The effect of ionizing radiation on regulatory T cells in health and disease

Tumor Microenvironment as A "Game Changer" in Cancer Radiotherapy

Radiotherapy (RT), besides cancer cells, also affects the tumor microenvironment (TME): tumor blood vessels and cells of the immune system. It damages endothelial cells and causes radiation-induced inflammation. Damaged vessels inhibit the infiltration of CD8+ T lymphocytes into tumors, and immunosuppressive pathways are activated. They lead to the accumulation of radioresistant suppressor cells, including tumor-associated macrophages (TAMs) with the M2 phenotype, myeloid-derived suppressor cells (MDSCs), and regulatory T cells (Tregs). The area of tumor hypoxia increases. Hypoxia reduces oxygen-dependent DNA damage and weakens the anti-cancer RT effect. It activates the formation of new blood vessels and leads to cancer relapse after irradiation. Irradiation may also activate the immune response through immunogenic cell death induction. This leads to the "in situ" vaccination effect. In this article, we review how changes in the TME affect radiation-induced anticancer efficacy. There is a very delicate balance between the activation of the immune system and the immunosuppression induced by RT. The effects of RT doses on immune system reactions and also on tumor vascularization remain unclear. A better understanding of these interactions will contribute to the optimization of RT treatment, which may prevent the recurrence of cancer.

Safety of combining radiotherapy with immune-checkpoint inhibition

Immune-checkpoint inhibitors targeting cytotoxic T- lymphocyte antigen 4 (CTLA-4), programmed cell death protein 1 (PD-1), or programmed cell death 1 ligand 1 (PD-L1) have transformed the care of patients with a wide range of advanced-stage malignancies. More than half of these patients will also have an indication for treatment with radiotherapy. The effects of both radiotherapy and immune-checkpoint inhibition (ICI) involve a complex interplay with the innate and adaptive immune systems, and accumulating evidence suggests that, under certain circumstances, the effects of radiotherapy synergize with those of ICI to augment the antitumour responses typically observed with either modality alone and thus improve clinical outcomes. However, the mechanisms by which radiotherapy and immune-checkpoint inhibitors synergistically modulate the immune response might also affect both the type and severity of treatment-related toxicities. Moreover, in patients receiving immune-checkpoint inhibitors, the development of immune-related adverse events has been linked with superior treatment responses and patient survival durations, suggesting a relationship between the antitumour and adverse autoimmune effects of these agents. In this Review, we discuss the emerging data on toxicity profiles related to immune-checkpoint inhibitors and radiotherapy, both separately and in combination, their potential mechanisms, and the approaches to managing these toxicities.

Rationale for Combining Radiotherapy and Immune Checkpoint Inhibition for Patients With Hypoxic Tumors

In order to compensate for the increased oxygen consumption in growing tumors, tumors need angiogenesis and vasculogenesis to increase the supply. Insufficiency in this process or in the microcirculation leads to hypoxic tumor areas with a significantly reduced pO2, which in turn leads to alterations in the biology of cancer cells as well as in the tumor microenvironment. Cancer cells develop more aggressive phenotypes, stem cell features and are more prone to metastasis formation and migration. In addition, intratumoral hypoxia confers therapy resistance, specifically radioresistance. Reactive oxygen species are crucial in fixing DNA breaks after ionizing radiation. Thus, hypoxic tumor cells show a two- to threefold increase in radioresistance. The microenvironment is enriched with chemokines (e.g., SDF-1) and growth factors (e.g., TGFβ) additionally reducing radiosensitivity. During recent years hypoxia has also been identified as a major factor for immune suppression in the tumor microenvironment. Hypoxic tumors show increased numbers of myeloid derived suppressor cells (MDSCs) as well as regulatory T cells (Tregs) and decreased infiltration and activation of cytotoxic T cells. The combination of radiotherapy with immune checkpoint inhibition is on the rise in the treatment of metastatic cancer patients, but is also tested in multiple curative treatment settings. There is a strong rationale for synergistic effects, such as increased T cell infiltration in irradiated tumors and mitigation of radiation-induced immunosuppressive mechanisms such as PD-L1 upregulation by immune checkpoint inhibition. Given the worse prognosis of patients with hypoxic tumors due to local therapy resistance but also increased rate of distant metastases and the strong immune suppression induced by hypoxia, we hypothesize that the subgroup of patients with hypoxic tumors might be of special interest for combining immune checkpoint inhibition with radiotherapy.

Combining Immunotherapy with Radiotherapy for the Treatment of Genitourinary Malignancies

CONTEXT

Immunotherapy drugs, particularly checkpoint inhibitors, have recently been approved by the Food and Drug Administration for various malignancies. Preclinical and early clinical data show that combining these agents with radiotherapy may produce an even more potent antitumor effect in the treatment of cancer.

OBJECTIVE

To describe the rationale, available data, and emerging data on the use of combined immunotherapy and radiation therapy in the setting of genitourinary (GU) malignancies.

