI cancers is still being investigated.

In GC, Cesana et al. [45] reported that neoadjuvant IL-2 could eliminate the post-operative decrease in peripheral and peritumoral lymphocytes, as there was a significantly smaller decrease of CD3 + and CD4 + T-cells (p < 0.05) in patients who underwent IL-2 treatment prior to surgical intervention than those who underwent surgery alone. In Krastev et al.’s [46] evaluation of 16 patients with stage 3/4 GI cancers, the authors found that direct intra-peritoneal injection of dissolved recombinant human IL-2 was feasible and safe to administer locally to the tumor site, as patients had minimal/manageable adverse effects, with moderate fever being the most common. The authors determined that local IL-2 treatment induced a modest but important clinical gain. Six of the 16 (37.5 %) patients benefited from this treatment; four had stable disease, and two had a reduction of ascites.

There has been some promising, but not convincing, data on the ability of IL-2 to aid in the treatment of CRC. Brivio et al. [47] showed that in patients with Dukes' stage B and C CRC, the post-operative immunosuppression progression rate was significantly lower in those pre-treated with IL-2 than in controls who underwent surgery alone: 9/42 (21.4 %) IL-2 group vs. 19/44 (43.1 %) controls (p < 0.03), median follow-up time: 54 months [48]. In a phase 1 clinical trial by Liu et al. [49], IL-2 was found to be feasible and safe to treat CRC in adjuvant to carcinoembryonic antigen (CEA)-pulsed dendritic cells mixed with tetanus toxoid. There was a statistically significant increase in proliferation against CEA by T-cells collected after vaccination in two of the nine patients when IL-2 was added; however, clinical benefit was minimal. In another phase 1 clinical trial investigating the safety, toxicity, and antitumor response of IL-2 gene therapy, Sobol et al. [50] treated ten patients with a fixed dose of tumor cells and increasing doses of fibroblasts secreting IL-2 injected by vaccine. In terms of safety, fatigue and/or flu-like symptoms were experienced by seven patients and delayed-type hypersensitivity-like skin reactions were seen at the sites of the second or subsequent vaccinations in five patients. Low amounts of tumor cytotoxic T-cell precursors were detected before therapy in four of the seven patients. Following treatment, there was a 5-fold increase in the frequency of tumor cytotoxic T-cell precursors in two of the six evaluable patients.

In HCC, Chen et al. [51] investigated the therapeutic potential of IL-2 by trying to recreate an HCC tumor microenvironment with tumor-associated macrophages (TAMs). The authors found that exosomes derived from TAMs promote the development and progression of HCC in vivo and in vitro. The authors found that when IL-2 was added, there was an increase in exosomal miR-375. The prognosis of the low miR-375 expression group was worse than that of the high miR-375 expression group, suggesting the absence of miR-375 was unfavorable for the patients. Sun et al. [52] investigated recombinant adenovirus expressing IL-2 injection as a gene therapy for HCC in a tumor model. The regulatory and effector cell‑mediated tumor suppression by antitumor cluster of differentiation CD4 + and CD8 + T-cells stimulated by rAd‑IL‑2 was found to be tumor‑specific. Furthermore, rAd‑IL‑2 significantly stimulated tumor‑specific cytotoxic T-lymphocyte responses, increased IFN‑γ release, and enhanced antitumor immunity. It increased CD4 + and CD8 + T-cell recruitment into the tumor and induced memory to protect tumor‑bearing mice against tumor challenge. Treatment with rAd‑IL‑2 led to tumor regression and long‑term survival of mice in the 120‑day treatment period when tumor challenge experiments were invoked.

