Local radiation therapy inhibits tumor growth through the generation of tumor-specific CTL: its potentiation by combination with Th1 cell therapy

Treatment of Cancer with Radio-Immunotherapy: What We Currently Know and What the Future May Hold

Radiotherapy and immunotherapy are most effective as cancer therapies in the setting of low-volume disease. Although initial studies of radio-immunotherapy in patients with metastatic cancer have not confirmed the efficacy of this approach, the role of radio-immunotherapy in patients with limited metastatic burden is unclear. We propose that further investigation of radio-immunotherapy in metastatic patients should focus upon patients with oligometastatic disease.

Parallels Between the Antiviral State and the Irradiated State

Improved understanding of host antiviral defense and antitumor immunity have elucidated molecular pathways important to both processes. During viral infection, RNA or DNA in the host cell serves as a danger signal that initiates the antiviral response. Recent studies have elucidated similarities in the signaling pathways activated by viruses and the signaling pathways induced by tumor DNA that is released into the cytoplasm of irradiated tumor cells. Both the host defense to viral infection and the sterile inflammation provoked by radiotherapy induce a type I interferon response that is necessary for pathogen control and immune-mediated tumor control, respectively. These findings have led to the hypothesis that radiotherapy employs a form of viral mimicry.

Overcoming Resistance to Immunotherapy in Head and Neck Cancer Using Radiation: A Review

Radiation therapy remains at the center of head and neck cancer treatment. With improvements in treatment delivery, radiation therapy has become an affective ablative modality for head and neck cancers. Immune checkpoint inhibitors are now also playing a more active role both in the locally advanced and metastatic setting. With improved systemic options, local noninvasive modalities including radiation therapy are playing a critical role in overcoming resistance in head and neck cancer. The aim of this review is to describe the role of radiation therapy in modulating the tumor microenvironment and how radiation dose, fractionation and treatment field can impact the immune system and potentially effect outcomes when combined with immunotherapy. The review will encompass several common scenarios where radiation is used to improve outcomes and overcome potential resistance that may develop with immunotherapy in head and neck squamous cell carcinoma (HNSCC), including upfront locally advanced disease receiving definitive radiation and recurrent disease undergoing re-irradiation. Lastly, we will review the potential toxicities of combined therapy and future directions of their role in the management of HNSCC.

Radiotherapy and Immunotherapy Combinations in the Treatment of Patients with Metastatic Disease: Current Status and Future Focus

Radiotherapy and immunotherapy benefit subsets of patients with metastatic cancer. Here, we review selected laboratory and clinical studies investigating the utility of combining radiotherapy and immunotherapy in metastatic patients. We examine potential approaches to increase the therapeutic ratio of radioimmunotherapy in the treatment of metastatic cancers moving forward.

Treatment strategies for early stage hepatocellular carcinoma: a systematic review and network meta-analysis of randomised clinical trials

BACKGROUND

Several treatment strategies for early stage hepatocellular cancers (HCC) have been evaluated in randomised controlled trials (RCTs). This network meta-analysis (NMA) aimed to explore the relative effectiveness of these different approaches on their impact on overall (OS) and recurrence-free survival (RFS).

METHODS

A systematic review was conducted to identify RCT's reported up to 23rd January 2020. Indirect comparisons of all regimens were simultaneously compared using random-effects NMA.

RESULTS

Twenty-eight RCT's, involving 3,618 patients, reporting 13 different treatment strategies for early stage HCC were identified. Median follow-up, reported in 22 studies, ranged from 12-93 months. In this NMA, RFA in combination with iodine-125 was ranked first for both RFS (HR: 0.50, 95% CI: 0.19-1.31) and OS (HR: 0.41, 95% CI: 0.19-0.94). In subgroup with solitary HCC, lack of studies reporting RFS precluded reliable analysis. However, RFA in combination with iodine-125 was associated with markedly better OS (HR: 0.21, 95% CI: 0.05-0.93).

CONCLUSION

This NMA identified RFA in combination with iodine-125 as a treatment delivering better RFS and OS, in patients with early stage HCC, especially for those with solitary HCC. This technique warrants further evaluation in both Asia and Western regions.

10 ns PEFs induce a histological response linked to cell death and cytotoxic T-lymphocytes in an immunocompetent mouse model of peritoneal metastasis

PURPOSE

The application of nanosecond pulsed electric fields (nsPEFs) could be an effective therapeutic strategy for peritoneal metastasis (PM) from colorectal cancer (CRC). The aim of this study was to evaluate in vitro the sensitivity of CT-26 CRC cells to nsPEFs in combination with chemotherapeutic agents, and to observe the subsequent in vivo histologic response.

METHODS

In vitro cellular assays were performed to assess the effects of exposure to 1, 10, 100, 500 and 1000 10 ns pulses in a cuvette or bi-electrode system at 10 and 200 Hz. nsPEF treatment was applied alone or in combination with oxaliplatin and mitomycin. Cell death was detected by flow cytometry, and permeabilization and intracellular calcium levels by fluorescent confocal microscopy after treatment. A mouse model of PM was used to investigate the effects of in vivo exposure to pulses delivered using a bi-electrode system; morphological changes in mitochondria were assessed by electron microscopy. Fibrosis was measured by multiphoton microscopy, while the histological response (HR; hematoxylin-eosin-safran stain), proliferation (KI67, DAPI), and expression of immunological factors (CD3, CD4, CD8) were evaluated by classic histology.

RESULTS

10 ns PEFs exerted a dose-dependent effect on CT-26 cells in vitro and in vivo, by inducing cell death and altering mitochondrial morphology after plasma membrane permeabilization. In vivo results indicated a specific CD8+ T cell immune response, together with a strong HR according to the Peritoneal Regression Grading Score (PRGS).

CONCLUSIONS

The effects of nsPEFs on CT-26 were confirmed in a mouse model of CRC with PM.

Predictive biomarkers of anti-PD-1/PD-L1 therapy in NSCLC

Immunotherapy, especially anti-programmed cell death protein 1/programmed cell death ligand 1 (PD-1/PD-L1) treatment has significantly improved the survival of non-small cell lung cancer (NSCLC) patients. However, the overall response rate remains unsatisfactory. Many factors affect the outcome of anti-PD-1/PD-L1 treatment, such as PD-L1 expression level, tumor-infiltrating lymphocytes (TILs), tumor mutation burden (TMB), neoantigens, and driver gene mutations. Further exploration of biomarkers would be favorable for the best selection of patients and precisely predict the efficacy of anti-PD-1/PD-L1 treatment. In this review, we summarized the latest advances in this field, and discussed the potential applications of these laboratory findings in the clinic.