EVIDENCE ACQUISITION

We performed a search of primary studies from PubMed/Medline that included combinations of the search terms "radiation therapy," "radiotherapy," "abscopal effect," "immunotherapy," "combined," and "combination."

EVIDENCE SYNTHESIS

Preclinical and clinical data support both immune-stimulating and immune-suppressing effects of radiotherapy. Preclinical and clinical studies investigating the combination of radiotherapy with immunotherapy, primarily in the setting of non-GU malignancies, have suggested efficacy and tolerability. Early randomized trials combining radiotherapy and immunotherapy have demonstrated success in lung cancer. Although a trial investigating combined immunotherapy and radiotherapy use for prostate cancer did not clearly improve survival, trials are ongoing in multiple GU malignancies to identify synergy between immunotherapy and radiotherapy. Several practical and technical questions remain about the optimal combination of radiotherapy and immunotherapy.

CONCLUSIONS

Preclinical and clinical trials show that the combination of the immunotherapy and radiation therapy has the potential to provide a synergistic effect in treating cancer, including GU malignancies, although more work is needed to uncover the mechanism and determine the optimal delivery of this treatment.

PATIENT SUMMARY

This paper reviews evidence that immunotherapy drugs can be given together with radiation therapy to improve outcomes in cancers of the genitourinary tract. We find promising initial results and raise important questions that need to be answered before this type of treatment can be utilized successfully.

Immunomodulation of the Tumor Microenvironment: Turn Foe Into Friend

Immunotherapy, where the patient's own immune system is exploited to eliminate tumor cells, has become one of the most prominent new cancer treatment options in the last decade. The main hurdle for classical cancer vaccines is the need to identify tumor- and patient specific antigens to include in the vaccine. Therefore, in situ vaccination represents an alternative and promising approach. This type of immunotherapy involves the direct intratumoral administration of different immunomodulatory agents and uses the tumor itself as the source of antigen. The ultimate aim is to convert an immunodormant tumor microenvironment into an immunostimulatory one, enabling the immune system to eradicate all tumor lesions in the body. In this review we will give an overview of different strategies, which can be exploited for the immunomodulation of the tumor microenvironment and their emerging role in the treatment of cancer patients.

miRNA miR-21 Is Largely Dispensable for Intrathymic T-Cell Development

Development of T cells in the thymus is tightly controlled to continually produce functional, but not autoreactive, T cells. miRNAs provide a layer of post-transcriptional gene regulation to this process, but the role of many individual miRNAs in T-cell development remains unclear. miR-21 is prominently expressed in immature thymocytes followed by a steep decline in more mature cells. We hypothesized that such a dynamic expression was indicative of a regulatory function in intrathymic T-cell development. To test this hypothesis, we analyzed T-cell development in miR-21-deficient mice at steady state and under competitive conditions in mixed bone-marrow chimeras. We complemented analysis of knock-out animals by employing over-expression in vivo. Finally, we assessed miR-21 function in negative selection in vivo as well as differentiation in co-cultures. Together, these experiments revealed that miR-21 is largely dispensable for physiologic T-cell development. Given that miR-21 has been implicated in regulation of cellular stress responses, we assessed a potential role of miR-21 in endogenous regeneration of the thymus after sublethal irradiation. Again, miR-21 was completely dispensable in this process. We concluded that, despite prominent and highly dynamic expression in thymocytes, miR-21 expression was not required for physiologic T-cell development or endogenous regeneration.

SMAC Mimetic Debio 1143 and Ablative Radiation Therapy Synergize to Enhance Antitumor Immunity against Lung Cancer

PURPOSE

Adaptive antitumor immunity following ablative radiotherapy (ART) is attenuated by host myeloid-derived suppressor cell (MDSC), tumor-associated macrophage (TAM), and regulatory T-cell (Treg) infiltrates. We hypothesized treatment with ART and a secondary mitochondrial-derived activators of caspase (SMAC) mimetic could reverse the immunosuppressive lung cancer microenvironment to favor adaptive immunity.

EXPERIMENTAL DESIGN

To evaluate for synergy between ART and the SMAC mimetic Debio 1143 and the dependence upon CD8⁺ T cells and TNFα, we used LLC-OVA syngeneic mouse model of lung cancer and treated them with Debio 1143 and/or ART (30 Gy) with or without anti-CD8, anti-TNFα, or anti-IFNγ antibodies. Tumor-infiltrating OVA-specific CD8⁺ T cells, Tc1 effector cells, MDSCs, TAMs, and Tregs, were quantified by flow cytometry. Tc1-promoting cytokines TNFα, IFNγ, and IL1β and the immunosuppressive IL10 and Arg-1 within LLC-OVA tumor tissue or mouse serum were measured by RT-PCR and ELISA.