In PDAC, Pakola et al. [53] investigated whether chemotherapy with IL-2 enabled programmed cell death ligand 1 (PD-L1) inhibition in pancreatic cancer models. Ad5/3-E2F-d24-vIL2 in combination with anti-PD-L1 showed synergistic activation of T-cells in clinical PDAC samples. In addition, an in vivo animal experiment showed that treatment with Ad5/3-E2F-d24-vIL2 leads to increased amounts of CD8 + and CD4 + T-cells infiltrating the tumors, which helps to improve the response of PDAC to immunotherapy. Piper et al.'s [54] analysis with flow cytometry showed that PD1-IL2v [a combination of a programmed cell death protein 1 (PD-1) antibody and an IL-2 variant], with or without radiation therapy, results in significant CD8 + T-cell expansion and decreased Tregs across compartments. Using a bispecific PD1-IL2v antibody construct designed to bind to IL-2Rβγ selectively, but not IL-2Rα, while simultaneously binding to PD-1 on effector immune cells, showed a significant impact. The bispecific PD1-IL2v antibody corrected effector immune cell exhaustion, enhanced their proliferation and expansion, and improved their cytotoxic abilities. The authors also found that polyfunctional and antigen-specific cytotoxic T-lymphocyte (CTL) subsets following radiation therapy (RT) + PD1-IL2v treatment significantly improved survival.

IL-2 has shown some promise as an adjuvant to both surgical and medical oncology management of GI cancers. Some studies have demonstrated that IL-2 is safe for both systemic and local use when modified, as IL-2 alone is generally toxic. The current literature shows that IL-2 is promising as an adjuvant immunotherapy for GI cancers but has not been extensively investigated as an immunotherapy on its own. More research is required to understand the true clinical implications of IL-2 as an anti-tumorigenic therapy for GI cancers. Table 3 summarizes the key literature findings pertaining to the roles of IL-2 in GI cancers.

IFN-γ is a pleiotropic cytokine integral to adaptive and innate immunity [55], [56]. IFN-γ is mainly produced by T-lymphocytes and NK-cells in response to inflammation, viruses, bacteria, and tumor cells [55]. IFN-γ has several anti-tumorigenic properties due to its pro-apoptotic, anti-proliferative, cytostatic, and angiogenesis-inhibitory functions [57]. More specifically, as a result of IFN-γ release, the JAK/STAT1 pathway is activated, leading to cell cycle arrest and apoptosis through gene transcription as well as increasing pro-apoptotic proteins (BAK) and decreasing anti-apoptotic proteins (Bcl-2, Bcl-X) [58]. This property can be exemplified in various GI cancers and can be seen in Fig. 2. Zhang et al. [59] utilized pancreatic cancer cells, and Shyu et al. [60] investigated human gastric cancer cells, and both found IFN-γ’s direct role in suppressing tumor cell growth by upregulating BAK protein levels and downregulating Bcl-2 and Bcl-X. In addition, Zhao et al. [61] also studied gastric cancer cells and found that when exposed to IFN-γ, there was a reduction in colony formation, and flow cytometry showed that IFN-γ arrested the cells in G1/S phase, which slowed the tumor progression.

Activation of IFN-γ has other downstream effects of the JAK/STAT1 pathway, including its link with Prospero-related homeobox 1 (Prox1), a gene implicated in many GI cancers [62]. A study with esophageal squamous cell carcinoma (ESCC) cells found that IFN-γ induces Prox1, and the increased expression of Prox1 led to the anti-proliferation of the ESCC cells [62]. Similarly, a decreased expression of Prox1 in HCC and pancreatic cancer cells is associated with further progression of tumor differentiation [63], [64]. However, this association seems to be tissue-dependent, as Petrova et al. found that Prox1 induced colorectal tumorigenesis [65].

IFN-γ also amplifies tumor immune surveillance by directing a type 1 immune response and thereby activating macrophages, differentiating Th1 CD4 + T-cells, and upregulating major histocompatibility complex (MHC) molecules [66], [67]. This type of immune response leads to antigen presentation and recognition, and elimination of target or tumor cells by cytotoxic T-lymphocytes and NK cells [67]. Zhang et al. [68] demonstrated this concept by analyzing intestinal tumorigenesis in mouse models with and without IFN-γ receptors. In the mice without IFN-γ receptors, the tumor cells had a higher probability of progression to invasive adenocarcinomas and had an increase in genes related to inflammation and tissue remodeling. Furthermore, there were more tumor-associated macrophages, more of which were M2-polarized.

