Interferon- and STING-independent induction of type I interferon stimulated genes during fractionated irradiation

IFN-Type-I Response and Systemic Immunity in Rectal Adenocarcinoma Patients Treated with Conventional or Hypofractionated Neoadjuvant Radiotherapy

The IFN-type-I pathway is involved in radiotherapy (RT)-mediated immune responses. Large RT fractions have been suggested to potently induce this pathway. Neoadjuvant hypofractionated short-course (scRT) and conventional long-course (lcRT) RT applied for the treatment of locally advanced rectal adenocarcinoma patients provides a unique model to address the immuno-stimulatory properties of RT on a systemic level. We prospectively analyzed the IFNβ plasma levels and lymphocyte counts (LCs) of rectal adenocarcinoma patients before and after treatment with scRT (n = 22) and lcRT (n = 40). Flow cytometry was conducted to assess the effects on lymphocytic subpopulations in a subset of 20 patients. A statistically significant increase in the post-RT IFNβ plasma levels was noted in patients undergoing scRT (p = 0.004). Improved pathological tumor regression was associated with elevated post-RT IFNβ levels (p = 0.003). Although all patients experienced substantial lymphopenia after treatment, the post-RT LC of patients treated with scRT were significantly higher compared to lcRT (p = 0.001). Patients undergoing scRT displayed significantly lower percentages of regulatory CD4+/CD25+ T-cells after therapy (p = 0.02). scRT enables effective stimulation of the IFN-type-I pathway on a systemic level and confers decreased lymphocytic cytotoxicity and limited regulatory T-cell activation compared to lcRT, supporting its increasing role in immuno-RT trials.

Single-cell and bulk transcriptional profiling of mouse ovaries reveals novel genes and pathways associated with DNA damage response in oocytes

Immature oocytes enclosed in primordial follicles stored in female ovaries are under constant threat of DNA damage induced by endogenous and exogenous factors. Checkpoint kinase 2 (CHEK2) is a key mediator of the DNA damage response in all cells. Genetic studies have shown that CHEK2 and its downstream targets, p53 and TAp63, regulate primordial follicle elimination in response to DNA damage, however the mechanism leading to their demise is still poorly characterized. Single-cell and bulk RNA sequencing were used to determine the DNA damage response in wildtype and Chek2-deficient ovaries. A low but oocyte-lethal dose of ionizing radiation induces a DNA damage response in ovarian cells that is solely dependent on CHEK2. DNA damage activates multiple ovarian response pathways related to apoptosis, p53, interferon signaling, inflammation, cell adhesion, and intercellular communication. These pathways are differentially employed by different ovarian cell types, with oocytes disproportionately affected by radiation. Novel genes and pathways are induced by radiation specifically in oocytes, shedding light on their sensitivity to DNA damage, and implicating a coordinated response between oocytes and pre-granulosa cells within the follicle. These findings provide a foundation for future studies on the specific mechanisms regulating oocyte survival in the context of aging, as well as therapeutic and environmental genotoxic exposures.

cGAS-STING at the crossroads in cancer therapy

DNA is highly immunogenic, both exogenous and endogenous DNA can activate the pathogen-associated molecular pattern (PAMP) and danger-associated molecular pattern (DAMP), respectively, and hence activate the evolutionarily conserved cGAS-STING pathway for inflammatory responses. The cGAS-STING signaling pathway plays a very important role in the pathogenesis and progression of neoplastic diseases. For cancer therapy, there are some discrepancies on whether cGAS-STING should be inhibited or activated. Deregulated cGAS-STING signaling pathway might be the origin and pathogenesis of tumor, understanding and modulating cGAS-STING signaling holds great promise for cancer therapy. In this review article, we discuss the molecular mechanisms underlying cGAS-STING deregulation, highlighting the tumor inhibiting and promoting roles and challenges with cGAS-STING agonists in the context of cancer therapies.