Brain Radiation Induced Extracranial Abscopal Effects in Metastatic Melanoma

Historically, the brain has been viewed as a specialized neurovascular inert organ with a distinctive immune privilege. Therefore, radiation-induced extracranial abscopal effects would be considered an unusual phenomenon due to the difficulty of the immunogenic signaling molecules to travel across the blood-brain barrier (BBB). However, it is now possible that localized central nervous system radiation has the ability to disrupt the structural integrity of the BBB and increase its endothelial permeability allowing the free passage of immunogenic responses between the intracranial and extracranial compartments. Thus, the nascent tumor-associated antigens produced by localized brain radiation can travel across the BBB into the rest of the body to modulate the immune system and induce extracranial abscopal effects. In clinical practice, localized brain radiation therapy-induced extracranial abscopal effects are a rarely seen phenomenon in metastatic melanoma and other advanced cancers. In this article, we provide a detailed overview of the current state of knowledge and clinical experience of central nervous system radiation-induced extracranial abscopal effects in patients with malignant melanoma. Emerging data from a small number of case reports and cohort studies of various malignancies has significantly altered our earlier understanding of this process by revealing that the brain is neither isolated nor passive in its interactions with the body's immune system. In addition, these studies provide clinical evidence that the brain is capable of interacting actively with the extracranial peripheral immune system. Thus, localized radiation treatment to 1 or more locations of brain metastases can induce extracranial abscopal responses. Collectively, these findings clearly demonstrate that localized brain radiation therapy-induced abscopal effects traverses the BBB and trigger tumor regression in the nonirradiated extracranial locations.

The split nature of tumor-infiltrating leukocytes: Implications for cancer surveillance and immunotherapy

An important development in tumor immunology was the identification of highly diverse tumor-infiltrating leukocyte subsets that can play strikingly antagonistic functions. Namely, “anti-tumor” vs. “pro-tumor” roles have been suggested for Th1 and Th17 subsets of CD4⁺ T cells, Type I or Type II NKT cells, M1 and M2 macrophages, or N1 and N2 neutrophils, respectively. While these findings are being validated in cancer patients, it is also clear that the balance between infiltrating CD8⁺ cytotoxic and Foxp3⁺ regulatory T cells has prognostic value. Here we review the pre-clinical and clinical data that have shaped our current understanding of tumor-infiltrating leukocytes.

Radiotherapy-Immunotherapy Combination: How Will We Bridge the Gap Between Pre-Clinical Promise and Effective Clinical Delivery?

Radiotherapy (RT) is highly effective at directly killing tumor cells and plays an important part in cancer treatments being delivered to around 50% of all cancer patients. The additional immunomodulatory properties of RT have been investigated, and if exploited effectively, have the potential to further improve the efficacy of RT and cancer outcomes. The initial results of combining RT with immunomodulatory agents have generated promising data in pre-clinical studies, which has in turn led to a large number of RT and immunotherapy clinical trials. The overarching aim of these combinations is to enhance anti-tumor immune responses and improve responses rates and patient outcomes. In order to maximize this undoubted opportunity, there remain a number of important questions that need to be addressed, including: (i) the optimal RT dose and fractionation schedule; (ii) the optimal RT target volume; (iii) the optimal immuno-oncology (IO) agent(s) to partner with RT; (iv) the optimal site(s)/route(s) of administration of IO agents; and finally, the optimal RT schedule. In this review, we will summarize progress to date and identify current gaps in knowledge that need to be addressed in order to facilitate effective clinical translation of RT and IO agent combinations.

Enlightening the Immune Mechanism of the Abscopal Effect in a Murine HCC Model and Overcoming the Late Resistance With Anti-PD-L1

PURPOSE

The establishment of a preclinical model of the abscopal effect on hepatocellular carcinoma (HCC) and evaluation of whether the hypofractionated radiation therapy (RT) multitumor Hepa1-6 mouse HCC model could be used to suppress nonradiated tumor mass was performed in this study.

METHODS AND MATERIALS

Hepa1-6 mouse liver cancer cell lines were used to form tumors. Immunogenicity was analyzed using ELISpot and immune cell labeled antibody. Interferon (IFN) β expression was confirmed through polymerase chain reaction.

RESULTS

After investigation, the intratumoral transcription of type Ⅰ IFN increased by 2-fold. The antitumor immune response to Hepa 1-6 cells induced by radiation was increased. Moreover, the influx of activated CD8⁺ T cells was increased in nonirradiated tumors. The number of dendritic cells and activation status were evaluated by flow cytometry on the second day after irradiation. Flow cytometry revealed a significantly increased dendritic cell population expressing the CD11c molecule in tumor-draining lymph nodes. Furthermore, because irradiation leads to adaptation of immune resistance of tumor cells against RT, we sought to elucidate a potent tool to overcome the resistance and confirm the ability of PD-L1 antibody to survive late RT resistance.

CONCLUSIONS

The immunologic mechanism of the abscopal effect was revealed and the application of PD-L1 inhibitor successfully performed as a breakthrough in late RT resistance in the Hepa1-6 tumor model.

Immunomodulatory Effects of Radiotherapy

Radiation therapy (RT), an integral component of curative treatment for many malignancies, can be administered via an increasing array of techniques. In this review, we summarize the properties and application of different types of RT, specifically, conventional therapy with x-rays, stereotactic body RT, and proton and carbon particle therapies. We highlight how low-linear energy transfer (LET) radiation induces simple DNA lesions that are efficiently repaired by cells, whereas high-LET radiation causes complex DNA lesions that are difficult to repair and that ultimately enhance cancer cell killing. Additionally, we discuss the immunogenicity of radiation-induced tumor death, elucidate the molecular mechanisms by which radiation mounts innate and adaptive immune responses and explore strategies by which we can increase the efficacy of these mechanisms. Understanding the mechanisms by which RT modulates immune signaling and the key players involved in modulating the RT-mediated immune response will help to improve therapeutic efficacy and to identify novel immunomodulatory drugs that will benefit cancer patients undergoing targeted RT.

Challenges in Combining Immunotherapy with Radiotherapy in Recurrent/Metastatic Head and Neck Cancer

Immunotherapy with immune checkpoint inhibitors (ICI) has recently become a standard part of the treatment of recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC), although the response rates are low. Numerous preclinical and clinical studies have now illuminated several mechanisms by which radiotherapy (RT) enhances the effect of ICI. From RT-induced immunogenic cancer cell death to its effect on the tumor microenvironment and vasculature, the involved mechanisms are diverse and intertwined. Moreover, the research of these interactions is challenging because of the thin line between immunostimulatory and the immunosuppressive effect of RT. In the era of active research of immunoradiotherapy combinations, the significance of treatment and host-related factors that were previously seen as being less important is being revealed. The impact of dose and fractionation of RT is now well established, whereas selection of the number and location of the lesions to be irradiated in a multi-metastatic setting is something that is only now beginning to be understood. In addition to spatial factors, the timing of irradiation is as equally important and is heavily dependent on the type of ICI used. Interestingly, using smaller-than-conventional RT fields or even partial tumor volume RT could be beneficial in this setting. Among host-related factors, the role of the microbiome on immunotherapy efficacy must not be overlooked nor can we neglect the role of gut irradiation in a combined RT and ICI setting. In this review we elaborate on synergistic mechanisms of immunoradiotherapy combinations, in addition to important factors to consider in future immunoradiotherapy trial designs in R/M HNSCC.

