Enhancement of antitumor radiation efficacy and consistent induction of the abscopal effect in mice by ECI301, an active variant of macrophage inflammatory protein-1alpha

Radiotherapy in cutaneous lymphomas: Recommendations from the EORTC cutaneous lymphoma tumour group

The number of primary cutaneous lymphoma patients receiving low-dose radiotherapy is increasing, though controlled clinical trials defining the standard radiation dose for each specific entity have not yet been completed. Radiation oncologists are left with making highly individualized decisions that would be better enriched by additional clinical evidence. In this expert opinion, we aim to provide a clear recommendation to improve the current practice of radiation oncology. In addition, existing literature has been reviewed to develop recommendations for all types of primary cutaneous lymphoma. A prospective trial is urgently needed to identify the factors influencing patient outcomes following different radiation doses.

Irradiation combined with PD-L1-/- and autophagy inhibition enhances the antitumor effect of lung cancer via cGAS-STING-mediated T cell activation

Radiotherapy combined with immune checkpoint blockade has gradually revealed the superiority in the antitumor therapy; however, the contribution of host PD-L1 remains elusive. In this study, we found that the activation of CD8⁺ T cells was strikingly increased in both irradiated PD-L1-expressing primary tumor and distant non-irradiated syngeneic tumor in PD-L1-deficient mouse host, and thus enhanced radiation-induced antitumor abscopal effect (ATAE) by activating cGAS-STING pathway. Notably, the autophagy inhibitors distinctively promoted dsDNA aggregation in the cytoplasm and increased the release of cGAS-STING-regulated IFN-β from irradiated cells, which further activated bystander CD8⁺ T cells to release IFN-γ and contributed to ATAE. These findings revealed a signaling cascade loop that the cytokines released from irradiated tumor recruit CD8⁺ T cells that in turn act on the tumor cells with amplified immune responses in PD-L1-deficient host, indicating a potential sandwich therapy strategy of RT combined with PD-L1 blockage and autophagy inhibition.

Synergistic effects of radiotherapy and targeted immunotherapy in improving tumor treatment efficacy: a review

Radiotherapy (RT), unlike chemotherapy, is one of the most routinely used and effective genotoxic and immune response inducing cancer therapies with an advantage of reduced side effects. However, cancer can relapse after RT owing to multiple factors, including acquired tumor resistance, immune suppressive microenvironment buildup, increased DNA repair, thus favoring tumor metastasis. Efforts to mitigate these undesirable effects have drawn interest in combining RT with immunotherapy, particularly the use of immune checkpoint inhibitors, to tilt the pre-existing tumor stromal microenvironment into long-lasting therapy-induced antitumor immunity at multiple metastatic sites (abscopal effects). This multimodal therapeutic strategy can alleviate the increased T cell priming and decrease tumor growth and metastasis, thus emerging as a significant approach to sustain as long-term antitumor immunity. To understand more about this synergism, a detailed cellular mechanism underlying the dynamic interaction between tumor and immune cells within the irradiated tumor microenvironment needs to be explored. Hence, in the present review, we have attempted to evaluate various RT-inducible immune factors, which can be targeted by immunotherapy and provide detailed explanation to optimally maximize their synergy with immunotherapy for long-lasting antitumor immunity. Moreover, we have critically assessed various combinatorial approaches along with their challenges and described strategies to modify them in addition to providing approaches for optimal synergistic effects of the combination.

From Photon Beam to Accelerated Particle Beam: Antimetastasis Effect of Combining Radiotherapy With Immunotherapy

Cancer is one of the major diseases that seriously threaten the human health. Radiotherapy is a common treatment for cancer. It is noninvasive and retains the functions of the organ where the tumor is located. Radiotherapy includes photon beam radiotherapy, which uses X-rays or gamma rays, and particle beam radiotherapy, using beams of protons and heavy ions. Compared with photon beam radiotherapy, particle beam radiotherapy has excellent dose distribution, which enables it to kill the primary tumor cells more effectively and simultaneously minimize the radiation-induced damage to normal tissues and organs surrounding the tumor. Despite the excellent therapeutic effect of particle beam radiotherapy on the irradiated tumors, it is not an effective treatment for metastatic cancers. Therefore, developing novel and effective treatment strategies for cancer is urgently needed to save patients with distant cancer metastasis. Immunotherapy enhances the body's own immune system to fight cancer by activating the immune cells, and consequently, to achieve the systemic anticancer effects, and it is considered to be an adjuvant therapy that can enhance the efficacy of particle beam radiotherapy. This review highlights the research progress of the antimetastasis effect and the mechanism of the photon beam or particle beam radiotherapy combined with immunotherapy and predicts the development prospects of this research area.

The roles of CC chemokines in response to radiation

Radiotherapy is an effective regimen for cancer treatment alone or combined with chemotherapy or immunotherapy. The direct effect of radiotherapy involves radiation-induced DNA damage, and most studies have focused on this area to improve the efficacy of radiotherapy. Recently, the immunomodulatory effect of radiation on the tumour microenvironment has attracted much interest. Dying tumour cells can release multiple immune-related molecules, including tumour-associated antigens, chemokines, and inflammatory mediators. Then, immune cells are attracted to the irradiated site, exerting immunostimulatory or immunosuppressive effects. CC chemokines play pivotal roles in the trafficking process. The CC chemokine family includes 28 members that attract different immune subsets. Upon irradiation, tumour cells or immune cells can release different CC chemokines. Here, we mainly discuss the importance of CCL2, CCL3, CCL5, CCL8, CCL11, CCL20 and CCL22 in radiotherapy. In irradiated normal tissues, released chemokines induce epithelial to mesenchymal transition, thus promoting tissue injury. In the tumour microenvironment, released chemokines recruit cancer-associated cells, such as tumour-infiltrating lymphocytes, myeloid-derived suppressor cells and tumour-associated macrophages, to the tumour niche. Thus, CC chemokines have protumour and antitumour properties. Based on the complex roles of CC chemokines in the response to radiation, it would be promising to target specific chemokines to alleviate radiation-induced injury or promote tumour control.