Ultra-Hypofractionated Re-Irradiation with Anti-PD-1 Immunotherapy for Locoregionally Recurrent (after Radical Chemo-Radiotherapy) Non-Small Cell Lung Cancer

Large fractions of radiotherapy of 8 Gy (ultra-hypofractionated RT, ultra-hypoRT) promote anti-tumor immune responses that have been clinically substantiated in combination trials with immune checkpoint inhibitors (ICIs). In the current study, we postulated that ultra-hypoRT in combination with ICIs may enhance tumor clearance in NSCLC patients with locoregional relapse after radical chemo-RT. Between 2019 and 2021, eleven patients received re-irradiation with one or two fractions of 8 Gy concurrently with anti-PD1 immunotherapy (nivolumab or pembrolizumab). RT-related toxicities were negligible, while immune-related adverse events enforced immunotherapy interruption in 36% of patients. The overall response rate was 81.8%. Tumor reduction between 80 and 100% was noted in 63.5% of patients. Within a median follow-up of 22 months, the locoregional relapse-free rate was 54.5%, while the projected 2-year disease-specific overall survival was 62%. The results were independent of PD-L1 status. The current report provides encouraging evidence that a relatively low biological dose of RT delivered with 8 Gy fractions is feasible and can be safely combined with anti-PD-1 immunotherapy. Despite the low number of patients, the significant tumor regression achieved and the long-lasting locoregional control and overall progression-free intervals provide a basis to pursue immuno-RT trials with U-hypoRT schemes in this group of NSCLC patients of poor prognosis.

Irradiation-induced IFN-type-I pathway activation in prostate cancer cell lines

The Interferon (ΙFN) Type-I pathway has an important role in the activation of an anti-tumor immune response. We investigated the effects of two different dose fractionations of radiation (3 daily 8 Gy fractions vs. one fraction of 20 Gy) on the activation of the Type-I IFN-pathway in three hormone-dependent (22Rv1) and independent (DU145, PC3), prostate cancer (PC) cell lines. Regardless of the dose schedules, radiation-induced the expression of IFN-stimulated genes in all PC cell lines, with a strong up-regulation of the IFI6v2 and IFI44 genes. In addition, strong up-regulation of the MX1 and MX2 genes was noted in the PC3 cell line. This effect was independent of the expression of IFNβ, cGAS, or TREX1 levels. It is suggested that the RT-induced IFN type-I response could be exploited for the development of immuno-RT policies for localized and metastatic PC.

Anti-Tumor Immunity and Preoperative Radiovaccination: Emerging New Concepts in the Treatment of Breast Cancer

Neoadjuvant chemotherapy (NACT) for certain breast cancer (BC) subtypes confers significant tumor regression rates and a survival benefit for patients with a complete pathologic response. Clinical and preclinical studies have demonstrated that immune-related factors are responsible for better treatment outcomes, and thus, neoadjuvant immunotherapy (IO) has emerged as a means to further improve patient survival rates. Innate immunological "coldness", however, of specific BC subtypes, especially of the luminal ones, due to their immunosuppressive tumor microenvironment, hinders the efficacy of immune checkpoint inhibitors. Treatment policies aiming to reverse this immunological inertia are, therefore, needed. Moreover, radiotherapy (RT) has been proven to have a significant interplay with the immune system and promote anti-tumor immunity. This "radiovaccination" effect could be exploited in the neoadjuvant setting of BC and significantly enhance the effects of the already established clinical practice. Modern stereotactic irradiation techniques directed to the primary tumor and involved lymph nodes may prove important for the RT-NACT-IO combination. In this review, we provide an overview and critically discuss the biological rationale, clinical experience, and ongoing research underlying the interplay between neoadjuvant chemotherapy, anti-tumor immune response, and the emerging role of RT as a preoperative adjunct with immunological therapeutic implications in BC.

Radioimmunotherapy in colorectal cancer treatment: present and future

Colorectal cancer (CRC) is a deadly form of cancer worldwide. Patients with locally advanced rectal cancer and metastatic CRC have a poor long-term prognosis, and rational and effective treatment remains a major challenge. Common treatments include multi-modal combinations of surgery, radiotherapy, and chemotherapy; however, recurrence and metastasis rates remain high. The combination of radiotherapy and immunotherapy (radioimmunotherapy [RIT]) may offer new solutions to this problem, but its prospects remain uncertain. This review aimed to summarize the current applications of radiotherapy and immunotherapy, elaborate on the underlying mechanisms, and systematically review the preliminary results of RIT-related clinical trials for CRC. Studies have identified several key predictors of RIT efficacy. Summarily, rational RIT regimens can improve the outcomes of some patients with CRC, but current study designs have limitations. Further studies on RIT should focus on including larger sample sizes and optimizing the combination therapy regimen based on underlying influencing factors.

