Augmentation of natural cytotoxicity by chronic low-dose ionizing radiation in murine natural killer cells primed by IL-2

Emerging Role of the p53 Pathway in Modulating NK Cell-Mediated Immunity

The p53 pathway plays an important role in role in cancer immunity. Mutation or downregulation of the proteins in the p53 pathway are prevalent in many cancers, contributing to tumor progression and immune dysregulation. Recent findings suggest that the activity of p53 within tumor cells, immune cells, and the tumor microenvironment can play an important role in modulating NK cell-mediated immunity. Consequently, efforts to restore p53 pathway activity are being actively pursued to modulate this form of immunity. This review focuses on p53 activity regulating the infiltration and activation of NK cells in the tumor immune microenvironment. Furthermore, the impact of p53 and its regulation of NK cells on immunogenic cell death within solid tumors and the abscopal effect are reviewed. Finally, future avenues for therapeutically restoring p53 activity to improve NK cell-mediated antitumor immunity and optimize the effectiveness of cancer therapies are discussed.

Low-Dose Ionizing Radiation and Male Reproductive Immunity: Elucidating Subtle Modulations and Long-Term Health Implications

Low-dose ionizing radiation (LDIR) is a prevalent environmental factor with profound impacts on male reproductive health, particularly on the testicular immune microenvironment. This review examines the multifaceted effects of LDIR, emphasizing its ability to induce genotoxic stress, oxidative damage, and epigenetic modifications in reproductive cells. These alterations compromise DNA repair, disrupt chromatin structure, and induce immune dysregulation. Immune cells such as macrophages, T cells, natural killer cells, and dendritic cells exhibit significant functional changes under LDIR exposure, destabilizing the immune privilege critical for normal spermatogenesis. The long-term health implications of LDIR include impaired sperm quality, reduced fertility, and transgenerational risks through heritable genomic instability. This review underscores the importance of exploring the mechanisms underlying immune dysregulation and developing effective protective strategies. While LDIR's full impact on male reproductive health remains to be elucidated, addressing the gaps in our understanding of immune microenvironmental changes is crucial for mitigating its adverse effects and improving reproductive health outcomes.

Radiotherapy as salvage therapy and an adjunct to immunotherapy: exploring local and abscopal mechanisms to overcome immunotherapy resistance: a narrative review

Background and Objective

Immune checkpoint inhibitors (ICIs) have ushered in a new era of therapies and play a significant role in the clinical treatment of a variety of tumors. However, immune resistance has increasingly created a bottleneck in treatment, making the question of how to overcome drug resistance an urgent issue to address. In this article, the mechanism of drug resistance is briefly described with a focus on how radiotherapy (RT) acts on the immune system to reverse immunotherapy failure. Combinations of existing treatment modalities need to be optimized to overcome resistance problems. Research has shown that some RT modalities reverse immune resistance or enhance efficacy when used in combination, which shows some value for immune resistance and is worthy of in-depth research.

Methods

In this review, we searched the literature published from 2000 to 2023 surrounding immunotherapy, RT and cancer.

Key Content and Findings

Based on the immune effects and immunosuppressive effects induced by RT, this review examined the preclinical rationales of RT and its clinical results. The findings indicate that RT might provide a novel regimen for patients with locally advanced tumors, especially oligometastatic tumors.

Conclusions

Salvage therapy with RT after immunotherapy resistance is the focus of current research. Other strategies, such as multidrug combination therapies, have made preliminary progress in preclinical experiments. Further research on the roles of different RT doses, fractionation regimens, and other treatment sequences in salvage therapy need to be conducted in the future. The optimal site and timing of low-dose radiotherapy are also undetermined, and prospective studies are need to determine the best regimen for optimizing patient treatment.

Enhancing immunotherapy efficacy with synergistic low-dose radiation in metastatic melanoma: current insights and prospects

Recent advances in oncology research have highlighted the promising synergy between low-dose radiation therapy (LDRT) and immunotherapies, with growing evidence highlighting the unique benefits of the combination. LDRT has emerged as a potent tool for stimulating the immune system, triggering systemic antitumor effects by remodeling the tumor microenvironment. Notably, LDRT demonstrates remarkable efficacy even in challenging metastatic sites such as the liver (uveal) and brain (cutaneous), particularly in advanced melanoma stages. The increasing interest in utilizing LDRT for secondary metastatic sites of uveal, mucosal, or cutaneous melanomas underscores its potential efficacy in combination with various immunotherapies. This comprehensive review traverses the journey from laboratory research to clinical applications, elucidating LDRT's immunomodulatory role on the tumor immune microenvironment (TIME) and systemic immune responses. We meticulously examine the preclinical evidence and ongoing clinical trials, throwing light on the promising prospects of LDRT as a complementary therapy in melanoma treatment. Furthermore, we explore the challenges associated with LDRT's integration into combination therapies, addressing crucial factors such as optimal dosage, fractionation, treatment frequency, and synergy with other pharmacological agents. Considering its low toxicity profile, LDRT presents a compelling case for application across multiple lesions, augmenting the antitumor immune response in poly-metastatic disease scenarios. The convergence of LDRT with other disciplines holds immense potential for developing novel radiotherapy-combined modalities, paving the way for more effective and personalized treatment strategies in melanoma and beyond. Moreover, the dose-related toxicities of immunotherapies may be reduced by synergistic amplification of antitumor efficacy with LDRT.