RESULTS

ART delayed tumor growth, and the addition of Debio 1143 greatly enhanced its efficacy, which included several complete responses. These complete responders rejected an LLC-OVA tumor rechallenge. ART and Debio 1143 synergistically induced a tumor-specific, Tc1 cellular and cytokine response while eliminating immunosuppressive cells and cytokines from the tumor microenvironment. Depletion of CD8⁺ cells, TNFα, and IFNγ with blocking antibody abrogated synergy between ART and Debio 1143 and partially restored tumor-infiltrating MDSCs.

CONCLUSIONS

Debio 1143 augments the tumor-specific adaptive immunity induced by ART, while reversing host immunosuppressive cell infiltrates in the tumor microenvironment in a TNFα, IFNγ, and CD8⁺ T-cell-dependent manner. This provides a novel strategy to enhance the immunogenicity of ART.

Anti-glucocorticoid-induced Tumor Necrosis Factor-Related Protein (GITR) Therapy Overcomes Radiation-Induced Treg Immunosuppression and Drives Abscopal Effects

Despite the potential to cure metastatic disease, immunotherapy on its own often fails outright or early on due to tumor immune evasion. To address this obstacle, we investigated combinations of anti-GITR, anti-PD1 and radiation therapy (XRT) in our previously developed anti-PD1 resistant 344SQ non-small cell lung adenocarcinoma preclinical tumor model. We hypothesized that targeting multiple mechanisms of immune evasion with this triple therapy would lead to an enhanced tumor-specific immune response and improve survival more so than any mono- or dual therapy. In a two tumor 344SQR murine model, treatment with anti-GITR, anti-PD1, and XRT led to significantly improved survival and an abscopal response, with half of the mice becoming tumor free. These mice showed durable response and increased CD4+ and CD8+ effector memory on tumor rechallenge. Regulatory T cells (Tregs) expressed the highest level of GITR at the tumor site and anti-GITR therapy drastically diminished Tregs at the tumor site. Anti-tumor effects were largely dependent on CD4+ T cells and partially dependent on CD8+ T cells. Anti-GITR IgG2a demonstrated superior efficacy to anti-GITR IgG1 in driving antitumor effects. Collectively, these results suggest that combinatorial strategies targeting multiple points of tumor immune evasion may lead to a robust and lasting antitumor response.

Impact of curative radiotherapy on the immune status of patients with localized prostate cancer

Combination of radiotherapy with immunotherapy has become an attractive concept for the treatment of cancer. The objective of this study was to assess the effect of curative, normofractionated radiotherapy on peripheral immune lymphocytes in prostate cancer patients, in order to propose a rationale for scheduling of normofractionated radiotherapy with T-cell based immunotherapy. In a prospective study (clinicaltrials.gov: NCT01376674), eighteen patients with localized prostate cancer were treated with radiotherapy with or without hormonal therapy. Irradiation volumes encompassed prostate and, in select cases, elective pelvic nodal regions. Blood samples were collected from all patients before, during, and after radiotherapy, as well as from 6 healthy individuals as control. Normofractionated radiotherapy of prostate cancer over eight weeks had a significant influence on the systemic immune status of patients compared to healthy controls. Absolute leukocyte and lymphocyte counts decreased during treatment as did peripheral blood immune subsets (T cells, CD8+ and naïve CD4+ T cells, B cells). Regulatory T cells and NK cells increased. Proliferation of all immune cells except regulatory T cells increased during RT. Most of these changes were transient. Importantly, the functionality of T lymphocytes and the frequency of antigen-specific CD8+ T cells were not affected during therapy. Our data indicate that combination of normofractionated radiotherapy with immunotherapy might be feasible for patients with prostate cancer. Conceptually, beginning with immunotherapy early during the course of radiotherapy could be beneficial, as the percentage of T cells is highest, the percentage of regulatory T cells is lowest, and as the effects of radiotherapy did not completely subside 3 months after end of radiotherapy.

Biological effects of radiation on cancer cells

With the development of radiotherapeutic oncology, computer technology and medical imaging technology, radiation therapy has made great progress. Research on the impact and the specific mechanism of radiation on tumors has become a central topic in cancer therapy. According to the traditional view, radiation can directly affect the structure of the DNA double helix, which in turn activates DNA damage sensors to induce apoptosis, necrosis, and aging or affects normal mitosis events and ultimately rewires various biological characteristics of neoplasm cells. In addition, irradiation damages subcellular structures, such as the cytoplasmic membrane, endoplasmic reticulum, ribosome, mitochondria, and lysosome of cancer cells to regulate various biological activities of tumor cells. Recent studies have shown that radiation can also change the tumor cell phenotype, immunogenicity and microenvironment, thereby globally altering the biological behavior of cancer cells. In this review, we focus on the effects of therapeutic radiation on the biological features of tumor cells to provide a theoretical basis for combinational therapy and inaugurate a new era in oncology.