Combining radiotherapy and immunotherapy in definitive treatment of head and neck squamous cell carcinoma: review of current clinical trials

Background Head and neck squamous cell carcinoma (HNSCC) presents as locally advanced disease in a majority of patients and is prone to relapse despite aggressive treatment. Since immune checkpoint inhibitors (ICI) have shown clinically significant efficacy in patients with recurrent/metastatic HNSCC (R/M HNSCC), a plethora of trials are investigating their role in earlier stages of disease. At the same time, preclinical data showed the synergistic role of concurrently administered radiotherapy and ICIs (immunoradiotherapy) and explained several mechanisms behind it. Therefore, this approach is prospectively tested in a neoadjuvant, definitive, or adjuvant setting in non-R/M HNSCC patients. Due to the intricate relationship between host, immunotherapy, chemotherapy, and radiotherapy, each of these approaches has its advantages and disadvantages. In this narrative review we present the biological background of immunoradiotherapy, as well as a rationale for, and possible flaws of, each treatment approach, and provide readers with a critical summary of completed and ongoing trials. Conclusions While immunotherapy with ICIs has already become a standard part of treatment in patients with R/M HNSCC, its efficacy in a non-R/M HNSCC setting is still the subject of extensive clinical testing. Irradiation can overcome some of the cancer's immune evasive manoeuvres and can lead to a synergistic effect with ICIs, with possible additional benefits of concurrent platinum-based chemotherapy. However, the efficacy of this combination is not robust and details in trial design and treatment delivery seem to be of unprecedented importance.

Tumor-draining lymph node is important for a robust abscopal effect stimulated by radiotherapy

Background

Radiotherapy (RT) has been shown to stimulate an antitumor immune response in irradiated tumors as well as unirradiated distant sites (abscopal effect). Previous studies have demonstrated a role for the tumor-draining lymph node (LN) in mediating an anti-programmed death-1 (PD-1)/programmed death ligand-1 (PD-L1) stimulated antitumor immune response. Here, we investigated whether the LN is also important in mediating a RT alone stimulated abscopal response.

Methods

We used a subcutaneous modified B16F10 flank tumor model injected bilaterally. Our B16F10 cell line has an inserted viral glycoprotein which facilitated identification of tumor-specific T-cells. RT was directed at one flank tumor alone or one flank tumor and the tumor-draining LN. We evaluated response by tumor growth measurements and flow cytometry of both tumor-infiltrating and LN T-cells.

Results

We show that local tumor irradiation improves distant tumor control (abscopal effect). Depletion of CD8⁺ T-cells significantly reduced this abscopal response. We have previously shown, in a chronic lymphocytic choriomeningitis virus (LCMV) infection, that the T-cell proliferative burst following blockade of PD-1/L1 is provided by a ‘stem-like’ CD8⁺ T-cell subset which then differentiate into terminally differentiated effectors. These terminally differentiated effectors have the potential to kill virally infected or tumor cells following PD-1/L1 blockade. In the chronic LCMV infection, stem-like CD8⁺ T-cells were found exclusively in secondary lymphoid organs. Similarly, here we found these cells at high frequencies in the tumor-draining LN, but at low frequencies within the tumor. The effect of RT on this T-cell subset in unknown. Interestingly, tumor irradiation stimulated total CD8⁺ and stem-like CD8⁺ T-cell proliferation in the LN. When the LN and the tumor were then targeted with RT, the abscopal effect was reduced, and we found a concomitant reduction in the number of total tumor-specific CD8⁺ T-cells and stem-like CD8⁺ T-cells in both the irradiated and unirradiated tumor.

Conclusions

These correlative results suggest the tumor-draining LN may be an important mediator of the abscopal effect by serving as a stem-like CD8⁺ T-cell reservoir, a site for stem-like T-cell expansion, and a site from which they can populate the tumor.

Radiotherapy-Mediated Immunomodulation and Anti-Tumor Abscopal Effect Combining Immune Checkpoint Blockade

Radiotherapy (RT) is a conventional method for clinical treatment of local tumors, which can induce tumor-specific immune response and cause the shrinkage of primary tumor and distal metastases via mediating tumor infiltration of CD8+ T cells. Ionizing radiation (IR) induced tumor regression outside the radiation field is termed as abscopal effect. However, due to the mobilization of immunosuppressive signals by IR, the activated CD8+T cells are not sufficient to maintain a long-term positive feedback to make the tumors regress completely. Eventually, the "hot" tumors gradually turn to "cold". With the advent of emerging immunotherapy, the combination of immune checkpoint blockade (ICB) and local RT has produced welcome changes in stubborn metastases, especially anti-PD-1/PD-L1 and anti-CTLA-4 which have been approved in clinical cancer treatment. However, the detailed mechanism of the abscopal effect induced by combined therapy is still unclear. Therefore, how to formulate a therapeutic schedule to maximize the efficacy should be took into consideration according to specific circumstance. This paper reviewed the recent research progresses in immunomodulatory effects of local radiotherapy on the tumor microenvironment, as well as the unique advantage for abscopal effect when combined with ICB, with a view to exploring the potential application value of radioimmunotherapy in clinic.

Reduction of Lung Metastases in a Mouse Osteosarcoma Model Treated With Carbon Ions and Immune Checkpoint Inhibitors

PURPOSE

The combination of radiation therapy and immunotherapy is recognized as a very promising strategy for metastatic cancer treatment. The purpose of this work is to compare the effectiveness of x-ray and high-energy carbon ion therapy in combination with checkpoint inhibitors in a murine model.

METHODS AND MATERIALS

We used an osteosarcoma mouse model irradiated with either carbon ions or x-rays in combination with 2 immune checkpoint inhibitors (anti-PD-1 and anti-CTLA-4). LM8 osteosarcoma cells were injected in both hind limbs of female C3H/He mice 7 days before exposure to carbon ions or x-rays. In experimental groups receiving irradiation, only the tumor on the left limb was exposed, whereas the tumor on the right limb served as an abscopal mimic. Checkpoint inhibitors were injected intraperitoneally 1 day before exposure as well as concomitant to and after exposure. Tumor growth was measured regularly up to day 21 after exposure, when mice were sacrificed. Both tumors as well as lungs were extracted.

RESULTS

A reduced growth of the abscopal tumor was most pronounced after the combined protocol of carbon ions and the immune checkpoint inhibitors administered sequentially. Radiation or checkpoint inhibitors alone were not sufficient to reduce the growth of the abscopal tumors. Carbon ions alone reduced the number of lung metastases more efficiently than x-rays, and in combination with immunotherapy both radiation types essentially suppressed the metastasis, with carbon ions being again more efficient. Investigation of the infiltration of immune cells in the abscopal tumors of animals treated with combination revealed an increase in CD8+ cells.

CONCLUSIONS

Combination of checkpoint inhibitors with high-energy carbon ion radiation therapy can be an effective strategy for the treatment of advanced tumors.

