Extracellular vesicles derived from radioresistant oral squamous cell carcinoma cells contribute to the acquisition of radioresistance via the miR-503-3p-BAK axis

Despite advancements in treatments, oral squamous cell carcinoma (OSCC) has not significantly improved in prognosis or survival rate primarily due to the presence of treatment-resistant OSCC. The intercellular communication between tumour cells is a molecular mechanism involved in acquiring OSCC treatment resistance. Extracellular vesicles (EVs) and encapsulated miRNAs are important mediators of intercellular communication. Here, we focused on EVs released from clinically relevant radioresistant (CRR) OSCC cells. Additionally, we evaluated the correlation between miRNA expression in the serum samples of patients who showed resistance to radiotherapy and in EVs released from CRR OSCC cells. We found that EVs released from CRR OSCC cells conferred radioresistance to radiosensitive OSCC cells via miR-503-3p contained in EVs. This miR-503-3p inhibited BAK and impaired the caspase cascade to suppress radiation-induced apoptosis. Furthermore, OSCC cells with BAK knockdown had increased radioresistance. Additionally, the expression of circulating miR-503-3p in patients with OSCC was correlated with a poor treatment response and prognosis of radiotherapy. Our results provide new insights into the relationship between EVs and the radioresistance of OSCC and suggest that the miR-503-3p-BAK axis may be a therapeutic target and that circulating miR-503-3p is a useful prognostic biomarker in the radiotherapy of OSCC.

Abscopal Effect of Radiotherapy Enhanced with Immune Checkpoint Inhibitors of Triple Negative Breast Cancer in 4T1 Mammary Carcinoma Model

Local radiotherapy (RT) is important to manage metastatic triple-negative breast cancer (TNBC). Although RT primarily reduces cancer cells locally, this control can be enhanced by triggering the immune system via immunotherapy. RT and immunotherapy may lead to an improved systemic effect, known as the abscopal effect. Here, we analyzed the antitumor effect of combination therapy using RT with an anti-programmed cell death-1 (PD-1) antibody in primary tumors, using poorly immunogenic metastatic mouse mammary carcinoma 4T1 model. Mice were injected subcutaneously into both flanks with 4T1 cells, and treatment was initiated 12 days later. Mice were randomly assigned to three treatment groups: (1) control (no treatment with RT or immune checkpoint inhibitor (ICI)), (2) RT alone, and (3) RT+ICI. The same RT dose was prescribed in both RT-alone and RT+ICI groups as 10Gy/fx in two fractions and delivered to only one of the two tumor burdens injected at both sides of flanks. In the RT+ICI group, 200 µg fixed dose of PD-1 antibody was intraperitoneally administered concurrently with RT. The RT and ICI combination markedly reduced tumor cell growth not only in the irradiated site but also in non-irradiated sites, a typical characteristic of the abscopal effect. This was observed only in radiation-sensitive cancer cells. Lung metastasis development was lower in RT-irradiated groups (RT-only and RT+ICI groups) than in the non-irradiated group, regardless of the radiation sensitivity of tumor cells. However, there was no additive effect of ICI on RT to control lung metastasis, as was already known regarding the abscopal effect. The combination of local RT with anti-PD-1 blockade could be a promising treatment strategy against metastatic TNBC. Further research is required to integrate our results into a clinical setting.

Valproic Acid-Like Compounds Enhance and Prolong the Radiotherapy Effect on Breast Cancer by Activating and Maintaining Anti-Tumor Immune Function

Inadequate sustained immune activation and tumor recurrence are major limitations of radiotherapy (RT), sustained and targeted activation of the tumor microenvironment can overcome this obstacle. Here, by two models of a primary rat breast cancer and cell co-culture, we demonstrated that valproic acid (VPA) and its derivative (HPTA) are effective immune activators for RT to inhibit tumor growth by inducing myeloid-derived macrophages and polarizing them toward the M1 phenotype, thus elevate the expression of cytokines such as IL-12, IL-6, IFN-γ and TNF-α during the early stage of the combination treatment. Meanwhile, activated CD8+ T cells increased, angiogenesis of tumors is inhibited, and the vasculature becomes sparse. Furthermore, it was suggested that VPA/HPTA can enhance the effects of RT via macrophage-mediated and macrophage-CD8+ T cell-mediated anti-tumor immunity. The combination of VPA/HPTA and RT treatment slowed the growth of tumors and prolong the anti-tumor effect by continuously maintaining the activated immune response. These are promising findings for the development of new effective, low-cost concurrent cancer therapy.

IL-32 Promotes the Radiosensitivity of Esophageal Squamous Cell Carcinoma Cell through STAT3 Pathway

OBJECTIVE

This study is set out to determine the relationship between IL-32 and radiosensitivity of esophageal squamous cell carcinoma (ESCC).

METHODS

Western blot was adopted for measuring IL-32 expression in Eca-109 and TE-10 cells. Eca-109 and TE-10 cells with interference or overexpression of IL-32 were treated with the presence or absence of X-ray irradiation. Then, the use of CCK8 assay was to detect proliferation ability, and effects of IL-32 expression on radiosensitivity of ESCC were tested by colony formation assay. The cell apoptosis was detected using flow cytometry. STAT3 and p-STAT expression, and apoptotic protein Bax were detected by western blot.

RESULTS

Colony formation assay and CCK8 assay showed that compared with the NC group without treatment, the growth of the ESCC cells, that is Eca-109 and TE-10, was significantly inhibited in the OE+IR group with highly expressed IL-32 and irradiation. In flow cytometry analysis, in Eca-109 and TE-10 cells, highly expressed IL-32 combined with irradiation significantly increased apoptosis compared with the control group. Highly expressed IL-32 has a synergistic effect with irradiation, inhibiting STAT3 and p-STAT3 expression and increasing apoptotic protein Bax expression.

CONCLUSION

IL-32 can improve the radiosensitivity of ESCC cells by inhibiting the STAT3 pathway. Therefore, IL-32 can be used as a new therapeutic target to provide a new attempt for radiotherapy of ESCC.

Immune Infiltrate in the Primary Tumor Predicts Effect of Adjuvant Radiotherapy in Breast Cancer; Results from the Randomized SweBCG91RT Trial

PURPOSE

Tumor-infiltrating immune cells play a key role in tumor progression. The purpose of this study was to analyze whether the immune infiltrate predicts benefit from postoperative radiotherapy in a large randomized breast cancer radiotherapy trial.

