Role of Probiotics in Enhancing Immune Function and Improving the Effectiveness of Treatments for Pancreatic Cancer

1. Introduction and Background

Pancreatic cancer is an aggressive disease often diagnosed late due to its vague early symptoms, diverse tumor types, and poor prognosis, with a 5-year survival rate of less than 10% [1,2]. Early detection is tough because symptoms usually arise only after the tumor grows significantly or spreads. It’s been one of the top causes of cancer-related deaths worldwide, with little improvement in survival rates over the years [1]. Common symptoms include fatigue, weakness, unexplained weight loss, abdominal pain radiating to the back, jaundice, digestive problems like nausea or bloating, new-onset diabetes, and blood clots. Tumors in the pancreas head often cause early jaundice from bile duct obstruction, while tumors in the body or tail typically result in pain and weight loss later, often after metastasis [3]. The causes are not fully understood but are linked to genetic mutations, hereditary factors, smoking, obesity, heavy alcohol use, chronic pancreatitis, aging (65-74 years), family history, chemical exposure, and diabetes [3,4]. Diagnosis usually involves imaging tests like computed tomography (CT) scans, magnetic resonance imaging (MRI), positron emission tomography (PET) scans, and endoscopic ultrasound. Blood tests for markers like cancer antigen 19-9 (CA 19-9) can help monitor the disease, but aren’t definitive, and biopsies are often guided by imaging [1,5].

Most pancreatic tumors (90-95%) are exocrine, primarily pancreatic adenocarcinomas (PDAC), which arise from enzyme-producing cells near the ducts, grow rapidly, and spread early [6]. The remaining 5-10% are pancreatic neuroendocrine tumors (PNETs), originating from hormone-producing cells, growing more slowly, and offering a better prognosis [7]. PDAC progresses due to a mix of genetic mutations, disrupted signaling pathways, tumor microenvironment interactions, and cellular adaptability [6,8]. Key genetic drivers include KRAS mutations, found in about 95% of PDAC cases, which activate growth and survival pathways, along with mutations in tumor suppressor genes like TP53, CDKN2A (p16), and SMAD4, causing uncontrolled cell growth, avoidance of cell death, and tumor development [8,9]. Early detection significantly improves outcomes, and PNETs generally have better survival rates than adenocarcinomas [9]. Pancreatic cancer patients often face severe nutritional deficiencies, muscle wasting, and bone issues, with the first case of bone metastasis documented in Russian literature in 1963 [10]. Pancreatic cancer often spreads to the liver, peritoneal cavity, lungs, bones, adrenal glands, and brain [10,11,12,13,14,15,16]. The liver (50-70%) is the primary site for metastasis due to portal circulation, worsening the prognosis [11,13]. The peritoneum (around 50% in advanced cases) often develops carcinomatosis, causing symptoms and limiting treatment options [12]. Pulmonary metastases (15-30%) affect survival as tumor cells become trapped in the lung’s capillaries. Bone metastases (10-20%) are less common but cause pain and fractures [10]. Adrenal gland involvement (5-10%) is rare but can disrupt hormonal balance [14]. Brain metastases, occurring in less than 1% of cases, are a rare complication with poor outcomes [15,16].

The pancreatic tumor microenvironment (TME) is characterized by a dense fibrotic stroma, cancer-associated fibroblasts (CAFs), immune-suppressive cells like regulatory T cells and myeloid-derived suppressor cells, extracellular matrix (ECM), and cytokines [17,18,19]. This environment facilitates tumor growth, hinders drug delivery, enables immune evasion, and promotes metastasis [20]. Secreted factors and cytokines, such as TGF-β, further modify the microenvironment to foster tumor growth, fibrosis, angiogenesis, metastasis, and immune suppression [9,21]. Treatment for pancreatic cancer depends on the stage, location, and the patient’s overall health [22]. Surgery, including the Whipple procedure, distal pancreatectomy, or total pancreatectomy, offers the only potential cure but is limited to localized cases [22,23]. Chemotherapy (e.g.; FOLFIRINOX, gemcitabine) and radiation therapy are used to control the disease and shrink tumors [22]. Other strategies involve MAPK pathway inhibitors like Trametinib and Binimetinib, KRAS-specific inhibitors such as Sotorasib and Adagrasib, and immunotherapy, though immune evasion remains a challenge [22,24]. Targeted therapies and immunotherapies hold promise for specific genetic subtypes or advanced cases, while palliative care focuses on relieving symptoms, particularly pain [22]. Strategies to modify TME, using a combination of CAR-T with immune checkpoint inhibitors and cytokine modulations, are also under investigation to boost pancreatic cancer therapeutics [25]. The effectiveness of natural killer (NK) cell-based therapies has been demonstrated in various solid tumors [26,27,28,29,30,31].