Prospective Evaluation of Radiotherapy-Induced Immunologic and Genetic Effects in Colorectal Cancer Oligo-Metastatic Patients with Lung-Limited Disease: The PRELUDE-1 Study

BACKGROUND

in recent years, the management of advanced colorectal cancer (CRC) has been greatly improved with integrated strategies including stereotactic radiation therapy (SRT). The administration of SRT has been demonstrated, particularly in oligo-metastatic (om) CRC, to be a safe and effective option. Interestingly, it has been demonstrated that SRT can induce regression of tumors in non-irradiated regions ("abscopal effect") through stimulation of anti-tumor immune effects ("radiation-induced immunity"). We have recently shown that lung-limited omCRC is characterized by regression of tumor clones bearing specific key driver gene mutations.

AIMS

to assess the genetic evolution on tumor cancer cells induced by SRT in lung-limited omCRC. Secondary objectives included descriptions of the abscopal effect, responses' duration, toxicity, and progression-free survival. A translational research will be performed to evaluate tumor genetic evolution (through liquid biopsies and Next Generation Sequencing), HLA class I repertoire, peripheral immune cells, and cytokine dynamics.

METHODS

PRELUDE-1 is a prospective translational study. SRT will be administered only to the largest nodule (with a maximum diameter ≤ 25 mm) in omCRC with two or three radiologically evident lesions. The sample size is based on the innovative hypothesis that radiation-induced immunity could induce regression of tumor clones bearing KRAS oncogene mutations. According to the binomial test, considering the frequency of KRAS mutations and assuming a probability of mutant KRAS→wild type KRAS of p0 = 0.0077, with α = 0.05 and 1-β = 0.60, the final sample size is 25 patients.

Local Destruction of Tumors and Systemic Immune Effects

Current immune-based therapies signify a major advancement in cancer therapy; yet, they are not effective in the majority of patients. Physically based local destruction techniques have been shown to induce immunologic effects and are increasingly used in order to improve the outcome of immunotherapies. The various local destruction methods have different modes of action and there is considerable variation between the different techniques with respect to the ability and frequency to create a systemic anti-tumor immunologic effect. Since the abscopal effect is considered to be the best indicator of a relevant immunologic effect, the present review focused on the tissue changes associated with this effect in order to find determinants for a strong immunologic response, both when local destruction is used alone and combined with immunotherapy. In addition to the T cell-inflammation that was induced by all methods, the analysis indicated that it was important for an optimal outcome that the released antigens were not destroyed, tumor cell death was necrotic and tumor tissue perfusion was at least partially preserved allowing for antigen presentation, immune cell trafficking and reduction of hypoxia. Local treatment with controlled low level hyperthermia met these requisites and was especially prone to result in abscopal immune activity on its own.

Cisplatin nanoparticles boost abscopal effect of radiation plus anti-PD1 therapy

The abscopal effect of radiation therapy (RT) is clinically significant but occurs rarely. Although anti-programmed cell death protein 1 antibody (anti-PD1) is likely to enhance the abscopal effect in patients receiving RT, the incidence rate remains less than 30%. One major limitation is the paucity of CD8⁺ T cells within non-irradiated tumors. Here, cisplatin (CDDP) loaded poly(l-glutamic acid)-graft-methoxy poly(ethylene glycol) complex nanoparticles (CDDP-NPs) are confirmed to increase CD8⁺ T cells within non-irradiated tumors and boost the abscopal effect of RT plus anti-PD1, and more strongly than CDDP. Compared to RT and RT + CDDP, RT + CDDP-NPs induced greater immunogenic cell death (ICD) with enhanced proportion of Calreticulin⁺ Lewis lung cancer (LLC) cells (16.47%, 20.53% and 27.03%), along with which more CD8⁺ T cells were infiltrated into CDDP-NP treated irradiated tumors in the unilateral LLC tumor model. In the bilateral LLC tumor model, RT + CDDP-NPs significantly induced more chemokine (C-X-C motif) ligand 10 (CXCL10) secretion (36.3, 44.19 and 56.37 pg mL^-1), which corresponded to greater CD8⁺ T cell infiltration in the non-irradiated tumors (0.19%, 0.20% and 0.72%). Finally, compared to RT + anti-PD1 and RT + anti-PD1 + CDDP, RT + anti-PD1 + CDDP-NPs significantly inhibited the growth of non-irradiated tumors more forcefully, as indicated by the respective tumor volumes of 1141, 1146 and 585 mm³. This is the first study to show that CDDP-NPs can amplify RT-induced immune activation and break through the efficiency limitation of the RT plus anti-PD1 induced abscopal effect.

