Low-dose total body irradiation augments the therapeutic effect of interleukin-2 in a mouse model for metastatic malignant melanoma

Radiation dose, schedule, and novel systemic targets for radio-immunotherapy combinations

Immunotherapy combinations are being investigated to expand the benefit of immune checkpoint blockade across many cancer types. Radiation combinations, in particular using stereotactic body radiotherapy, are of keen interest because of underlying mechanistic rationale, safety, and availability as a standard of care in certain cancers. In addition to direct tumor cytotoxicity, radiation therapy has immunomodulatory effects such as induction of immunogenic cell death, enhancement of antigen presentation, and expansion of the T-cell receptor repertoire as well as recruitment and increased activity of tumor-specific effector CD8+ cells. Combinations of radiation with cytokines and/or chemokines and anti-programmed death 1 and anticytotoxic T-lymphocyte antigen 4 therapies have demonstrated safety and feasibility, as well as the potential to improve long-term outcomes and possibly induce out of irradiated field or abscopal responses. Novel immunoradiotherapy combinations represent a promising therapeutic approach to overcome radioresistance and further enhance systemic immunotherapy. Potential benefits include reversing CD8+ T-cell exhaustion, inhibiting myeloid-derived suppressor cells, and reversing M2 macrophage polarization as well as decreasing levels of colony-stimulating factor-1 and transforming growth factor-β. Here, we discuss current data and mechanistic rationale for combining novel immunotherapy agents with radiation therapy.

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

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

Radiotherapy in Combination With Cytokine Treatment

Radiotherapy (RT) plays an important role in the management of cancer patients. RT is used in more than 50% of patients during the course of their disease in a curative or palliative setting. In the past decades it became apparent that the abscopal effect induced by RT might be dependent on the activation of immune system, and that the induction of immunogenic cancer cell death and production of danger-associated molecular patterns from dying cells play a major role in the radiotherapy-mediated anti-tumor efficacy. Therefore, the combination of RT and immunotherapy is of a particular interest that is reflected in designing clinical trials to treat patients with various malignancies. The use of cytokines as immunoadjuvants in combination with RT has been explored over the last decades as one of the immunotherapeutic combinations to enhance the clinical response to anti-cancer treatment. Here we review mainly the data on the efficacy of IFN-α, IL-2, IL-2-based immunocytokines, GM-CSF, and TNF-α used in combinations with various radiotherapeutic techniques in clinical trials. Moreover, we discuss the potential of IL-15 and its analogs and IL-12 cytokines in combination with RT based on the efficacy in preclinical mouse tumor models.

Radiation effects on antitumor immune responses: current perspectives and challenges

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

Clinical trials exploring the benefit of immunotherapy and radiation in cancer treatment: A review of the past and a look into the future

Cancer immunotherapy is rapidly redefining the standard of cancer care. The role of radiation therapy in eliciting antitumoral immune response is also being actively investigated in combination with various immunotherapeutic agents to exploit potential synergy between the 2 modalities. In this review, we summarize the rationale and results of past and ongoing clinical trials that combined the use of radiation therapy and immunogenic agents such as vaccines, cytokines, immune checkpoint inhibitors, costimulatory agonists, and myeloid activators.

Radiation meets immunotherapy - a perfect match in the era of combination therapy?

PURPOSE

This review focuses on recent advances in the field of combining radiation with immunotherapy for the treatment of malignant diseases, since various combinatorial cancer therapy approaches have lately proven highly successful.

RESULTS

With initial case reports and anecdotes progressively converting into solid clinical data, interest in cancer immunotherapy (CIT) has risen steeply. Especially immune checkpoint blockade therapies have recently celebrated tremendous successes in the treatment of severe malignancies resistant to conventional treatment strategies. Nevertheless, the high variability of patient responses to CIT remains a major hurdle, clearly indicating an urgent need for improvement. It has been suggested that successful cancer therapy most probably involves combinatorial treatment approaches. Radiotherapy (RT) has been proposed as a powerful partner for CIT due to its broad spectrum of immune modulatory characteristics. Several preclinical studies, supported by an increasing number of clinical observations, have demonstrated synergistic interactions between RT and CIT resulting in significantly improved therapy outcomes.