Radiation-induced bystander and abscopal effects: important lessons from preclinical models

Radiotherapy is a pivotal component in the curative treatment of patients with localised cancer and isolated metastasis, as well as being used as a palliative strategy for patients with disseminated disease. The clinical efficacy of radiotherapy has traditionally been attributed to the local effects of ionising radiation, which induces cell death by directly and indirectly inducing DNA damage, but substantial work has uncovered an unexpected and dual relationship between tumour irradiation and the host immune system. In clinical practice, it is, therefore, tempting to tailor immunotherapies with radiotherapy in order to synergise innate and adaptive immunity against cancer cells, as well as to bypass immune tolerance and exhaustion, with the aim of facilitating tumour regression. However, our understanding of how radiation impacts on immune system activation is still in its early stages, and concerns and challenges regarding therapeutic applications still need to be overcome. With the increasing use of immunotherapy and its common combination with ionising radiation, this review briefly delineates current knowledge about the non-targeted effects of radiotherapy, and aims to provide insights, at the preclinical level, into the mechanisms that are involved with the potential to yield clinically relevant combinatorial approaches of radiotherapy and immunotherapy.

A liposomal RNA vaccine inducing neoantigen-specific CD4+ T cells augments the antitumor activity of local radiotherapy in mice

Antigen-encoding, lipoplex-formulated RNA (RNA-LPX) enables systemic delivery to lymphoid compartments and selective expression in resident antigen-presenting cells. We report here that the rejection of CT26 tumors, mediated by local radiotherapy (LRT), is further augmented in a CD8⁺ T cell-dependent manner by an RNA-LPX vaccine that encodes CD4⁺ T cell-recognized neoantigens (CD4 neoantigen vaccine). Whereas CD8⁺ T cells induced by LRT alone were primarily directed against the immunodominant gp70 antigen, mice treated with LRT plus the CD4 neoantigen vaccine rejected gp70-negative tumors and were protected from rechallenge with these tumors, indicating a potent poly-antigenic CD8⁺ T cell response and T cell memory. In the spleens of CD4 neoantigen-vaccinated mice, we found a high number of activated, poly-functional, Th1-like CD4⁺ T cells against ME1, the immunodominant CD4 neoantigen within the poly-neoantigen vaccine. LRT itself strongly increased CD8⁺ T cell numbers and clonal expansion. However, tumor infiltrates of mice treated with CD4 neoantigen vaccine/LRT, as compared to LRT alone, displayed a higher fraction of activated gp70-specific CD8⁺ T cells, lower PD-1/LAG-3 expression and contained ME1-specific IFNγ⁺ CD4⁺ T cells capable of providing cognate help. CD4 neoantigen vaccine/LRT treatment followed by anti-CTLA-4 antibody therapy further enhanced the efficacy with complete remission of gp70-negative CT26 tumors and survival of all mice. Our data highlight the power of combining synergistic modes of action and warrants further exploration of the presented treatment schema.

Abscopal effect in lung cancer: three case reports and a concise review

The abscopal effect describes the ability of locally administered radiotherapy to induce systemic antitumor effects. Over the past 40 years, reports on the abscopal effect following conventional radiation have been relatively rare, especially in less immunogenic tumors such as lung cancer. However, with the continued development and use of immunotherapy, reports on the abscopal effect have become increasingly frequent during the last decade. Here, we present three illustrative case reports from our own institution and previous published cases of the abscopal effect in patients with non-small cell lung cancer, treated with immune checkpoint inhibitors and radiotherapy. We also present a concise review of the clinical and experimental literature on the abscopal effect in non-small cell lung cancer.

Adjuvant Nodal Radiation Therapy for Melanoma in the Era of Immunotherapy

In the last few years there have been dramatic changes in the management of patients with melanoma with locally advanced disease. Previously, standard therapy for melanoma patients with nodal disease involved completion lymph node dissection followed by adjuvant radiation therapy for high-risk features, as defined by TROG 02.01. Adjuvant systemic therapy with interferon could be offered, but many eligible patients did not receive this agent in the context of significant toxicity. New, effective, and often well-tolerated systemic therapies, such as immune checkpoint inhibitors and targeted MAPK pathway inhibitors, have shown impressive responses in metastatic disease and are now being applied to the locally advanced setting. Currently, for patients with occult nodal disease found at sentinel lymph node biopsy, completion lymph node dissection is uncommon with adjuvant anti-PD1 therapy often recommended. For patients with clinically apparent nodal disease, neoadjuvant immunotherapy has shown impressive pathologic response rates, which thus far have correlated well with longer term disease outcomes. However, not all patients exhibit a robust pathologic response. In circumstances of either occult nodal disease or clinically evident nodal disease without a robust pathologic response to neoadjuvant immunotherapy, there is a dearth of evidence regarding the optimal use of radiation therapy. Prospective studies investigating the role of adjuvant nodal radiation therapy for melanoma patients in the modern immunotherapy era are much needed.

[Immunotherapy in head and neck squamous cell carcinoma : Abscopal effects in combination with radiotherapy, extraordinary responses in combination with chemotherapy, and pseudoprogression]

BACKGROUND

The clinical implementation of immunotherapy has broadened the therapeutic options for recurrent and/or metastatic head and neck squamous cell carcinoma (HNSCC). Until 2016, the only molecularly targeted therapy was epidermal growth factor receptor (EGFR) blockade. However, immune checkpoint inhibition has recently become part of first-line treatment in recurrent and/or metastatic HNSCC.

OBJECTIVES

The occurrence of abscopal effects of radiotherapy and synergisms between immunotherapy and chemotherapy as well as the phenomenon of pseudoprogression in HNSCC were investigated.

MATERIALS AND METHODS

Key publications of recent clinical trials and preclinical studies on the underlying biological mechanisms were analyzed.

RESULTS

As already observed in other tumor entities, synergistic effects upon combination of immunotherapy with radio- and/or chemotherapy are observed in the clinical management of recurrent and/or metastatic HNSCC, and this is mediated by (re)activation of host antitumor immune mechanisms. In selected patients, this may be radiologically detected as pseudoprogression. Reliable biomarkers for these phenomena have not yet been clinically established.

CONCLUSIONS

For recurrent and/or metastatic HNSCC, the occurrence of systemic effects upon radiochemoimmunotherapy in the clinic is on the rise. Hence, the identification of biomarkers for abscopal effects of radiotherapy and unexpected synergisms between chemotherapy and immunotherapy as well as for pseudoprogression is gaining in importance.

Liver metastases and the efficacy of the PD-1 or PD-L1 inhibitors in cancer: a meta-analysis of randomized controlled trials

Objective: To explore the relations between liver metastases (LM) and the efficacy of the treatments with programmed cell death 1 (PD-1) or programmed cell death ligand 1 (PD-L1) inhibitors.

Method: Pubmed, Embase, American Society of Clinical Oncology and the European Society for Medical Oncology were searched to select eligible studies about PD-1 or PD-L1 inhibitors (Nivolumab, Pembrolizumab, Cemiplimab, Avelumab, Durvalumab, and Atezolizumab). We included only the original randomized controlled trials (RCTs), including the hazard ratios (HR) of death in both patients with LM and patients without LM. Then the data were extracted for the meta-analysis. Subgroup analyses of cancer types and drug types were also performed.

