Systemic immune response to a CD40 agonist antibody in nonhuman primates.

The cell surface molecule CD40 is a member of the tumor necrosis factor receptor superfamily and is broadly expressed by immune cells including B cells, dendritic cells, and monocytes, as well as other normal cells and some malignant cells. CD40 is constitutively expressed on antigen-presenting cells, and ligation promotes functional maturation, leading to an increase in antigen presentation and cytokine production, and a subsequent increase in the activation of antigen-specific T cells. It is postulated that CD40 agonists can mediate both T cell-dependent and T cell-independent immune mechanisms of tumor regression in mice and patients. In addition, it is believed that CD40 activation also promotes apoptotic death of tumor cells and that the presence of the molecule on the surface of cancer cells is an important factor in the generation of tumor-specific T cell responses that contribute to tumor cell elimination. Notably, CD40 agonistic therapies were evaluated in patients with solid tumors and hematologic malignancies with reported success as a single agent. Preclinical studies have shown that subcutaneous administration of CD40 agonistic antibodies reduces systemic toxicity and elicits a stronger and localized pharmacodynamic response. Two independent studies in cynomolgus macaque (Macaca fascicularis) were performed to further evaluate potentially immunotoxicological effects associated with drug-induced adverse events seen in human subjects. Studies conducted in monkeys showed that when selicrelumab is administered at doses currently used in clinical trial patients, via subcutaneous injection, it is safe and effective at stimulating a systemic immune response.

The TLR2/TLR6 ligand FSL-1 mitigates radiation-induced hematopoietic injury in mice and nonhuman primates.

Thrombocytopenia, hemorrhage, anemia, and infection are life-threatening issues following accidental or intentional radiation exposure. Since few therapeutics are available, safe and efficacious small molecules to mitigate radiation-induced injury need to be developed. Our previous study showed the synthetic TLR2/TLR6 ligand fibroblast stimulating lipopeptide (FSL-1) prolonged survival and provided MyD88-dependent mitigation of hematopoietic acute radiation syndrome (H-ARS) in mice. Although mice and humans differ in TLR number, expression, and function, nonhuman primate (NHP) TLRs are like those of humans; therefore, studying both animal models is critical for drug development. The objectives of this study were to determine the efficacy of FSL-1 on hematopoietic recovery in small and large animal models subjected to sublethal total body irradiation and investigate its mechanism of action. In mice, we demonstrate a lack of adverse effects, an easy route of delivery (subcutaneous) and efficacy in promoting hematopoietic progenitor cell proliferation by FSL-1. NHP given radiation, followed a day later with a single subcutaneous administration of FSL-1, displayed no adversity but showed elevated hematopoietic cells. Our analyses revealed that FSL-1 promoted red blood cell development and induced soluble effectors following radiation exposure. Cytologic analysis of bone marrow aspirates revealed a striking enhancement of mononuclear progenitor cells in FSL-1-treated NHP. Combining the efficacy of FSL-1 in promoting hematopoietic cell recovery with the lack of adverse effects induced by a single administration supports the application of FSL-1 as a viable countermeasure against H-ARS.

Assessment of Blood Pressure in Irradiated Rhesus Macaques (Macaca mulatta).

There is increasing evidence that circulatory disease incidence and mortality is associated with radiation exposure. Wake Forest School of Medicine is home to a unique cohort of total-body irradiated macaques, some with evidence of vascular end-organ disease in the brain, kidney and heart. Because there is a link between high blood pressure and vascular disease in all these sites, we undertook a retrospective study to evaluate blood pressure and radiation in this cohort of animals. In this work, we utilized a cohort of nonhuman primates (rhesus macaques, Macaca mulatta) long-term survivors of high-dose total-body irradiation (1.1-8.5 Gy, N = 129) and controls (N = 37) to evaluate the effects of radiation on blood pressure and obesity. Subjects were between 3 and 22 years of age (median 9 years). Blood pressure (BP) was measured 1-14 years postirradiation (median 4 years). Subjects were sedated with a combination of ketamine HCl (15 mg/kg body weight, IM) and midazolam (0.1 mg/kg body weight, IM) and systolic, diastolic, and mean arterial pressures were measured using a high definition oscillometer. Obesity was defined by dual energy X-ray absorptiometry as a body fat percentage >35%. Statistical analysis of the collected data indicated significant increases in blood pressure with increasing age and obesity. However, radiation did not significantly alter blood pressure in irradiated animals relative to controls, radiation dose, or age of irradiation.