Abscopal Effect of Frozen Autograft Reconstruction Combined with an Immune Checkpoint Inhibitor Analyzed Using a Metastatic Bone Tumor Model

We evaluated the abscopal effect of re-implantation of liquid nitrogen-treated tumor-bearing bone grafts and the synergistic effect of anti-PD-1 (programmed death-1) therapy using a bone metastasis model, created by injecting MMT-060562 cells into the bilateral tibiae of 6-8-week-old female C3H mice. After 2 weeks, the lateral tumors were treated by excision, cryotreatment using liquid nitrogen, excision with anti-PD-1 treatment, and cryotreatment with anti-PD-1 treatment. Anti-mouse PD-1 4H2 was injected on days 1, 6, 12, and 18 post-treatment. The mice were euthanized after 3 weeks; the abscopal effect was evaluated by focusing on growth inhibition of the abscopal tumor. The re-implantation of frozen autografts significantly inhibited the growth of the remaining abscopal tumors. However, a more potent abscopal effect was observed in the anti-PD-1 antibody group. The number of CD8+ T cells infiltrating the abscopal tumor and tumor-specific interferon-γ (IFN-γ)-producing spleen cells increased in the liquid nitrogen-treated group compared with those in the excision group, with no significant difference. The number was significantly higher in the anti-PD-1 antibody-treated group than in the non-treated group. Overall, re-implantation of tumor-bearing frozen autograft has an abscopal effect on abscopal tumor growth, although re-implantation of liquid nitrogen-treated bone grafts did not induce a strong T-cell response or tumor-suppressive effect.

Abscopal but desirable: The contribution of immune responses to the efficacy of radiotherapy

Radiotherapy applies ionizing irradiation to selected areas of the body with the scope of destroying cancer cells, either as part of curative therapies to remove a primary malignant tumor and to prevent tumor recurrence after surgery, or as part of palliative measures to avoid local advancement of bone and brain metastases. Intriguingly, radiotherapy does not only have local effects but may lead to the delayed regression of distant non-irradiated lesions. Most likely, these “abscopal” effects are mediated by the immune system.

Gas plasma irradiation of breast cancers promotes immunogenicity, tumor reduction, and an abscopal effect in vivo

While many new and emerging therapeutic concepts have appeared throughout the last decades, cancer still is fatal in many patients. At the same time, the importance of immunology in oncotherapy is increasingly recognized, not only since the advent of checkpoint therapy. Among the many types of tumors, also breast cancer has an immunological dimension that might be exploited best by increasing the immunogenicity of the tumors in the microenvironment. To this end, we tested a novel therapeutic concept, gas plasma irradiation, for its ability to promote the immunogenicity and increase the toxicity of breast cancer cells in vitro and in vivo. Mechanistically, this emerging medical technology is employing a plethora of reactive oxygen species being deposited on the target cells and tissues. Using 2D cultures and 3D tumor spheroids, we found gas plasma-irradiation to drive apoptosis and immunogenic cancer cell death (ICD) in vitro, as evidenced by an increased expression of calreticulin, heat-shock proteins 70 and 90, and MHC-I. In 4T1 breast cancer-bearing mice, the gas plasma irradiation markedly decreased tumor burden and increased survival. Interestingly, non-treated tumors injected in the opposite flank of mice exposed to our novel treatment also exhibited reduced growth, arguing for an abscopal effect. This was concomitant with an increase of apoptosis and tumor-infiltrating CD4⁺ and CD8⁺ T-cells as well as dendritic cells in the tissues. In summary, we found gas plasma-irradiated murine breast cancers to induce toxicity and augmented immunogenicity, leading to reduced tumor growth at a site remote to the treatment area.

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.

Research Progress and Existing Problems for Abscopal Effect

Radiation therapy plays a vital role in the treatment of tumours. In particular, the occurrence of the “abscopal effect” brings about a favourable turn for the treatment of patients with advanced metastatic malignant tumours. Because of the abscopal effect, non-irradiated areas are also treated. However, the abscopal effect occurs by chance, not through seeking. Although the abscopal effect has been studied enthusiastically, the desired result does not appear to be achieved. Moreover, its combination with immunotherapy appears to be overwhelming. There is an opinion that abscopal effect is difficult to achieve by irradiation of a single tumour, and irradiation of multiple or total lesions is advocated to increase the possibility of obtaining clinically meaningful outcomes. Obviously, there are still questions about the mechanism, condition and possibility underlying the occurrence of the abscopal effect. Can the abscopal effect truly change the future treatment strategy as the researchers expect? What are the current problems? This article reviewed the research in recent years to explore the progress and controversy surrounding the abscopal effect of radiation therapy.

Evaluation of Anti-Tumor Effects of Whole-Body Low-Dose Irradiation in Metastatic Mouse Models

Low-dose irradiation (LDI) has recently been shown to have various beneficial effects on human health, such as on cellular metabolic activities, DNA repair, antioxidant activity, homeostasis potency, and immune activation. Although studies on the immunogenic effects of LDI are rapidly accumulating, clinical trials for cancer treatment are considered premature owing to the lack of available preclinical results and protocols. Here, we aim to investigate anti-tumor and anti-metastatic effects of whole-body LDI in several tumor-bearing mouse models. Mice were exposed to single or fractionated whole-body LDI prior to tumor transplantation, and tumor growth and metastatic potential were determined, along with analysis of immune cell populations and expression of epithelial-mesenchymal transition (EMT) markers. Whole-body fractionated-LDI decreased tumor development and lung metastasis not only by infiltration of CD4⁺, CD8⁺ T-cells, and dendritic cells (DCs) but also by attenuating EMT. Moreover, a combination of whole-body LDI with localized high-dose radiation therapy reduced the non-irradiated abscopal tumor growth and increased infiltration of effector T cells and DCs. Therefore, whole-body LDI in combination with high-dose radiation therapy could be a potential therapeutic strategy for treating cancer.

Pure abscopal effect of radiotherapy in a salivary gland carcinoma: Case report, literature review, and a search for new approaches

We report the case of an 84-year-old woman with poorly differentiated non-small cell carcinoma of the right parotid who presented with headache, was found to have a primary right parotid gland cancer as well as metastatic disease, and underwent palliative radiotherapy to the primary site. The patient received no chemotherapy or immunotherapy, but both the primary site and several non-irradiated foci in the lungs regressed or completely resolved. The patient remained free of disease for about one year before progression. The case is a rare instance of abscopal regression of metastatic disease in the absence of pharmacologic immunomodulation. A literature review surveys the history of the abscopal effect of radiation therapy, attempts to understand the mechanisms of its successes and failures, and points to new approaches that can inform and improve the outcomes of radioimmunotherapy.