Interplay of immune modulation, adaptive response and hormesis: Suggestive of threshold for clinical manifestation of effects of ionizing radiation at low doses?

The health impacts of low-dose ionizing radiation exposures have been a subject of debate over the last three to four decades. While there has been enough evidence of "no adverse observable" health effects at low doses and low dose rates, the hypothesis of "Linear No Threshold" continues to rule and govern the principles of radiation protection and the formulation of regulations and public policies. In adopting this conservative approach, the role of the biological processes underway in the human body is kept at abeyance. This review consolidates the available studies that discuss all related biological pathways and repair mechanisms that inhibit the progression of deleterious effects at low doses and low dose rates of ionizing radiation. It is pertinent that, taking cognizance of these processes, there is a need to have a relook at policies of radiation protection, which as of now are too stringent, leading to undue economic losses and negative public perception about radiation.

Synergistic treatment strategy: combining CAR-NK cell therapy and radiotherapy to combat solid tumors

Immunotherapy, notably chimeric antigen receptor (CAR) modified natural killer (NK) cell therapy, has shown exciting promise in the treatment of hematologic malignancies due to its unique advantages including fewer side effects, diverse activation mechanisms, and wide availability. However, CAR-NK cell therapies have demonstrated limited efficacy against solid tumors, primarily due to challenges posed by the solid tumor microenvironment. In contrast, radiotherapy, a well-established treatment modality, has been proven to modulate the tumor microenvironment and facilitate immune cell infiltration. With these observations, we hypothesize that a novel therapeutic strategy integrating CAR-NK cell therapy with radiotherapy could enhance the ability to treat solid tumors. This hypothesis aims to address the obstacles CAR-NK cell therapies face within the solid tumor microenvironment and explore the potential efficacy of their combination with radiotherapy. By capitalizing on the synergistic advantages of CAR-NK cell therapy and radiotherapy, we posit that this could lead to improved prognoses for patients with solid tumors.

Low-dose radiotherapy effects the progression of anti-tumor response

The history of low-dose radiotherapy (LDRT or LDR) as a treatment modality for malignant tumors dates back to the 1920s. Even with the minimal total dose administered during treatment, LDRT can result in long-lasting remission. Autocrine and paracrine signaling are widely recognized for fostering the growth and development of tumor cells. LDRT exerts systemic anti-tumor effects through various mechanisms, such as enhancing the activity of immune cells and cytokines, shifting the immune response towards an anti-tumor phenotype, influencing gene expression, and blocking crucial immunosuppressive pathways. Additionally, LDRT has been demonstrated to enhance the infiltration of activated T cells and initiate a series of inflammatory processes while modulating the tumor microenvironment. In this context, the objective of receiving radiation is not to directly kill tumor cells but to reprogram the immune system. Enhancing anti-tumor immunity may be a critical mechanism by which LDRT plays a role in cancer suppression. Therefore, this review primarily focuses on the clinical and preclinical efficacy of LDRT in combination with other anti-cancer strategies, such as the interaction between LDRT and the tumor microenvironment, and the remodeling of the immune system.

Combining radiotherapy and NK cell-based therapies: The time has come

Natural killer (NK) cells are innate lymphoid cells that play an essential role in the anti-tumor response through immunosurveillance, multiple mechanisms of cytotoxicity and the synthesis of cytokines modulating the immune tumor microenvironment (TME). After the dramatic advances in immunotherapy targeting T cells including the success of checkpoint inhibitors or autologous chimeric antigen receptor (CAR) expressing T cells in clinical practice, NK cells have gained growing interest for the development of new therapies. Although NK cells have shown promising responses in leukemia patients, the effects of NK-targeted therapies are currently limited in the treatment of solid tumors. Thus, radiotherapy could provide a valuable solution to improve treatments targeting NK cells. Indeed, ionizing radiations represent a powerful immuno-modulator that can either induce a pro-inflammatory and anti-tumor TME, or conversely lead to immunosuppression of effector immune cells in favor of tumor growth and therapeutic escape, depending on how it is delivered and tumor models. However, the effects of ionizing radiation on NK cells are only partially understood. Therefore, we review the effects of radiotherapy on the NK cell-mediated anti-tumor response, and propose potential strategies to reinvigorate NK cells by combining radiotherapy with NK cell-targeted therapies.