EXPERIMENTAL DESIGN

In the SweBCG91RT trial, patients with stage I and II breast cancer were randomized to breast-conserving surgery (BCS) and postoperative radiotherapy or to BCS only and followed for a median time of 15.2 years. The primary tumor immune infiltrate was quantified through two independent methods: IHC and gene expression profiling. For IHC analyses, the absolute stromal area occupied by CD8⁺ T cells and FOXP3⁺ T cells, respectively, was used to define the immune infiltrate. For gene expression analyses, immune cells found to be prognostic in independent datasets were pooled into two groups consisting of antitumoral and protumoral immune cells, respectively.

RESULTS

An antitumoral immune response in the primary tumor was associated with a reduced risk of breast cancer recurrence and predicted less benefit from adjuvant radiotherapy. The interaction between radiotherapy and immune phenotype was significant for any recurrence in both the IHC and gene expression analyses (P = 0.039 and P = 0.035) and was also significant for ipsilateral breast tumor recurrence in the gene expression analyses (P = 0.025).

CONCLUSIONS

Patients with an antitumoral immune infiltrate in the primary tumor have a reduced risk of any recurrence and may derive less benefit from adjuvant radiotherapy. These results may impact decisions regarding postoperative radiotherapy in early breast cancer.

The Reciprocity between Radiotherapy and Cancer Immunotherapy

The clinical success of immune checkpoint inhibitors in treating metastatic and refractory cancers has generated significant interest in investigating their role in treating locally advanced diseases, thus requiring them to be combined with standard treatments in the hope of producing synergistic antitumor responses. Radiotherapy, in particular, has long been hypothesized to have actions complementary to those of immune checkpoint blockade, and a growing body of evidence indicates that cancer immunotherapy may also have radiosensitizing effects, which would provide unique benefit for locoregional treatments. Recent studies have demonstrated that when immune cells are activated by immunotherapeutics, they can reprogram the tumor microenvironment in ways that may potentially increase the radiosensitivity of the tumor. In this review, we highlight the evidence that supports reciprocal interactions between cancer immunotherapy and radiotherapy, where in addition to the traditional notion that radiation serves to enhance the activation of antitumor immunity, an alternative scenario also exists in which T-cell activation by cancer immunotherapy may sensitize tumors to radiation treatment through mechanisms that include normalization of the tumor vasculature and tissue hypoxia. We describe the empirical observations from preclinical models that support such effects and discuss their implications for future research and trial design.

P2Y2R-mediated inflammasome activation is involved in tumor progression in breast cancer cells and in radiotherapy-resistant breast cancer

In the tumor microenvironment, extracellular nucleotides are released and accumulate, and can activate the P2Y2 receptor (P2Y2R), which regulates various responses in tumor cells, resulting in tumor progression and metastasis. Moreover, the inflammasome has recently been reported to be associated with tumor progression. However, the role of P2Y2R in inflammasome activation in breast cancer cells is not yet well defined. Therefore, in this study, we investigated the role of P2Y2R in inflammasome-mediated tumor progression in breast cancer using breast cancer cells and radiotherapy-resistant (RT‑R) breast cancer cells. We established RT‑R-breast cancer cells (RT‑R‑MDA‑MB‑231, RT‑R‑MCF‑7, and RT‑R-T47D cells) by repeated irradiation (2 Gy each, 25 times) in a previous study. In this study, we found that the RT‑R breast cancer cells exhibited an increased release of adenosine triphosphate (ATP) and P2Y2R activity. In particular, the RT‑R‑MDA‑MB‑231 cells derived from highly metastatic MDA‑MB‑231 cells, exhibited a markedly increased ATP release, which was potentiated by tumor necrosis factor (TNF)-α. The MDA‑MB‑231 cells exhibited inflammasome activation, as measured by caspase‑1 activity and interleukin (IL)-1β secretion following treatment with TNF‑α and ATP; these effects were enhanced in the RT‑R‑MDA‑MB‑231 cells. However, the increased caspase‑1 activities and IL‑1β secretion levels induced in response to treatment with TNF‑α or ATP were significantly reduced by P2Y2R knockdown or the presence of apyrase in both the MDA‑MB‑231 and RT‑R‑MDA‑MB‑231 cells, suggesting the involvement of ATP-activated P2Y2R in inflammasome activation. In addition, TNF‑α and ATP increased the invasive and colony-forming ability of the MDA‑MB‑231 and RT‑R‑MDA‑MB‑231 cells, and these effects were caspase‑1-dependent. Moreover, matrix metalloproteinase (MMP)-9 activity was modulated by caspase-1, in a P2Y2R-dependent manner in the MDA‑MB‑231 and RT‑R‑MDA‑MB‑231 cells. Finally, nude mice injected with the RT‑R‑MDA‑MB‑231-EV cells (transfected with the empty vector) exhibited increased tumor growth, and higher levels of MMP-9 in their tumors and IL‑1β levels in their serum compared with the mice injected with the RT‑R‑MDA‑MB‑231-P2Y2R shRNA cells (transfected with P2Y2R shRNA). On the whole, the findings of this study suggest that extracellular ATP promotes tumor progression in RT‑R-breast cancer cells and breast cancer cells by modulating invasion and associated molecules through the P2Y2R-inflammasome activation pathway.

Tumour radiosensitivity is associated with immune activation in solid tumours

PURPOSE

Our goal was to determine whether tumour radiosensitivity is associated with activation of the immune system across all tumour types as measured by two gene expression signatures (GESs).

METHODS

We identified 10,240 genomically profiled distinct solid primary tumours with gene expression analysis available from an institutional de-identified database. Two separate GESs were included in the analysis, the radiosensitivity index (RSI) GES (a 10-gene GES as a measure of radiosensitivity) and the 12-chemokine (12-CK) signature (a 12-gene GES as a measure of immune activation). We tested whether the RSI and 12-CK were associated with each other across all tumour samples and, in an exploratory analysis, their prognostic significance in predicting distant metastasis-free survival (DMFS) among a well-characterised, independent cohort of 282 early-stage breast cancer cases treated with surgery and post-operative radiation alone without systemic therapy. The lower the RSI score, the higher the tumour radiosensitivity; whereas, the higher the 12-CK score the higher the immune activation.

