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Checkpoint blockade immunotherapy has received mainstream attention as a result of striking and durable clinical responses in some patients with metastatic disease and a reasonable response rate in many tumour types. The activity of checkpoint blockade immunotherapy is not restricted to melanoma or lung cancer, and additional indications are expected in the future, with responses already reported in renal cancer, bladder cancer, and Hodgkin's lymphoma among many others. Additionally, the interactions between radiation and the immune system have been investigated, with several studies describing the synergistic effects on local and distant tumour control when radiation therapy is combined with immunotherapy. Clinical enthusiasm for this approach is strengthened by the many ongoing trials combining immunotherapy with definitive and palliative radiation. Herein, we discuss the biological and mechanistic rationale behind combining radiation with checkpoint blockade immunotherapy, with a focus on the preclinical data supporting this potentially synergistic combination. We explore potential hypotheses and important considerations for clinical trial designs. Finally, we reintroduce the notion of radiosensitising immunotherapy, akin to radiosensitising chemotherapy, as a potential definitive therapeutic modality.

Background Insufficient migration and activation of tumor specific effector T cells in the tumor is one of the main reasons for inadequate host anti-tumor immune response. External radiation seems to induce inflammation and activate the immune response. This phase I/II clinical trial aims to evaluate whether low dose single fraction radiotherapy can improve T cell associated antitumor immune response in patients with colorectal liver metastases. Methods/Design This is an investigator-initiated, prospective randomised, 4-armed, controlled Phase I/II trial. Patients undergoing elective hepatic resection due to colorectal cancer liver metastasis will be enrolled in the study. Patients will receive 0 Gy, 0.5 Gy, 2 Gy or 5 Gy radiation targeted to their liver metastasis. Radiation will be applied by external beam radiotherapy using a 6 MV linear accelerator (Linac) with intensity modulated radiotherapy (IMRT) technique two days prior to surgical resection. All patients admitted to the Department of General-, Visceral-, and Transplantion Surgery, University of Heidelberg for elective hepatic resection are consecutively screened for eligibility into this trial, and written informed consent is obtained before inclusion. The primary objective is to assess the effect of active local external beam radiation dose on, tumor infiltrating T cells as a surrogate parameter for antitumor activity. Secondary objectives include radiogenic treatment toxicity, postoperative morbidity and mortality, local tumor control and recurrence patterns, survival and quality of life. Furthermore, frequencies of systemic tumor reactive T cells in blood and bone marrow will be correlated with clinical outcome. Discussion This is a randomized controlled patient blinded trial to assess the safety and efficiency of low dose radiotherapy on metastasis infiltrating T cells and thus potentially enhance the antitumor immune response. Trial registration ClinicalTrials.gov: NCT01191632

The efficacy and side effects of radiotherapy (RT) depend on parameters like dose and the volume of irradiated tissue. RT induces modulations of the tumor immune microenvironment (TIME) that are dependent on the dose. Low dose RT (LDRT, i.e., single doses of 0.5–2 Gy) has been shown to promote immune infiltration into the tumor. Here we hypothesize that partial tumor irradiation combining the immunostimulatory/non-lethal properties of LDRT with cell killing/shrinkage properties of high dose RT (HDRT) within the same tumor mass could enhance anti-tumor responses when combined with immunomodulators. In models of colorectal and breast cancer in immunocompetent female mice, partial irradiation (PI) with millimetric precision to deliver LDRT (2 Gy) and HDRT (16 Gy) within the same tumor induces substantial tumor control when combined with anti-PD1. Using flow cytometry, cytokine profiling and single-cell RNA sequencing, we identify a crosstalk between the TIME of the differentially irradiated tumor volumes. PI reshapes tumor-infiltrating CD8 + T cells into more cytotoxic and interferon-activated phenotypes but also increases the infiltration of pro-tumor neutrophils driven by CXCR2. The combination of the CXCR2 antagonist SB225002 with PD1 blockade and PI improves tumor control and mouse survival. Our results suggest a strategy to reduce RT toxicity and improve the therapeutic index of RT and immune checkpoint combinations. Low dose-radiation therapy (LDRT) can promote anti-tumor immune responses. Here the authors propose to combine the immunostimulatory properties of LDRT with the cell killing/shrinkage properties of high dose RT within the same tumor mass as a strategy to optimize RT-induced anti-tumor immune responses.

Immune checkpoint inhibitors targeting programmed cell death 1 (PD-1), programmed cell death ligand-1 (PD-L1), and others have shown potent clinical efficacy and have revolutionized the treatment protocols of a broad spectrum of tumor types, especially non–small-cell lung cancer (NSCLC). Despite the substantial optimism of treatment with PD-1/PD-L1 inhibitors, there is still a large proportion of patients with advanced NSCLC who are resistant to the inhibitors. Preclinical and clinical trials have demonstrated that radiotherapy can induce a systemic antitumor immune response and have a great potential to sensitize refractory “cold” tumors to immunotherapy. Stereotactic body radiation therapy (SBRT), as a novel radiotherapy modality that delivers higher doses to smaller target lesions, has shown favorable antitumor effects with significantly improved local and distant control as well as better survival benefits in various solid tumors. Notably, research has revealed that SBRT is superior to conventional radiotherapy, possibly because of its more powerful immune activation effects. Thus, PD-1/PD-L1 inhibitors combined with SBRT instead of conventional radiotherapy might be more promising to fight against NSCLC, further achieving more favorable survival outcomes. In this review, we focus on the underlying mechanisms and recent advances of SBRT combined with PD-1/PD-L1 inhibitors with an emphasis on some future challenges and directions that warrant further investigation.