Anti-Metastatic Benefits Produced by Hyperthermia and a CCL3 Derivative

Significant numbers of malignant tumor cells that have spread to surrounding tissues and other distant organs are often too small to be picked up in a diagnostic test, and prevention of even such small metastases should improve patient outcomes. Using a mouse model, we show in this article that intravenous administration of a human CCL3 variant carrying a single amino acid substitution after mild local hyperthermia not only induces tumor growth inhibition at the treated site but also inhibits metastasis. Colon26 adenocarcinoma cells (1 × 10⁵ cells/mouse) were grafted subcutaneously into the right hind leg of syngeneic BALB/c mice and after nine days, when tumor size reached ~11 mm in diameter, the local tumor mass was exposed to high-frequency waves, by which intratumoral temperature was maintained at 42 °C for 30 min. Mice received the CCL3 variant named eMIP (2 μg/mouse/day) intravenously for five consecutive days starting one day after heat treatment. We found that tumor growth in eMIP recipients after hyperthermia was inhibited markedly but no effect was seen in animals treated with either hyperthermia or eMIP alone. Furthermore, the number of lung metastases evaluated at 18 days after hyperthermia treatment was dramatically reduced in animals receiving the combination therapy compared with all other controls. These results encourage future clinical application of this combination therapy.

Accelerated, but not conventional, radiotherapy of murine B-cell lymphoma induces potent T cell-mediated remissions

Conventional local tumor irradiation (LTI), delivered in small daily doses over several weeks, is used clinically as a palliative, rather than curative, treatment for chemotherapy-resistant diffuse large B-cell lymphoma (DLBCL) for patients who are ineligible for hematopoietic cell transplantation. Our goal was to test the hypothesis that accelerated, but not conventional, LTI would be more curative by inducing T cell-mediated durable remissions. We irradiated subcutaneous A20 and BL3750 lymphoma tumors in mice with a clinically relevant total radiation dose of 30 Gy LTI, delivered in 10 doses of 3 Gy over 4 days (accelerated irradiation) or as 10 doses of 3 Gy over 12 days (conventional irradiation). Compared with conventional LTI, accelerated LTI resulted in more complete and durable tumor remissions. The majority of these mice were resistant to rechallenge with lymphoma cells, demonstrating the induction of memory antitumor immunity. The increased efficacy of accelerated LTI correlated with higher levels of tumor cell necrosis vs apoptosis and expression of "immunogenic cell death" markers, including calreticulin, heat shock protein 70 (Hsp70), and Hsp90. Accelerated LTI-induced remissions were not seen in immunodeficient Rag-2 ^-/- mice, CD8⁺ T-cell-depleted mice, or Batf-3 ^-/- mice lacking CD8α⁺ and CD103⁺ dendritic cells. Accelerated, but not conventional, LTI in immunocompetent hosts induced marked increases in tumor-infiltrating CD4⁺ and CD8⁺ T cells and MHCII⁺CD103⁺CD11c⁺ dendritic cells and corresponding reductions in exhausted PD-1⁺Eomes⁺CD8⁺ T cells and CD4⁺CD25⁺FOXP3⁺ regulatory T cells. These findings raise the possibility that accelerated LTI can provide effective immune control of human DLBCL.

Gamma knife radiosurgery compared to whole brain radiation therapy enhances immunity via immunoregulatory molecules in patients with metastatic brain tumours

Background: There is lack of data on the effect of stereotactic radiosurgery in modulation of the immune system for cancer patients with metastatic brain tumours. Therefore, we investigated the change in levels of immunoregulatory molecules after Gamma Knife radiosurgery (GKR) and whole brain radiation therapy (WBRT) in patients with brain metastases.Methods: Peripheral blood samples were collected from 15 patients who received GKR, nine patients who received WBRT for brain metastases and 10 healthy controls. Samples were obtained at three time points such as before, 1h after and 1 week after the index procedure for patients treated with GKR or WBRT. All patients' demographic data and radiosurgical parameters were retrospectively reviewed. We analyzed the change in the levels of T-lymphocyte-associated antigen 4 (CTLA-4) and programmed cell death ligand-1 (PD-L1), and cytokines such as IL-2, IL-10, IFN-γ, TNF-α after GKR and WBRT using Enzyme-linked immunosorbent assays (ELISA).Results: Baseline level of IFN-γ was found to be lower and that of PD-L1 was higher in the GKR group compared to WBRT group and healthy controls (p < 0.05 and p < 0.01, respectively). Levels of IFN-γ and IL-2 were increased (p < 0.01 and p < 0.01, respectively), while CTLA-4 and PD-L1 were decreased (p = 0.05 and p = 0.01, respectively) after GKR compared to pre-GKR levels, while there was no change after WBRT.Conclusion: GKR regulates immunoregulatory molecules towards enhancing the immune system, while WBRT did not exert any effect. These findings suggested that treatment of metastatic brain lesion with GKR might stimulate a systemic immune response against the tumour.