RESULTS

Using an RSI cut-point of ≤0.3745, RSI-low tumours (n = 4,291, 41.9%) had a significantly higher median 12-CK GES value (0.54 [-0.136, 1.095]) compared with RSI-high tumours (-0.17 [-0.82, 0.42]; p < 0.001) across all tumour samples, indicating that radiosensitivity is associated with immune activation. In an exploratory analysis of early-stage breast cancer cases, a multivariable model with patient age, RSI and 12-CK provided a strong composite model for DMFS (p = 0.02), with RSI (hazard ratio [HR] 0.63 [95% confidence interval 0.36, 1.09]) and 12-CK (HR 0.66 [0.41, 1.04]) each providing comparable contributions.

CONCLUSIONS

Tumour radiosensitivity is associated with immune activation as measured by the two GESs.

A prosurvival DNA damage-induced cytoplasmic interferon response is mediated by end resection factors and is limited by Trex1

Radiotherapy and chemotherapy are effective treatment methods for many types of cancer, but resistance is common. Recent findings indicate that antiviral type I interferon (IFN) signaling is induced by these treatments. However, the underlying mechanisms still need to be elucidated. Expression of a set of IFN-stimulated genes comprises an IFN-related DNA damage resistance signature (IRDS), which correlates strongly with resistance to radiotherapy and chemotherapy across different tumors. Classically, during viral infection, the presence of foreign DNA in the cytoplasm of host cells can initiate type I IFN signaling. Here, we demonstrate that DNA-damaging modalities used during cancer therapy lead to the release of ssDNA fragments from the cell nucleus into the cytosol, engaging this innate immune response. We found that the factors that control DNA end resection during double-strand break repair, including the Bloom syndrome (BLM) helicase and exonuclease 1 (EXO1), play a major role in generating these DNA fragments and that the cytoplasmic 3'-5' exonuclease Trex1 is required for their degradation. Analysis of mRNA expression profiles in breast tumors demonstrates that those with lower Trex1 and higher BLM and EXO1 expression levels are associated with poor prognosis. Targeting BLM and EXO1 could therefore represent a novel approach for circumventing the IRDS produced in response to cancer therapeutics.

The NF-κB regulator Bcl-3 modulates inflammation during contact hypersensitivity reactions in radioresistant cells

Bcl-3 is an atypical member of the IκB family. Bcl-3 functions as a cofactor of p50/NF-κB1 or p52/NF-κB2 homodimers in nuclei, where it modulates NF-κB-regulated transcription in a context-dependent way. Bcl-3 has tumorigenic potential, is critical in host defense of pathogens, and has been reported to ameliorate or exacerbate inflammation, depending on disease model. However, cell-specific functions of Bcl-3 remain largely unknown. Here, we explored the role of Bcl-3 in a contact hypersensitivity (CHS) mouse model, which depends on the interplay between keratinocytes and immune cells. Bcl-3-deficient mice exhibited an exacerbated and prolonged CHS response to oxazolone. Increased inflammation correlated with higher production of chemokines CXCL2, CXCL9, and CXCL10, and consequently increased recruitment of neutrophils and CD8(+) T cells. BM chimera experiments indicated that the ability of Bcl-3 to reduce the CHS response depended on Bcl-3 activity in radioresistant cells. Specific ablation of Bcl-3 in keratinocytes resulted in increased production of CXCL9 and CXCL10 and sustained recruitment of specifically CD8(+) T cells. These findings identify Bcl-3 as a critical player during the later stage of the CHS reaction to limit inflammation via actions in radioresistant cells, including keratinocytes.

[Individual variability of immunological markers, radiosensitivity and oxidative status in blood lymphocytes of Moscow residents]

Expression of activation (CD69) and proliferation (Ki67) markers, their connection with each other, with the oxidative status (reactive oxygen species--ROS) and with radiosensitivity (determined by micronucleus test) have been studied on stimulated blood lymphocytes from Moscow inhabitants. It was shown that the content of T-lymphocytes with the expressed CD69 and the content of T-lymphocytes with the expressed Ki67 markers correlate (r = 0.571; p = 0.0004). We can suppose that expression of the CD69 marker (24 h after PHA stimulation) is needed for the cell cycle progression, but it is not enough for the high expression of Ki67 markers 48 h after stimulation (DNA synthesis phase). It was discovered that T-lymphocytes with the CD69 marker or T-lymphocytes with the Ki67 marker are connected by the negative correlation with the frequency of irradiated cell with micronucleus (MN) r = -0.487; p = 0.010; r = -0.440; p = 0.008, respectively. So we can suppose that lymphocyte radiosensitivity decreased with the increase of expression activation and proliferation markers. It was shown that radiosensitivity determined by MN test is not connected with the oxidative status determined by the reactive oxygen species content including superoxide anion radicals. It is possible to explain by the fact that the ROS concentration has been determined in non-stimulated lymphocytes, but frequencies of cells with MN - in the stimulated cells 48 h after stimulation. Using separate analysis of individual differences by the studied parameters that were determined in the same people, it was shown that individual differences are high enough in the same cases. For example, the radiosensitivity when cells were irradiated 48 h after stimulation, ROS concentration, cell content with activation and proliferation markers. In conclusion, we can say that we failed to find important correlation between the parameters studied. However, the presence of individual differences in the marker expression, the frequency of MN cells, the oxidative status in the usual inhabitants, typical donors in Moscow, is very important.