Quantitative Assessment and Comparative Analysis of Longitudinal Lung CT Scans of Chest-Irradiated Nonhuman Primates.

Computed tomography (CT) imaging has been used to diagnose radiation-induced lung injury for decades. However, histogram-based quantitative tools have rarely been applied to assess lung abnormality due to radiation-induced lung injury (RILI). Here, we used first-order summary statistics to derive and assess threshold measures extracted from whole lung histograms of CT radiodensity in rhesus macaques. For the present study, CT scans of animals exposed to 10 Gy of whole thorax irradiation were utilized from a previous study spanning 2-9 months postirradiation. These animals were grouped into survivors and non-survivors based on their clinical and experimental endpoints. We quantified the change in lung attenuation after irradiation relative to baseline using three density parameters; average lung density (ALD), percent change in hyper-dense lung volume (PCHV), hyperdense volume as a percent of total volume (PCHV/TV) at 2-month intervals and compared each parameter between the two irradiated groups (non-survivors and survivors). We also correlated our results with histological findings. All the three indices (ALD, PCHV, PCHV/TV) obtained from density histograms showed a significant increase in lung injury in non-survivors relative to survivors, with PCHV relatively more sensitive to detect early RILI changes. We observed a significant positive correlation between histologic pneumonitis scores and each of the three CT measurements, indicating that CT density is useful as a surrogate for histologic disease severity in RILI. CT-based three density parameters, ALD, PCHV, PCHV/TV, may serve as surrogates for likely histopathology patterns in future studies of RILI disease progression.

Age effects on radiation response: summary of a recent symposium and future perspectives.

One of the principal uncertainties when estimating population risk of late effects from epidemiological data is that few radiation-exposed cohorts have been followed up to extinction. Therefore, the relative risk model has often been used to estimate radiation-associated risk and to extrapolate risk to the end of life. Epidemiological studies provide evidence that children are generally at higher risk of cancer induction than adults for a given radiation dose. However, the strength of evidence varies by cancer site and questions remain about site-specific age at exposure patterns. For solid cancers, there is a large body of evidence that excess relative risk (ERR) diminishes with increasing age at exposure. This pattern of risk is observed in the Life Span Study (LSS) as well as in other radiation-exposed populations for overall solid cancer incidence and mortality and for most site-specific solid cancers. However, there are some disparities by endpoint in the degree of variation of ERR with exposure age, with some sites (e.g., colon, lung) in the LSS incidence data showing no variation, or even increasing ERR with increasing age at exposure. The pattern of variation of excess absolute risk (EAR) with age at exposure is often similar, with EAR for solid cancers or solid cancer mortality decreasing with increasing age at exposure in the LSS. We shall review the human data from the Japanese LSS cohort, and a variety of other epidemiological data sets, including a review of types of medical diagnostic exposures, also some radiobiological animal data, all bearing on the issue of variations of radiation late-effects risk with age at exposure and with attained age. The paper includes a summary of several oral presentations given in a Symposium on "Age effects on radiation response" as part of the 67th Annual Meeting of the Radiation Research Society, held virtually on 3-6 October 2021.

Clinicopathologic and Transcriptomic Analysis of Radiation-Induced Lung Injury in Nonhuman Primates.

PURPOSE: Radiation-induced lung injury (RILI) is a progressive condition with an early phase (radiation pneumonitis) and a late phase (lung fibrosis). RILI may occur after partial-body ionizing radiation exposures or internal radioisotope exposure, with wide individual variability in timing and extent of lung injury. This study aimed to provide new insights into the pathogenesis and progression of RILI in the nonhuman primate (NHP) rhesus macaque model. METHODS AND MATERIALS: We used an integrative approach to understand RILI and its evolution at clinical and molecular levels in 17 NHPs exposed to 10 Gy of whole-thorax irradiation in comparison with 3 sham-irradiated control NHPs. Clinically, we monitored respiratory rates, computed tomography (CT) scans, plasma cytokine levels, and bronchoalveolar lavage (BAL) over 8 months and lung samples collected at necropsy for molecular and histopathologic analyses using RNA sequencing and immunohistochemistry. RESULTS: Elevated respiratory rates, greater CT density, and more severe pneumonitis with increased macrophage content were associated with early mortality. Radiation-induced lung fibrosis included polarization of macrophages toward the M2-like phenotype, TGF-ß signaling, expression of CDKN1A/p21 in epithelial cells, and expression of α-SMA in lung stroma. RNA sequencing analysis of lung tissue revealed SERPINA3, ATP12A, GJB2, CLDN10, TOX3, and LPA as top dysregulated transcripts in irradiated animals. In addition to transcriptomic data, we observed increased protein expression of SERPINA3, TGF-ß1, CCL2, and CCL11 in BAL and plasma samples. CONCLUSIONS: Our combined clinical, imaging, histologic, and transcriptomic analysis provides new insights into the early and late phases of RILI and highlights possible biomarkers and potential therapeutic targets of RILI. Activation of TGF-ß and macrophage polarization appear to be key mechanisms involved in RILI.