CONCLUSIONS

Numerous reports have shown that radiation is capable of tipping the scales from tumor immune evasion to elimination in different tumor types. The next puzzle to be solved is the question of logistics - including types, schedule and dosage of combinatorial RT and CIT strategies.

Combinations of radiation therapy and immunotherapy for melanoma: a review of clinical outcomes

Radiation therapy has long played a role in the management of melanoma. Recent advances have also demonstrated the efficacy of immunotherapy in the treatment of melanoma. Preclinical data suggest a biologic interaction between radiation therapy and immunotherapy. Several clinical studies corroborate these findings. This review will summarize the outcomes of studies reporting on patients with melanoma treated with a combination of radiation therapy and immunotherapy. Vaccine therapies often use irradiated melanoma cells, and may be enhanced by radiation therapy. The cytokines interferon-α and interleukin-2 have been combined with radiation therapy in several small studies, with some evidence suggesting increased toxicity and/or efficacy. Ipilimumab, a monoclonal antibody which blocks cytotoxic T-lymphocyte antigen-4, has been combined with radiation therapy in several notable case studies and series. Finally, pilot studies of adoptive cell transfer have suggested that radiation therapy may improve the efficacy of treatment. The review will demonstrate that the combination of radiation therapy and immunotherapy has been reported in several notable case studies, series and clinical trials. These clinical results suggest interaction and the need for further study.

The effect of ionizing radiation on the homeostasis and functional integrity of murine splenic regulatory T cells

OBJECTIVE

Radiotherapy affects antitumor immune responses; therefore, it is important to study radiation effects on various compartments of the immune system. Here we report radiation effects on the homeostasis and function of regulatory T (Treg) cells, which are important in down-regulating antitumor immune responses.

METHODS

C57Bl/6 mice were irradiated with 2 Gy and alterations in splenic lymphocyte fractions analyzed at different intervals.

RESULTS

Total CD4+ numbers showed stronger decrease after irradiation than CD4+Foxp3+ Tregs. Tregs were less prone to radiation-induced apoptosis than CD4+Foxp3- T cells. The ratio of CD4+Foxp3- and CD4+Foxp3+ fractions within the proliferating CD4+ pool progressively changed from 74:26 in control animals to 59:41 eleven days after irradiation, demonstrating a more dynamic increase in the proliferation and regeneration of the Treg pool. The CD4+Foxp3+ fraction expressing cell-surface CTLA4, an antigen associated with Treg cell activation increased from 5.3 % in unirradiated mice to 10.5 % three days after irradiation. The expression of IL-10 mRNA was moderately upregulated, while TGF-β expression was not affected. On the other hand, irradiation reduced Treg capacity to suppress effector T cell proliferation by 2.5-fold.

CONCLUSION

Tregs are more radioresistant, less prone to radiation-induced apoptosis, and have faster repopulation kinetics than CD4+Foxp3- cells, but irradiated Tregs are functionally compromised, having a reduced suppressive capacity.

Tetracycline-regulated intratumoral expression of interleukin-3 enhances the efficacy of radiation therapy for murine prostate cancer