Reciprocal complementation of the tumoricidal effects of radiation and natural killer cells

The tumor microenvironment is a key determinant for radio-responsiveness. Immune cells play an important role in shaping tumor microenvironments; however, there is limited understanding of how natural killer (NK) cells can enhance radiation effects. This study aimed to assess the mechanism of reciprocal complementation of radiation and NK cells on tumor killing. Various tumor cell lines were co-cultured with human primary NK cells or NK cell line (NK-92) for short periods and then exposed to irradiation. Cell proliferation, apoptosis and transwell assays were performed to assess apoptotic efficacy and cell viability. Western blot analysis and immunoprecipitation methods were used to determine XIAP (X-linked inhibitor of apoptosis protein) and Smac (second mitochondria-derived activator of caspase) expression and interaction in tumor cells. Co-culture did not induce apoptosis in tumor cells, but a time- and dose-dependent enhancing effect was found when co-cultured cells were irradiated. A key role for caspase activation via perforin/granzyme B (Grz B) after cell-cell contact was determined, as the primary radiation enhancing effect. The efficacy of NK cell killing was attenuated by upregulation of XIAP to bind caspase-3 in tumor cells to escape apoptosis. Knockdown of XIAP effectively potentiated NK cell-mediated apoptosis. Radiation induced Smac released from mitochondria and neutralized XIAP and therefore increased the NK killing. Our findings suggest NK cells in tumor microenvironment have direct radiosensitization effect through Grz B injection while radiation enhances NK cytotoxicity through triggering Smac release.

Augmentation of natural cytotoxicity by chronic low-dose ionizing radiation in murine natural killer cells primed by IL-2

The possible beneficial effects of chronic low-dose irradiation (LDR) and its mechanism of action in a variety of pathophysiological processes such as cancer are a subject of intense investigation. While animal studies involving long-term exposure to LDR have yielded encouraging results, the influence of LDR at the cellular level has been less well defined. We reasoned that since natural killer (NK) cells constitute an early responder to exogenous stress, NK cells may reveal sentinel alterations in function upon exposure to LDR. When purified NK cells received LDR at 4.2 mGy/h for a total of 0.2 Gy in vitro, no significant difference in cell viability was observed. Likewise, no functional changes were detected in LDR-exposed NK cells, demonstrating that LDR alone was insufficient to generate changes at the cellular level. Nonetheless, significant augmentation of cytotoxic, but not proliferative, function was detected when NK cells were stimulated with low-dose IL-2 prior to irradiation. This enhancement of NK cytotoxicity was not due to alterations in NK-activating receptors, NK1.1, NKG2D, CD69 and 2B4, or changes in the rate of early or late apoptosis. Therefore, LDR, in the presence of suboptimal cytokine levels, can facilitate anti-tumor cytotoxicity of NK cells without influencing cellular proliferation or apoptosis. Whether these results translate to in vivo consequences remains to be seen; however, our data provide initial evidence that exposure to LDR can lead to subtle immune-enhancing effects on NK cells and may explain, in part, the functional basis underlying, diverse beneficial effects seen in the animals chronically exposed to LDR.

Links between innate immunity and normal tissue radiobiology

The body senses "danger" from "damaged self" molecules through members of the same receptor superfamily it uses for microbial "non-self", triggering canonical signaling pathways that lead to the generation of acute inflammatory responses. For this reason, the biology of normal tissue responses to moderate and clinically relevant doses of radiation is inextricably connected to innate immunity. The complex sequence of inflammatory events that ensues causes further cell and tissue damage to eliminate potential invaders but also leads to cytoprotective responses that limit the spread of damage and to wound healing through tissue regeneration or replacement. These sequential processes are orchestrated through multiple feedback control mechanisms involving cyclical production of free radicals and cytokines that are common to both radiation and immune signaling. This requires a concerted effort by resident tissue and inflammatory cell types, with macrophages apparently leading the way. The initial response to moderate doses of radiation therefore feeds into a pro-inflammatory paradigm whose eventual outcome is critically dependent upon the properties of the immune cells that are involved in tissue damage, regeneration and repair and that are in part under genetic influence. Importantly, these canonical pathways provide targets for interventions aimed at modifying normal tissue radiation responses. In this review, we examine areas of intersection between innate immunity and normal tissue radiobiology.

DNA double strand break repair defects, primary immunodeficiency disorders, and 'radiosensitivity'

PURPOSE OF REVIEW

It is important to assess 'radiosensitivity' in patients suspected of immunodeficiency because underlying DNA double strand break (DSB) repair defects have considerable impact on V(D)J recombination, class switching and lymphocyte maturation, leading to increased infections and cancer risk. In addition, the phenotype of 'radiosensitivity' may identify patients with increased toxicity to radiation and chemotherapeutic agents and could impact upon their preparation for stem cell transplantation. To date, the gold standard for evaluating 'radiosensitivity' has been the colony-survival assay (CSA), which reflects the efficiency of DNA repair of DSBs as it impacts upon replication and cell survival. Other methods measure other aspects of DNA repair; however, their limited specificity often leads to false negatives for predicting 'radiosensitivity', especially clinical radiosensitivity. Lastly, clinical awareness of an overarching syndrome of DSB repair disorders, XCIND, could help to raise diagnostic levels of suspicion and, thereby, identify additional patients with new forms of immunodeficiency, cancer susceptibility and radiosensitivity.

RECENT FINDINGS

Within the past year, three new radiosensitivity disorders of DSB repair have been described, involving deficiencies of RNF168, RAD50, and DNA-PKcs. These are truly translational advances because they validate laboratory models and allow new patients to be identified.

SUMMARY

Recognizing compromised genome stability is important but difficult. We review the evidence for correlations between DSB repair, abnormal colony formation, clinical radiosensitivity and other laboratory methods.

Sensors of ionizing radiation effects on the immunological microenvironment of cancer

PURPOSE

When cancer develops in an immunocompetent host it represents the result of a successful deception of the immune system as to the nature of the danger and the type of response needed to reject the neoplastic tissue. We will briefly review some of the recently emerged evidence that irradiation of the tumor and its microenvironment can induce essential molecular signals required for an effective response of the immune system to the tumor.

CONCLUSIONS

The subversion of a highly organized tissue architecture is a hallmark of cancer, and results in uneven distribution of oxygen and nutrients, interstitial pressure gradients and areas of patchy necrosis and inflammation. In this microenvironment, cancer cells that carry mutations favoring survival rather than cell death in response to stress find a selection advantage. Importantly, the signals derived from the disruption of orderly physiology within tissues are also what the immune system has evolved to respond to. The type of response is tuned to be adequate to the cause of the disruption. An infectious organism will carry or elicit from the involved tissue a number of 'danger signals' leading to development of cell mediated and humoral responses to both eliminating the invader and preventing future infections. In contrast, a simple wound will call for a repair response. The sensors of the type of damage are complex molecular interactions between the damaged organ and cells of the innate and adaptive immune system. Progress in the identification of these interactions elucidates which pathways are specifically altered in cancer. It also provides a novel understanding of the radiation-induced effects on tumor immunogenicity. We propose that specific radiation-induced effects could be successfully exploited to improve the effectiveness of immunotherapy.