Reduced Number of Lymphocytes by X-ray Irradiation: A Problem in a Combination Therapy Trial that Elicits the Abscopal Effect in Preclinical Studies Using Electron Beam Irradiation

In preclinical studies with model animals, intravenous administration of a derivative of chemokine CCL3, named eMIP, after local electron-beam irradiation, not only enhanced tumor growth inhibition at a target site but also induced tumor killing beyond the treated site (a phenomenon known as the abscopal effect). eMIP works with alarmins such as high mobility group box 1 (HMGB1) and heat shock protein 70 (HSP70) released from overexpressed tumor cells by irradiation. These alarmins at the irradiated tumor bed trap injected eMIP and, by forming complexes with eMIP, play a key role to recruit and activate tumor inhibitory natural killer (NK) cells and CD4⁺ and CD8⁺ T cells. Tumor type-specific secretion of gamma interferon from splenocytes was also demonstrated, which may also activate NK cells. During Phase 1 clinical studies using X-rays, however, no apparent abscopal effect was observed. Instead, we saw frequent reduction in numbers of lymphocytes in the peripheral blood of irradiated patients. The reduced number of lymphocytes recovered poorly once depleted, in contrast to neutrophils, and persisted for months after the treatment. This might have affected outcome after combination treatment of irradiation and eMIP. To enhance host defense mechanisms during and after photon-beam (X-ray) radiotherapy of a deep-seated tumor, it seems essential to keep lymphocytes undamaged by eliminating reactive oxygen species that are formed in the peripheral blood during irradiation.

Combination PD-1 blockade and irradiation of brain metastasis induces an effective abscopal effect in melanoma

Nearly half of melanoma patients develop brain metastases during the course of their disease. Despite advances in both localized radiation and systemic immunotherapy, brain metastases remain difficult to treat, with most patients surviving less than 5 months from the time of diagnosis. While both treatment regimens have individually shown considerable promise in treating metastatic melanoma, there is interest in combining these strategies to take advantage of potential synergy. In order to study the ability of local radiation and anti-PD-1 immunotherapy to induce beneficial anti-tumor immune responses against distant, unirradiated tumors, we used two mouse models of metastatic melanoma in the brain, representing BRAF mutant and non-mutant tumors. Combination treatments produced a stronger systemic anti-tumor immune response than either treatment alone. This resulted in reduced tumor growth and larger numbers of activated, cytotoxic CD8⁺ T cells, even in the unirradiated tumor, indicative of an abscopal effect. The immune-mediated effects were present regardless of BRAF status. These data suggest that irradiation of brain metastases and anti-PD-1 immunotherapy together can induce abscopal anti-tumor responses that control both local and distant disease.

Immune Checkpoint Inhibitors in Early-Stage and Locally Advanced Non-Small Cell Lung Cancer

OPINION STATEMENT

Surgical resection ± chemotherapy ± radiation or stereotactic body radiation therapy (SBRT) are established treatment modalities for resectable stage non-small cell lung cancer (NSCLC), and concurrent chemotherapy with radiation is the therapy of choice for unresectable locally advanced disease. Despite treatment with curative intent, most patients subsequently relapse and develop distant disease. Treatment with checkpoint inhibitors represents a major advancement in the treatment of metastatic NSCLC. Therapy against programed cell death-1/programmed cell death ligand 1 (PD-1/PD-L1) is associated with a significant improvement in overall survival in stage IV disease, and these results have led to a great interest in evaluating these agents in earlier-stage NSCLC. The preliminary data from ongoing trials suggest that the integration of checkpoint blockage into the treatment of early-stage and locally advanced NSCLC is safe, tolerable, and has the potential to improve outcomes without adding substantial toxicity. In the current review, we provide an overview of the emerging data on the role of PD-1/PD-L1 and cytotoxic T lymphocyte-associated protein 4 (CTLA-4) inhibitors in the treatment of early-stage and locally advanced NSCLC, with a focus on ongoing clinical trials and combination strategies.

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.

Durvalumab: a potential maintenance therapy in surgery-ineligible non-small-cell lung cancer

Lung cancer is the most common cancer worldwide and the most common cause of cancer-related death. Non-small-cell lung cancer comprises ~87% of newly diagnosed cases of lung cancer, and nearly one-third of these patients have stage III disease. Despite improvements in the treatment of stage IV lung cancer, particularly with the introduction and dissemination of checkpoint inhibitors, very little progress has been made in the treatment of stage III lung cancer. In this article, we discuss the general staging criteria and treatment options for stage III lung cancer. We review how concurrent radiation and chemotherapy can have immunomodulatory effects, supporting the rationale for incorporating immunotherapy into existing treatment paradigms. Finally, we discuss the results of the PACIFIC trial and implications for the treatment of stage III lung cancer. In the PACIFIC trial, adding durvalumab as a maintenance therapy following the completion of chemoradiotherapy improved progression-free survival in patients with locally advanced unresectable stage III lung cancer. On the strength of these results, durvalumab has been approved by the US Food and Drug Administration for use in this setting, representing the first advance in the treatment of stage III lung cancer in nearly a decade.

Using immunotherapy to boost the abscopal effect

More than 60 years ago, the effect whereby radiotherapy at one site may lead to regression of metastatic cancer at distant sites that are not irradiated was described and called the abscopal effect (from 'ab scopus', that is, away from the target). The abscopal effect has been connected to mechanisms involving the immune system. However, the effect is rare because at the time of treatment, established immune-tolerance mechanisms may hamper the development of sufficiently robust abscopal responses. Today, the growing consensus is that combining radiotherapy with immunotherapy provides an opportunity to boost abscopal response rates, extending the use of radiotherapy to treatment of both local and metastatic disease. In this Opinion article, we review evidence for this growing consensus and highlight emerging limitations to boosting the abscopal effect using immunotherapy. This is followed by a perspective on current and potential cross-disciplinary approaches, including the use of smart materials to address these limitations.

Identification of the active portion of the CCL3 derivative reported to induce antitumor abscopal effect

•

Injected HSP70 and a partial peptide of a CCL3 variant elicit tumor growth inhibition.