The mechanobiology of NK cells- 'Forcing NK to Sense' target cells

Natural killer (NK) cells are innate immune lymphocytes that recognize and kill cancer and infected cells, which makes them unique 'off-the-shelf' candidates for a new generation of immunotherapies. Biomechanical forces in homeostasis and pathophysiology accrue additional immune regulation for NK immune responses. Indeed, cellular and tissue biomechanics impact NK receptor clustering, cytoskeleton remodeling, NK transmigration through endothelial cells, nuclear mechanics, and even NK-dendritic cell interaction, offering a plethora of unexplored yet important dynamic regulation for NK immunotherapy. Such events are made more complex by the heterogeneity of human NK cells. A significant question remains on whether and how biochemical and biomechanical cues collaborate for NK cell mechanotransduction, a process whereby mechanical force is sensed, transduced, and translated to downstream mechanical and biochemical signalling. Herein, we review recent advances in understanding how NK cells perceive and mechanotransduce biophysical cues. We focus on how the cellular cytoskeleton crosstalk regulates NK cell function while bearing in mind the heterogeneity of NK cells, the direct and indirect mechanical cues for NK anti-tumor activity, and finally, engineering advances that are of translational relevance to NK cell biology at the systems level.

Application of individualized multimodal radiotherapy combined with immunotherapy in metastatic tumors

Radiotherapy is one of the mainstays of cancer treatment. More than half of cancer patients receive radiation therapy. In addition to the well-known direct tumoricidal effect, radiotherapy has immunomodulatory properties. When combined with immunotherapy, radiotherapy, especially high-dose radiotherapy (HDRT), exert superior systemic effects on distal and unirradiated tumors, which is called abscopal effect. However, these effects are not always effective for cancer patients. Therefore, many studies have focused on exploring the optimized radiotherapy regimens to further enhance the antitumor immunity of HDRT and reduce its immunosuppressive effect. Several studies have shown that low-dose radiotherapy (LDRT) can effectively reprogram the tumor microenvironment, thereby potentially overcoming the immunosuppressive stroma induced by HDRT. However, bridging the gap between preclinical commitment and effective clinical delivery is challenging. In this review, we summarized the existing studies supporting the combined use of HDRT and LDRT to synergistically enhance antitumor immunity, and provided ideas for the individualized clinical application of multimodal radiotherapy (HDRT+LDRT) combined with immunotherapy.

Role of low-dose radiation in senescence and aging: A beneficial perspective

Cellular senescence refers to the permanent arrest of cell cycle caused by intrinsic and/or extrinsic stressors including oncogene activation, irradiation, DNA damage, oxidative stress, and certain cytokines (including senescence associated secretory phenotype). Cellular senescence is an important factor in aging. Accumulation of senescent cells has been implicated in the causation of various age-related organ disorders, tissue dysfunction, and chronic diseases. It is widely accepted that the biological effects triggered by low-dose radiation (LDR) are different from those caused by high-dose radiation. Experimental evidence suggests that LDR may promote growth and development, enhance longevity, induce embryo production, and delay the progression of chronic diseases. The underlying mechanisms of these effects include modulation of immune response, stimulation of hematopoietic system, antioxidative effect, reduced DNA damage and improved ability for DNA damage repair. In this review, we discuss the possible mechanisms by which LDR prevents senescence and aging from the perspectives of inhibiting cellular senescence and promoting the removal of senescent cells. We review a wide broad of evidence about the beneficial impact of LDR in senescence and aging models (including cardiovascular diseases, neurological diseases, arthritis and osteoporosis, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis) to highlight the potential value of LDR in preventing aging and age-related diseases. However, there is no consensus on the effect of LDR on human health, and several important aspects require further investigation.

Radon and Lung Cancer: Current Trends and Future Perspectives

Simple Summary

Radon represents the main risk factor of lung cancer in non-smokers and the second one in smoking patients. In Europe, there are several radon-prone areas, but regulatory policies may vary between countries. Radon causes DNA damage and high genomic tumor instability, but its exact carcinogenesis mechanism in lung cancer remains unknown. Molecular drivers in NSCLC are more often described in non-smoker patients and a potential association between radon exposure and oncogenic-driven NSCLC has been postulated. This is an updated review on indoor radon exposure and its role in lung cancer carcinogenesis, especially focusing on its potential relation with NSCLC with driver genomic alterations. We want to contribute to rising knowledge and awareness on this still silent but preventable lung cancer risk factor.

Abstract

Lung cancer is a public health problem and the first cause of cancer death worldwide. Radon is a radioactive gas that tends to accumulate inside homes, and it is the second lung cancer risk factor after smoking, and the first one in non-smokers. In Europe, there are several radon-prone areas, and although the 2013/59 EURATOM directive is aimed to regulate indoor radon exposition, regulating measures can vary between countries. Radon emits alpha-ionizing radiation that has been linked to a wide variety of cytotoxic and genotoxic effects; however, the link between lung cancer and radon from the genomic point of view remains poorly described. Driver molecular alterations have been recently identified in non-small lung cancer (NSCLC), such as somatic mutations (EGFR, BRAF, HER2, MET) or chromosomal rearrangements (ALK, ROS1, RET, NTRK), mainly in the non-smoking population, where no risk factor has been identified yet. An association between radon exposure and oncogenic NSCLC in non-smokers has been hypothesised. This paper provides a practical, concise and updated review on the implications of indoor radon in lung cancer carcinogenesis, and especially of its potential relation with NSCLC with driver genomic alterations.