Another tumor suppressor property of IFN-γ is its ability to induce autophagy, as exemplified in gastric cancer and HCC cells [69], [70]. Tu et al. [69] utilized transgenic mice with gastric cancer and either high or low stomach-specific IFN-γ expression levels. The authors found that IFN-γ upregulated Beclin-1, a tumor suppressor gene involved in phagolysosome formation, which inhibited carcinogenesis. IFN-γ also decreased IL-17-producing Th17 cells, preventing gastric dysplasia. Similarly, Li et al. [70] demonstrated IFN-γ-induced autophagy in Huh7 cells and human HCC cells through the interferon-regulatory factor-1 (IRF-1) pathway.

IFN-γ is involved in the pathophysiology of GI cancer but also has prognostic value. When oral squamous cell carcinoma (OSCC) tissue samples were analyzed, Wang et al. [71] concluded that low IFN-γ levels were associated with poorer overall survival (OS). Tian et al. [72] similarly found that IFN-γ mRNA and protein expression levels were lower in OSCC tissue samples but also analyzed the IFN-γ methylation rates in benign vs. malignant tumors. In doing so, the authors discovered that the IFN-γ methylation rate was statistically higher in malignant tumors (55.3 %) than in benign (38.3 %) or normal tissues (22.6 %) (p < 0.05). Another study of 63 patients with HCC prospectively looked at the predictive value of IFN-γ levels on the recurrence rate after curative treatment. The results showed that a low serum IFN-γ level (<50 pg/mL) was inversely correlated with tumor stage, according to the Barcelona Clinic Liver Cancer (BCLC) staging system, in which Stage A represents early stage and Stage B is intermediate stage cancer (Stage A: 25 %, Stage B: 61.25 %, p = 0.01). In addition, a reduced quantity of NK-cells, which produce IFN-γ, was associated with increased tumor size (p = 0.024) [73].

Though IFN-γ has several anti-tumorigenic properties against GI cancer, the literature also suggests that cancer cells can promote immune resistance and downregulate MHCs, thereby resulting in tumorigenesis [66], [74]. By activating the JAK/STAT1 pathway, IFN-γ upregulates PD-L1 expression, minimizing excessive immune activation. This results in inhibitory signals for cytokine production and T-cell proliferation. Therefore, tumor cells induce chronic inflammation and lead to persistently elevated IFN-γ levels, ultimately causing T-cell exhaustion and immune evasion [75]. This duality of anti- and pro-tumorigenic functions of IFN-γ has limited its therapeutic viability as a single agent in treating GI cancers [76].

Currently, recombinant human IFN-γ is FDA-approved for chronic granulomatous disease and malignant osteopetrosis but is not used as a first-line cancer treatment [77]. To combat the immune resistance, studies have analyzed the utilization of PD-1 blockade in conjunction with IFN-γ therapy in PC, HCC, and GC [59], [78], [79], [80]. In murine models with human pancreatic cancer cell lines, IFN-γ was found to amplify the effectiveness of anti-PD1 therapy by suppressing C-X-C motif chemokine ligand 8 (CXCL8), a chemokine produced by PC cells to induce inflammation, tumor-associated macrophage mobilization, and immune escape. Together, anti-PD1 and IFN-γ led to significant antitumor effects [59]. Another study specifically looked at nivolumab, brand name Opdivo®, a monoclonal antibody to block PD-1, in 88 peripheral T-lymphocyte samples, 48 PDAC, and 40 healthy donors. Their results showed that adding IFN-γ with nivolumab decreased PD-1 expression more so than nivolumab or IFN-γ as single agents, thereby improving therapeutic efficacy [78]. This synergistic effect of anti-PD-1 therapy and IFN-γ has treatment implications for HCC as well, given that anti-PD-L1 antibodies are first-line for unresectable HCC [79]. Furthermore, Li et al. [81] analyzed gastric cancer cells treated with chemotherapy (mFOLFOX6), camrelizumab, an anti-PD-1 monoclonal antibody, and IFN-γ, and found a similar synergistic effect as previously mentioned but also concluded that a high IFN-γ signature in CD8 + T-cells positively correlated with response to the neoadjuvant immunotherapy. Table 4 summarizes the key literature findings pertaining to the roles of IFN-γ in GI cancers.