Glioblastoma (GB) is the most frequent malignant and aggressive brain tumor in adults, accounting for approximately 15% of all intracranial neoplasms and 45–50% of all primary malignant brain tumors [1]. With a peak incidence in patients aged 55–85 years. The annual age-adjusted incidence rates for GB have increased in recent years to 3–6 cases per 100,000 people [2]. Its aggressive nature is reflected in its classification as a grade 4 glioma by the World Health Organization (WHO), characterized by rapid cell division, extensive infiltration into surrounding brain tissue, and the formation of abnormal blood vessels that support the tumor’s growth [3]. The intricate challenges posed by GB extend beyond its high recurrence rate and resistance to conventional therapies. The tumor exhibits molecular and genetic heterogeneity, with distinct subtypes: gliosarcoma, giant cell GB, and epithelioid GB, each presenting unique biological behaviors and therapeutic responses [4, 5]. This diversity underscores the complexity of GB and emphasizes the need for personalized treatment approaches. Despite advancements in neuro-oncology, the GB prognosis remains poor, with a median overall survival of approximately 12 to 15 months, even with aggressive treatment strategies [6]. Current treatments like surgery, radiation, and chemotherapy have limits. This emphasizes the urgent need for innovative solutions to deal with the complexities of GB’s biology. These constraints emanate from the blood-brain barrier (BBB), imposing restrictions on the effective delivery of therapeutic agents to the tumor site. This resistance, coupled with the high rate of recurrence. Oncolytic viruses (OVs) are special viruses, either natural or genetically modified, made to specifically find and kill cancer cells [7]. GB’s unique characteristics make it an ideal candidate for oncolytic virotherapy; the viruses can navigate the intricate brain environment, overcoming barriers that hamper traditional treatments [8]. GB is known for its immunologically “cold” tumor microenvironment (TME), characterized by a lack of immune cell infiltration and an immunosuppressive environment. OVs have shown potential in transforming this “cold” environment into a more “hot” and immune-responsive state. Studies have indicated that OVs can induce immunogenic cell death (ICD), leading to the release of tumor antigens and the activation of anti-tumor immune responses [9–11]. This process involves the stimulation of various immune cells, such as dendritic cells (DCs), natural killer (NK) cells, and cytotoxic T lymphocytes, which can then target and eliminate cancer cells [12]. Additionally, OVs can modulate the TME by reducing immunosuppressive factors, such as regulatory T cells (Tregs) and myeloid-derived suppressor cells, while enhancing the infiltration of effector T cells. Moreover, OVs stimulate the immune system, triggering a robust anti-tumor response that extends beyond the initial viral attack [13].

In unraveling the history of OVs in GB treatment, we witness not only a response to the shortcomings of conventional therapies but also a promising leap toward more effective and targeted interventions. The interaction between OVs and the neuroinflammatory cytokines in GB is a complex area of study. Neuroinflammation is a process involving the activation of inflammatory responses in the central nervous system (CNS), and cytokines play a crucial role in mediating these responses [14]. In the context of GB, neuroinflammation is often associated with the presence of tumor-associated macrophages (TAMs) and microglia, which release various cytokines [15]. When OVs infect GB cells, they can induce a local immune response. This response may involve the release of cytokines and chemokines, which can modulate the TME [16]. The specific effects on neuroinflammatory cytokines can vary depending on the OVs used, the characteristics of the tumor, and the host’s immune response [17]. Some OVs have been engineered to express therapeutic transgenes, including cytokines, to enhance their antitumor effects [17]. These transgenes can further influence the local cytokine TME and potentially stimulate an anti-tumor immune response. This review aims to focus centers on the intricate interplay between OVs and neuroinflammatory cytokines within the GB TME. We explore the therapeutic approaches of oncolytic virotherapy and OVs combined with other treatment protocols. We seek to contribute valuable insights that may pave the way for novel and personalized therapeutic strategies, offering renewed hope for patients grappling with this challenging malignancy.

