Innate immunity: Looking beyond T-cells in radiation and immunotherapy combinations

Radiation therapy is an established and effective anti-cancer treatment modality. Extensive pre-clinical experimentation has demonstrated that the pro-inflammatory properties of irradiation may be synergistic with checkpoint immunotherapy. Radiation induces double-stranded DNA breaks (dsDNA). Sensing of the dsDNA activates the cGAS/STING pathway, producing Type 1 interferons essential to recruiting antigen-presenting cells (APCs). Radiation promotes cytotoxic CD8 T-cell recruitment by releasing tumour-associated antigens captured and cross-presented by surveying antigen-presenting cells. Radiation-induced vascular normalisation may further promote T-cell trafficking and drug delivery. Radiation is also immunosuppressive. Recruitment of regulatory T cells (Tregs) and innate cells such as myeloid-derived suppressive cells (m-MDSCs) all counteract the immunostimulatory properties of radiation. Many innate immune cell types operate at the interface of the adaptive immune response. Innate immune cells, such as m-MDSCs, can exert their immunosuppressive effects by expressing immune checkpoints such as PD-L1, further highlighting the potential of combined radiation and checkpoint immunotherapy. Several early-phase clinical studies investigating the combination of radiation and immunotherapy have been disappointing. A greater appreciation of radiotherapy's impact on the innate immune system is essential to optimise radioimmunotherapy combinations. This review will summarise the impact of radiotherapy on crucial cells of the innate immune system and vital immunosuppressive cytokines.

Modulation of immune response to induced-arthritis by low-level laser therapy

As low-level laser therapy immune cells responses are not always clarified, this study aimed to evaluate cytokines and immune cells profile after low-level laser therapy (LLLT) on arthritis-induced model. Arthritis was induced in C57BL/6 mice divided into five groups: euthanized 5 hours after inflammation induction; untreated; dexamethasone treated; LLLT at 3 Jcm^-2 ; LLLT at 30 Jcm^-2 . Cytokine measurements by enzyme-linked immunosorbent assay and mRNA cytokine relative levels by real-time quantitative polymerase chain reaction were performed with arthritic ankle (IL-1β, IL-6, TNF-α, IL-10 and TGF-β). Macrophages, dendritic cells, natural killer cells, lymphocytes CD4⁺ , CD8⁺ , Treg and costimulatory proteins were quantified in proximal lymph node by flow cytometry. Data showed decrease in all cytokine levels after LLLT and alteration in mRNA relative levels, depending on the energy density used. LLLT was able to increase of immune cell populations analyzed in the lymph node as well as costimulatory proteins expression on macrophages and dendritic cells. Treg TCD4⁺ and TCD8⁺ population enrichment were observed in LLLT at 3 and 30 Jcm^-2 groups, respectively. Furthermore, Treg TCD8⁺ cells expressing higher levels of CD25 were observed at LLLT at 30 Jcm^-2 group. Our results indicate that LLLT could change the inflammatory course of arthritis, tending to accelerate its resolution through immune cells photobiostimulation.

Radiation combined with macrophage depletion promotes adaptive immunity and potentiates checkpoint blockade

Emerging evidence suggests a role for radiation in eliciting anti-tumour immunity. We aimed to investigate the role of macrophages in modulating the immune response to radiation. Irradiation to murine tumours generated from colorectal (MC38) and pancreatic (KPC) cell lines induced colony-stimulating factor 1 (CSF-1). Coincident with the elevation in CSF-1, macrophages increased in tumours, peaking 5 days following irradiation. These tumour-associated macrophages (TAMs) were skewed towards an immunosuppressive phenotype. Macrophage depletion via anti-CSF (aCSF) reduced macrophage numbers, yet only achieved tumour growth delay when combined with radiation. The tumour growth delay from aCSF after radiation was abrogated by depletion of CD8 T cells. There was enhanced recognition of tumour cell antigens by T cells isolated from irradiated tumours, consistent with increased antigen priming. The addition of anti-PD-L1 (aPD-L1) resulted in improved tumour suppression and even regression in some tumours. In summary, we show that adaptive immunity induced by radiation is limited by the recruitment of highly immunosuppressive macrophages. Macrophage depletion partly reduced immunosuppression, but additional treatment with anti-PD-L1 was required to achieve tumour regression.

Daily very low UV dose exposure enhances adaptive immunity, compared with a single high-dose exposure. Consequences for the control of a skin infection

Ultraviolet radiation (UVr) promotes several well-known molecular changes, which may ultimately impact on health. Some of these effects are detrimental, like inflammation, carcinogenesis and immunosuppression. On the other hand, UVr also promotes vitamin D synthesis and other beneficial effects. We recently demonstrated that exposure to very low doses of UVr on four consecutive days [repetitive low UVd (rlUVd)] does not promote an inflammatory state, nor the recruitment of neutrophils or lymphocytes, as the exposure to a single high UV dose (shUVd) does. Moreover, rlUVd reinforce the epithelium by increasing antimicrobial peptides transcription and epidermal thickness. The aim of this study was to evaluate the adaptive immune response after shUVd and rlUVd, determining T-cell and B-cell responses. Finally, we challenged animals exposed to both irradiation procedures with Staphylococcus aureus to study the overall effects of both innate and adaptive immunity during a cutaneous infection. We observed, as expected, a marked suppression of T-cell and B-cell responses after exposure to an shUVd but a novel and significant increase in both specific responses after exposure to rlUVd. However, the control of the cutaneous S. aureus infection was defective in this last group, suggesting that responses against pathogens cannot be ruled out from isolated stimuli.