Effects of Radiation on the Tumor Microenvironment

A malignant tumor consists of malignant cells as well as a wide array of normal host tissues including stroma, vasculature, and immune infiltrate. The interaction between cancer and these host tissues is critical as these host tissues play a variety of roles in supporting or resisting disease progression. Radiotherapy (RT) has direct effects on malignant cells, but, also, critically important effects on these other components of the tumor microenvironment (TME). Given the growing role of immune checkpoint inhibitors and other immunotherapy strategies, understanding how RT affects the TME, particularly the immune compartment, is essential to advance RT in this new era of cancer therapy. The interactions between RT and the TME are complex, affecting the innate and adaptive arms of the immune system. RT can induce both proinflammatory effects and immune suppressive effects that can either promote or impede antitumor immunity. It is likely that the initial proinflammatory effects of RT eventually lead to rebound immune-suppression as chronic inflammation sets in. The exact kinetics and nature of how RT changes the TME likely depends on timing, dose, fractionation, site irradiated, and tumor type. With increased understanding of the effects of RT on the TME, in the future it is likely that we will be able to personalize RT by varying the dose, site, and timing of intervention to generate the desired response to partner with immunotherapy strategies.

Radium-223 dichloride causes transient changes in natural killer cell population and cytotoxic function

RATIONALE

Natural killer (NK) cells play an important role in both the innate and adaptive arms of the immune system. While previous studies have demonstrated the effects of ionizing radiation on cytotoxic function of NK cells, little is known about how a chronic exposure to high LET alpha particles emitted by radionuclides will affect both NK population size and function. This study was conducted to determine the effects of ²²³RaCl₂ on splenic NK cell population size and function in Swiss Webster mice.

METHODS

Swiss Webster mice were administered intravenously with 0, 50, or 600 kBq/kg ²²³RaCl₂. Spleens were harvested at 5, 12, and 19 days post-administration. The numbers of splenocytes per spleen were enumerated and flow cytometry was used to assess changes in the distribution of splenocyte subpopulations of B, CD4 and CD8 T lymphocytes, and NK cells. NK functional activity was quantified using YAC-1 target cells and the ⁵¹Cr-release assay.

RESULTS

The total number of splenocytes was unaffected by ²²³RaCl₂. However, significant changes in the distribution of splenocyte subpopulations were observed for NK cells and CD8 T lymphocytes. NK functional activity was enhanced substantially relative to controls at 12 days post-administration, but decreased markedly by day 19.

CONCLUSION

NK functional activity is both diminished and enhanced by ²²³RaCl₂ depending on both administered activity and time post-administration. These results suggest that there may be an optimum window of time to combine the ²²³RaCl₂-induced antitumor NK cell response with other cancer therapies that elicit immune activation.

Effects of Chronic Low-Dose Internal Radiation on Immune-Stimulatory Responses in Mice

The Linear-No-Threshold (LNT) model predicts a dose-dependent linear increase in cancer risk. This has been supported by biological and epidemiological studies at high-dose exposures. However, at low-doses (LDR ≤ 0.1 Gy), the effects are more elusive and demonstrate a deviation from linearity. In this study, the effects of LDR on the development and progression of mammary cancer in FVB/N-Tg(MMTVneu)202Mul/J mice were investigated. Animals were chronically exposed to total doses of 10, 100, and 2000 mGy via tritiated drinking water, and were assessed at 3.5, 6, and 8 months of age. Results indicated an increased proportion of NK cells in various organs of LDR exposed mice. LDR significantly influenced NK and T cell function and activation, despite diminishing cell proliferation. Notably, the expression of NKG2D receptor on NK cells was dramatically reduced at 3.5 months but was upregulated at later time-points, while the expression of NKG2D ligand followed the opposite trend, with an increase at 3.5 months and a decrease thereafter. No noticeable impact was observed on mammary cancer development, as measured by tumor load. Our results demonstrated that LDR significantly influenced the proportion, proliferation, activation, and function of immune cells. Importantly, to the best of our knowledge, this is the first report demonstrating that LDR modulates the cross-talk between the NKG2D receptor and its ligands.

Low-dose radiotherapy for COVID 19: A radioimmunological perspective

The world is fighting the onslaught of COVID 19 for the last 10 months, ever since the first case was reported in December 2019 in Wuhan, China. Now, it has spread to over 200 countries. COVID 19-associated respiratory syndrome is causing a lot of mortality and morbidity. There are reports suggesting that the complications and ARDS associated with COVID 19 is an immune response reaction. The cytokine storm associated with severe cases of COVID 19 acts as a cause of death in many sick patients. It has been shown that COVID 19 is associated with a peculiar immune profile: Decrease in CD3, CD4, CD8, natural killer cell and B-cells; Rise in interleukin (IL)-4, IL-6 and tumor necrosis factor (TNF) alpha; Decrease in IL-10; Decrease in interferon-gamma. Low-dose radiotherapy (LDRT) immunosuppressive features resulting from M2 macrophage phenotype activation, increase in IL-10, transforming growth factor beta, a decrease in IL-6, TNF alpha and an increase in CD3, CD4, and CD8 T cell counts may negate the harmful effects of cytokine release syndrome. Literature review shows that radiation was previously used to treat viral pneumonia with a good success rate. This practice was discontinued in view of the availability of effective antibiotics and antivirals. As there are no scientifically proven treatment for severe COVID 19-associated respiratory distress today, it is prudent that we understand the benefits of LDRT at this critical juncture and take rational decisions to treat the same. This article provides an radioimmunological rationale for the treatment of immune crisis mediated complications in severe cases of COVID 19.