NK cells play a key role in inhibiting pancreatic cancer through their effector functions, such as direct cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC). They also regulate or activate the anti-cancer activity of other immune effectors through the cytokines and chemokines they secrete [32,33,34]. As vital components of innate immunity, NK cells identify and destroy tumor and virus-infected cells without prior sensitization [35,36,37]. The proper functioning of NK cells or NK cell-based therapies is crucial for improving the prognosis of pancreatic cancer patients and reducing tumor relapse [38,39,40,41,42,43,44,45,46,47]. Maintaining balanced numbers and anti-cancer activity of peripheral blood-derived NK cells, along with increased NK cell infiltration in tumor tissues, significantly enhances patient outcomes [48,49,50,51,52]. However, studies have shown reduced numbers and diminished anti-cancer activity of NK cells in cancer patients, both in tumor tissues and peripheral blood-derived immune subsets [48,49,50,51,52]. To address this, several technologies have been developed to expand and activate NK cells, enabling large-scale production for therapeutic use [53,54,55,56,57]. This review focuses on combining probiotics with feeder cells to promote significant NK cell expansion and enhance their anti-cancer functionality [51,58,59,60].

Probiotics, discovered by Elie Metchnikoff in the early 20th century, are crucial for maintaining gut balance [61,62]. They may influence pancreatic cancer by impacting gut microbiota, immune responses, and tumor pathways, though the evidence is mixed and context-dependent, with risks like potentially promoting tumor growth [63,64,65]. In vivo studies show probiotic treatments can enhance tumor immune cell recruitment, boost anti-cancer activity, improve PBMC cytotoxicity and cytokine secretion, and reduce tumor burden [59,66]. Clinical trials reveal better immune markers and therapy outcomes in cancer patients using probiotics [63]. Some probiotic regimens, combined with standard therapy, have been shown to improve survival, reduce complications, and enhance quality of life [63]. Host factors like baseline microbiome, genetics, diet, and immune status also play a significant role in these effects [63].

This review discusses how activating immune cells through probiotics can directly or indirectly contribute to the breakdown and inhibition of pancreatic cancer growth. Combining probiotic treatments with feeder cells has been shown to promote NK cell expansion and functional activity. Probiotic-based NK cell therapies have demonstrated enhanced lifespan, cell proliferation, cytotoxic effects, and cytokine secretion, improving the ability to target and destroy pancreatic cancer both in vivo and in vitro. Administering probiotics orally, alongside surgery, radiotherapy, chemotherapy, and NK cell therapy, has shown additive benefits in reducing tumor burden, restoring immune function, and preventing bone loss in pancreatic cancer models in mice or humans.

2. Probiotics Boost the Ability of Immune Cells to Fight Cancer

Probiotics help balance the gut microbiome, activate peripheral blood mononuclear cells (PBMCs), reduce pathogen-induced inflammation, and lower exposure to systemic carcinogens [67]. They support the intestinal barrier and microbial balance by boosting proteins and mucus that block pathogens and prevent excessive immune reactions [68]. Through direct interaction and signaling with immune cells, probiotics enhance immunity, strengthen anti-cancer properties, and maintain gut tolerance [68,69]. Their benefits are strain-specific, as outlined in Table 1, with beneficial formulations including Lactobacillus and Bifidobacterium [67,69].