Hepatic irradiation persistently eliminates liver resident NK cells

Hepatic irradiation for the treatment of hepatobiliary malignancies often indirectly damages liver tissue and promotes the development of liver fibrosis. However, little is known concerning the effects of hepatic irradiation on the liver immune system, including natural killer (NK) cells. The aim of this study was therefore to investigate how hepatic irradiation influences the functions and characteristics of liver resident NK cells. An established murine hepatic irradiation model was used to examine the specific effects of hepatic irradiation on immune cell populations and metastasis. This analysis demonstrated that hepatic irradiation decreased the number of liver resident NK cells (DX5-TRAIL+), but did not affect the total NK number or proportions of NK cells in the liver or spleen. This effect was correlated with the hepatic irradiation dose. Surprisingly, the liver resident NK population had not recovered by two months after hepatic irradiation. We also found that hepatic irradiation limited the cytotoxic effects of liver-derived lymphocytes against a mouse hepatoma cell line and promoted hepatic metastases in an in vivo model, although adoptive transfer of activated NK cells could alleviate metastatic growth. Finally, we demonstrated that hepatic irradiation disrupted the development of liver-resident NK cells, even after the adoptive transfer of precursor cells from the bone marrow, liver, and spleen, suggesting that irradiation had altered the developmental environment of the liver. In summary, our data demonstrated that hepatic irradiation abolished the DX5-TRAIL+ liver-resident NK cell population and dampened antitumor activities in the liver for at least two months. Additionally, hepatic irradiation prevented differentiation of precursor cells into liver-resident NK cells.

[Inflammatory and immune biomarkers of radiation response]

In radiotherapy, the treatment is adapted to each individual to protect healthy tissues but delivers most of time a standard dose according to the tumor histology and site. The only biomarkers studied to individualize the treatment are the HPV status with radiation dose de-escalation strategies, and tumor hypoxia with dose escalation to hypoxic subvolumes using FMISO- or FAZA-PET imaging. In the last decades, evidence has grown about the contribution of the immune system to radiation tumor response. Many preclinical studies have identified some of the mechanisms involved. In this context, we have realised a systematic review to highlight potential inflammatory and immune biomarkers of radiotherapy response. Some are inside the tumor microenvironment, as lymphocyte infiltration or PD-L1 expression, others are circulating biomarkers, including different types of hematological cells, cytokines and chemokines.

The TLR7 agonist imiquimod induces anti-cancer effects via autophagic cell death and enhances anti-tumoral and systemic immunity during radiotherapy for melanoma

Toll-like receptor (TLR) ligands are strongly considered immune-adjuvants for cancer immunotherapy and have been shown to exert direct anti-cancer effects. This study was performed to evaluate the synergistic anti-cancer and anti-metastatic effects of the TLR7 agonist imiquimod (IMQ) during radiotherapy for melanoma. The pretreatment of B16F10 or B16F1 cells with IMQ combined with γ-ionizing radiation (IR) led to enhanced cell death via autophagy, as demonstrated by increased expression levels of autophagy-related genes, and an increased number of autophagosomes in both cell lines. The results also confirmed that the autophagy process was accelerated via the reactive oxygen species (ROS)-mediated MAPK and NF-κB signaling pathway in the cells pretreated with IMQ combined with IR. Mice subcutaneously injected with melanoma cells showed a reduced tumor growth rate after treatment with IMQ and IR. Treatment with 3-methyladenine (3-MA), ameliorated the anti-cancer effect of IMQ combined with IR. Additionally, the combination therapy enhanced anti-cancer immunity, as demonstrated by an increased number of CD8⁺ T cells and decreased numbers of regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSCs) in the tumor lesions. Moreover, the combination therapy decreased the number of metastatic nodules in the lungs of mice that were injected with B16F10 cells via the tail vein. In addition, the combination therapy enhanced systemic anti-cancer immunity by increasing the abundances of T cell populations expressing IFN-γ and TNF-α. Therefore, these findings suggest that IMQ could serve as a radiosensitizer and immune booster during radiotherapy for melanoma patients.

Proton beam therapy and immunotherapy: an emerging partnership for immune activation in non-small cell lung cancer

Proton beam therapy (PBT) is becoming an increasingly common option for patients undergoing radiation therapy (RT). With the concurrent emergence of immunotherapy as an effective systemic treatment for historically treatment-resistant disease such as advanced non-small cell lung cancer (NSCLC), the combination of RT's immunoadjuvant effects with immunotherapy is gaining widespread attention. However, pre-clinical and clinical studies have shown potential immunosuppressive mechanisms associated with conventional RT that may restrict its immunogenic potential. Protons, as charged particles, exhibit both dosimetric and biological differences in normal and cancer cells that may be able to not only enhance the immunoadjuvant effects of RT, but also reduce immunosuppressive mechanisms. Here, we review the rationale, preclinical and clinical evidence, and ongoing efforts in combining PBT with immunotherapy in cancer treatment with a focus on NSCLC.