NF-kappa B-mediated adaptive resistance to ionizing radiation

Ionizing radiation (IR) began to be a powerful medical modality soon after Wilhelm Röntgen's discovery of X-rays in 1895. Today, more than 50% of cancer patients receive radiotherapy at some time during the course of their disease. Recent technical developments have significantly increased the precision of dose delivery to the target tumor, making radiotherapy more efficient in cancer treatment. However, tumor cells have been shown to acquire a radioresistance that has been linked to increased recurrence and failure in many patients. The exact mechanisms by which tumor cells develop an adaptive resistance to therapeutic fractional irradiation are unknown, although low-dose IR has been well defined for radioadaptive protection of normal cells. This review will address the radioadaptive response, emphasizing recent studies of molecular-level reactions. A prosurvival signaling network initiated by the transcription factor NF-kappa B, DNA-damage sensor ATM, oncoprotein HER-2, cell cyclin elements (cyclin B1), and mitochondrial functions in radioadaptive resistance is discussed. Further elucidation of the key elements in this prosurvival network may generate novel targets for resensitizing the radioresistant tumor cells.

[On the problem of radioadaptation in small mammals (ecological specialization of species, radioresistance, hemopoiesis, immunity)]

The data illustrating ambivalent nature of radioresistance of rodents having different ecological specialization: wood mice (Apodemus uralensis Pallas 1811) and mole-voles (Ellobius talpinus Pallas 1770) to acute (laboratory experiment) and chronic (long-term inhabiting the East Ural Radioactive Trace - EURT) radiation action are presented. These species are greatly distinguished by a way of life, a migratory activity, an average life span etc. Numerous immunological, hematological disturbances were found in more radioresistant wood mice inhabiting in radioactively-polluted biogeocenosis (density of pollution 90Sr - 18.5 MBq/m2 = 500 Ci/km2). On the contrary there are no pathological shifts in more radiosensitive mole-voles from the EURT zone (density of pollution 90Sr - 37 MBq/m2 = 1000 Ci/km2). Comparative analysis of the hematological and immunological parameters and absorbed dose loads in rodents from radiocontaminated environment testify about the possibility of radioadaptation in a series of generations in Ellobius talpinus Pall. The leading role in development of radioadaptation of mole-voles belongs to ecophysiological peculiarities of the species.

Breaking Chemoresistance and Radioresistance with [213Bi]anti-CD45 Antibodies in Leukemia Cells

Chemoresistance and radioresistance are considered one of the primary reasons for therapeutic failure in leukemias and solid tumors. Targeted radiotherapy using monoclonal antibodies radiolabeled with alpha-particles is a promising treatment approach for high-risk leukemia. We found that targeted radiotherapy using monoclonal CD45 antibodies radiolabeled with the alpha-emitter (213)Bi ([(213)Bi]anti-CD45) induces apoptosis, activates apoptosis pathways, and breaks beta-irradiation-, gamma-irradiation-, doxorubicin-, and apoptosis-resistance in leukemia cells. In contrast to beta-irradiation-, gamma-irradiation-, and doxorubicin-mediated apoptosis and DNA damage, [(213)Bi]anti-CD45-induced DNA damage was not repaired, and apoptosis was not inhibited by the nonhomologous end-joining DNA repair mechanism. Depending on the activation of caspase-3, caspase-8, and caspase-9, [(213)Bi]anti-CD45 activated apoptosis pathways in leukemia cells through the mitochondrial pathway but independent of CD95 receptor/CD95 ligand interaction. Furthermore, [(213)Bi]anti-CD45 reversed deficient activation of caspase-3, caspase-8, and caspase-9, deficient cleavage of poly(ADP-ribose) polymerase, and deficient activation of mitochondria in chemoresistant and in radioresistant and apoptosis-resistant leukemia cells. These findings show that [(213)Bi]anti-CD45 is a promising therapeutic agent to break chemoresistance and radioresistance by overcoming DNA repair mechanisms in leukemia cells and provide the foundation for discovery of novel anticancer compounds.

Science to practice: why is the liver a radiosensitive organ?

Christiansen et al irradiated rat livers in vivo; isolated rat hepatocytes in vitro; and measured hepcidin, hemojuvelin, and ferroportin-1 gene expression. They also evaluated the influence of proinflammatory cytokines (interleukin [IL]- 1beta, IL-6, and tumor necrosis factor [TNF]-alpha) on the expression of these proteins. In this issue of Radiology, Christiansen et al conclude that radiation-induced cell-cell interactions by way of the cytokines can lead to death of irradiated hepatocytes.

The radiosensitizing effect of immunoadjuvant OM-174 requires cooperation between immune and tumor cells through interferon-gamma and inducible nitric oxide synthase

PURPOSE

To explore whether antitumor immunoadjuvant OM-174 can stimulate immune cells to produce interferon-gamma (IFN-gamma) and thereby radiosensitize tumor cells.

METHODS AND MATERIALS

Splenocytes from BALB/c mice were stimulated by OM-174 at plasma-achievable concentrations (0.03-3 mug/mL), and afterward analyzed for the expression and secretion of IFN-gamma by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Stimulated splenocytes were used as a source of IFN-gamma to radiosensitize hypoxic EMT-6 tumor cells through the cytokine-inducible isoform of nitric oxide synthase (iNOS).

RESULTS

OM-174 activated the production of IFN-gamma at high levels that reached 70 ng/mL in normoxia (21% oxygen) and 27 ng/mL in tumor-relevant hypoxia (1% oxygen). This caused up to 2.1-fold radiosensitization of EMT-6 tumor cells, which was associated with the iNOS-mediated production of the radiosensitizing molecule nitric oxide, as confirmed by accumulation of its oxidative metabolite nitrite, Western blot analysis, and reverse transcriptase-polymerase chain reaction. Both iNOS activation and radiosensitization were counteracted by neutralizing antibodies against IFN-gamma. The same mechanism of radiosensitization through the IFN-gamma secretion pathway was identified for IL-12 + IL-18, which are known to mediate IFN-gamma responses. Hypoxia displayed a dual effect on the immune-tumor cell interaction, by downregulating the expression of the IFN-gamma gene while upregulating iNOS at transcriptional level.