PBMCs or PBMCs-derived lymphocytes, such as T cells and NK cells, are vital for anti-tumor immunity [99,100]. Probiotics, often Lactobacillus and Bifidobacterium, interact directly or indirectly with PBMCs to enhance their anti-tumor effects [98] (Figure 1). These bacteria produce short-chain fatty acids (SCFAs) like butyrate, acetate, and propionate, which promote PBMCs or PBMCs-derived NK cells and T cells-mediated apoptosis of pancreatic cancer via Fas/FasL pathways and support T-cell differentiation and activation [101,102,103]. Probiotics also create bioactive compounds like bacteriocins and exopolysaccharides (EPS) that boost PBMC activation and selectively target tumor cells [104]. Enhanced PBMC cytotoxicity can halt tumor cell cycles at G0/G1 or G2/M phases, inhibiting tumor growth and metastasis [105]. Probiotic treatments increase anti-angiogenic cytokines, particularly IFN-γ and TNF-α in PBMCs, NK cells, and T cells (CD8+. CD4+ and γδ T cells); these cytokines can inhibit tumor growth by promoting differentiation [70]. Differentiated tumors proliferate more slowly and express more surface molecules like major histocompatibility complex-class I (MHC-I), CD54, and PD-L1, improving immune recognition and reducing tumor-supportive microenvironments [70,106].

Probiotics, especially lactic acid bacteria like Lactobacillus and Bifidobacterium, provide significant immunomodulatory benefits by enhancing NK cell-driven anti-cancer responses [70]. Probiotic-treated NK cells exhibit increased cytolytic activity against cancer cells, producing more perforins and granzyme B for precise cancer cell targeting [70]. They activate NK cells through cytokine stimulation, promoting tumor differentiation, growth inhibition, and improved immune recognition via upregulated expression of MHC-class I, CD54, and PD-L1 [70]. Strains like Lactobacillus paracasei support Th1- and Th17-mediated anti-tumor immunity, indirectly activating NK cells [70]. Probiotics also stimulate dendritic cells (DCs) and other antigen-presenting cells to present antigens more effectively, bolstering NK cells and T cells’ anti-cancer functions [107]. They enhance DC maturation by upregulating CD80 and CD86, improving antigen presentation to naive T cells. Activated DCs release cytokines like IL-10, IL-12, and TGF-β, guiding naive T cells to differentiate into regulatory T cells (Tregs) to suppress excessive inflammation [108,109]. Effector T cells, including Th1 and Th17, play a role in anti-tumor immunity and work in synergy with chemotherapy drugs like cyclophosphamide and gemcitabine [110].

Probiotic treatment in PBMCs shows increased CD8+ T cell/Treg cell ratios, higher IFN-γ production by NK, CD4+ T, and γδ T cells, improved tumor recognition, and enhanced cytotoxicity and tumor growth inhibition via differentiation. These effects may boost cancer therapy by restoring immune surveillance, suppressing tumor progression, and improving outcomes. Additionally, these mechanisms amplify the effectiveness of conventional therapies, including immunotherapy [111,112,113] (Figure 1).