Posttreatment Immune Parameters Predict Cancer Control and Pneumonitis in Stage I Non-Small-Cell Lung Cancer Patients Treated With Stereotactic Ablative Radiotherapy

PURPOSE

Stereotactic ablative body radiotherapy (SABR) represents an exciting, tolerable, and highly effective form of radiotherapy. Ongoing investigations into the interactions between radiotherapy and the immune system have uncovered new mechanisms that can be exploited to improve efficacy. We determined whether baseline or posttreatment immune parameters could predict disease control and toxicity in stage I non-small-cell lung cancer (NSCLC) patients treated with SABR.

PATIENTS AND METHODS

Peripheral blood samples were collected from 62 patients 24 hours before treatment and within 4 weeks after treatment for lymphocyte subset count analysis. All peripheral blood samples were analyzed by flow cytometry. Associated parameters were evaluated to determine their association with progression-free survival (PFS) and symptomatic radiation pneumonitis (grade 2 or higher). The survival rates were estimated with Kaplan-Meier and multivariable analyses using binary logistic regression analysis or a Cox proportional hazards model.

RESULTS

At a median follow-up time of 36.0 months, the PFS rates for years 1, 2, and 3 were 91.0%, 82.5%, and 48.9%, respectively. The multivariable logistic regression analysis showed that only proportion of lung receiving 20 Gy of radiotherapy (odds ratio = 1.41; 95% confidence interval, 1.05-1.87; P = .023) and mean lung dose (odds ratio = 2.02; 95% confidence interval, 1.16-3.53; P = .016) were associated with symptomatic radiation pneumonitis (grade 2 or higher). Moreover, the immune parameters had no predictive value. In the multivariable Cox regression analysis, an elevated posttreatment cytotoxic CD8⁺ T-cell level was an independent prognostic factor for longer PFS in stage I NSCLC (hazard ratio, 1.16; 95% confidence interval, 1.01-1.28; P = .01).

CONCLUSION

A higher posttreatment cytotoxic CD8⁺ T-cell level was predictive of better PFS in stage I NSCLC patients receiving SABR. Thus, enhancing tumor antigen-specific cellular immunity by combining radiotherapy and immunotherapy might be a crucial strategy for improving survival in these patients.

Irradiation Enhances Abscopal Anti-tumor Effects of Antigen-Specific Immunotherapy through Regulating Tumor Microenvironment

Ionizing radiation therapy is a well-established method of eradicating locally advanced tumors. Here, we examined whether local RT enhanced the potency of an antigen-specific DNA vaccine, and we investigated the possible underlying mechanism. Using the HPV16 E6/E7⁺ syngeneic TC-1 tumor, we evaluated the combination of CTGF/E7 vaccination with local irradiation with regard to synergistic antigen-specific immunity and anti-tumor effects. Tumor-bearing mice treated with local RT (6 Gy twice weekly) and CTGF/E7 DNA vaccination exhibited dramatically increased numbers of E7-specific CD8⁺ cytotoxic T cell precursors, higher titers of anti-E7 Abs, and significantly reduced tumor size. The combination of local RT and CTGF/E7 vaccination also elicited abscopal effects on non-irradiated local subcutaneous and distant pulmonary metastatic tumors. Local irradiation induced the expression of high-mobility group box 1 protein (HMGB-1) in apoptotic tumor cells and stimulated dendritic cell (DC) maturation, consequently inducing antigen-specific immune responses. Additionally, local irradiation eventually increased the effector-to-suppressor cell ratio in the tumor microenvironment. Overall, local irradiation enhanced the antigen-specific immunity and anti-tumor effects on local and distant metastatic tumors generated by an antigen-specific DNA vaccine. These findings suggest that the combination of irradiation with antigen-specific immunotherapy is a promising new clinical strategy for cancer therapy.

Stereotactic Ablative Radiation Therapy Combined With Immunotherapy for Solid Tumors

Immunotherapy, particularly immune-checkpoint inhibition, is producing encouraging clinical responses and affecting the way numerous cancers are treated. Yet immune-checkpoint therapy is not effective for many patients, and even those who initially respond can experience relapse, fueling interest in finding new processes or tools to improve the effectiveness of these novel therapeutics. One such tool is radiation. Both preclinical and clinical studies have demonstrated that the systemic effects of immunotherapy can be amplified when it is used in combination with radiation and, conversely, that the immunogenic effects of local irradiation can be amplified and extended to distant sites when used with immunotherapy. We review how stereotactic ablative radiation therapy, a technique specifically indicated for tumors treated with immune-checkpoint inhibitors, can potentiate the effects of immune-checkpoint therapy. We further explore how these novel therapeutics may transform radiation, previously considered a local treatment option, into powerful systemic therapy.