CONCLUSION

Immunoadjuvant OM-174 is an efficient radiosensitizer of tumor cells through activation of the IFN-gamma secretion pathway in immune cells. This finding indicates a rationale for combining immunostimulatory and radiosensitizing strategies and extends the potential therapeutic applications of OM-174.

No adaptation to UV-induced immunosuppression and DNA damage following exposure of mice to chronic UV-exposure

It is well known that ultraviolet (UV) radiation induces erythema, immunosuppression and carcinogenesis. We hypothesized that chronic exposure to solar UV radiation induces adaptation that eventually prevents the suppression of acquired immunity. We studied adaptation for UV-induced immunosuppression after chronic exposure of mice to a suberythemal dose of solar simulated radiation (SSR) with Cleo Natural lamps, and subsequent exposure to an immunosuppressive dose of solar or UVB radiation (TL12). After UV dosing, the mice were sensitized and challenged with either diphenylcyclopropenone (DPCP) or picryl chloride (PCl). To assess the adaptation induced by solar simulated radiation, we measured the proliferative response and cytokine production of skin-draining lymph node cells after immunization to DPCP, the contact hypersensitivity (CHS) response to PCl, and thymine-thymine (T-T) cyclobutane dimers in the skin of mice. After induction of immunosuppression by SSR or by TL12 lamps, the proliferative response of draining lymph node cells after challenge with DPCP, or the CHS after challenge with PCl, showed significant suppression of the immune response. Chronic irradiation from SSR preceding the immunosuppressive dose of UV failed to restore the suppressed immune response. Reduced lipopolysaccharide-triggered cytokine production (of IL-12p40, IFN-gamma, IL-6 and TNF-alpha) by draining lymph node cells of mice sensitized and challenged with DPCP indicated that no adaptation is induced. In addition, the mice were not protected from T-T dimer DNA damage after chronic solar irradiation. Our studies reveal no evidence that chronic exposure to low doses of SSR induces adaptation to UV-induced suppression of acquired immunity.

[The mechanism of MAb225 regulating radiosensitivity of Tca8113 cell]

PURPOSE

The objective of this study was to investigate the mechanism of MAb225 regulating radiosensitivity of Tca8113 cells.

METHODS

Tca8113 cells were treated with MAb225 of different concentrations. The apoptosis rate was analysed by FCM and bi-fluorescence stain, the repair of DNA damage after radiation was analysed by single cell gel electrophoresis, cells redistribution in each phase of cell cycle was analysed by FCM, and GSH level of cell were assessed by spectrophotometer.

RESULTS

Radiation alone (6 Gy) and MAb225 alone (0.5 microg/ml) produced a 2-fold induction of apoptosis respectively, whereas exposure to MAb225 (0.5 microg/ml) combination with 6 Gy of radiation induced apoptosis 5-6 fold, compared to untreated controls (F test). The length of comet tail of cells which treated with MAb225 was significantly longer than that of the control cells (t test, P<0.05). The percentage of cells in S phase was significantly decreased in MAb225 treated cells. Intracellular GSH level of MAb225 treated cells was significantly lower than that of untreated cells (t test, P<0.05).

CONCLUSION

MAb225 increased the radiosensitivity of Tca8113 cells by enhancing radiation-induced apoptosis, downregulating S phase percentage, inhibiting DNA repair after radiation and decreasing GSH level.

Human lymphoid and myeloid cell development in NOD/LtSz-scid IL2R gamma null mice engrafted with mobilized human hemopoietic stem cells

Ethical considerations constrain the in vivo study of human hemopoietic stem cells (HSC). To overcome this limitation, small animal models of human HSC engraftment have been used. We report the development and characterization of a new genetic stock of IL-2R common gamma-chain deficient NOD/LtSz-scid (NOD-scid IL2Rgamma(null)) mice and document their ability to support human mobilized blood HSC engraftment and multilineage differentiation. NOD-scid IL2Rgamma(null) mice are deficient in mature lymphocytes and NK cells, survive beyond 16 mo of age, and even after sublethal irradiation resist lymphoma development. Engraftment of NOD-scid IL2Rgamma(null) mice with human HSC generate 6-fold higher percentages of human CD45(+) cells in host bone marrow than with similarly treated NOD-scid mice. These human cells include B cells, NK cells, myeloid cells, plasmacytoid dendritic cells, and HSC. Spleens from engrafted NOD-scid IL2Rgamma(null) mice contain human Ig(+) B cells and lower numbers of human CD3(+) T cells. Coadministration of human Fc-IL7 fusion protein results in high percentages of human CD4(+)CD8(+) thymocytes as well human CD4(+)CD8(-) and CD4(-)CD8(+) peripheral blood and splenic T cells. De novo human T cell development in NOD-scid IL2Rgamma(null) mice was validated by 1) high levels of TCR excision circles, 2) complex TCRbeta repertoire diversity, and 3) proliferative responses to PHA and streptococcal superantigen, streptococcal pyrogenic exotoxin. Thus, NOD-scid IL2Rgamma(null) mice engrafted with human mobilized blood stem cells provide a new in vivo long-lived model of robust multilineage human HSC engraftment.

Targeted disruption of the Artemis murine counterpart results in SCID and defective V(D)J recombination that is partially corrected with bone marrow transplantation

Artemis is a mammalian protein, the absence of which results in SCID in Athabascan-speaking Native Americans (SCIDA). This novel protein has been implicated in DNA double-strand break repair and V(D)J recombination. We have cloned the Artemis murine counterpart, mArt, and generated a mouse with a targeted disruption of mArt. Artemis-deficient mice show a similar T-B- NK+ immunodeficiency phenotype, and carry a profound impairment in coding joint rearrangement, while retaining intact signal ends and close to normal signal joint formation. mArt-/- embryonic fibroblasts show increased sensitivity to ionizing radiation. Hemopoietic stem cell (HSC) transplantation using 500-5000 enriched congenic, but not allogeneic mismatched HSC corrected the T cell and partially corrected the B cell defect. Large numbers (40,000) of allogeneic mismatched HSC or pretreatment with 300 cGy of radiation overcame graft resistance, resulting in limited B cell engraftment. Our results suggest that the V(D)J and DNA repair defects seen in this mArt-/- mouse model are comparable to those in humans with Artemis deficiency, and that the recovery of immunity following HSC transplantation favors T rather than B cell reconstitution, consistent with what is seen in children with this form of SCID.