Effect of low-dose total-body radiotherapy on immune microenvironment

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LTBI (low-dose total-body irradiation) can change the immune microenvironment of tumor.

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LTBI (low-dose total-body irradiation) can regulate a variety of signal pathways (such as nuclear factor-κ B, p38 / MAPK, c-jun), thereby enhancing the expression and function of immune cells in the body, and it may even change the immune microenvironment of human body through an unknown signal pathway, such as enhancing the connection between PD-1 and PD-L1 and promoting the low expression of CTLA4.

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LTBI (low-dose total-body irradiation) can stably stimulate the immune function of cancer patients.

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LTBI (low-dose total-body irradiation) can be widely used as a new comprehensive anti-tumor therapy.

The history of low-dose total-body irradiation (LTBI) as a means of radiotherapy for treating malignant tumors can be traced back to the 1920s. Despite this very low total dose, LTBI can induce long-term remissions. Tumor cells are known to change and maintain their own survival and development conditions through autocrine and paracrine signaling. LTBI can change the tumor microenvironment, enhance the infiltration of activated T cells, and trigger inflammatory processes. LTBI-mediated immune response can exert systemic long-term anti-tumor effects, and can induce tumor regression at the primary site and metastatic sites. With a continuous improvement in the anti-tumor immune microenvironment in the field of tumor therapy, LTBI provides more choices to comprehensively treat of tumors. The present study aimed to explore the experimental research mechanism of LTBI and immune microenvironment, and discuss the difficulties and development prospects of applying LTBI to tumor treatment.

Low dose ionizing radiation effects on the immune system

Ionizing radiation interacts with the immune system in many ways with a multiplicity that mirrors the complexity of the immune system itself: namely the need to maintain a delicate balance between different compartments, cells and soluble factors that work collectively to protect, maintain, and restore tissue function in the face of severe challenges including radiation damage. The cytotoxic effects of high dose radiation are less relevant after low dose exposure, where subtle quantitative and functional effects predominate that may go unnoticed until late after exposure or after a second challenge reveals or exacerbates the effects. For example, low doses may permanently alter immune fitness and therefore accelerate immune senescence and pave the way for a wide spectrum of possible pathophysiological events, including early-onset of age-related degenerative disorders and cancer. By contrast, the so called low dose radiation therapy displays beneficial, anti-inflammatory and pain relieving properties in chronic inflammatory and degenerative diseases. In this review, epidemiological, clinical and experimental data regarding the effects of low-dose radiation on the homeostasis and functional integrity of immune cells will be discussed, as will be the role of immune-mediated mechanisms in the systemic manifestation of localized exposures such as inflammatory reactions. The central conclusion is that ionizing radiation fundamentally and durably reshapes the immune system. Further, the importance of discovery of immunological pathways for modifying radiation resilience amongst other research directions in this field is implied.

Irradiated Tumor Fibroblasts Avoid Immune Recognition and Retain Immunosuppressive Functions Over Natural Killer Cells

Recent studies have demonstrated that radiotherapy is able to induce anti-tumor immune responses in addition to mediating direct cytotoxic effects. Cancer-associated fibroblasts (CAFs) are central constituents of the tumor stroma and participate actively in tumor immunoregulation. However, the capacity of CAFs to influence immune responses in the context of radiotherapy is still poorly understood. This study was undertaken to determine whether ionizing radiation alters the CAF-mediated immunoregulatory effects on natural killer (NK) cells. CAFs were isolated from freshly resected non-small cell lung cancer tissues, while NK cells were prepared from peripheral blood of healthy donors. Functional assays to study NK cell immune activation included proliferation rates, expression of cell surface markers, secretion of immunomodulators, cytotoxic assays, as well as production of intracellular activation markers such as perforin and granzyme B. Our data show that CAFs inhibit NK cell activation by reducing their proliferation rates, the cytotoxic capacity, the extent of degranulation, and the surface expression of stimulatory receptors, while concomitantly enhancing surface expression of inhibitory receptors. Radiation delivered as single high-dose or in fractioned regimens did not reverse the immunosuppressive features exerted by CAFs over NK cells in vitro, despite triggering enhanced surface expression of several checkpoint ligands on irradiated CAFs. In summary, CAFs mediate noticeable immune inhibitory effects on cytokine-activated NK cells during co-culture in a donor-independent manner. However, ionizing radiation does not interfere with the CAF-mediated immunosuppressive effects.