•

The peptide also enhances tumor growth inhibition after local irradiation.

•

The sequence of the peptide corresponds to the beta sheet region of the valiant.

•

Chemotactic-inducing activity and tumor grow inhibition are independent phenomena.

•

The results will help to open the way for therapeutic application of like peptides.

Background and purpose

Intravenous administration of a single amino acid-substituted chemokine CCL3 derivative named eMIP elicits the abscopal effect (an effect distal to the target), after local irradiation at a tumor-bearing site. To distinguish the active portion of eMIP, we tested the antitumor activity of chemically synthesized partial peptides of eMIP. Synthetic peptide has various advantages in its clinical application.

Material and methods

Colon26 adenocarcinoma cells were implanted subcutaneously in the right and left flanks of mice. eMIP, CCL3 or any of synthesized peptides was administered intravenously, either after irradiating the right flank. The effect was evaluated by tumor-growth inhibition.

Results

Q/C peptide, a synthetic peptide of amino acids 22–51 of eMIP has no chemotaxis-inducing ability but yet enhanced tumor growth inhibition at the non-irradiated sites, recapitulating the effect of eMIP with local irradiation. Co-administration of this peptide and HSP70 also inhibited tumor growth.

Conclusions

Q/C peptide maps to the eMIP β-sheet: 3 adjacent anti-parallel strands connected by the β-hairpins, is the active portion of eMIP necessary for an immunomodulatory antitumor effect. This experimental reduction furthers our understanding of the underlying mechanism of the abscopal effect. The data will open the way for therapeutic application of like peptides.

Abscopal effect of radiation on bone metastases of breast cancer: A case report

The abscopal effect is defined as the clearance of distant tumors after applying localized irradiation to a particular tumor site. It has been proposed that a mechanism for the abscopal effect might be the activation of the immune system, which leads to immunogenic tumor cell death. Here, we describe a woman with advanced breast cancer that received modified ablative radiation therapy that targeted her primary breast tumor. She experienced an apparent regression of metastatic mass in the thoracic spine. This case supported the hypothesis that the abscopal effect might be attributable to an activation of the systemic immune response.

Radiation enhanced the local and distant anti-tumor efficacy in dual immune checkpoint blockade therapy in osteosarcoma

Radiation therapy has been long utilized as localized cancer treatment. Recent studies have also demonstrated that it has a distant effect by the enhanced immunity, but it rarely occurs. The purpose of this study was to investigate whether X-ray irradiation combined with anti-PD-L1 and anti-CTLA-4 antibodies (P1C4) provides a higher probability of this distant effect as well as enhanced local antitumor efficacy for osteosarcoma. LM8 mouse osteosarcoma cells were inoculated into both legs of C3H mice assigned to one of four groups, namely no treatment (No Tx), P1C4, X-ray irradiation (RAD) to the leg of one side, and combination (COMB) groups. Survival and treatment-related immune molecular changes were analyzed. Administration of P1C4 produced a tumor growth delay on day 30 in 18% of the mice. In contrast, combination therapy produced the strongest tumor growth inhibition not only at the irradiated tumor but also at unirradiated tumor in 67% of the mice. Accordingly, lung metastasis in the COMB group was strongly reduced by 98%, with a significant survival benefit. Unirradiated tumor in mice in the COMB group significantly recruited CD8 + tumor-infiltrating lymphocytes with a moderate reduction of Treg, producing a significant increase in the CD8/Treg ratio. These results suggest that radiation enhances the efficacy of P1C4 treatment against distant metastasis as well as local control in osteosarcoma. Our data suggest that radiation therapy combined with dual checkpoint blockade may be a promising therapeutic option for osteosarcoma.

CCL3 augments tumor rejection and enhances CD8+ T cell infiltration through NK and CD103+ dendritic cell recruitment via IFNγ

Inflammatory chemokines are critical contributors in attracting relevant immune cells to the tumor microenvironment and driving cellular interactions and molecular signaling cascades that dictate the ultimate outcome of host anti-tumor immune response. Therefore, rational application of chemokines in a spatial-temporal dependent manner may constitute an attractive adjuvant in immunotherapeutic approaches against cancer. Existing data suggest that the macrophage inflammatory protein (MIP)-1 family and related proteins, consisting of CCL3 (MIP-1α), CCL4 (MIP-1β), and CCL5 (RANTES), can be major determinant of immune cellular infiltration in certain tumors through their direct recruitment of antigen presenting cells, including dendritic cells (DCs) to the tumor site. In this study, we examined how CCL3 in a murine colon tumor microenvironment, CT26, enhances antitumor immunity. We identified natural killer (NK) cells as a major lymphocyte subtype that is preferentially recruited to the CCL3-rich tumor site. NK cells contribute to the overall IFNγ content, CD103+ DC accumulation, and augment the production of chemokines CXCL9 and CXCL10 for enhanced T cell recruitment. We further demonstrate that both soluble CCL3 and CCL3-secreting irradiated tumor vaccine can effectively halt the progression of established tumors in a spatial-dependent manner. Our finding implies an important contribution of NK in the CCL3 - CD103+ DC - CXCL9/10 signaling axis in determining tumor immune landscape within the tumor microenvironment.

Abscopal effect of metastatic pancreatic cancer after local radiotherapy and granulocyte-macrophage colony-stimulating factor therapy

The role of immunotherapy in combination with traditional treatment regime in improving the survival of cancer patients has attracted more and more attention. Especially the abscopal effect that describes the phenomenon of localized radiotherapy leading to regression of distant unirradiated tumors and the role of enhanced radiotherapy-induced immunogenic cell death and activation of immune system have become a focus of the studies. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is known a powerful stimulator of the generation, migration and activation of antigen presenting cells such as dendritic cells (DC) and macrophages. Here we report a case of a 67-year-old refractory metastatic pancreatic cancer patient who obtained evident abscopal effect and survival benefit from concurrent localized radiotherapy and GM-CSF.