Cancer Cell Death-Inducing Radiotherapy: Impact on Local Tumour Control, Tumour Cell Proliferation and Induction of Systemic Anti-tumour Immunity

Radiotherapy (RT) predominantly is aimed to induce DNA damage in tumour cells that results in reduction of their clonogenicity and finally in tumour cell death. Adaptation of RT with higher single doses has become necessary and led to a more detailed view on what kind of tumour cell death is induced and which immunological consequences result from it. RT is capable of rendering tumour cells immunogenic by modifying the tumour cell phenotype and the microenvironment. Danger signals are released as well as the senescence-associated secretory phenotype. This results in maturation of dendritic cells and priming of cytotoxic T cells as well as in activation of natural killer cells. However, RT on the other hand can also result in immune suppressive events including apoptosis induction and foster tumour cell proliferation. That's why RT is nowadays increasingly combined with selected immunotherapies.

Predictive value of peripheral regulatory T cells in non-small cell lung cancer patients undergoing radiotherapy

BACKGROUND

Studies increasingly focus on the impact of radiotherapy on immunity; however, the role of peripheral cellular immunity prior to radiotherapy in cancer patients remains largely unknown. In this study, we investigated the predictive roles of lymphocyte subsets on tumor progression in non-small cell lung cancer (NSCLC) patients undergoing radiotherapy, and their expression in NSCLC patients at first relapse.

METHODS

We enrolled 70 NSCLC patients and 14 age- and sex-matched healthy donors and tested the lymphocyte subsets in their peripheral blood by flow cytometry. Among them, 40 newly diagnosed patients received radiotherapy and were enrolled to investigate the predictive value of lymphocyte subsets on tumor progression after radiotherapy by uni- and multivariate analyses; 30 patients at first relapse were included to evaluate the differences of lymphocyte subsets between them and first diagnosed patients and healthy volunteers.

RESULTS

Increased proportions of regulatory T cells, CD8+ T cells, and CD8+CD28- T cells and decreased CD4+ T cells and CD4/CD8 ratios were observed in NSCLC patients at first relapse compared to newly diagnosed patients. In the 40 first diagnosed patients undergoing radiotherapy, uni- and multivariate analyses showed that increased level of regulatory T cells correlated with poor progression-free survival (hazard ratio = 2.55 and 3.76, P = 0.022 and 0.010, respectively).

CONCLUSIONS

Peripheral regulatory T cells were increased and independently predict tumor progression in NSCLC patients undergoing radiotherapy, suggesting the promising combination of radiotherapy and immunotherapy.

Review of the mechanisms involved in the abscopal effect and future directions with a focus on thymic carcinoma

The abscopal effect is a rare phenomenon in radiotherapy, leading to impressive tumor regression outside the radiotherapy field. In this article we describe the occurrence of a postradiotherapy abscopal effect in an 89-year-old patient suffering from a metastatic neuroendocrine large-cell thymic carcinoma, the first case of the abscopal effect related to a thymic carcinoma reported in the literature. Along with the description of this case, we discuss and review the main potential mechanisms of bystander and abscopal effects in solid tumors so as to enable clinicians to identify and control these effects more resourcefully in the age of immunotherapy and stereotactic radiotherapy.

Immune biomarkers of treatment failure for a patient on a phase I clinical trial of pembrolizumab plus radiotherapy

BACKGROUND

Pembrolizumab is a monoclonal antibody that is designed against programmed cell death protein 1 (PD-1). Pembrolizumab and other immunocheckpoint-blocking monoclonal antibodies work by modulating a patient's own immune system to increase anti-tumor activity. While immunocheckpoint blockade has shown promising results, only 20-40 % of patients experience objective clinical benefit. Differences in individual tumor biology and the presence multiple immune checkpoints present a challenge for treatment. Because radiotherapy has immunomodulatory effects on the tumor microenvironment, it has the potential to synergize with immunotherapy and augment tumor response. NCT02318771 is a phase 1 clinical trial designed to investigate the immunomodulatory effects of radiation therapy in combination with pembrolizumab.

CASE PRESENTATION

The patient is a 64-year-old male with metastatic clear cell renal cell carcinoma, Fuhrman grade 4, pathologically staged as T3 N0. Metastatic disease was well controlled for several years with sunitinib. Following disease progression, he was switched to axitinib. When disease progression continued, the patient was enrolled in NCT02318771, a phase 1 clinical trial combining radiotherapy and pembrolizumab. The patient experienced unusually rapid disease progression during treatment, which was confirmed by repeated CT scans to rule out pseudoprogression. Tissue biopsies and peripheral blood draws were obtained before, during, and after treatment. Samples were analyzed to provide plausible rationale for rapid treatment failure.

CONCLUSIONS

Biomarker analysis demonstrated an absence of TILs, which may be a cause of treatment failure as pembrolizumab works through T cell-dependent mechanisms. Furthermore, the presence of other non-redundant immune checkpoints in the periphery and tumor microenvironment presents a treatment challenge. Additionally, the radiation dose and fractionation schedule may have played a role in treatment failure as these factors play a role in the effect radiotherapy on the tumor microenvironment as well as the potential for synergy with immunotherapy.