[Syngeneic and allogeneic immunosupression effects of post-irradiation volatile excretions of mice]

It was shown that immune and olfactory highly reactive CBA mice have reduced the ability to immune response in more extent under influence of volatile excretions of irradiated (4 Gy) singene mice, than allogene (C57Bl/6) mice. In lowreactive C57BL/6 mice deterioration of immune response also took place after influence of excretions of singene irradiated mice. There were no difference between the effects caused by excretions of intact and irradiated allogene (CBA) mice.

Persistence of recipient lymphocytes in NOD mice after irradiation and bone marrow transplantation

The non-obese diabetic (NOD) mouse is a unique and invaluable model of autoimmune disease, in particular type 1 diabetes. Bone marrow transplantation as a therapy for type 1 diabetes has been explored in NOD mice. NOD mice require higher doses of conditioning irradiation for successful allogeneic bone marrow transplantation, suggesting that NOD hematopoietic cells are radioresistant compared to those of other mouse strains. However, studies of hematopoietic reconstitution in NOD mice are hampered by the lack of mice bearing a suitable cell-surface marker that would allow transferred cells or their progeny to be distinguished. In order to monitor hematopoietic reconstitution in NOD mice we generated congenic NOD mice that carry the alternative allelic form of the pan-leukocyte alloantigen CD45. Following irradiation and congenic bone marrow transplantation, we found that the myeloid lineage was rapidly reconstituted by cells of donor origin but substantial numbers of recipient T lymphocytes persisted even after supra-lethal irradiation. This indicates that radiation resistance in the NOD hematopoietic compartment is a property primarily of mature T lymphocytes.

Individual radiosensitivity measured with lymphocytes may be used to predict the risk of fibrosis after radiotherapy for breast cancer

BACKGROUND AND PURPOSE

To analyse the relationship of individual cellular radiosensitivity and fibrosis after breast conserving therapy. A new model was used describing the percentage of patients developing fibrosis per year and per patient at risk.

PATIENTS AND METHODS

In a retrospective study, 86 patients were included, who had undergone breast conserving surgery and irradiation of the breast with a median dose of 55 Gy (54-55 Gy) given at 2.5 Gy/fraction (n=57) or 2 Gy/fraction (n=29). Median age was 62 years (range 44-86) and median follow-up was 7.5 years (range 5-17). Patients were examined for fibrosis according to the LENT/SOMA score. For analysis, fibrosis was classified as grade 0 and grade 1 (G0-1) or present grade 2 and grade 3 (G2-3). The time to complete development of fibrosis was determined by analysis of yearly mammograms. Individual cellular radiosensitivity was determined by scoring lethal chromosomal aberrations in in vitro irradiated (6 Gy) lymphocytes using metaphase technique. Patients with low/intermediate cellular radiosensitivity were compared with patients with high cellular radiosensitivity using actuarial methods.

RESULTS

Ten patients developed fibrosis at 1-8 years after radiotherapy. Individual cellular radiosensitivity was described by normal distribution of lethal chromosomal aberrations, the average was 5.47 lethal aberrations per cell (standard deviation (SD) 0.71). Cellular radiosensitivity was defined as low/intermediate (< or =6.18 lethal aberrations) in 73 patients and high (>6.18 lethal aberrations; mean+SD) in 13 patients. In both groups, the actuarial rate of fibrosis-free patients decreased exponentially with time after radiotherapy. Patients with high cellular radiosensitivity showed a 2.3-fold higher annual rate for fibrosis than patients with intermediate and low radiosensitivity (3.6 versus 1.6% per year).

CONCLUSIONS

In breast cancer patients, high individual cellular radiosensitivity as determined by the number of lethal chromosome aberrations in in vitro irradiated lymphocytes might be associated with an enhanced annual rate of fibrosis.

IL-15R alpha expression on CD8+ T cells is dispensable for T cell memory

The generation and maintenance of immunological memory requires the activation, expansion, and persistent proliferation of antigen-specific T cells. Recent work suggests that IL-15 may be important for this process. Surprisingly, we now find that expression of the high-affinity receptor for IL-15, IL-15R alpha, on T cells is dispensable for the generation or maintenance of memory CD8(+) T cells. By contrast, IL-15R alpha expression on cells other than T cells is absolutely critical for this function. These findings may be related to IL-15R alpha's ability to present IL-15 in trans to low-affinity IL-15R beta gamma(c) receptors on memory CD8(+) T cells. These unexpected results provide insights into how IL-15R alpha supports memory CD8(+) T cells.

In vivo maintenance of T-lymphocyte unresponsiveness induced by thymic medullary epithelium requires antigen presentation by radioresistant cells

The T-cell repertoire developing in the thymus is rid of autospecific cells by the process of thymic negative selection. Recognition of major histocompatibility complex (MHC)/self-peptide complexes expressed by thymic antigen-presenting cells (APC) of bone marrow origin leads to induction of apoptotic death of autospecific thymocytes. Induction of tolerance to self-antigens not presented by thymic APC is mediated by medullary thymic epithelial cells (mTEC) which express a very wide range of proteins, e.g. inducible and tissue-specific proteins. The main type of tolerance induced by mTEC is non-deletional and the issue of how it is maintained outside the thymus is therefore of crucial interest. We have previously shown that the non-T-cell receptor (TCR) -transgenic T-cell repertoire developing in conditions in which tolerance to self-MHC/peptide ligands is exclusively induced by mTEC is tolerant to syngeneic targets in vivo but lyses such targets in vitro. Here we report that this non-deletional in vivo self-tolerance is not due to active tolerance assured by known naturally occurring regulatory or immune-modulating T lymphocytes. Importantly, we show that in vivo maintenance of this therefore probably anergic state requires continued interaction of autospecific T cells with self-MHC/peptide ligands expressed by radioresistant cells while APC are incapable of maintaining the tolerant state. Therefore, maintenance of non-deletional T-lymphocyte tolerance to the wide range of self-antigens expressed by mTEC depends on continued interaction with radioresistant cells that very probably express a much more limited repertoire of antigens. Our data may therefore have important consequences for tolerance to tissue-specific and inducible self-antigens.