Can local radiotherapy and IL-12 synergise to overcome the immunosuppressive tumor microenvironment and allow "in situ tumor vaccination"?

The abscopal effect, which is the spontaneous regression of tumors or metastases outside the radiation field, occurs rarely in cancer patients. Interestingly, radiotherapy (RT) triggers an immunogenic cell death (ICD) that is able to generate tumor-specific cytotoxic CD8+ T cells that are efficient in killing cancer cells. The key question is: why is this "abscopal effect" so uncommon in cancer patients treated with RT? Most probably, the main reason may be related to the highly immunosuppressive tumor microenvironment of well-established tumors that constantly antagonizes the anti-tumor immune responses triggered by RT. In this case, additional or combinatorial immunotherapy is needed to attenuate these immunosuppressive networks and, therefore, substantially increases the efficacy of RT. Here, we describe a potentially promising synergistic radio-immunotherapy "in situ tumor vaccination" protocol by antagonizing the tumor-immunosuppressive microenvironment with a combinatorial approach using local RT and IL-12-based TH1 response augmentation.

Intercellular Communication of Tumor Cells and Immune Cells after Exposure to Different Ionizing Radiation Qualities

Ionizing radiation can affect the immune system in many ways. Depending on the situation, the whole body or parts of the body can be acutely or chronically exposed to different radiation qualities. In tumor radiotherapy, a fractionated exposure of the tumor (and surrounding tissues) is applied to kill the tumor cells. Currently, mostly photons, and also electrons, neutrons, protons, and heavier particles such as carbon ions, are used in radiotherapy. Tumor elimination can be supported by an effective immune response. In recent years, much progress has been achieved in the understanding of basic interactions between the irradiated tumor and the immune system. Here, direct and indirect effects of radiation on immune cells have to be considered. Lymphocytes for example are known to be highly radiosensitive. One important factor in indirect interactions is the radiation-induced bystander effect which can be initiated in unexposed cells by expression of cytokines of the irradiated cells and by direct exchange of molecules via gap junctions. In this review, we summarize the current knowledge about the indirect effects observed after exposure to different radiation qualities. The different immune cell populations important for the tumor immune response are natural killer cells, dendritic cells, and CD8+ cytotoxic T-cells. In vitro and in vivo studies have revealed the modulation of their functions due to ionizing radiation exposure of tumor cells. After radiation exposure, cytokines are produced by exposed tumor and immune cells and a modulated expression profile has also been observed in bystander immune cells. Release of damage-associated molecular patterns by irradiated tumor cells is another factor in immune activation. In conclusion, both immune-activating and -suppressing effects can occur. Enhancing or inhibiting these effects, respectively, could contribute to modified tumor cell killing after radiotherapy.

Following the Preclinical Data: Leveraging the Abscopal Effect More Efficaciously

Radiotherapy is employed in the treatment of over 50% of cancer patients. However, this therapy approach is limited to mainly treating localized disease. In 1953, Mole described the remarkable abscopal effect, whereby, localized radiotherapy of a patient’s primary tumor might engender regression of cancer at distant sites, which were not irradiated. Current consensus is that if the abscopal effect can be efficaciously leveraged, it would transform the field of radiation oncology, extending the use of radiotherapy to treatment of both localized and metastatic disease. A close examination of the literature on the abscopal effect proffers a disruptive new hypothesis for consideration in future clinical trials. This hypothesis is that generating a subcutaneous human tumor autograft as the primary tumor may be a more efficacious approach to prime the abscopal effect. Following the preclinical data, the merits and demerits of such an approach are examined in this article.

A meta-analysis of the abscopal effect in preclinical models: Is the biologically effective dose a relevant physical trigger?

BACKGROUND

Preclinical in vivo studies using small animals are considered crucial in translational cancer research and clinical implementation of novel treatments. This is of paramount relevance in radiobiology, especially for any technological developments permitted to deliver high doses in single or oligo-fractionated regimens, such as stereotactic ablative radiotherapy (SABR). In this context, clinical success in cancer treatment needs to be guaranteed, sparing normal tissue and preventing the potential spread of disease or local recurrence. In this work we introduce a new dose-response relationship based on relevant publications concerning preclinical models with regard to delivered dose, fractionation schedule and occurrence of biological effects on non-irradiated tissue, abscopal effects.

METHODS

We reviewed relevant publications on murine models and the abscopal effect in radiation cancer research following PRISMA methodology. In particular, through a log-likelihood method, we evaluated whether the occurrence of abscopal effects may be related to the biologically effective dose (BED). To this aim, studies accomplished with different tumor histotypes were considered in our analysis including breast, colon, lung, fibrosarcoma, pancreas, melanoma and head and neck cancer. For all the tumors, the α / β ratio was assumed to be 10 Gy, as generally adopted for neoplastic cells.

RESULTS

Our results support the hypothesis that the occurrence rate of abscopal effects in preclinical models increases with BED. In particular, the probability of revealing abscopal effects is 50% when a BED of 60 Gy is generated.

CONCLUSION

Our study provides evidence that SABR treatments associated with high BEDs could be considered an effective strategy in triggering the abscopal effect, thus shedding light on the promising outcomes revealed in clinical practice.