Immunomodulation of NK Cells by Ionizing Radiation

Natural killer (NK) cells play a critical role in the antitumor immunity. Ionizing radiation (IR) has a pronounced effect on modifying NK cell biology, while the molecular mechanisms remain elusive. In this review, we briefly introduce the anti-tumor activity of NK cells and summarize the impact of IR on NK cells both directly and indirectly. On one hand, low-dose ionizing radiation (LDIR) activates NK functions while high-dose ionizing radiation (HDIR) is likely to partially impair NK functions, which can be reversed by interleukin (IL)-2 pretreatment. On the other hand, NK functions may be adjusted by other immune cells and the alternated malignant cell immunogenicity under the settings of IR. Various immune cells, such as the tumor-associated macrophage (TAM), dendritic cell (DC), regulatory T cell (Treg), myeloid-derived suppressor cell (MDSC), and tumor exhibited ligands, such as the natural killer group 2 member D ligand (NKG2DL), natural cytotoxicity receptors (NCR) ligand, TNF-related apoptosis-inducing ligand-receptor (TRAIL-R), and FAS, have been involved in this process. Better understanding the molecular basis is a promising way in which to augment NK-cell-based antitumor immunity in combination with IR.

A preliminary Study on the Effect of Head and Neck Chemoradiotherapy on Systematic Immunity

Background

This study was designed initially to explore the effect of chemoradiotherapy on patients diagnosed with head and neck cancer (HNC) with respect to the alteration of systematic immunity.

Methods

We did a retrospective study enrolling patients received concurrent chemoradiotherapy (CCRT), with or without induction chemotherapy (IC). Blood tests were performed before IC, before and after CCRT. Flow cytometric analysis and turbidimetric inhibition immunoassay were used for detection.

Results

A total number of 58 patients were included from April 1, 2018, to March 31, 2019. Levels of immunoglobulins (Ig), including IgA, IgG, and IgM, declined after 2 to 3 cycles of IC and CCRT, respectively. Serum level of total hemolytic complement (CH50) increased (P < .001) after IC, but kept stably post-CCRT. Natural killer (NK) cells decreased (P < .01) after IC and enhanced (P < .001) post-CCRT. The number of CD3⁺CD4⁺ T cells got increased (P < .01) after IC and decreased (P < .001) post-CCRT. Consistently, both IC and CCRT induced the increase in CD3⁺CD8⁺ T cells significantly (P < .001 vs P < .01).

Conclusion

Both radiotherapy (RT) and chemotherapy (CT) induced dual effect of immune response. Concurrent chemoradiotherapy created an active immune response based on the effect induced by IC, suggesting that RT exerted a potential function on mobilizing immune system.

Hormesis and immunity: A review

The hormesis concept demonstrates that in contrast to the toxic effect of high doses of materials, irradiation, etc., low doses of them are beneficial and, in addition, help to eliminate (prevent) the deleterious effect of high doses given after it. By this effect, it is an important factor of (human) evolution protecting man from harmful impacts, similarly to the role of immunity. However, immunity is also continuously influenced by hormetic effects of environmental [chemical (pollutions), physical (background irradiations and heat), etc.] and medical (drugs and therapeutic irradiations) and food interactions. In contrast to earlier beliefs, the no-threshold irradiation dogma is not valid in low-dose domains and here the hormesis concept is valid. Low-dose therapeutic irradiation, as well as background irradiations (by radon spas or moderately far from the epicenter of atomic bomb or nuclear facilities), is rather beneficial than destructive and the fear from them seems to be unreasonable from immunological point of view. Practically, all immune parameters are beneficially influenced by all forms of low-dose radiations.

Re-evaluation of the linear no-threshold (LNT) model using new paradigms and modern molecular studies

The linear no-threshold (LNT) model is currently used to estimate low dose radiation (LDR) induced health risks. This model lacks safety thresholds and postulates that health risks caused by ionizing radiation is directly proportional to dose. Therefore even the smallest radiation dose has the potential to cause an increase in cancer risk. Advances in LDR biology and cell molecular techniques demonstrate that the LNT model does not appropriately reflect the biology or the health effects at the low dose range. The main pitfall of the LNT model is due to the extrapolation of mutation and DNA damage studies that were conducted at high radiation doses delivered at a high dose-rate. These studies formed the basis of several outdated paradigms that are either incorrect or do not hold for LDR doses. Thus, the goal of this review is to summarize the modern cellular and molecular literature in LDR biology and provide new paradigms that better represent the biological effects in the low dose range. We demonstrate that LDR activates a variety of cellular defense mechanisms including DNA repair systems, programmed cell death (apoptosis), cell cycle arrest, senescence, adaptive memory, bystander effects, epigenetics, immune stimulation, and tumor suppression. The evidence presented in this review reveals that there are minimal health risks (cancer) with LDR exposure, and that a dose higher than some threshold value is necessary to achieve the harmful effects classically observed with high doses of radiation. Knowledge gained from this review can help the radiation protection community in making informed decisions regarding radiation policy and limits.