A promising strategy for cancer immunotherapy is to disrupt key pathways regulating immune tolerance, such as cytotoxic T lymphocyte-associated protein 4 (CTLA-4). However, the determinants of response to anti-CTLA-4 mAb treatment remain incompletely understood. In murine models, anti-CTLA-4 mAbs alone fail to induce effective immune responses to poorly immunogenic tumors but are successful when combined with additional interventions, including local ionizing radiation (IR) therapy. We employed an established model based on control of a mouse carcinoma cell line to study endogenous tumor-infiltrating CD8+ T lymphocytes (TILs) following treatment with the anti-CTLA-4 mAb 9H10. Alone, 9H10 monotherapy reversed the arrest of TILs with carcinoma cells in vivo. In contrast, the combination of 9H10 and IR restored MHC class I-dependent arrest. After implantation, the carcinoma cells had reduced expression of retinoic acid early inducible-1 (RAE-1), a ligand for natural killer cell group 2D (NKG2D) receptor. We found that RAE-1 expression was induced by IR in vivo and that anti-NKG2D mAb blocked the TIL arrest induced by IR/9H10 combination therapy. These results demonstrate that anti-CTLA-4 mAb therapy induces motility of TIL and that NKG2D ligation offsets this effect to enhance TILs arrest and antitumor activity.

Hydrogen peroxide (H 2 O 2 ) induces oxidative stress and cytotoxicity, and can be used for treating cancers in combination with radiotherapy. A product comprising H 2 O 2 and sodium hyaluronate has been developed as a radiosensitizer. However, the effects of H 2 O 2 on antitumor immunity remain unclear. To investigate the effects of H 2 O 2 , especially the abscopal effect when combined with radiotherapy (RT), we implanted murine tumor cells simultaneously in two locations in mouse models: the hind limb and back. H 2 O 2 mixed with sodium hyaluronate was injected intratumorally, followed by irradiation only at the hind limb lesion. No treatment was administered to the back lesion. The H 2 O 2 /RT combination significantly reduced tumor growth at the noninjected/nonirradiated site in the back lesion, whereas H 2 O 2 or RT individually did not reduce tumor growth. Flow cytometric analyses of the tumor‐draining lymph nodes in the injected/irradiated areas showed that the number of dendritic cells increased significantly with maturation in the H 2 O 2 /RT combination group. In addition, analyses of tumor‐infiltrating lymphocytes showed that the number of CD8 + (cluster of differentiation 8) T cells and the frequency of IFN‐γ + (interferon gamma) CD8 + T cells were higher in the noninjected/nonirradiated tumors in the H 2 O 2 /RT group compared to those in the other groups. PD‐1 (programmed death receptor 1) blockade further increased the antitumor effect against noninjected/nonirradiated tumors in the H 2 O 2 /RT group. Intratumoral injection of H 2 O 2 combined with RT therefore induces an abscopal effect by activating antitumor immunity, which can be further enhanced by PD‐1 blockade. These findings promote the development of H 2 O 2 /RT therapy combined with cancer immunotherapies, even for advanced cancers.

Human Papillomavirus (HPV)-negative head and neck squamous cell carcinoma (HNSCC) remains a challenging malignancy, with radiotherapy, alone or combined with immune checkpoint inhibitors, often failing to achieve durable disease control. Here, by conducting longitudinal multi-omic analyses of pre- and post-radiation biopsies from patients receiving a pre-operative hypofractionated radiation regimen, we uncover that radiation rapidly depletes a subpopulation of tumor-infiltrating lymphocytes (TIL), characterized by a proliferative, cytotoxic, and tissue-resident gene signature (T Prolif_Tox ). We provide multi-dimensional evidence for tumor antigen-specificity of T Prolif_Tox clonotypes and show that post-radiation tumors are instead repopulated by regulatory and non-specific clones. Finally, TIL depletion correlates with radiorecurrent disease after conventional radiation, emphasizing the potential impact of radiation-induced TIL loss regardless of fractionation. Thus, this study provides key insights into radiotherapy-induced alterations in the immune microenvironment that drive immunologic radioresistance and proposes restoring tumor antigen-specific T cell clonotypes as a strategy to improve radioimmunotherapy responses in HNSCC. Combining radiation therapy (RT) with immunotherapy has had limited therapeutic benefits in the treatment of head and neck cancer (HNSCC). Here, the authors present a multi-omics analysis of patient biopsies pre- and post- hypofractionated RT and uncover RT-mediated depletion of tumor-reactive CD8+ T cells as the underlying cause of immunologic radioresistance in HNSCC.