3. Probiotics, When Combined with Feeder Cells, Contribute to Improving the Development of NK Cell-Based Immunotherapies

Natural killer (NK) cells, known for their strong anti-tumor activity, can effectively target cells that lack or have altered major histocompatibility complex (MHC) class I molecules [114,115]. While NK cell-based therapies are considered safe, their effectiveness is limited due to challenges in enhancing their expansion and anti-tumor capabilities [116,117]. Autologous NK cells from pancreatic cancer patients often face impairments caused by prior immunosuppression, making their expansion more difficult compared to those from healthy donors [118,119,120]. Studies show that NK cells expanded from pancreatic cancer patients demonstrate lower cytotoxicity and reduced IFN-γ secretion [121]. These cells also exhibit decreased levels of activating receptors like CD16, CD56, Nkp30, Nkp44, Nkp46, NKG2D, and CD54 [121]. To address these issues, healthy allogeneic NK cells are being explored for pancreatic cancer therapies and are under clinical investigation [122]. These allogeneic cells, sourced from peripheral blood, cord blood, hematopoietic stem cells, or induced pluripotent stem cells, can be expanded and cryopreserved for convenient use [123,124,125]. Several methods have been developed to expand NK cells ex vivo, often using feeder cells with or without cytokines and other activation signals [53,55,56,126,127,128,129,130,131,132]. Feeder cells play a vital role in activating and proliferating NK cells by providing receptor-ligand interactions and cytokine support, enabling large-scale therapeutic applications [132,133,134,135]. Cytokines like IL-2, IL-15, and IL-21, along with membrane-bound cytokines and antibodies, are commonly used to supplement feeder cell cultures [136,137]. When there’s a donor-recipient mismatch, donor NK cells with inhibitory receptors like KIR don’t recognize HLA class I on recipient cells. This lack of recognition activates the donor NK cells, allowing them to attack cancer cells that lack the MHC ligands needed for KIR inhibition. As a result, alloreactive NK cells destroy these cancer cells [122,138,139]. Engineered or feeder-expanded NK cells, with enhanced KIR expression, increased cytokine secretion, improved ADCC through elevated levels of CD16 and NKG2D, reduced inhibitory receptors like NKG2A, and the ability to kill tumor cells regardless of MHC-class I expression, show great promise as allogeneic cancer therapies [132,140,141,142,143]. Additionally, the absence of graft-versus-host disease (GVHD) in NK cells ensures their safety in adoptive cell-based therapies [144,145].

Combining probiotics with feeder cells has been shown to enhance the effectiveness of NK cell therapy compared to using feeder cells alone (Figure 2) [132]. Selected probiotic strains like Streptococcus thermophilus, Bifidobacterium longum, Bifidobacterium breve, Bifidobacterium infantis, Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus paracasei, and Lactobacillus bulgaricus boosted NK cell activation and cytokine secretion [70]. NK cells expanded with probiotics and feeder cells displayed improved expansion, longer lifespan, increased cytotoxicity, and higher cytokine secretion compared to those expanded with feeder cells alone [132,146]. These expanded NK cells also showed a greater ability to induce pancreatic tumor killing and differentiation in both in vivo and in vitro studies [59,66]. They exhibited enhanced survival in the pancreatic tumor microenvironment due to higher anti-apoptotic protein levels like BCL2 and reduced pro-apoptotic proteins, allowing them to resist tumor-induced cell death. Elevated cytotoxic granules and Trail expression further improved their cytotoxic function [66,140]. Additionally, these expanded NK cells showed better regulatory functions, with most cells in an active cycling phase, increased expression of proliferation- and memory-associated genes, and enhanced activating receptors (e.g., CD16, CD56, Nkp30, Nkp44, Nkp46, NKG2D) while reducing inhibitory receptors like NKG2A, PD-1, and TIGIT [132,140]. Compared to NK cells expanded without probiotics, those expanded with probiotics demonstrated remarkable anti-cancer properties [132] (Figure 2).

The effectiveness of probiotic combined with feeder cells expanded NK cells therapies has been shown in vivo using humanized mouse models, highlighting their potential for clinical use [59,66,146]. Infusing these expanded NK cells into healthy and pancreatic cancer-bearing humanized mice over eight weeks resulted in no toxicity, pain, distress, or adverse events such as cytokine-release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS) [66]. Combining this NK cell-based therapy with chemotherapy or checkpoint inhibitors in pancreatic tumor-bearing humanized mice enhanced the effectiveness of both treatments [146]. Advances in NK cell expansion techniques have opened up exciting new therapeutic possibilities for pancreatic cancer [55,147].