The aim of this study was to investigate means of increasing the efficiency with which cancer cell death following local radiation therapy (RT) is translated into the generation of tumor immunity since, if this were to be achieved, it would be expected to enhance the rates of disease-free recurrence and survival. Our investigations centered around the use of interleukin-3 (IL-3), expressed intratumorally using an inducible adenoviral vector, to alter the immunogenicity of established murine TRAMP-C1 prostate cancer receiving a course of fractionated local RT (7 Gy per fraction per day for 5 days). Because high systemic levels of IL-3 can be associated with toxicity, a tetracycline-regulated gene delivery system was employed. The results show that while intratumoral IL-3 expression or RT alone caused a modest delay in TRAMP-C1 tumor growth, the combination was synergistic with 50% of mice being cured and developing a long-term, tumor-specific state of immunity. Immunological analyses performed on splenic lymphocytes demonstrated that, compared to RT or IL-3 alone, combined treatment significantly increased the number of tumor-specific IFN-gamma-secreting and cytotoxic T cells. The study demonstrates that tetracycline-regulated IL-3 gene expression within tumors can enhance the immune response to prostate cancer and this can augment the efficacy of a course of RT without additional side effects.

A phase II trial of low-dose total body irradiation and subcutaneous interleukin-2 in metastatic melanoma

BACKGROUND AND PURPOSE

Our own experimental data suggests a therapeutic synergism between low-dose total body irradiation (LTBI) and interleukin-2 (IL-2).

PATIENTS AND METHODS

Forty-five patients received a maximum of 2 cycles of high dose subcutaneous (s.c.) IL-2 and LTBI. One treatment cycle included 5 weeks treatment followed by 2 weeks break and composed of a single radiation fraction 0.1 Gy on days 1, 8, 22 and 30 and IL-2: 18 MU x 2 daily s.c. on days 2 to 5 and days 16-19 as well as 9 MU x 2 daily s.c. on days 9-12 and 31-34. In 17 patients, flow cytometric analyses of the various subpopulations of immune cells were done on blood samples before the first LTBI fraction and 24h after LTBI as well as after the first week of treatment.

RESULTS

Two patients (4.4%) had a partial response (PR) and 13 patients (29%) had stable disease (SD). The duration of the partial remission and stable disease did not exceed 3 months. The median overall survival was 5.8 months (95% CI, 4-8 months). Thirty-four of the 58 treatment cycles (74%) were given in 100% of the intended dose without modification or delay. The dose was modified in 15 cycles (26%) because of progression (6), liver toxicity (3), CNS toxicity (2), thrombocytopenia (1), lung morbidity (1) and itching (1). There were no treatment-related deaths. Flowcytometry data showed a significant increase in the percentage of cells carrying the beta chain of IL-2 receptor (CD122+), a significant increase in the percentage of NK cells (CD56+ cells) as well as a significant reduction in the percentage of B cells (CD20+) and monocytes (CD14+).

CONCLUSIONS

This LTBI and IL-2 regimen was well tolerated, however it cannot be recommended because of its low clinical efficacy. No indication of increased efficacy or altered toxicity was seen using LTBI.

Combined radiation therapy and dendritic cell vaccine for treating solid tumors with liver micro-metastasis

BACKGROUND

Tumor metastasis and relapse are major obstacles in combating human malignant diseases. Neither radiotherapy alone nor injection of dendritic cells (DCs) can successfully overcome this problem. Radiation induces tumor cell apoptosis and necrosis, resulting in the release of tumor antigen and danger signals, which are favorable for DC capturing antigens and maturation. Hence, the strategy of combined irradiation and DC vaccine may be a novel approach for treating human malignancies and early metastasis.

METHODS

To develop an effective combined therapeutic approach, we established a novel concomitant local tumor and liver metastases model through subcutaneous (s.c.) and intravenous (i.v.) injection. We selected the optimal time for DC injection after irradiation and investigated the antitumor effect of combining irradiation with DC intratumoral injection and the related mechanism.

RESULTS

Combined treatment with radiotherapy and DC vaccine could induce a potent antitumor immune response, resulting in a significant decrease in the rate of local tumor relapse and the numbers of liver metastases. The related mechanisms for this strong antitumor immunity of this combined therapy might be associated with the production of apoptotic and necrotic tumor antigens and heat shock proteins after irradiation, phagocytosis, migration and maturation of DCs, and induction of more efficient tumor-specific cytotoxic T lymphocyte activity through a cross-presentation pathway.

