Targeted Accumulation of Macrophages Induced by Microbeam Irradiation in a Tissue-Dependent Manner

Proceedings of the National Cancer Institute Workshop on combining immunotherapy with radiotherapy: challenges and opportunities for clinical translation

Radiotherapy both promotes and antagonises tumour immune recognition. Some clinical studies show improved patient outcomes when immunotherapies are integrated with radiotherapy. Safe, greater than additive, clinical response to the combination is limited to a subset of patients, however, and how radiotherapy can best be combined with immunotherapies remains unclear. The National Cancer Institute-Immuno-Oncology Translational Network-Society for Immunotherapy of Cancer-American Association of Immunology Workshop on Combining Immunotherapy with Radiotherapy was convened to identify and prioritise opportunities and challenges for radiotherapy and immunotherapy combinations. Sessions examined the immune effects of radiation, barriers to anti-tumour immune response, previous clinical trial data, immunological and computational assessment of response, and next-generation radiotherapy-immunotherapy combinations. Panel recommendations included: developing and implementing patient selection and biomarker-guided approaches; applying mechanistic understanding to optimise delivery of radiotherapy and selection of immunotherapies; using rigorous preclinical models including companion animal studies; embracing data sharing and standardisation, advanced modelling, and multidisciplinary cross-institution collaboration; interrogating clinical data, including negative trials; and incorporating novel clinical endpoints and trial designs.

The Impact of Synchrotron Microbeam Radiation Therapy Combined With Broad Beam in a Preclinical Breast Cancer Model

Purpose

Both local tumor control and distant metastasis are important indicators of the efficacy of radiation therapy treatment. Synchrotron microbeam radiation therapy (MRT), spatially fractionated radiation delivered at ultrahigh dose rates, shows remarkable normal tissue sparing with excellent local control in some models. Some MRT regimens trigger an antitumor immune response that contributes not only to the local but also to systemic treatment efficacy. Despite recent advances in the treatment of primary breast cancer, metastatic disease is still the major cause of treatment failure in the clinic. Here, in an aggressive preclinical triple-negative breast cancer model, we compared local tumor response and metastasis following different MRT treatment programs.

Methods and Materials

4T1.2 mouse mammary tumors were treated with 300 Gy peak/7 Gy valley dose MRT and/or 8 Gy broad beam (BB) radiation, all delivered as daily fractionated programs (3 consecutive daily sessions of either MRT or BB or 1 MRT combined with 2 BB sessions, the first or last of the 3 fractions). The mice were euthanized on day 9 post last irradiation, when unirradiated control animals reached an ethical endpoint. Primary tumors were collected to evaluate immune cell prevalence, while lungs, spinal cords, and locoregional lymph nodes were collected to measure metastatic burden. In parallel, local tumor growth and survival were monitored.

Results

The combined MRT/BB treatment shifted the balance between pro- and antitumorigenic macrophages toward the accumulation of antitumorigenic macrophages in the tumor. Monitoring of the tumor volume and animal health indicated the benefit of the combined MRT/BB treatment for local control and treatment tolerance, while animal survival was only marginally longer for one combined schedule. The metastatic burden was similar for all 4 treatment schedules.

Conclusions

The addition of a single MRT to BB treatment improved the primary tumor response. This provides a basis for future experiments incorporating adjuvant immunotherapy or chemotherapy to improve local and systemic treatment outcomes.

Towards melanoma in situ vaccination with multiple ultra-narrow X-ray beams

Despite the recent progress, current treatment modalities are not able to eradicate cancer. We show that Microbeam Radiotherapy (MRT), an innovative type of Spatially Fractionated Radiotherapy, can control murine melanoma by activating the host's own immune system. The beneficial effects are very pronounced in comparison to uniform radiotherapy traditionally employed in the clinic. Our results show that MRT increased antigen presentation, activating Cytotoxic T Lymphocytes (CTLs) which are essential to MRT's treatment efficacy in melanoma. Depletion of CTLs abrogated treatment response. Multiplex nucleic acid hybridization technology revealed key features of lymphocyte populations such as proliferation, differentiation, and ligand-receptor interactions. In addition, CTLs were shown to be essential for locoregional metastatic control and systemic abscopal effects confirmed by activation of antigen presenting cells and CTL trafficking in the tumour-draining lymph nodes. MRT also showed a synergistic effect with immunotherapy. Overall, MRT induces a robust antitumour immune response, acting like an in situ vaccination, which could be exploited to treat a variety of treatment-resistant malignancies.

Therapeutic applications of stem cell-derived exosomes in radiation-induced lung injury

Radiation-induced lung injury is a common complication of chest tumor radiotherapy; however, effective clinical treatments are still lacking. Stem cell-derived exosomes, which contain various signaling molecules such as proteins, lipids, and miRNAs, not only retain the tissue repair and reconstruction properties of stem cells but also offer improved stability and safety. This presents significant potential for treating radiation-induced lung injury. Nonetheless, the clinical adoption of stem cell-derived exosomes for this purpose remains limited due to scientific, practical, and regulatory challenges. In this review, we highlight the current pathology and therapies for radiation-induced lung injury, focusing on the potential applications and therapeutic mechanisms of stem cell-derived exosomes. We also discuss the limitations of existing stem cell-derived exosomes and outline future directions for exosome-based treatments for radiation-induced lung injury.