Immune recognition of irradiated cancer cells

Ionizing irradiation has been extensively employed for the clinical management of solid tumors, with therapeutic or palliative intents, for decades. Until recently, radiation therapy (RT) was believed to mediate antineoplastic activity mostly (if not only) as a consequence of cancer cell-intrinsic effects. Indeed, the macromolecular damage imposed to malignant cells by RT initiates one or multiple signal transduction cascades that drive a permanent proliferative arrest (cellular senescence) or regulated cell death. Both these phenomena show a rather linear dose-response correlation. However, RT also mediates consistent immunological activity, not only as an "on-target effect" originating within irradiated cancer cells, but also as an "off-target effect" depending on the interaction between RT and stromal, endothelial, and immune components of the tumor microenvironment. Interestingly, the immunological activity of RT does not exhibit linear dose-response correlation. Here, we discuss the mechanisms whereby RT alters the capacity of the immune system to recognize and eliminate irradiated cancer cells, either as an "on-target" or as on "off-target" effect. In particular, we discuss the antagonism between the immunostimulatory and immunosuppressive effects of RT as we delineate combinatorial strategies to boost the former at the expenses of the latter.

Radiation effects on antitumor immune responses: current perspectives and challenges

Radiotherapy (RT) is currently used in more than 50% of cancer patients during the course of their disease in the curative, adjuvant or palliative setting. RT achieves good local control of tumor growth, conferring DNA damage and impacting tumor vasculature and the immune system. Formerly regarded as a merely immunosuppressive treatment, pre- and clinical observations indicate that the therapeutic effect of RT is partially immune mediated. In some instances, RT synergizes with immunotherapy (IT), through different mechanisms promoting an effective antitumor immune response. Cell death induced by RT is thought to be immunogenic and results in modulation of lymphocyte effector function in the tumor microenvironment promoting local control. Moreover, a systemic immune response can be elicited or modulated to exert effects outside the irradiation field (so called abscopal effects). In this review, we discuss the body of evidence related to RT and its immunogenic potential for the future design of novel combination therapies.

Cancer immunotherapy: how low-level ionizing radiation can play a key role

The cancer immunoediting hypothesis assumes that the immune system guards the host against the incipient cancer, but also "edits" the immunogenicity of surviving neoplastic cells and supports remodeling of tumor microenvironment towards an immunosuppressive and pro-neoplastic state. Local irradiation of tumors during standard radiotherapy, by killing neoplastic cells and generating inflammation, stimulates anti-cancer immunity and/or partially reverses cancer-promoting immunosuppression. These effects are induced by moderate (0.1-2.0 Gy) or high (>2 Gy) doses of ionizing radiation which can also harm normal tissues, impede immune functions, and increase the risk of secondary neoplasms. In contrast, such complications do not occur with exposures to low doses (≤0.1 Gy for acute irradiation or ≤0.1 mGy/min dose rate for chronic exposures) of low-LET ionizing radiation. Furthermore, considerable evidence indicates that such low-level radiation (LLR) exposures retard the development of neoplasms in humans and experimental animals. Here, we review immunosuppressive mechanisms induced by growing tumors as well as immunomodulatory effects of LLR evidently or likely associated with cancer-inhibiting outcomes of such exposures. We also offer suggestions how LLR may restore and/or stimulate effective anti-tumor immunity during the more advanced stages of carcinogenesis. We postulate that, based on epidemiological and experimental data amassed over the last few decades, whole- or half-body irradiations with LLR should be systematically examined for its potential to be a viable immunotherapeutic treatment option for patients with systemic cancer.

Modulating Both Tumor Cell Death and Innate Immunity Is Essential for Improving Radiation Therapy Effectiveness

Radiation therapy is one of the cornerstones of cancer treatment. In tumor cells, exposure to ionizing radiation (IR) provokes DNA damages that trigger various forms of cell death such as apoptosis, necrosis, autophagic cell death, and mitotic catastrophe. IR can also induce cellular senescence that could serve as an additional antitumor barrier in a context-dependent manner. Moreover, accumulating evidence has demonstrated that IR interacts profoundly with tumor-infiltrating immune cells, which cooperatively drive treatment outcomes. Recent preclinical and clinical successes due to the combination of radiation therapy and immune checkpoint blockade have underscored the need for a better understanding of the interplay between radiation therapy and the immune system. In this review, we will present an overview of cell death modalities induced by IR, summarize the immunogenic properties of irradiated cancer cells, and discuss the biological consequences of IR on innate immune cell functions, with a particular attention on dendritic cells, macrophages, and NK cells. Finally, we will discuss their potential applications in cancer treatment.

Hormetic Response to Low-Dose Radiation: Focus on the Immune System and Its Clinical Implications

The interrelationship between ionizing radiation and the immune system is complex, multifactorial, and dependent on radiation dose/quality and immune cell type. High-dose radiation usually results in immune suppression. On the contrary, low-dose radiation (LDR) modulates a variety of immune responses that have exhibited the properties of immune hormesis. Although the underlying molecular mechanism is not fully understood yet, LDR has been used clinically for the treatment of autoimmune diseases and malignant tumors. These advancements in preclinical and clinical studies suggest that LDR-mediated immune modulation is a well-orchestrated phenomenon with clinical potential. We summarize recent developments in the understanding of LDR-mediated immune modulation, with an emphasis on its potential clinical applications.

Immunomodulatory effects of radiation: what is next for cancer therapy?