Antibodies targeting the T-cell immune checkpoint cytotoxic T-lymphocyte antigen-4 (CTLA4) enhance the effectiveness of radiotherapy for melanoma patients, but many remain resistant. To further improve response rates, we explored combining anti-CTLA4 blockade with antisense suppression of CD47, an inhibitory receptor on T cells that limit T-cell receptor signaling and killing of irradiated target cells. Human melanoma data from The Cancer Genome Atlas revealed positive correlations between CD47 mRNA expression and expression of T-cell regulators including CTLA4 and its counter receptors CD80 and CD86. Antisense suppression of CD47 on human T cells in vitro using a translational blocking morpholino (CD47 m) alone or combined with anti-CTLA4 enhanced antigen-dependent killing of irradiated melanoma cells. Correspondingly, the treatment of locally irradiated B16F10 melanomas in C57BL/6 mice using combined blockade of CD47 and CTLA4 significantly increased the survival of mice relative to either treatment alone. CD47 m alone or in combination with anti-CTLA4 increased CD3+ T-cell infiltration in irradiated tumors. Anti-CTLA4 also increased CD3+ and CD8+ T-cell infiltration as well as markers of NK cells in non-irradiated tumors. Anti-CTLA4 combined with CD47 m resulted in the greatest increase in intratumoral granzyme B, interferon-γ, and NK-cell marker mRNA expression. These data suggest that combining CTLA4 and CD47 blockade could provide a survival benefit by enhancing adaptive T- and NK-cell immunity in irradiated tumors.

Immunotherapy has revolutionized cancer treatment, offering new hope for many patients. However, while some individuals show remarkable responses, the overall success rate remains limited. This has spurred interest in combination therapies, particularly with established treatments like radiation therapy (RT), to improve outcomes. RT is a cornerstone of cancer therapy and known to influence the immune landscape, yet a systematic characterization of its effects on tumor-infiltrating leukocytes (TILs) and a rationale-based therapy is still lacking. In this study, we employed a diverse set of pre-clinical syngeneic murine tumor models with varying immune profiles to investigate the immunological impact of tumor targeted RT. We observed that immunologically ‘hot’ tumors showed stronger tumor growth inhibition (TGI) after RT compared to ‘cold’ tumors. Additionally, RT induced both pro- and anti-inflammatory shifts within the tumor immune microenvironment. Importantly, RT led to an intra-tumoral increase in proliferating CD8 + T cells, while the population of proliferating macrophages was notably reduced. To identify immune-modulatory pathways that shape the response to RT across different tumor immune contexts, we tested RT in HPK1 (Hematopoietic Progenitor Kinase 1) and STING (Stimulator of Interferon Genes) deficient mice. These experiments revealed that STING deficiency compromises TGI in tumors with a high baseline population of myeloid cells expressing an interferon response signature. Moreover, we identified a synergistic effect on survival in tumor-bearing mice when combining HPK1 deficiency with RT. Thus, RT promotes expansion of cytotoxic T cells while limiting macrophage proliferation, with therapeutic outcomes strongly influenced by STING and HPK1 pathways. Collectively, these results highlight the complex interplay between RT, tumor immune microenvironment and response to therapy, offering potential avenues for novel therapeutic combinations.

Background. Radioimmunotherapy has become one of the most promising strategies for cancer treatment. Preclinical and clinical studies have demonstrated that antiangiogenic therapy can improve the efficacy of immunotherapy and sensitize radiotherapy through a variety of mechanisms. However, it is undefined whether angiogenesis inhibitors can enhance the effect of radioimmunotherapy. In this study, we aim to explore the role of anlotinib (AL3818) on the combination of radiotherapy and immune checkpoint inhibitors in Lewis lung carcinoma mouse. Methods. C57BL/6 mouse subcutaneous tumor model was used to evaluate the ability of different treatment regimens in tumor growth control. Immune response and immunophenotyping including the quantification and activation were determined by flow cytometry, multiplex immunofluorescence, and multiplex immunoassay. Results. Triple therapy (radiotherapy combined with anti-PD-L1 and anlotinib) increased tumor-infiltrating lymphocytes and reversed the immunosuppressive effect of radiation on the tumor microenvironment in mouse model. Compared with radioimmunotherapy, the addition of anlotinib also boosted the infiltration of CD8+ T cells and M1 cells and caused a decrease in the number of MDSCs and M2 cells in mice. The levels of IFN-gamma and IL-18 were the highest in the triple therapy group, while the levels of IL-23, IL-13, IL-1 beta, IL-2, IL-6, IL-10, and Arg-1 were significantly reduced. NF-κB, MAPK, and AKT pathways were downregulated in triple therapy compared with radioimmunotherapy. Thus, the tumor immune microenvironment was significantly improved. As a consequence, triple therapy displayed greater benefit in antitumor efficacy. Conclusion. Our findings indicate that anlotinib might be a potential synergistic treatment for radioimmunotherapy to achieve better antitumor efficacy in NSCLC patients by potentiating the tumor immune microenvironment.