TRIAL REGISTRATION

An Exploratory Study to Investigate the Immunomodulatory Activity of Radiation Therapy (RT) in Combination With MK-3475 in Patients With Recurrent/Metastatic Head and Neck, Renal Cell Cancer, Melanoma and Lung Cancer, NCT02318771 .

The Future of Combining Carbon-Ion Radiotherapy with Immunotherapy: Evidence and Progress in Mouse Models

After >60 years since the first treatment, particle radiation therapy (RT) is now used to treat various types of tumors worldwide. Particle RT results in favorable outcomes, especially in local control, because of its biological properties and excellent dose distribution. However, similar to other types of cancer treatment, metastasis control is a crucial issue. Notably, immunotherapy is used for cancer treatment with high risk for recurrence and/or metastasis. These 2 cancer therapies could be ideal, complementary partners for noninvasive cancer treatment. In this review, we will focus on preclinical studies combining particle RT, especially carbon ion RT, and immunotherapy.

Development of a Modular Assay for Detailed Immunophenotyping of Peripheral Human Whole Blood Samples by Multicolor Flow Cytometry

The monitoring of immune cells gained great significance in prognosis and prediction of therapy responses. For analyzing blood samples, the multicolor flow cytometry has become the method of choice as it combines high specificity on single cell level with multiple parameters and high throughput. Here, we present a modular assay for the detailed immunophenotyping of blood (DIoB) that was optimized for an easy and direct application in whole blood samples. The DIoB assay characterizes 34 immune cell subsets that circulate the peripheral blood including all major immune cells such as T cells, B cells, natural killer (NK) cells, monocytes, dendritic cells (DCs), neutrophils, eosinophils, and basophils. In addition, it evaluates their functional state and a few non-leukocytes that also have been associated with the outcome of cancer therapy. This DIoB assay allows a longitudinal and close-meshed monitoring of a detailed immune status in patients requiring only 2.0 mL of peripheral blood and it is not restricted to peripheral blood mononuclear cells. It is currently applied for the immune monitoring of patients with glioblastoma multiforme (IMMO-GLIO-01 trial, NCT02022384), pancreatic cancer (CONKO-007 trial, NCT01827553), and head and neck cancer (DIREKHT trial, NCT02528955) and might pave the way for immune biomarker identification for prediction and prognosis of therapy outcome.

Regulatory T Cells in the Tumor Microenvironment and Cancer Progression: Role and Therapeutic Targeting

Recent years have seen significant efforts in understanding and modulating the immune response in cancer. In this context, immunosuppressive cells, including regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs), have come under intense investigation for their proposed roles in suppressing tumor-specific immune responses and establishing an immunosuppressive tumor microenvironment, thus enabling tumor immune evasion. Additionally, recent evidence indicates that Tregs comprise diverse and heterogeneous subsets; phenotypically and functionally distinct subsets of tumor-infiltrating Tregs could contribute differently to cancer prognosis and clinical outcomes. Understanding Treg biology in the setting of cancer, and specifically the tumor microenvironment, is important for designing effective cancer therapies. In this review, we critically examine the role of Tregs in the tumor microenvironment and in cancer progression focusing on human studies. We also discuss the impact of current therapeutic modalities on Treg biology and the therapeutic opportunities for targeting Tregs to enhance anti-tumor immune responses and clinical benefits.

Selective internal radiation therapy in treatment of hepatocellular carcinoma: new concepts of personalization

Hepatocellular carcinoma (HCC) is a global health problem, with more than half a million new cases diagnosed annually and mortality rates at similar level. The majority of HCC is diagnosed at intermediate-advanced stages being, therefore, an issue for palliative rather than curative care. Selective internal radiation therapy (SIRT) is one of the best appropriate palliative treatment modalities in HCC management. Although delivering satisfactory results, SIRT application comes along with frequent complications and tumor recurrence. Recent studies suggest treatment algorithm tailored to the person as improving individual outcomes and reducing treatment-related complications. This review provides insights to implicate innovative concepts of predictive, preventive and personalized medicine in SIRT application to HCC cohorts.

Adenosine can thwart antitumor immune responses elicited by radiotherapy : Therapeutic strategies alleviating protumor ADO activities

BACKGROUND

By studying the bioenergetic status we could show that the development of tumor hypoxia is accompanied, apart from myriad other biologically relevant effects, by a substantial accumulation of adenosine (ADO). ADO has been shown to act as a strong immunosuppressive agent in tumors by modulating the innate and adaptive immune system. In contrast to ADO, standard radiotherapy (RT) can either stimulate or abrogate antitumor immune responses. Herein, we present ADO-mediated mechanisms that may thwart antitumor immune responses elicited by RT.

MATERIALS AND METHODS

An overview of the generation, accumulation, and ADO-related multifaceted inhibition of immune functions, contrasted with the antitumor immune effects of RT, is provided.