CONCLUSIONS

Co-administration of local irradiation and intratumoral DC injection may be a promising strategy for treating radiosensitive tumors and eliminating metastasis in the clinic.

Bone marrow transplantation can attenuate the progression of mesangial sclerosis

Bone marrow (BM) transplantation has been shown to provide beneficial effects in injured organs, including heart, liver, and kidney. We explored the therapeutic potential of BM transplantation (BMT) in Wilms' tumor suppressor 1 (Wt1) heterozygous mice, which represent a model of mesangial sclerosis. After transplantation of wild-type BM, there is statistically significantly lower urinary albumin and increased survival in Wt1+/- recipients. Control BMT using Wt1+/- donors showed no significant beneficial effects. The long-term beneficial effect of BMT was dependent on the dose of irradiation applied to the recipients before BMT. At a lethal dose of 1,000 cGy, the decrease in albuminuria and prolongation of lifespan in Wt1+/- mice were transient, with maximal amelioration at 12 weeks and resumption of albuminuria by 24 weeks after BMT. This was, at least in part, due to irradiation and not Wt1 heterozygosity because wild-type recipients also developed albuminuria within 24 weeks of BMT with 1,000 cGy. In contrast, Wt1+/- mice transplanted after 400 cGy showed long-term improvement in albuminuria and lifespan. Approximately 0.4% of podocytes were marrow derived, a level that is unlikely to be responsible for the therapeutic effects. In addition, donor BM cells formed rings surrounding the glomeruli, and approximately one third of the cells in these rings were macrophages. In conclusion, transplantation of wild-type BM attenuates progression of mesangial sclerosis in the Wt1+/- model of renal disease, and the mechanism by which this occurs may involve engraftment of BM-derived cells in the renal parenchyma.

Tumour burden and interleukin-2 dose affect the interaction between low-dose total body irradiation and interleukin 2

Low-dose total body irradiation (LTBI) has a synergistic immune-mediated antitumour effect when used in combination with interleukin 2 (IL-2) in a murine metastatic malignant melanoma model. To optimise the use of this combination treatment this study was performed to test the effect of tumour burden and dose of both LTBI and IL-2 on the therapeutic potential of this treatment strategy. Ten-week-old female C57BL/6 mice were inoculated intravenously (day 0) with 1 million B16F1 malignant melanoma cells. Groups of mice received no treatment, a single fraction of LTBI alone, IL-2 treatment alone, or a combination of LTBI and IL-2. Two doses of LTBI and IL-2 were tested. LTBI was given on day +10 and IL-2 treatment started on day +11. On day +18 the mice were killed. The lungs were removed and analysed for tumour burden. Lung sections were also tested for infiltrating leucocytes using immunohistochemical staining. In one experiment, mice were treated at day +7 with low-dose IL-2 with and without LTBI. LTBI (in the two tested doses) showed no independent therapeutic effects. An IL-2 dose of 300,000 Cetus units (CU) that was effective and showed synergism with LTBI when mice were treated on day +7 failed to show a therapeutic effect when mice were treated on day +10, at which time the initial tumour burden had doubled. High-dose IL-2 (600,000 CU), in contrast, led to a significant reduction in metastatic burden compared to the control group. Combining high-dose IL-2 with LTBI led to a further significant reduction in tumour burden. Moreover, this combination was associated with a less severe vascular leakage syndrome compared to IL-2 alone. IL-2 and combination treatment was associated with an increase in the number of tumour-infiltrating immune cells, but only the number of tumour-infiltrating natural killer cells reflected therapeutic efficacy. It was concluded that tumour burden at the time of treatment and IL-2 dose are two crucial factors affecting the synergism between LTBI and IL-2. The combination may not only be more effective than IL-2 alone but also less toxic.