Results: 5293 patients [1246 (24%) patients with LM, and 4047 (76%) patients without LM] from the eight RCTs were included for the final analysis. The pooled hazard ratio (HR) of death in the patients with LM was 0.82 (95% CI, 0.71 to 0.93, P = .003) while the pooled HR in the patients without LM was 0.72 (95% CI, 0.66 to 0.79, P < .001). Additionally, no significant difference was found between the two groups (P = .137).

Conclusion: No statistically significant association of liver metastases with the efficacy of treatments with PD-1 or PD-L1 inhibitors in the treatment of advanced or metastatic cancer was found in the stratified analyses. Moreover, future studies about the safety of the PD-1 or PD-L1 inhibitors in patients with or without liver metastases are warranted.

Immunotherapy and radiation therapy for gastrointestinal malignancies: hope or hype?

Immunotherapy represents the newest pillar in cancer care. Although there are increasing data showing the efficacy of immunotherapy there is a spectrum of response across unselected populations of cancer patients. In fact, response rates can be poor even among patients with immunogenic tumors for reasons that remain poorly understood. A promising clinical strategy to improve outcomes, which is supported by an abundance of preclinical data, is combining immunotherapy with radiation therapy. Here we review the existing evidence and future directions for combining immunotherapy and radiation therapy for patients with gastrointestinal cancers.

Immune biological rationales for the design of combined radio- and immunotherapies

Cancer immunotherapies are promising treatments for many forms of cancer. Nevertheless, the response rates to, e.g., immune checkpoint inhibitors (ICI), are still in low double-digit percentage. This calls for further therapy optimization that should take into account combination of immunotherapies with classical tumor therapies such as radiotherapy. By designing multimodal approaches, immune modulatory properties of certain radiation schemes, additional immune modulation by immunotherapy with ICI and hyperthermia, as well as patient stratification based on genetic and immune constitutions have to be considered. In this context, both the tumor and its microenvironment including cells of the innate and adaptive immune system have to be viewed in synopsis. Knowledge of immune activation and immune suppression by radiation is the basis for well-elaborated addition of certain immunotherapies. In this review, the focus is set on additional immune stimulation by hyperthermia and restoration of an immune response by ICI. The impact of radiation dose and fractionation on immune modulation in multimodal settings has to be considered, as the dynamics of the immune response and the timing between radiotherapy and immunotherapy. Another big challenge is the patient stratification that should be based on matrices of biomarkers, taking into account genetics, proteomics, radiomics, and “immunomics”. One key aim is to turn immunological “cold” tumors into “hot” tumors, and to eliminate barriers of immune-suppressed or immune-excluded tumors. Comprehensive knowledge of immune alterations induced by radiation and immunotherapy when being applied together should be utilized for patient-adapted treatment planning and testing of innovative tumor therapies within clinical trials.

Integration of stereotactic radiosurgery or whole brain radiation therapy with immunotherapy for treatment of brain metastases

The prognosis of brain metastases (BM) is traditionally poor. BM are mainly treated by local radiotherapy, including stereotactic radiosurgery (SRS) or whole brain radiation therapy (WBRT). Recently, immunotherapy (i.e., immune checkpoint inhibitors, ICI) has demonstrated a survival advantage in multiple malignancies commonly associated with BM. Individually, radiotherapy and ICI both treat BM efficiently; hence, their combination seems logical. In this review, we summarize the existing preclinical and clinical evidence that supports the applicability of radiotherapy as a sensitizer of ICI for BM. Further, we discuss the optimal timing at which radiotherapy and ICI should be administered and review the safety of the combination therapy. Data from a few clinical studies suggest that combining SRS or WBRT with ICI simultaneously rather than consecutively potentially enhances brain abscopal-like responses and survival. However, there is a lack of conclusion about the definition of "simultaneous"; the cumulative toxic effect of the combined therapies also requires further study. Thus, ongoing and planned prospective trials are needed to further explore and validate the effect, safety, and optimal timing of the combination of immunotherapy with radiotherapy for patients with BM.

Alteration in tumoural PD-L1 expression and stromal CD8-positive tumour-infiltrating lymphocytes after concurrent chemo-radiotherapy for non-small cell lung cancer

Background

Consolidation treatment with an anti-PD-L1 antibody, durvalumab, following concurrent chemo-radiotherapy (cCRT) has become a new standard of care for locally advanced non-small cell lung cancer (NSCLC). The rationale of PD-L1 blockade after cCRT is based on preclinical evidence suggesting that chemotherapy and radiotherapy up-regulate tumoural PD-L1 expression, which has not been shown in clinical studies.

Methods

To examine alteration in tumoural PD-L1 expression (tumour proportion score, TPS) and density of stromal CD8-positive tumour-infiltrating lymphocytes (CD8 + TILs) after cCRT, paired NSCLC samples obtained before and after cCRT were reviewed in comparison with those obtained before and after drug therapy.

Results

PD-L1 expression was significantly up-regulated after cCRT (median TPS, 1.0 at baseline versus 48.0 after cCRT; P < 0.001), but not after drug therapy. There was no significant correlation between baseline TPS and post-cCRT TPS. CD8 + TIL density was significantly increased after cCRT (median, 10.6 versus 39.1; P < 0.001), and higher post-cCRT CD8 + TIL density was associated with a higher pathologic response and with a favourable survival (P = 0.019).

Conclusion

Tumoural PD-L1 expression was up-regulated after cCRT, which provides pathologic rationale for PD-L1 blockade following cCRT to improve prognosis. Stromal CD8 + TIL density was also increased after cCRT, and higher post-cCRT CD8 + TIL density was a favourable prognostic indicator.

A translational concept of immuno-radiobiology

BACKGROUND

Traditional concepts of radiobiology model the direct radiation-induced cellular cytotoxicity but are not focused on late and sustained effects of radiation. Recent experimental data show the close involvement of immunological processes.

METHODS

Based on systematic PubMed searches, experimental data on immunological radiation effects are summarized and analyzed in a non-quantitative descriptive manner to provide a translational perspective on the immuno-modulatory impact of radiation in cancer.

RESULTS

Novel experimental findings document that sustained radiation effects are ultimately mediated through systemic factors such as cytotoxic CD8+ T cells and involve a local immuno-stimulation. Increased tumor infiltration of CD8+ T cell is a prerequisite for long-term radiation effects. CD8+ T cell depletion induces radio-resistance in experimental tumors. The proposed sequence of events involves radiation-damaged cells that release HMGB1, which activates macrophages via TLR4 to a local immuno-stimulation via TNF, which contributes to maturation of DCs. The mature DCs migrate to lymph nodes where they trigger effective CD8+ T cell responses. Radiation effects are boosted, when the physiological self-terminating negative feedback of immune reactions is antagonised via blocking of TGF-β or via checkpoint inhibition with involvement of CD8+ T cells as common denominator.

CONCLUSION

The concept of immuno-radiobiology emphasizes the necessity for a functional integrity of APCs and T cells for the long-term effects of radiotherapy. Local irradiation at higher doses induces tumor infiltration of CD8+ T cells, which can be boosted by immunotherapy. More systematic research is warranted to better understand the immunological effects of escalating radiation doses.