4. Benefits of Incorporating Probiotics as an Additional Therapy in the Treatment of Pancreatic Cancer

Several probiotics are being studied in preclinical and clinical settings for their potential benefits in cancer patients. A diet rich in probiotics has been linked to reduced rates of pancreatitis and pancreatic cancer [148,149]. Probiotics like Lactobacillus and Bifidobacterium spp. help maintain gut microbial balance, strengthen intestinal barriers, and decrease pro-inflammatory microbial products reaching the pancreas [91,150]. Animal studies indicate they may reduce pancreatic inflammation, suppress enzyme activity, and enhance proteins like occludin and claudins to prevent tumors [151]. Probiotics can also boost immune responses and promote cancer cell death, with compounds like heptelidic acid from Aspergillus oryzae and ferrichrome from Lactobacillus casei showing tumor-inhibiting properties [152]. Ferrichrome from Lactobacillus casei, an iron chelate derivative, has demonstrated antitumor effects in refractory and 5-fluorouracil-resistant pancreatic cancer by regulating the tumor cell cycle through p53 activation [152,153]. They may also inhibit angiogenesis, EMT, and metastasis, potentially slowing tumor growth. Using Lactobacillus plantarum to ferment stevia extract generated bioactive metabolite clonogenic acid methyl ester (CAME) was found to arrest pancreatic cancer cells (PANC-1) in the G0/G1 phase and induce apoptosis suggesting its role as pancreatic cancer therapeutic[88]. The effects on pancreatic cancer depend on specific strains and the overall context, making strain selection crucial for achieving therapeutic goals (Table 1).

Short-chain fatty acids (SCFAs) derived from probiotics, like butyrate, acetate, and propionate, can activate tumor suppressor genes epigenetically and inhibit pancreatic cancer cell invasion and metastasis by reducing integrin β4 expression or inhibiting histone deacetylase (HDAC) activity [149,154,155]. Probiotic treatments also decrease VEGF expression in tumors, limiting angiogenesis, promoting differentiation, and inducing tumor-antigen surface expression in pancreatic tumors [156]. Strains such as Lactobacillus casei and Lactobacillus reuteri show promise in suppressing pancreatic tumors by downregulating TLR4, encouraging macrophage M1 polarization, and supporting gut microbial balance [85,105]. Probiotics may also reduce cancer cell growth, prevent PanIN progression, and curb metastasis through mechanisms possibly involving the TGF-β signaling pathway [157]. Probiotic exposure, including strains like Lactobacillus rhamnosus, Lactobacillus helveticus, Lactobacillus casei, and Saccharomyces boulardii, has been associated with improved survival in pancreatic cancer patients under palliative care [158]. Additionally, patients consuming Streptococcus thermophiles, Bifidobacterium strains, Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus paracasei, and Lactobacillus bulgaris (125 billion CFU per capsule, three times daily for four weeks) demonstrated enhanced IFN-γ levels and increased cytotoxic activity in PBMCs and NK cells [159].

Probiotics as an additional treatment for pancreatic conditions are still in the early stages of research, with limited data available. Common strains like Bifidobacteria and Lactobacillus are often used in multistrain formulations, with optimal doses generally ranging from 10⁸ to over 10¹⁰ CFU daily [160,161,162,163,164]. Recent studies suggest potential benefits in pancreatic cancer for both mouse models and humans, especially when combined with surgery, chemotherapy, radiotherapy, or NK cell-based therapies [66,105,160,165,166]. In mice, probiotics have been shown to enhance drug effectiveness, lessen chemotherapy side effects, and slow tumor progression [152]. For human patients on palliative chemotherapy, probiotics are associated with improved survival outcomes. They also help reduce gastrointestinal side effects from aggressive therapies, boosting treatment adherence and quality of life [105,160,165,166]. Additionally, probiotics have been linked to increased tumor-infiltrating CD8+ T cells, higher IFN-γ expression, reduced inflammatory cytokines, and fewer postoperative complications like anastomotic leakage and bacteremia[59,66,167].