The GB TME is a critical factor in tumor progression. It promotes invasion, immune evasion, angiogenesis, and therapeutic resistance, making GB one of the most challenging cancers to treat. The GB microenvironment refers to the complex and dynamic surroundings in which GB cells, exist and interact with neighboring cells and components [18]. GB is classified as a “cold” tumor due to several features of its microenvironment that hinder an effective immune response against the tumor. GB tumors often exhibit a low rate of lymphocyte infiltration, particularly T cells, which are crucial for anti-tumor immunity [19]. This plays a role in inhibiting primary inflammation and immune responses within the CNS, where GB develops, further limiting immune cell infiltration and function [20]. Even if immune cells manage to infiltrate the tumor, the CNS has unique immunosuppressive mechanisms that can inhibit their function, contributing to the immunosuppressive nature of the GB microenvironment [21]. Additionally, GB tumors have a relatively low mutation rate and thus a low chance of neoantigen formation, which are key targets for the immune system to recognize and attack cancer cells [22]. These features collectively create an immunosuppressive TME in GB, making it less responsive to immunotherapy. The GB TME includes various cellular and non-cellular components such as tumor cells, immune cells, blood vessels, extracellular matrix (ECM), and signaling molecules. This dynamic network of interactions contributes to the unique characteristics of GB, including its invasiveness and resistance to treatment [22]. Among the cellular components, GB cells exhibit rapid proliferation, infiltration into surrounding brain tissues, and the formation of abnormal blood vessels, which are essential for sustaining their growth. Concurrently, immune cells such as TAMs, microglia, and other immune cells play a pivotal role in the microenvironment, influencing inflammation and modulating the immune response. ECM, provides structural support and regulates cell behavior [23]. Changes in the ECM composition have a profound impact on tumor invasion and progression [24]. Abnormal angiogenesis leads to the formation of leaky and disorganized blood vessels, contributing to the tumor’s nutrient supply and growth [25]. Additionally, signaling molecules such as cytokines, chemokines, and various growth factors released by tumor cells and immune cells influence immuno-inflammatory response, and the overall dynamics of the TME [26]. OVs can remodel this hostile environment by targeting tumor cells. OVs selectively infect and replicate within tumor cells, leading to their lysis. This process releases tumor-associated antigens (TAAs) into the TME, which can stimulate an immune response by exposing these antigens to immune cells, particularly DCs. OVs can also modulate immune cell dynamics and can enhance the maturation and activation of DCs, which are crucial for effective antigen presentation. By providing novel tumor antigens and promoting DC infiltration, OVs help overcome the immune tolerance typically induced by the TME. Infection with OVs can lead to the upregulation of pro-inflammatory cytokines. This change not only enhances the infiltration of cluster of differentiation 4⁺ (CD4⁺) and CD8⁺ T cells but also restores major histocompatibility complex (MHC) class I expression on tumor cells, facilitating better recognition and destruction by T cells [12, 22]. Understanding these intricate interactions is critical for developing targeted therapeutic strategies against GB.

Neuroinflammatory cytokines play a prominent role in the intricate dynamics of the CNS during the inflammatory response in GB. Within the GB microenvironment, immune cells, particularly TAMs and microglia, are attracted and undergo activation, releasing a diverse array of cytokines. Glioma-derived cytokines, including tumor necrosis factor-alpha (TNF-α), interleukins (ILs): IL-1α and IL-1β, IL-4, IL-6, and IL-8, play pivotal roles as inflammatory mediators. These factors trigger and sustain the inflammatory cycle in GB, while also promoting carcinogenesis. They achieve this by bypassing growth suppression mechanisms, promoting angiogenesis and metastasis, resisting apoptosis, and maintaining the stemness of cancer cells [27–29]. ILs, especially IL-6 and IL-8, play a crucial role, with IL-6 being involved in the proliferation of GB cells [30, 31]. Recent studies have identified a fourth subtype of alternative M2 macrophages, activated by IL-6 and toll-like receptors (TLRs) agonists through adenosine receptors. Activation of these receptors triggers the secretion of