Novel treatment planning approaches to enhance the therapeutic ratio: targeting the molecular mechanisms of radiation therapy

Radiation acts not only through cell death but has also angiogenic, immunomodulatory and bystander effects. The realization of its systemic implications has led to extensive research on the combination of radiotherapy with systemic treatments, including immunotherapy and antiangiogenic agents. Parameters such as dose, fractionation and sequencing of treatments are key determinants of the outcome. However, recent high-quality research indicates that these are not the only radiation therapy parameters that influence its systemic effect. To effectively integrate systemic agents with radiation therapy, these new aspects of radiation therapy planning will have to be taken into consideration in future clinical trials. Our aim is to review these new treatment planning parameters that can influence the balance between contradicting effects of radiation therapy so as to enhance the therapeutic ratio.

Combining Radiation and Immune Checkpoint Blockade in the Treatment of Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a significant cause of morbidity and mortality worldwide. Current treatment options, even though potentially curative, have many limitations including a high rate of complications. Over the past few years immune checkpoint inhibitors (ICI) targeting cytotoxic lymphocyte antigen-4 (CTLA-4), programmed cell death protein 1 (PD-1), and programmed cell death ligand 1 (PD-L1) have changed treatment paradigms in many malignancies and are currently under investigation in HNSCC as well. Despite improvements in treatment outcomes and the implementation of combined modality approaches long-term survival rates in patients with locally advanced HNSCC remain suboptimal. Accumulating evidence suggests that under certain conditions, radiation may be delivered in conjunction with ICI to augment efficacy. In this review, we will discuss the immune modulating mechanisms of ICI and radiation, how changing the dose, fractionation, and field of radiation may alter the tumor microenvironment (TME), and how these two treatment modalities may work in concert to generate durable treatment responses against HNSCC.

90Y-NM600 targeted radionuclide therapy induces immunologic memory in syngeneic models of T-cell Non-Hodgkin's Lymphoma

Finding improved therapeutic strategies against T-cell Non-Hodgkin’s Lymphoma (NHL) remains an unmet clinical need. We implemented a theranostic approach employing a tumor-targeting alkylphosphocholine (NM600) radiolabeled with ⁸⁶Y for positron emission tomography (PET) imaging and ⁹⁰Y for targeted radionuclide therapy (TRT) of T-cell NHL. PET imaging and biodistribution performed in mouse models of T-cell NHL showed in vivo selective tumor uptake and retention of ⁸⁶Y-NM600. An initial toxicity assessment examining complete blood counts, blood chemistry, and histopathology of major organs established ⁹⁰Y-NM600 safety. Mice bearing T-cell NHL tumors treated with ⁹⁰Y-NM600 experienced tumor growth inhibition, extended survival, and a high degree of cure with immune memory toward tumor reestablishment. ⁹⁰Y-NM600 treatment was also effective against disseminated tumors, improving survival and cure rates. Finally, we observed a key role for the adaptive immune system in potentiating a durable anti-tumor response to TRT, especially in the presence of microscopic disease.

Hernandez et al. show the effectiveness of ⁹⁰Y for targeted radionucleotide therapy of T-cell Non-Hodgkin’s Lymphoma (NHL). This study suggests that delivering radiation to all NHL disease sites elicits minimal toxicity and induces a memory T-cell response, inviting combination therapies with immune activating agents.

Harnessing Radiation Biology to Augment Immunotherapy for Glioblastoma

Glioblastoma is the most common adult primary brain tumor and carries a dismal prognosis. Radiation is a standard first-line therapy, typically deployed following maximal safe surgical debulking, when possible, in combination with cytotoxic chemotherapy. For other systemic cancers, standard of care is being transformed by immunotherapies, including checkpoint-blocking antibodies targeting CTLA-4 and PD-1/PD-L1, with potential for long-term remission. Ongoing studies are evaluating the role of immunotherapies for GBM. Despite dramatic responses in some cases, randomized trials to date have not met primary outcomes. Challenges have been attributed in part to the immunologically "cold" nature of glioblastoma relative to other malignancies successfully treated with immunotherapy. Radiation may serve as a mechanism to improve tumor immunogenicity. In this review, we critically evaluate current evidence regarding radiation as a synergistic facilitator of immunotherapies through modulation of both the innate and adaptive immune milieu. Although current preclinical data encourage efforts to harness synergistic biology between radiation and immunotherapy, several practical and scientific challenges remain. Moreover, insights from radiation biology may unveil additional novel opportunities to help mobilize immunity against GBM.

Radiotherapy toxicity

Radiotherapy is used in >50% of patients with cancer, both for curative and palliative purposes. Radiotherapy uses ionizing radiation to target and kill tumour tissue, but normal tissue can also be damaged, leading to toxicity. Modern and precise radiotherapy techniques, such as intensity-modulated radiotherapy, may prevent toxicity, but some patients still experience adverse effects. The physiopathology of toxicity is dependent on many parameters, such as the location of irradiation or the functional status of organs at risk. Knowledge of the mechanisms leads to a more rational approach for controlling radiotherapy toxicity, which may result in improved symptom control and quality of life for patients. This improved quality of life is particularly important in paediatric patients, who may live for many years with the long-term effects of radiotherapy. Notably, signs and symptoms occurring after radiotherapy may not be due to the treatment but to an exacerbation of existing conditions or to the development of new diseases. Although differential diagnosis may be difficult, it has important consequences for patients.

Combinatorial Approach to Improve Cancer Immunotherapy: Rational Drug Design Strategy to Simultaneously Hit Multiple Targets to Kill Tumor Cells and to Activate the Immune System

Cancer immunotherapy, including immune checkpoint blockade and adoptive CAR T-cell therapy, has clearly established itself as an important modality to treat melanoma and other malignancies. Despite the tremendous clinical success of immunotherapy over other cancer treatments, this approach has shown substantial benefit to only some of the patients while the rest of the patients have not responded due to immune evasion. In recent years, a combination of cancer immunotherapy together with existing anticancer treatments has gained significant attention and has been extensively investigated in preclinical or clinical studies. In this review, we discuss the therapeutic potential of novel regimens combining immune checkpoint inhibitors with therapeutic interventions that (1) increase tumor immunogenicity such as chemotherapy, radiotherapy, and epigenetic therapy; (2) reverse tumor immunosuppression such as TAMs, MDSCs, and Tregs targeted therapy; and (3) reduce tumor burden and increase the immune effector response with rationally designed dual or triple inhibitory chemotypes.

Immunotherapy for High Grade Gliomas: A Clinical Update and Practical Considerations for Neurosurgeons

The current standard of care for patients with high grade gliomas includes surgical resection, chemotherapy, and radiation; but even still the majority of patients experience disease progression and succumb to their illness within a few years of diagnosis. Immunotherapy, which stimulates an anti-tumor immune response, has been revolutionary in the treatment of some hematological and solid malignancies, generating substantial excitement for its potential for patients with glioblastoma. The most commonly used immunotherapies include dendritic cell and peptide vaccines, checkpoint inhibitors, and adoptive T cell therapy. However, to date, the preclinical success of these approaches against high-grade glioma models has not been replicated in human clinical trials. Moreover, the complex response to these biologically active treatments can complicate management decisions, and the neurosurgical oncology community needs to be actively involved in and up to date on the use of these agents in high grade glioma patients. In this review, we discuss the challenges immunotherapy faces for high grade gliomas, the completed and ongoing clinical trials for the major immunotherapies, and the nuances in management for patients being actively treated with one of these agents.