Harnessing the Immunological Effects of Radiation to Improve Immunotherapies in Cancer

Ionizing radiation (IR) is used to treat 50% of cancers. While the cytotoxic effects related to DNA damage with IR have been known since the early 20th century, the role of the immune system in the treatment response is still yet to be fully determined. IR can induce immunogenic cell death (ICD), which activates innate and adaptive immunity against the cancer. It has also been widely reported that an intact immune system is essential to IR efficacy. However, this response is typically transient, and wound healing processes also become upregulated, dampening early immunological efforts to overcome the disease. This immune suppression involves many complex cellular and molecular mechanisms that ultimately result in the generation of radioresistance in many cases. Understanding the mechanisms behind these responses is challenging as the effects are extensive and often occur simultaneously within the tumor. Here, we describe the effects of IR on the immune landscape of tumors. ICD, along with myeloid and lymphoid responses to IR, are discussed, with the hope of shedding light on the complex immune stimulatory and immunosuppressive responses involved with this cornerstone cancer treatment. Leveraging these immunological effects can provide a platform for improving immunotherapy efficacy in the future.

Radiation-Induced Remodeling of the Tumor Microenvironment Through Tumor Cell-Intrinsic Expression of cGAS-STING in Esophageal Squamous Cell Carcinoma

PURPOSE

Radiation therapy (RT) has the potential to activate the tumor-microenvironment (TME) and promote the efficacy of immune checkpoint blockade therapy. Tumor cell-intrinsic expression of cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) plays an important role in regulations of radiation-induced activation of immune cells in the TME. However, the role of tumor cell-intrinsic cGAS-STING in radiation-mediated remodeling of the TME in esophageal squamous cell carcinoma (ESCC) is not completely understood; thus, we investigated its effect on the radiation-mediated remodeling of the TME in ESCC.

METHODS

We assessed the effect of tumor cell-intrinsic cGAS-STING on the expression of mediators of the immune system, including type I interferon, T-cell chemo-attractants, colony-stimulating factor-1, and interleukin 34 (IL-34), induced by radiation in ESCC cell lines. We also quantified the association between tumor cell-intrinsic expression of cGAS-STING and infiltrations of immune cells, including CD8⁺ T cells and CD163⁺ M2-tumor-associated macrophages (TAMs), in ESCC tissues before and after neoadjuvant chemo-RT (n = 47).

RESULTS

We found that tumor cell-intrinsic expression of cGAS-STING was involved in radiation-induced infiltration of CD8⁺ T cells and expression of type I interferon and T-cell chemo-attractants in ESCC cells. Surprisingly, tumor cell-intrinsic cGAS-STING was also involved in radiation-triggered infiltration and/or M2-polarization of CD163⁺ TAMs and expression of IL-34, an important cytokine for recruitment and M2-polarization of TAMs, in ESCC cells. The number of CD163⁺ M2-TAMs was significantly associated with IL-34 expression in tumor cells in irradiated ESCC tissues.

CONCLUSIONS

The tumor cell-intrinsic expression of cGAS-STING is essential for radiation-induced activation of immune cells in the TME, but it is also involved in the recruitment of tumor-promoting M2-TAMs in ESCC. Therefore, blocking of M2-TAM infiltration by targeting IL-34 might improve the efficacy of RT and combination therapy of RT with immune checkpoint inhibitors in ESCC.

Exploiting radiation immunostimulatory effects to improve glioblastoma outcome

Cancer treatment protocols depend on tumor type, localization, grade, and patient. Despite aggressive treatments, median survival of patients with Glioblastoma (GBM), the most common primary brain tumor in adults, does not exceed 18 months, and all patients eventually relapse. Thus, novel therapeutic approaches are urgently needed. Radiotherapy (RT) induces a multitude of alterations within the tumor ecosystem, ultimately modifying the degree of tumor immunogenicity at GBM relapse. The present manuscript reviews the diverse effects of RT radiotherapy on tumors, with a special focus on its immunomodulatory impact to finally discuss how RT could be exploited in GBM treatment through immunotherapy targeting. Indeed, while further experimental and clinical studies are definitively required to successfully translate preclinical results in clinical trials, current studies highlight the therapeutic potential of immunotherapy to uncover novel avenues to fight GBM.