Oral administration of Streptococcus thermophiles, Bifidobacterium longum, Bifidobacterium breve, Bifidobacterium infantis, Lactobacillus acidophilus, Lactobacillus plantarum, and Lactobacillus paracasei, combined with NK cell therapy, significantly reduced tumor growth in pancreatic tumor-bearing humanized mice [59,66]. This combination enhanced NK cell activation in vivo, leading to tumors with increased PD-L1, CD54, and MHC-class I expression, slower growth, and greater sensitivity to checkpoint inhibitors and chemotherapy [59]. These changes likely improved CD8+ T cell-induced killing due to higher MHC-class I expression. Treated mice showed increased infiltration of human CD45+ immune cells, elevated IFN-γ secretion, and reduced IL-6 secretion in the tumor microenvironment, emphasizing the therapeutic benefits of probiotics and NK cells [59]. Probiotics also boosted tumor-infiltrating lymphocyte activity, particularly CD8+ T cell recruitment and cytotoxicity, enhancing cancer-specific immunity. Immune cells from peripheral blood, bone marrow, spleen, pancreas, oral mucosa, liver, and peri-pancreatic fatty tissue in probiotic and NK cell-treated mice exhibited higher cytotoxicity and cytokine secretion compared to those treated with NK cells alone [59]. Additionally, combining probiotics with NK cell therapy not only inhibited tumors but also reduced pancreatic tumor-induced bone defects and restored bone integrity [66].

Probiotics could potentially enhance the effectiveness of standard therapy by reducing immunosuppression and inflammation in the tumor microenvironment. However, clinical validation is necessary to identify the best strains, dosage, duration, and combinations with therapy. While adverse events are uncommon, they can occur in immunocompromised individuals, so their use requires careful consideration, especially for those who are immunocompromised or have metastatic conditions.

Figure 3. The combination of probiotics and NK cells improved immune function and reduced tumor load in a pancreatic tumor-bearing mouse model. These mice were orthotopically injected with human pancreatic tumors into the pancreas. One to two weeks after tumor implantation, they received NK cells via tail-vein injection and were given 5 billion CFU probiotics orally every 48 hours, starting a week before tumor implantation. At the end of the experiment, hu-BLT mice were sacrificed, and their tissues and tumors were collected and analyzed. Tumors from the probiotic and NK cell-treated group showed enhanced immune function, immune cell infiltration, and differentiation compared to the NK cell-only group. Tissues from the probiotic and NK cell-treated group had higher immune function and a greater percentage of CD3+CD8+ T cells compared to the NK cell-only group. Bones from the probiotic and NK cell-treated group displayed fewer defects and showed recovery from tumor-induced bone loss compared to the NK cell-only group. Illustration created with https://BioRender.com on September 26, 2025. https://app.biorender.com/illustrations/68cedfb1c9e8ad7e0f109b30?slideId=b6075359-d4a7-4a6b-8d8d-1b825340710f.

Figure 3. The combination of probiotics and NK cells improved immune function and reduced tumor load in a pancreatic tumor-bearing mouse model. These mice were orthotopically injected with human pancreatic tumors into the pancreas. One to two weeks after tumor implantation, they received NK cells via tail-vein injection and were given 5 billion CFU probiotics orally every 48 hours, starting a week before tumor implantation. At the end of the experiment, hu-BLT mice were sacrificed, and their tissues and tumors were collected and analyzed. Tumors from the probiotic and NK cell-treated group showed enhanced immune function, immune cell infiltration, and differentiation compared to the NK cell-only group. Tissues from the probiotic and NK cell-treated group had higher immune function and a greater percentage of CD3+CD8+ T cells compared to the NK cell-only group. Bones from the probiotic and NK cell-treated group displayed fewer defects and showed recovery from tumor-induced bone loss compared to the NK cell-only group. Illustration created with https://BioRender.com on September 26, 2025. https://app.biorender.com/illustrations/68cedfb1c9e8ad7e0f109b30?slideId=b6075359-d4a7-4a6b-8d8d-1b825340710f.

5. Conclusion

This review highlights the significance of probiotics, particularly the strains listed in Table 1, in activating immune cells or signals to fight pancreatic cancer, their role in advancing cancer therapies, and enhancing the effectiveness of treatments. It emphasizes the benefits of probiotic bacteria and combination therapies, especially NK cell-based treatments, in reducing pancreatic tumor growth and spread. Probiotics offer advantages as a supplementary therapy, including gut health support, improved immune response, and fewer side effects from conventional treatments. Additionally, oral probiotics, alone or with NK cell infusions, help prevent tumor-related bone damage. These findings suggest that probiotics, whether used alone or alongside surgery, radiation, chemotherapy, and immunotherapies, hold promise for treating pancreatic cancer.