anti-inflammatory cytokines like IL-10 and IL-12, as well as angiogenic factors such as vascular endothelial growth factor (VEGF). These findings provide additional evidence supporting the critical role of TAMs in tumor maintenance and progression [31, 32]. In vitro and in vivo studies suggest that the interaction between protein kinase B (Akt) and IL-6 depends on the autocrine/paracrine release of IL-6. This release increases Akt activity, which in turn boosts IL-6 secretion into the TME, inhibiting caspase-3. This interplay between IL-6 and Akt promotes chemoresistance and gliomagenesis [33]. IL-6 and colony-stimulating factor-1 (CSF-1) activate mammalian target of rapamycin (mTOR), promoting cell survival and the growth of alternatively activated macrophages in the TME [34]. Additionally, several studies have shown increased nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activity in various GB models [35]. IL-1β activates the NF-κB pathway by binding to the IL-1 receptor, leading to sustained stimulation of pro-inflammatory genes [36]. Transforming growth factor-beta (TGF-β) increases microRNA-182 (miR-182) levels, prolonging NF-κB activation in GB samples [37]. NF-κB activation in glioma cells upregulates the pro-angiogenic gene IL-8 [38]. Inhibition of both NF-κB and signal transducer and activator of transcription 3 (STAT3) with antagonists reduces IL-6 levels, enhancing anti-invasive and cytotoxic effects in GB [39]. IL-8 is a strong pro-angiogenic factor, especially during tumorigenesis and progression [30]. It stimulates angiogenesis by promoting endothelial cell migration and the production of matrix metalloproteinases (MMPs) [40]. Targeting IL-8 in therapies could reduce tumor angiogenesis, improve permeability, hinder GB formation, and potentially enhance drug delivery. TNF-α and interferon-gamma (IFN-γ), released by immune cells, play complex roles in inflammation and tumor progression, affecting cell invasion and interactions with surrounding tissues [41]. These cytokines also impact the BBB, altering its integrity and allowing immune cell infiltration and other factors into brain tissue [42]. This disruption adds complexity to the GB microenvironment, where cytokines influence both the immune response and potentially exert anti-tumor effects, particularly IFN-γ [43]. GB cells contribute to this dynamic by showing cytokine expression heterogeneity, highlighting the complexity of the TME. Understanding how neuroinflammatory cytokines function is crucial for developing specific treatments to improve outcomes in treating GB. Figure 1 illustrates the TME in GB, highlighting the secretions of immune cells and other cellular components.

GB represents a disease with a pressing need for innovative therapeutic approaches. The positive results seen in preclinical studies, demonstrating improved effectiveness without added toxicity, suggest that combining new OVs with radiation and chemotherapy could be a promising new treatment approach for GB cases [95]. The existing standard of care permits the incorporation of virotherapy as a novel therapy, enabling the evaluation of cooperative effects with radiation/chemotherapy without deviating from the established treatment protocol. Where GL261 cells were injected into anesthetized C57BL/6 mice, the use of oncolytic adenovirus (DNX2401) led to an increased infiltration of CD4⁺ T cells and T-bet⁺CD8⁺ T cells [49, 52]. Likewise, injecting the Zika virus (ZIKV) directly into tumors triggers an inflammatory response that activates microglia and myeloid cells. This activation boosts antigen presentation and contributes to an antitumor effect mediated by CD8⁺ T cells [96]. Numerous OVs targeting GB have progressed through different stages of clinical trials. Notable candidates such as DNX-2401 (Delta-24-RGD; tasadenoturev), Toca 511 (vocimagene amiretrorepvec), PVS-RIPO (recombinant nonpathogenic polio-rhinovirus), and G207 have reported results from phase-I clinical trials [7, 97]. DNX2401, an oncolytic adenovirus that selectively targets tumors, has demonstrated encouraging outcomes in phase-I clinical trials. Published data indicates that the median overall survival of GB patients treated with DNX2401 reached 9.5 months. Importantly, 20% of these patients survived for more than 3 years after treatment, indicating a positive and long-lasting response in a subset of individuals. Additionally, following treatment with DNX2401, the tumor site exhibited signs of inflammation and necrosis [50]. Histopathological analysis showed the infiltration of CD8⁺ T cells and T-bet⁺ cells [98]. This finding indicates that DNX-2401 not only causes tumor regression