Immunotherapy Mythbusters in Head and Neck Cancer: The Abscopal Effect and Pseudoprogression

Atypical patterns of response to immunotherapy have been observed, including the abscopal effect and pseudoprogression. Although both are infrequent in head and neck squamous cell carcinoma, the synergism between radiation and checkpoint blockade therapy has generated excitement for exploitation of the abscopal effect. However, robust abscopal tumor regression observed in preclinical models has not translated to clinical experience. The optimal sequencing of radiotherapy with immunotherapy and dosage of radiation to target lesions to elicit this effect is being explored in clinical trials. Predictive markers of efficacy must be studied further to identify patients who may benefit from an abscopal effect and continued checkpoint inhibitor blockade beyond initial signs of radiologic progression. Given the rarity of pseudoprogression in head and neck squamous cell carcinoma, patients should be carefully selected to continue on immunotherapy, despite early radiologic signs of progression, given the risk of aggressive true progression and clinical deterioration that may result in missed opportunities for alternate treatments.

Targeted and Off-Target (Bystander and Abscopal) Effects of Radiation Therapy: Redox Mechanisms and Risk/Benefit Analysis

SIGNIFICANCE

Radiation therapy (from external beams to unsealed and sealed radionuclide sources) takes advantage of the detrimental effects of the clustered production of radicals and reactive oxygen species (ROS). Research has mainly focused on the interaction of radiation with water, which is the major constituent of living beings, and with nuclear DNA, which contains the genetic information. This led to the so-called target theory according to which cells have to be hit by ionizing particles to elicit an important biological response, including cell death. In cancer therapy, the Poisson law and linear quadratic mathematical models have been used to describe the probability of hits per cell as a function of the radiation dose. Recent Advances: However, in the last 20 years, many studies have shown that radiation generates "danger" signals that propagate from irradiated to nonirradiated cells, leading to bystander and other off-target effects.

CRITICAL ISSUES

Like for targeted effects, redox mechanisms play a key role also in off-target effects through transmission of ROS and reactive nitrogen species (RNS), and also of cytokines, ATP, and extracellular DNA. Particularly, nuclear factor kappa B is essential for triggering self-sustained production of ROS and RNS, thus making the bystander response similar to inflammation. In some therapeutic cases, this phenomenon is associated with recruitment of immune cells that are involved in distant irradiation effects (called "away-from-target" i.e., abscopal effects).

FUTURE DIRECTIONS

Determining the contribution of targeted and off-target effects in the clinic is still challenging. This has important consequences not only in radiotherapy but also possibly in diagnostic procedures and in radiation protection.

Characterization of a B16-F10 melanoma model locally implanted into the ear pinnae of C57BL/6 mice

The common experimental use of B16-F10 melanoma cells focuses on exploring their metastatic potential following intravenous injection into mice. In this study, B16-F10 cells are used to develop a primary tumor model by implanting them directly into the ears of C57BL/6J mice. The model represents a reproducible and easily traceable tool for local tumor growth and for making additional in vivo observations, due to the localization of the tumors. This model is relatively simple and involves (i) surgical opening of the ear skin, (ii) removal of a square-piece of cartilage followed by (iii) the implantation of tumor cells with fibrin gel. The remodeling of the fibrin gel within the cartilage chamber, accompanying tumor proliferation, results in the formation of blood vessels, lymphatics and tissue matrix that can be readily distinguished from the pre-existing skin structures. Moreover, this method avoids the injection-enforced artificial spread of cells into the pre-existing lymphatic vessels. The tumors have a highly reproducible exponential growth pattern with a tumor doubling time of around 1.8 days, reaching an average volume of 85mm³ 16 days after implantation. The melanomas are densely cellular with proliferative indices of between 60 and 80%. The induced angiogenesis and lymphangiogenesis resulted in the development of well-vascularized tumors. Different populations of immunologically active cells were also present in the tumor; the population of macrophages decreases with time while the population of T cells remained quasi constant. The B16-F10 tumors in the ear frequently metastasized to the cervical lymph nodes, reaching an incidence of 75% by day 16. This newly introduced B16-F10 melanoma model in the ear is a powerful tool that provides a new opportunity to study the local tumor growth and metastasis, the associated angiogenesis, lymphangiogenesis and tumor immune responses. It could potentially be used to test different treatment strategies.

The concept of rapid rescue radiosurgery in the acute management of critically located brain metastases: A retrospective short-term outcome analysis

Background:

Adaptive hypofractionated gamma knife radiosurgery has been used to treat brain metastases in the eloquent regions while limiting the risk of adverse radiation effect (ARE). Ablative responses might be achieved within days to weeks with the goal to preserve the neurological function. The application of this treatment modality in selected acute/subacute settings has been termed Rapid Rescue Radiosurgery (RRR) in our department. We report the expeditious effects of RRR during treatment and 4 weeks after treatment completion.

Methods:

In all, 34 patients with 40 brain metastases, each treated over a period of 7 days in three separate gamma knife radiosurgery sessions (GKRS 1-3) between November 2013 and August 2017, were retrospectively analyzed in terms of tumor volume reduction, salvage of organs at risk (OAR), and radiation induced toxicity under the period of treatment (GKRS 1-3 = one week) and at first follow-up magnetic resonance imaging (MRI) (4 weeks after GKRS 3).

Results:

Mean tumor volume at GKRS 1 was 12.8 cm3. Mean peripheral doses at GKRS 1, GKRS 2, and GKRS 3 were 7.7 Gy, 8.1 Gy, and 8.4 Gy (range: 6.0-9.5 Gy) at the 35% to 50% isodose lines. In the surviving group at first follow-up (n = 28), mean tumor volume reduction was − 10% at GKRS 3 (1 week) and − 48% four weeks after GKRS 3. There was no further clinical deterioration between GKRS 3 and first follow-up in 21 patients. Six patients died prior to first follow-up due to extracranial disease. No ARE was noticed/reported.

Conclusions:

In this study, RRR proved effective in terms of rapid tumor volume reduction, debulking, and preservation/rescue of neurological function.

Tumor-specific CD8-positive T cell-mediated antitumor immunity is implicated in the antitumor effect of local hyperthermia

PURPOSE

This study aimed to elucidate the contribution of T cell-mediated antitumor immunity in the antitumor effect of local hyperthermia (LH).

MATERIALS AND METHODS

C57BL/6J mice were injected with the mouse lymphoma cell line, E.G7-OVA, in the right femur on day 0. LH was induced by immersing the right femur in a water bath at 42 °C for 60 min on day 7, followed by administration of anti-CD8 monoclonal antibodies (mAb) or anti-CTLA-4 mAb (days 8, 11, and 14). The effect of LH on tumor growth (TG) was assessed by measuring the duration until tumor volume reached 1000 mm³ and survival time. Tumor-specific T cell responses were measured using enzyme-linked immunospot (ELISpot) assay.