Radiation-Induced Enhancement of Antitumor T-cell Immunity by VEGF-Targeted 4-1BB Costimulation

Radiotherapy can elicit systemic immune control of local tumors and distant nonirradiated tumor lesions, known as the abscopal effect. Although this effect is enhanced using checkpoint blockade or costimulatory antibodies, objective responses remain suboptimal. As radiotherapy can induce secretion of VEGF and other stress products in the tumor microenvironment, we hypothesized that targeting immunomodulatory drugs to such products will not only reduce toxicity but also broaden the scope of tumor-targeted immunotherapy. Using an oligonucleotide aptamer platform, we show that radiation-induced VEGF-targeted 4-1BB costimulation potentiated both local tumor control and abscopal responses with equal or greater efficiency than 4-1BB, CTLA-4, or PD1 antibodies alone. Although 4-1BB and CTLA-4 antibodies elicited organ-wide inflammatory responses and tissue damage, VEGF-targeted 4-1BB costimulation produced no observable toxicity. These findings suggest that radiation-induced tumor-targeted immunotherapy can improve the therapeutic index and extend the reach of immunomodulatory agents. Cancer Res; 77(6); 1310-21. ©2017 AACR.

Radiation-induced immune responses: mechanisms and therapeutic perspectives

Recent advancement in the radiotherapy technology has allowed conformal delivery of high doses of ionizing radiation precisely to the tumors while sparing large volume of the normal tissues, which have led to better clinical responses. Despite this technological advancement many advanced tumors often recur and they do so within the previously irradiated regions. How could tumors recur after receiving such high ablative doses of radiation? In this review, we outlined how radiation can elicit anti-tumor responses by introducing some of the cytokines that can be induced by ionizing radiation. We then discuss how tumor hypoxia, a major limiting factor responsible for failure of radiotherapy, may also negatively impact the anti-tumor responses. In addition, we highlight how there may be other populations of immune cells including regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), and tumor-associated macrophages (TAMs) that can be recruited to tumors interfering with the anti-tumor immunity. Finally, the impact of irradiation on tumor hypoxia and the immune responses according to different radiotherapy regimen is also delineated. It is indeed an exciting time to see that radiotherapy is being combined with immunotherapy in the clinic and we hope that this review can add an excitement to the field.

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.

Immune modulation by hypofractionated stereotactic radiation therapy: Therapeutic implications

Stereotactic body radiation therapy (SBRT) has become an attractive treatment modality and a safe, non-invasive alternative to surgery to control primary or secondary malignant tumors. While emphasis has been on the local tumor control as a treatment objective for SBRT, the rare but intriguing observations of abscopal (or out-of-field) effects have pointed to the exciting possibility of activating anti-tumor immunity by using high-dose radiation. This review summarizes the available evidence supporting immune modulation by SBRT alone, as well as its potential combination with immunotherapy. Promising preclinical research has revealed an array of immune changes following SBRT, which could affect the balance between anti-tumor immunity and tumor-promoting immunosuppression. However, shifting this balance in the clinical setting to obtain survival benefits has rarely been achieved so far, emphasizing the need for a better understanding of the interactions between high-dose radiotherapy and immunity or immunotherapy. Nevertheless, the combination of SBRT with immunotherapy, particularly with immune checkpoint blockers, has the clear potential to substantially increase the rate of abscopal effects. This warrants further research in this area, both in mechanistic preclinical studies and in clinical trials incorporating correlative studies.

[Alpha-Radioimmunotherapy: principle and relevance in anti-tumor immunity]

Alpha-radioimmunotherapy (α-RIT) is a targeted anti-tumor therapy using usually a monoclonal antibody specific for a tumor antigen that is coupled to an α-particle emitter. α-emitters represent an ideal tool to eradicate disseminated tumors or metastases. Recent data demonstrate that ionizing radiation in addition to its direct cytotoxic ability can also induce an efficient anti-tumor immunity. This suggests that biologic effects on irradiated tissues could be used to potentiate immunotherapy efficacy and opens the way for development of new therapies combining α-RIT and different types of immunotherapy.

Abscopal Effects and Yttrium-90 Radioembolization

We present the case of an 80-year-old male with squamous cell carcinoma with bilobar hepatic metastases who underwent targeted Yttrium-90 radioembolization of the right hepatic lobe lesion. Subsequently, there was complete regression of the nontargeted, left hepatic lobe lesion. This may represent the first ever reported abscopal effect in radioembolization. The abscopal effect refers to the phenomenon of tumor response in nontargeted sites after targeted radiotherapy. In this article, we briefly review the immune-mediated mechanisms responsible for the abscopal effect.

Radio-Immunotherapy-Induced Immunogenic Cancer Cells as Basis for Induction of Systemic Anti-Tumor Immune Responses - Pre-Clinical Evidence and Ongoing Clinical Applications

Radiotherapy (RT) primarily aims to locally destroy the tumor via the induction of DNA damage in the tumor cells. However, the so-called abscopal, namely systemic and immune–mediated, effects of RT move over more and more in the focus of scientists and clinicians since combinations of local irradiation with immune therapy have been demonstrated to induce anti-tumor immunity. We here summarize changes of the phenotype and microenvironment of tumor cells after exposure to irradiation, chemotherapeutic agents, and immune modulating agents rendering the tumor more immunogenic. The impact of therapy-modified tumor cells and damage-associated molecular patterns on local and systemic control of the primary tumor, recurrent tumors, and metastases will be outlined. Finally, clinical studies affirming the bench-side findings of interactions and synergies of radiation therapy and immunotherapy will be discussed. Focus is set on combination of radio(chemo)therapy (RCT) with immune checkpoint inhibitors, growth factor inhibitors, and chimeric antigen receptor T-cell therapy. Well-deliberated combination of RCT with selected immune therapies and growth factor inhibitors bear the great potential to further improve anti-cancer therapies.