Early gene expression analysis in 9L orthotopic tumor-bearing rats identifies immune modulation in molecular response to synchrotron microbeam radiation therapy

Synchrotron Microbeam Radiation Therapy (MRT) relies on the spatial fractionation of the synchrotron photon beam into parallel micro-beams applying several hundred of grays in their paths. Several works have reported the therapeutic interest of the radiotherapy modality at preclinical level, but biological mechanisms responsible for the described efficacy are not fully understood to date. The aim of this study was to identify the early transcriptomic responses of normal brain and glioma tissue in rats after MRT irradiation (400Gy). The transcriptomic analysis of similarly irradiated normal brain and tumor tissues was performed 6 hours after irradiation of 9 L orthotopically tumor-bearing rats. Pangenomic analysis revealed 1012 overexpressed and 497 repressed genes in the irradiated contralateral normal tissue and 344 induced and 210 repressed genes in tumor tissue. These genes were grouped in a total of 135 canonical pathways. More than half were common to both tissues with a predominance for immunity or inflammation (64 and 67% of genes for normal and tumor tissues, respectively). Several pathways involving HMGB1, toll-like receptors, C-type lectins and CD36 may serve as a link between biochemical changes triggered by irradiation and inflammation and immunological challenge. Most immune cell populations were involved: macrophages, dendritic cells, natural killer, T and B lymphocytes. Among them, our results highlighted the involvement of Th17 cell population, recently described in tumor. The immune response was regulated by a large network of mediators comprising growth factors, cytokines, lymphokines. In conclusion, early response to MRT is mainly based on inflammation and immunity which appear therefore as major contributors to MRT efficacy.

Neonatal irradiation sensitizes mice to delayed pulmonary challenge

Significant differences exist between the physiology of the immature, neonatal lung compared to that of the adult lung that may affect acute and late responses to irradiation. Identifying these differences is critical to developing successful mitigation strategies for this special population. Our current hypothesis proposes that irradiation during the neonatal period will alter developmental processes, resulting in long-term consequences, including altered susceptibility to challenge with respiratory pathogens. C57BL/6J mice, 4 days of age, received 5 Gy whole-body irradiation. At subsequent time points (12, 26 and 46 weeks postirradiation), mice were intranasally infected with 120 HAU of influenza A virus. Fourteen days later, mice were sacrificed and tissues were collected for examination. Morbidity was monitored following changes in body weight and survival. The magnitude of the pulmonary response was determined by bronchoalveolar lavage, histological examination and gene expression of epithelial and inflammatory markers. Viral clearance was assessed 7 days post-influenza infection. Following influenza infection, irradiated animals that were infected at 26 and 46 weeks postirradiation lost significantly more weight and demonstrated reduced survival compared with those infected at 12 weeks postirradiation, with the greatest deleterious effect seen at the late time point. The results of these experiments suggest that radiation injury during early life may affect the lung's response to a subsequent pathogenic aerial challenge, possibly through a chronic and progressive defect in the immune system. This finding may have implications for the development of countermeasures in the context of systemic radiation exposure.

Adaptive response of blood lymphocytes as a marker of hemopoiesis status in exposed persons

After the onset of a long-term low dose rate radiation exposure (55-60 y later) of the Techa riverside residents within a range of individual red bone marrow (RBM) doses from 0.01 to 1.79 Gy, it was established that there was an obvious association between the type of reaction manifested by peripheral blood lymphocytes to small dose irradiation in vitro (adaptive potential) and the RBM cell composition (during the period of the major exposure), as well as the peripheral blood cell composition (at a late time period coincident with the studies of induced radioresistance). The nature of these dependencies observed in chronically exposed individuals differs from that revealed in the controls. Based on the results of the study, it can be suggested that the capacity for adaptive response shown by peripheral blood lymphocytes donated by exposed persons at late time after exposure can be regarded as a biological marker of the functional state of the hemopoietic stem cell pool.

The efficacy of radiotherapy relies upon induction of type i interferon-dependent innate and adaptive immunity

The most widely held explanation for the efficacy of local radiotherapy (RT) is based on direct cytotoxicity to cancer cells through the induction of lethal DNA damage. Recent studies have shown that local ablative radiation of established tumors can lead to increased T-cell priming and T-cell-dependent tumor regression, but the underlying mechanism remains unclear. Here, we describe an essential role for type I IFN in local RT-mediated tumor control. We show that ablative RT increases intratumoral production of IFN-β and, more surprisingly, the antitumor effect of RT is abolished in type I IFN nonresponsive hosts. Furthermore, the major target of RT-induced type I IFN is the hematopoietic compartment. RT drastically enhances the cross-priming capacity of tumor-infiltrating dendritic cells (TIDC) from wild-type mice but not type I IFN receptor-deficient mice. The enhanced cross-priming ability of TIDCs after RT was dependent on autocrine production of type I IFNs. By using adenoviral-mediated expression of IFN-β, we show that delivery of exogenous IFN-β into the tumor tissue in the absence of RT is also sufficient to selectively expand antigen-specific T cells leading to complete tumor regression. Our study reveals that local high-dose RT can trigger production of type I IFN that initiates a cascading innate and adaptive immune attack on the tumor.