Despite its former reputation as being immunosuppressive, it has become evident that radiation therapy can enhance antitumor immune responses. This quality can be harnessed by utilizing radiation as an adjuvant to cancer immunotherapies. Most studies combine the standard radiation dose and regimens indicated for the given disease state, with novel cancer immunotherapies. It has become apparent that low-dose radiation, as well as doses within the hypofractionated range, can modulate tumor cells making them better targets for immune cell reactivity. Herein, we describe the range of phenotypic changes induced in tumor cells by radiation, and explore the diverse mechanisms of immunogenic modulation reported at these doses. We also review the impact of these doses on the immune cell function of cytotoxic cells in vivo and in vitro.

Tumor Therapeutics Work as Stress Inducers to Enhance Tumor Sensitivity to Natural Killer (NK) Cell Cytolysis by Up-regulating NKp30 Ligand B7-H6

Immune cells are believed to participate in initiating anti-tumor effects during regular tumor therapy such as chemotherapy, radiation, hyperthermia, and cytokine injection. One of the mechanisms underlying this process is the expression of so-called stress-inducible immunostimulating ligands. Although the activating receptor NKG2D has been proven to play roles in tumor therapy through targeting its ligands, the role of NKp30, another key activating receptor, is seldom addressed. In this study, we found that the NKp30 ligand B7-H6 was widely expressed in tumor cells and closely correlated to their susceptibility to NK cell lysis. Further studies showed that treatment of tumor cells with almost all standard tumor therapeutics, including chemotherapy (cisplatin, 5-fluorouracil), radiation therapy, non-lethal heat shock, and cytokine therapy (TNF-α), could up-regulate the expression of B7-H6 in tumor cells and enhance tumor sensitivity to NK cell cytolysis. B7-H6 shRNA treatment effectively dampened sensitization of tumor cells to NK-mediated lysis. Our study not only reveals the possibility that tumor therapeutics work as stress inducers to enhance tumor sensitivity to NK cell cytolysis but also suggests that B7-H6 could be a potential target for tumor therapy in the future.

Low-dose ionizing radiation induces direct activation of natural killer cells and provides a novel approach for adoptive cellular immunotherapy

Recent evidence indicates that limited availability and cytotoxicity have restricted the development of natural killer (NK) cells in adoptive cellular immunotherapy (ACI). While it has been reported that low-dose ionizing radiation (LDIR) could enhance the immune response in animal studies, the influence of LDIR at the cellular level has been less well defined. In this study, the authors aim to investigate the direct effects of LDIR on NK cells and the potential mechanism, and explore the application of activation and expansion of NK cells by LDIR in ACI. The authors found that expansion and cytotoxicity of NK cells were markedly augmented by LDIR. The levels of IFN-γ and TNF-α in the supernatants of cultured NK cells were significantly increased after LDIR. Additionally, the effect of the P38 inhibitor (SB203580) significantly decreased the expanded NK cell cytotoxicity, cytokine levels, and expression levels of FasL and perforin. These findings indicate that LDIR induces a direct expansion and activation of NK cells through possibly the P38-MAPK pathway, which provides a potential mechanism for stimulation of NK cells by LDIR and a novel but simplified approach for ACI.

Sam68 is cleaved by caspases under apoptotic cell death induced by ionizing radiation

The RNA-binding protein Sam68, a mitotic substrate of tyrosine kinases, has been reported to participate in the cell cycle, apoptosis, and signaling. In particular, overexpression of Sam68 protein is known to suppress cell growth and cell cycle progression in NIH3T3 cells. Although Sam68 is involved in many cellular activities, the function of Sam68, especially in response to apoptotic stimulation, is not well understood. In this study, we found that Sam68 protein is cleaved in immune cells undergoing apoptosis induced by γ-radiation. Moreover, we found that Sam68 cleavage was induced by apoptotic stimuli containing γ-radiation in a caspase-dependent manner. In particular, we showed that activated casepase-3, 7, 8 and 9 can directly cleave Sam68 protein through in vitro protease cleavage assay. Finally, we found that the knockdown of Sam68 attenuated γ-radiation-induced cell death and growth suppression. Conclusively, the cleavage of Sam68 is a new indicator for the cell damaging effects of ionizing radiation.

The effect of radiation on the immune response to cancers

In cancer patients undergoing radiation therapy, the beneficial effects of radiation can extend beyond direct cytotoxicity to tumor cells. Delivery of localized radiation to tumors often leads to systemic responses at distant sites, a phenomenon known as the abscopal effect which has been attributed to the induction and enhancement of the endogenous anti-tumor innate and adaptive immune response. The mechanisms surrounding the abscopal effect are diverse and include trafficking of lymphocytes into the tumor microenvironment, enhanced tumor recognition and killing via up-regulation of tumor antigens and antigen presenting machinery and, induction of positive immunomodulatory pathways. Here, we discuss potential mechanisms of radiation-induced enhancement of the anti-tumor response through its effect on the host immune system and explore potential combinational immune-based strategies such as adoptive cellular therapy using ex vivo expanded NK and T cells as a means of delivering a potent effector population in the context of radiation-enhanced anti-tumor immune environment.