RESULTS

Upon hypoxic stress, cancer cells release ATP into the extracellular space where nucleotides are converted into ADO by hypoxia-sensitive, membrane-bound ectoenzymes (CD39/CD73). ADO actions are mediated upon binding to surface receptors, mainly A2A receptors on tumor and immune cells. Receptor activation leads to a broad spectrum of strong immunosuppressive properties facilitating tumor escape from immune control. Mechanisms include (1) impaired activity of CD4 (+) T and CD8 (+) T, NK cells and dendritic cells (DC), decreased production of immuno-stimulatory lymphokines, and (2) activation of Treg cells, expansion of MDSCs, promotion of M2 macrophages, and increased activity of major immunosuppressive cytokines. In addition, ADO can directly stimulate tumor proliferation and angiogenesis.

CONCLUSION

ADO mechanisms described can thwart antitumor immune responses elicited by RT. Therapeutic strategies alleviating tumor-promoting activities of ADO include respiratory hyperoxia or mild hyperthermia, inhibition of CD39/CD73 ectoenzymes or blockade of A2A receptors, and inhibition of ATP-release channels or ADO transporters.

Increasing radiation dose improves immunotherapy outcome and prolongation of tumor dormancy in a subgroup of mice treated for advanced intracerebral melanoma

Previously, we developed a clinically relevant therapy model for advanced intracerebral B16 melanomas in syngeneic mice combining radiation and immunotherapies. Here, 7 days after B16-F10-luc2 melanoma cells were implanted intracerebrally (D7), syngeneic mice with bioluminescent tumors that had formed (1E10(5) to 7E10(6) photons per minute (>1E10(6), large; <1E10(6), small) were segregated into large-/small-balanced subgroups. Then, mice received either radiation therapy alone (RT) or radiation therapy plus immunotherapy (RT plus IT) (single injection of mAbPC61 to deplete regulatory T cells followed by multiple injections of irradiated granulocyte macrophage colony stimulating factor transfected B16-F10 cells) (RT plus IT). Radiation dose was varied (15, 18.75 or 22.5 Gy, given on D8), while immunotherapy was provided similarly to all mice. The data support the hypothesis that increasing radiation dose improves the outcome of immunotherapy in a subgroup of mice. The tumors that were greatly delayed in beginning their progressive growth were bioluminescent in vivo-some for many months, indicating prolonged tumor "dormancy," in some cases presaging long-term cures. Mice bearing such tumors had far more likely received radiation plus immunotherapy, rather than RT alone. Radiotherapy is a very important adjunct to immunotherapy; the greater the tumor debulking by RT, the greater should be the benefit to tumor immunotherapy.

Systemic Tolerance Mediated by Melanoma Brain Tumors Is Reversible by Radiotherapy and Vaccination

PURPOSE

Immune responses to antigens originating in the central nervous system (CNS) are generally attenuated, as collateral damage can have devastating consequences. The significance of this finding for the efficacy of tumor-targeted immunotherapies is largely unknown.

EXPERIMENTAL DESIGN

The B16 murine melanoma model was used to compare cytotoxic responses against established tumors in the CNS and in the periphery. Cytokine analysis of tissues from brain tumor-bearing mice detected elevated TGFβ secretion from microglia and in the serum and TGFβ signaling blockade reversed tolerance of tumor antigen-directed CD8 T cells. In addition, a treatment regimen using focal radiation therapy and recombinant Listeria monocytogenes was evaluated for immunologic activity and efficacy in this model.

RESULTS

CNS melanomas were more tolerogenic than equivalently progressed tumors outside the CNS as antigen-specific CD8 T cells were deleted and exhibited impaired cytotoxicity. Tumor-bearing mice had elevated serum levels of TGFβ; however, blocking TGFβ signaling with a small-molecule inhibitor or a monoclonal antibody did not improve survival. Conversely, tumor antigen-specific vaccination in combination with focal radiation therapy reversed tolerance and improved survival. This treatment regimen was associated with increased polyfunctionality of CD8 T cells, elevated T effector to T regulatory cell ratios, and decreased TGFβ secretion from microglia.

CONCLUSIONS

These data suggest that CNS tumors may impair systemic antitumor immunity and consequently accelerate cancer progression locally as well as outside the CNS, whereas antitumor immunity may be restored by combining vaccination with radiation therapy. These findings are hypothesis-generating and warrant further study in contemporary melanoma models as well as human trials.

Uncovering the immune tumor microenvironment in non-small cell lung cancer to understand response rates to checkpoint blockade and radiation

The study of immunology has led to breakthroughs in treating non-small cell lung cancer (NSCLC). The recent approval of an anti-PD1 checkpoint drug for NSCLC has generated much interest in novel combination therapies that might provide further benefit for patients. However, a better understanding of which combinations may (or may not) work in NSCLC requires understanding the lung immune microenvironment under homeostatic conditions and the changes in that microenvironment in the setting of cancer progression and with radiotherapy. This review provides background information on immune cells found in the lung and the prognostic significance of these cell types in lung cancer. It also addresses current clinical directions for the combination of checkpoint inhibitors with radiation for NSCLC.