Non-Human Primates Receiving High-Dose Total-Body Irradiation are at Risk of Developing Cerebrovascular Injury Years Postirradiation.

Nuclear accidents and acts of terrorism have the potential to expose thousands of people to high-dose total-body iradiation (TBI). Those who survive the acute radiation syndrome are at risk of developing chronic, degenerative radiation-induced injuries [delayed effects of acute radiation (DEARE)] that may negatively affect quality of life. A growing body of literature suggests that the brain may be vulnerable to radiation injury at survivable doses, yet the long-term consequences of high-dose TBI on the adult brain are unclear. Herein we report the occurrence of lesions consistent with cerebrovascular injury, detected by susceptibility-weighted magnetic resonance imaging (MRI), in a cohort of non-human primate [(NHP); rhesus macaque, Macaca mulatta] long-term survivors of high-dose TBI (1.1-8.5 Gy). Animals were monitored longitudinally with brain MRI (approximately once every three years). Susceptibility-weighted images (SWI) were reviewed for hypointensities (cerebral microbleeds and/or focal necrosis). SWI hypointensities were noted in 13% of irradiated NHP; lesions were not observed in control animals. A prior history of exposure was correlated with an increased risk of developing a lesion detectable by MRI (P = 0.003). Twelve of 16 animals had at least one brain lesion present at the time of the first MRI evaluation; a subset of animals (n = 7) developed new lesions during the surveillance period (3.7-11.3 years postirradiation). Lesions occurred with a predilection for white matter and the gray-white matter junction. The majority of animals with lesions had one to three SWI hypointensities, but some animals had multifocal disease (n = 2). Histopathologic evaluation of deceased animals within the cohort (n = 3) revealed malformation of the cerebral vasculature and remodeling of the blood vessel walls. There was no association between comorbid diabetes mellitus or hypertension with SWI lesion status. These data suggest that long-term TBI survivors may be at risk of developing cerebrovascular injury years after irradiation.

Monocyte Polarization is Altered by Total-Body Irradiation in Male Rhesus Macaques: Implications for Delayed Effects of Acute Radiation Exposure.

Radiation-induced fibrosis (RIF) is a common delayed effect of acute ionizing radiation exposure (DEARE) affecting diverse tissues including the heart, lungs, liver and skin, leading to reduced tissue function and increased morbidity. Monocytes, which may be classified into classical (CD14++, CD16-), intermediate (CD14++, CD16+) and non-classical (CD14+/low, CD16++) subtypes in humans and non-human primates (NHPs), and monocyte-derived macrophages may play an integral role in the pathogenesis of RIF. We tested the hypothesis that moderate to high levels of total-body exposure to radiation would alter monocyte polarization and produce phenotypes that could promote multi-organ fibrosis in a wellestablished NHP model of DEARE. Subjects were 16 young adult male rhesus macaques, ten of which were exposed to high-energy, 4 Gy X-ray total-body irradiation (TBI) and six that received sham irradiation (control). Total monocytes assessed by complete blood counts were 89% depleted in TBI animals by day 9 postirradiation (P < 0.05), but recovered by day 30 postirradiation and did not differ from control levels thereafter. Monocytes were isolated from peripheral blood mononuclear cells (PBMCs) and sorted into classical, intermediate and non-classical subsets using fluorescence-activated cell sorting (FACS) prior to and at 6 months post-TBI. At 6 months postirradiation, monocyte polarization shifted towards lower classical (92% → 86%) and higher intermediate (7% → 12%) and non-classical monocyte subsets (0.6% → 2%) (all P < 0.05) in TBI animals compared to baseline. No change in monocyte subsets was observed in control animals. Transcriptional profiles in classical and intermediate monocyte subsets were assessed using RNAseq. Classical monocyte gene expression did not change significantly over time or differ cross-sectionally between TBI and control groups. In contrast, significant numbers of differentially expressed genes (DEGs) were detected in intermediate monocyte comparisons between the TBI animals and all animals at baseline (304 DEGs), and in the TBI versus control animals at 6 months postirradiation (67 DEGs). Intermediate monocytes also differed between baseline and 6 months in control animals (147 DEGs). Pathway analysis was used to identify genes within significant canonical pathways, yielding 52 DEGs that were specific to irradiated intermediate monocytes. These DEGs and significant canonical pathways were associated with pro-fibrotic and anti-inflammatory signaling pathways that have been noted to induce M2 macrophage polarization. These findings support the hypothesis that TBI may alter monocyte programming and polarization towards a profibrotic phenotype, providing a novel target opportunity for therapies to inhibit or prevent RIF.