Emerging Insights on Immunotherapy in Liver Cancer

Significance: Hepatocellular carcinoma (HCC) is a liver malignancy with high mortality rate, limited treatment options, and poor prognosis. Sorafenib has been the only systemic treatment option for patients with advanced HCC for more than a decade. HCC is a typical inflammation-related tumor with a distinct immunosuppressive microenvironment especially the upregulation of immune checkpoints. Recent Advances: Immunotherapy has shown persistent and powerful efficacy in HCC treatment. Several preclinical and clinical studies have prompted the application of immunotherapy in first-line, second-line, and postline treatment of HCC, which has profoundly shifted the paradigm for advanced HCC treatment in the past few years. Critical Issues and Future Directions: Major unaddressed challenges in HCC immunotherapy include the discovery and validation of biological markers that predict the efficacy, the application of immunotherapy in patients with impaired liver function and nonalcoholic steatohepatitis-associated HCC, and the exploration of immunotherapy combinations with better effectiveness. This review provides the latest advances in the research of immune microenvironment and immunotherapy in HCC. Antioxid. Redox Signal. 37, 1325-1338.

The molecular basis of immuno-radiotherapy

PURPOSE

Radiotherapy (RT) and immunotherapy are powerful anti-tumor treatment modalities. Experimental research has demonstrated an important interplay between the cytotoxic effects of RT and the immune system. This systematic review provides an overview of the basics of anti-tumor immunity and focuses on the mechanisms underlying the interplay between RT and immune anti-tumor response that set the molecular basis of immuno-RT.

CONCLUSIONS

An 'immunity acquired equilibrium' mimicking tumor dormancy can be achieved post-irradiation treatment, with the balance shifted toward tumor eradication or regrowth when immune cells' cytotoxic effects or cancer proliferation rate prevail, respectively. RT has both immunosuppressive and immune-enhancing properties. The latter effect is also known as radio-vaccination. Its mechanisms involve up- or down-regulation of membrane molecules, such as PD-L1, HLA-class-I, CD80/86, CD47, and Fas/CD95, that play a vital role in immune checkpoint pathways and increased cytokine expression (e.g. INFα,β,γ, IL1,2, and TNFα) by cancer or immune cells. Moreover, the interactions of radiation with the tumor microenvironment (fibroblasts, tumor-infiltrating lymphocytes, monocytes, and dendritic cells are also an important component of radio-vaccination. Thus, RT may have anti-tumor vaccine properties, whose sequels can be exploited by immunotherapy agents to treat different cancer subtypes effectively.

cGAS-STING pathway targeted therapies and their applications in the treatment of high-grade glioma

Median survival of patients with glioblastoma (GBM) treated with standard of care which consists of maximal safe resection of the contrast-enhancing portion of the tumor followed by radiation therapy with concomitant adjuvant temozolomide (TMZ) remains 15 months. The tumor microenvironment (TME) is known to contain immune suppressive myeloid cells with minimal effector T cell infiltration. Stimulator of interferon genes (STING) is an important activator of immune response and results in production of Type 1 interferon and antigen presentation by myeloid cells. This review will discuss important developments in STING agonists, potential biomarkers for STING response, and new combinatorial therapeutic approaches in gliomas.

Basic cancer immunology for radiation oncologists

Although the impressive clinical responses seen with modern cancer immunotherapy are currently limited to a subset of patients, the underlying paradigm shift has resulted in now hardly a segment in oncology that has not been touched by the immuno‐oncology revolution. A growing body of data indicates that radiation therapy (RT) can modulate the tumour immune microenvironment and complement cancer immunotherapy via non‐overlapping mechanisms to reinvigorate immunity against cancer. Thus, increasingly RT is viewed as a highly unique partner for immunotherapy across the spectrum of cancer settings, as radiobiology and cancer immunology foreseeably become more intertwined. Considering these developments, this review summarises the key concepts and terminology in immunology for the radiation oncologist, with a focus on the cancer setting and with reference to important recent advances. These concepts will provide a starting point for understanding the strategies that underlie current and emerging immunotherapy trials, as well as the indirect effects of RT by which immune responses against cancer are shaped.

cGAS-STING signaling pathway in gastrointestinal inflammatory disease and cancers

Cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has emerged as a key DNA-sensing machinery in innate immunity. Activation of cGAS-STING signaling pathway mediates the production of interferons and proinflammatory cytokines. Although cGAS-STING signaling pathway shows critical function in the maintenance of gut homeostasis, overactive cGAS-STING signaling pathway leads to gastrointestinal (GI) inflammation. Harnessing the effect and mechanism of the cGAS-STING signaling pathway could be beneficial for the development of novel strategies for the treatment of GI diseases. This review presents recent advances regarding the role of cGAS-STING signaling pathway in GI inflammatory disease and cancers and describes perspective therapeutic strategies targeting the signaling pathway.