RESULTS

TG with and without LH treatment was 9.0 ± 9.6 and 7.0 ± 1.6 days, respectively. TG was significantly slower with LH treatment (p = .01). The therapeutic effect of LH was mitigated by addition of anti-CD8 mAb (p < .05 for both TG and survival) compared with the untreated (control) group. Furthermore, addition of anti-CTLA-4 mAb did not significantly affect the therapeutic effect of LH. The ELISpot assay showed that the number of spots in the LH group (276.3 ± 14.5) was significantly greater than in the control group (59.0 ± 4.5, p < .001).

CONCLUSION

CD8-positive T cell-mediated antitumor immunity significantly contributes to the antitumor effect of LH.

Non-canonical NF-κB Antagonizes STING Sensor-Mediated DNA Sensing in Radiotherapy

The NF-κB pathway plays a crucial role in supporting tumor initiation, progression, and radioresistance of tumor cells. However, the role of the NF-κB pathway in radiation-induced anti-tumor host immunity remains unclear. Here we demonstrated that inhibiting the canonical NF-κB pathway dampened the therapeutic effect of ionizing radiation (IR), whereas non-canonical NF-κB deficiency promoted IR-induced anti-tumor immunity. Mechanistic studies revealed that non-canonical NF-κB signaling in dendritic cells (DCs) was activated by the STING sensor-dependent DNA-sensing pathway. By suppressing recruitment of the transcription factor RelA onto the Ifnb promoter, activation of the non-canonical NF-κB pathway resulted in decreased type I IFN expression. Administration of a specific inhibitor of the non-canonical NF-κB pathway enhanced the anti-tumor effect of IR in murine models. These findings reveal the potentially interactive roles for canonical and non-canonical NF-κB pathways in IR-induced STING-IFN production and provide an alternative strategy to improve cancer radiotherapy.

Inhibiting the CD8+ T cell infiltration in the tumor microenvironment after radiotherapy is an important mechanism of radioresistance

Endogenous immune response participates in tumor control, and radiotherapy has immune modulatory capacity, but the role of immune modulation in the tumor microenvironment invoked by radiotherapy in radiosensitivity is poorly defined. In the present study, a radio-resistant melanoma cell line was obtained after repeated irradiation to the parental tumor in C57BL/6 mice. Radiotherapy resulted in aggregation of CD8⁺ and CD3⁺ T cells, and decrease of myeloid-derived suppressor cells and dendritic cells in the parental tumor, but not in the resistant tumors. CD4⁺ T cells and B cells did not change significantly. The CD8⁺ T cell infiltration after radiotherapy is important for tumor response, because in the nude mice and CD8⁺ T cell-depleted C57BL/6 mice, the parental and resistant tumor has similar radiosensitivity. Patients with good radiation response had more CD8⁺ T cells aggregation after radiotherapy. Radiotherapy resulted in robust transcription of T cell chemoattractant in the parental cells, and the expression of CCL5 was much higher. These results reveal a novel mechanism of radioresistance, tumor cells inhibit the infiltration of CD8⁺ T cell after radiotherapy and become radioresistant. Increasing CD8⁺ T cell infiltration after RT may be an effective way to improve tumor radiosensitivity.

Combining Immune Checkpoint Inhibitors With Conventional Cancer Therapy

Immune checkpoint inhibitors (ICIs) have recently revolutionized cancer treatment, providing unprecedented clinical benefits. However, primary or acquired therapy resistance can affect up to two-thirds of patients receiving ICIs, underscoring the urgency to elucidate the mechanisms of treatment resistance and to design more effective therapeutic strategies. Conventional cancer treatments, including cytotoxic chemotherapy, radiation therapy, and targeted therapy, have immunomodulatory effects in addition to direct cancer cell-killing activities. Their clinical utilities in combination with ICIs have been explored, aiming to achieve synergetic effects with improved and durable clinical response. Here, we will review the immunomodulatory effects of chemotherapy, targeted therapy, and radiation therapy, in the setting of ICI, and their clinical implications in reshaping modern cancer immunotherapy.

Elective Nodal Irradiation Attenuates the Combinatorial Efficacy of Stereotactic Radiation Therapy and Immunotherapy

Purpose: In the proper context, radiotherapy can promote antitumor immunity. It is unknown if elective nodal irradiation (ENI), a strategy that irradiates tumor-associated draining lymph nodes (DLN), affects adaptive immune responses and combinatorial efficacy of radiotherapy with immune checkpoint blockade (ICB).Experimental Design: We developed a preclinical model to compare stereotactic radiotherapy (Tumor RT) with or without ENI to examine immunologic differences between radiotherapy techniques that spare or irradiate the DLN.Results: Tumor RT was associated with upregulation of an intratumoral T-cell chemoattractant chemokine signature (CXCR3, CCR5-related) that resulted in robust infiltration of antigen-specific CD8⁺ effector T cells as well as FoxP3⁺ regulatory T cells (Tregs). The addition of ENI attenuated chemokine expression, restrained immune infiltration, and adversely affected survival when combined with ICB, especially with anti-CLTA4 therapy. The combination of stereotactic radiotherapy and ICB led to long-term survival in a subset of mice and was associated with favorable CD8 effector-to-Treg ratios and increased intratumoral density of antigen-specific CD8⁺ T cells. Although radiotherapy technique (Tumor RT vs. ENI) affected initial tumor control and survival, the ability to reject tumor upon rechallenge was partially dependent upon the mechanism of action of ICB; as radiotherapy/anti-CTLA4 was superior to radiotherapy/anti-PD-1.Conclusions: Our results highlight that irradiation of the DLN restrains adaptive immune responses through altered chemokine expression and CD8⁺ T-cell trafficking. These data have implications for combining radiotherapy and ICB, long-term survival, and induction of immunologic memory. Clinically, the immunomodulatory effect of the radiotherapy strategy should be considered when combining stereotactic radiotherapy with immunotherapy. Clin Cancer Res; 24(20); 5058-71. ©2018 AACR.

Abscopal, immunological effects of radiotherapy: Narrowing the gap between clinical and preclinical experiences

Radiotherapy-despite being a local therapy that meanwhile is characterized by an impressively high degree of spatial accuracy-can stimulate systemic phenomena which occasionally lead to regression and rejection of non-irradiated, distant tumor lesions. These abscopal effects of local irradiation have been observed in sporadic clinical case reports since the beginning of the 20th century, and extensive preclinical work has contributed to identify systemic anti-tumor immune responses as the underlying driving forces. Although abscopal tumor regression still remains a rare event in the radiotherapeutic routine, increasing numbers of cases are being reported, particularly since the clinical implementation of immune checkpoint inhibiting agents. Accordingly, interests to systematically exploit the therapeutic potential of radiotherapy-stimulated systemic responses are constantly growing. The present review briefly delineates the history of radiotherapy-induced abscopal effects and the activation of systemic anti-tumor immune responses by local irradiation. We discuss preclinical and clinical reports with specific focus on the corresponding controversies, and we propose issues that should be addressed in the future in order to narrow the gap between preclinical knowledge and clinical experiences.