White Matter is the Predilection Site of Late-Delayed Radiation-Induced Brain Injury in Non-Human Primates.

Fractionated whole-brain irradiation for the treatment of intracranial neoplasia causes progressive neurodegeneration and neuroinflammation. The long-term consequences of single-fraction high-dose irradiation to the brain are unknown. To assess the late effects of brain irradiation we compared transcriptomic gene expression profiles from nonhuman primates (NHP; rhesus macaques Macaca mulatta) receiving single-fraction total-body irradiation (TBI; n = 5, 6.75-8.05 Gy, 6-9 years prior to necropsy) to those receiving fractionated whole-brain irradiation (fWBI; n = 5, 40 Gy, 8 × 5 Gy fractions; 12 months prior to necropsy) and control comparators (n = 5). Gene expression profiles from the dorsolateral prefrontal cortex (DLPFC), hippocampus (HC) and deep white matter (WM; centrum semiovale) were compared. Stratified analyses by treatment and region revealed that radiation-induced transcriptomic alterations were most prominent in animals receiving fWBI, and primarily affected white matter in both TBI and fWBI groups. Unsupervised canonical and ontologic analysis revealed that TBI or fWBI animals demonstrated shared patterns of injury, including white matter neuroinflammation, increased expression of complement factors and T-cell activation. Both irradiated groups also showed evidence of impaired glutamatergic neurotransmission and signal transduction within white matter, but not within the dorsolateral prefrontal cortex or hippocampus. Signaling pathways and structural elements involved in extracellular matrix (ECM) deposition and remodeling were noted within the white matter of animals receiving fWBI, but not of those receiving TBI. These findings indicate that those animals receiving TBI are susceptible to neurological injury similar to that observed after fWBI, and these changes persist for years postirradiation. Transcriptomic profiling reaffirmed that macrophage/microglial-mediated neuroinflammation is present in radiation-induced brain injury (RIBI), and our data provide novel evidence that the complement system may contribute to the pathogenesis of RIBI. Finally, these data challenge the assumption that the hippocampus is the predilection site of injury in RIBI, and indicate that impaired glutamatergic neurotransmission may occur in white matter injury.

Whole thorax irradiation of non-human primates induces persistent nuclear damage and gene expression changes in peripheral blood cells.

We investigated the cytogenetic and gene expression responses of peripheral blood cells of non-human primates (NHP, Macaca mulatta) that were whole-thorax irradiated with a single dose of 10 Gy. In this model, partial irradiation of NHPs in the thoracic region (Whole Thorax Lung Irradiation, WTLI) allows the study of late radiation-induced lung injury, while avoiding acute radiation syndromes related to hematopoietic and gastrointestinal injury. A transient drop in circulating lymphocytes and platelets was seen by 9 days, followed by elevations in respiratory rate, circulating neutrophils, lymphocytes, and monocytes at 60-100 days, corresponding to computed tomography (CT) and histologic evidence of pneumonitis, and elective euthanasia of four animals. To evaluate long-term DNA damage in NHP peripheral blood lymphocytes after 10 Gy WTLI, we used the cytokinesis-block micronucleus (CBMN) assay to measure chromosomal aberrations as post-mitotic micronuclei in blood samples collected up to 8 months after irradiation. Regression analysis showed significant induction of micronuclei in NHP blood cells that persisted with a gradual decline over the 8-month study period, suggesting long-term DNA damage in blood lymphocytes after WTLI. We also report transcriptomic changes in blood up to 30 days after WTLI. We isolated total RNA from peripheral blood at 3 days before and then at 2, 5 and 30 days after irradiation. We identified 1187 transcripts that were significantly changed across the 30-day time course. From changes in gene expression, we identified biological processes related to immune responses, which persisted across the 30-day study. Response to oxygen-containing compounds and bacteria were implicated by gene-expression changes at the earliest day 2 and latest, day 30 time-points. Gene expression changes suggest a persistent altered state of the immune system, specifically response to infection, for at least a month after WTLI.