through direct oncolysis but also triggers an antitumor immune response, which is consistent with results from preclinical studies [52, 69]. Combining DNX2401 with other treatments has advanced to phase-I/II clinical trials, including trials registered under NCT02798406, NCT02197169, and NCT01956734 [99]. Toca 511, another potential treatment, is a retrovirus that carries the cytosine deaminase gene. This virus can replicate selectively in tumor cells, producing cytosine deaminase. The cytosine deaminase enzyme encoded by Toca 511 converts the prodrug 5-fluorocytosine (5-FC) into the active chemotherapy drug 5-fluorouracil (5-FU) [100, 101]. This enzymatic process enables targeted chemotherapy within the tumor, minimizing the potential for systemic toxicity linked to 5-FU [102]. In an earlier investigation, GB patients treated with Toca 511 therapy had a median overall survival of 14.4 months. Additionally, five complete remissions were notably observed [103–105]. PVS-RIPO has demonstrated encouraging outcomes in treating recurrent GB, with a median overall survival of 24 months [106, 107]. PVS-RIPO employs a dual approach to directly eliminate cancer cells while simultaneously triggering an immune response in the host. These two modes of action are intricately linked both mechanistically and biologically, as evidenced by the immunostimulatory process of ICD. ICD is a non-canonical form of cell death induced by viruses, which promotes an immune response against the antigens present in the deceased cells. This process involves apoptosis accompanied by the release of adenosine triphosphate, the proinflammatory cytokine high-mobility group box 1, and calreticulin [108]. These released molecules immediately lead to the recruitment of DCs, antigen presentation to cytotoxic T lymphocytes, and activation of gamma-delta T cells [109]. As far as we know, 2Apro is the initial enzyme produced by PVS in tumor cells it infects [106]. Another way this virus causes cell death is through 2Apro, which is a protease that cleaves the cell’s normal protein synthesis machinery, potentially resulting in cell death [110]. Additionally, there is ongoing investigation into combining pembrolizumab, a PD-L1 inhibitor with this therapy, which has progressed to phase-II clinical trials (NCT04479241). Table 2 outlines the ongoing clinical trials using OVs for treating GB [99]. Vaccinia virus (TG6002) and adenovirus (DNX2401) show tumor-specific replication and microenvironment modulation, while reovirus and HSV variants (e.g., M032) leverage immune stimulation through GM-CSF or IL-12. PVS-RIPO demonstrates effective targeting of PVS receptor (CD155)-expressing cells with reduced neurotoxicity, and parvovirus H1 combines oncolysis with immune responses during the S-phase. However, challenges remain, including the immunosuppressive GB microenvironment, limited OV delivery across the BBB, and potential off-target effects. Further research is needed to optimize combination therapies, refine delivery methods, and identify biomarkers for patient selection, ensuring safety and efficacy in clinical applications.

Recent advancements in GB treatment, such as oncolytic virotherapy and immunotherapy, offer hope for patients. These approaches target GB cells while sparing healthy tissue. However, challenges remain, despite promising results, limiting the effectiveness of oncolytic virotherapy for GB.

The GB TME presents a challenging landscape for effective treatment due to its immunosuppressive nature and resistance to therapies. Neuroinflammatory cytokines play a crucial role in shaping this environment, promoting tumor progression and immune evasion. Understanding these interactions is key to developing targeted therapies. OVs offer a promising approach to modulating the GB TME. They can induce tumor cell lysis, release TAAs, and trigger an inflammatory immune response, enhancing antitumor immunity. Clinical trials with OVs, including those expressing cytokines like IL-12, show potential in treating GB. Future research should focus on optimizing OV therapy for GB. This includes addressing challenges such as restricted distribution within the tumor and clearance by host immunity. Combining OVs with other therapies, such as ICIs, DCs, NK, and CAR-T cell therapy, holds promise in enhancing therapeutic efficacy. Additionally, further understanding of the interactions between OVs and the GB microenvironment is needed to develop more effective immunotherapeutic strategies. Overall, OVs represent a promising avenue for improving outcomes in GB treatment, and continued research in this area is essential for advancing cancer therapy.