Postgestational lymphotoxin/lymphotoxin beta receptor interactions are essential for the presence of intestinal B lymphocytes

Lymphotoxin (LT), a cytokine belonging to the TNF family, has established roles in the formation of secondary lymphoid structures and in the compartmentalization of T and B lymphocyte areas of the spleen. In this study, we examine the role of LT in directing the composition of intestinal lymphocytes. We report that mice deficient in LT have a normal composition of intestinal lamina propria (LP) T lymphocytes, and an absence of intestinal LP B lymphocytes. We further refine this observation to demonstrate that the interaction of LT with the LTbetaR is essential for the presence LP B lymphocytes. The LT/LTbetaR-dependent events relevant for the presence of LP B lymphocytes occur after birth, do not require the presence of Peyer's patches, lymph nodes, or the spleen; and therefore, are distinct and independent from the previously identified roles of LT/LTbetaR. The LT-dependent signal relevant for the presence of LP B lymphocytes is optimally supplied by a LT-sufficient B lymphocyte, and requires a LTbetaR-sufficient radio-resistant, non-bone marrow-derived cell. Based upon the severity of the deficit of LP B lymphocytes we observed, these novel LT/LTbetaR-dependent events are of primary importance in directing the entry and residence of LP B lymphocytes.

Inhibition of radiation-induced nuclear factor-kappaB activation by an anti-Ras single-chain antibody fragment: lack of involvement in radiosensitization

We have shown previously that the transduction of a number of human tumor cell lines with an adenovirus (AV1Y28) expressing a single-chain antibody fragment (scFv) directed against Ras proteins results in radiosensitization. Because Ras is involved in the regulation of a number of transcription factors, we have determined the effects of this adenovirus on the activation of nuclear factor-kappaB (NF-kappaB), a radiation-responsive transcription factor associated with cell survival. In U251 human glioma cells, radiation-induced NF-kappaB was significantly attenuated by prior transduction of the anti-Ras scFv adenovirus. This effect appeared to involve an inhibition of IkappaB kinase activity and IkappaBalpha phosphorylation. Inhibitors to the Ras effectors mitogen-activated protein kinase kinase, phosphatidylinositol 3-kinase, and p38, however, did not reduce radiation-induced NF-kappaB. Whereas AV1Y28 inhibited NF-kappaB activation by hydrogen peroxide and ferricyanide, it had no effect of tumor necrosis factor-alpha-induced NF-kappaB activation. These results are consistent with a novel Ras-dependent, oxidant-specific signaling pathway mediating the activation of NF-kappaB. In additional cell lines radiosensitized by AV1Y28, radiation-induced NF-kappaB activation was also inhibited by the anti-Ras scFv, whereas in cell lines not radiosensitized, radiation did not activate NF-kappaB. This correlation suggested that AV1Y28-mediated radiosensitization involved the inhibition of radiation-induced NF-kappaB activation. However, inhibition of NF-kappaB activation via the expression of a dominant-negative form of IkappaBalpha in U251 cells had no effect on radiation-induced cell killing and did not influence AV1Y28-mediated radiosensitization. Therefore, whereas AV1Y28 inhibits radiation-induced NF-kappaB activation, this process does not appear to play a direct role in its radiosensitizing actions.

MIB-1 and p53 expression in radiotherapy-resistant T1aN0M0 glottic squamous cell carcinoma

Radiotherapy of T1aN0M0 glottic carcinoma results in a local control rate of 80-94%. This homogenous group, which is the earliest recognisable invasive malignancy in the head and neck region, provides a 'unique model' for studying possible biological markers of radiosensitivity. p53 and MIB-1 were investigated as possible markers of radiosensitivity in such a group. In all, 107 patients with T1aN0M0 glottic squamous cell carcinoma treated with radiotherapy were identified. Cases not responsive to radiotherapy were compared with matched radiosensitive controls by immunohistochemistry using monoclonal primary antibodies to MIB-1 (n = 18; controls = 10) and p53 (n = 6; controls = 11). No significant difference in p53 expression was noted between the two groups (P = 0.73). A greater MIB-1 expression was found in the radiosensitive group but only a trend towards significance was observed (P = 0.06). MIB-1 is a potential marker of radiosensitivity. A larger multicentre study is required for a more definitive answer.

Suppression of IgE responses in CD23-transgenic animals is due to expression of CD23 on nonlymphoid cells

Serum IgE is suppressed in CD23-transgenic (Tg) mice where B cells and some T cells express high levels of CD23, suggesting that CD23 on B and T cells may cause this suppression. However, when Tg B lymphocytes were compared with controls in B cell proliferation and IgE synthesis assays, the two were indistinguishable. Similarly, studies of lymphokine production suggested that T cell function in the Tg animals was normal. However, adoptive transfer studies indicated that suppression was seen when normal lymphocytes were used to reconstitute Tg mice, whereas reconstitution of controls with Tg lymphocytes resulted in normal IgE responses, suggesting that critical CD23-bearing cells are irradiation-resistant, nonlymphoid cells. Follicular dendritic cells (FDC) are irradiation resistant, express surface CD23, and deliver iccosomal Ag to B cells, prompting us to reason that Tg FDC may be a critical cell. High levels of transgene expression were observed in germinal centers rich in FDC and B cells, and IgE production was inhibited when Tg FDCs were cultured with normal B cells. In short, suppressed IgE production in CD23-Tg mice appears to be associated with a population of radioresistant nonlymphoid cells. FDCs that interface with B cells in the germinal center are a candidate for explaining this CD23-mediated IgE suppression.

Vascular endothelial growth factor receptor-2-blocking antibody potentiates radiation-induced long-term control of human tumor xenografts

Antiangiogenic therapy can enhance radiation-induced tumor growth inhibition. However, the effects of combined antiangiogenic and radiation therapy on long-term tumor control and normal tissue response have not been reported. We treated mice bearing two different human tumor xenografts with anti-vascular endothelial growth factor receptor-2 antibody (DC101) and five dose fractions of local radiation and followed them for at least 6 months. DC101 significantly decreased the dose of radiation necessary to control 50% of tumors locally. The decrease was 1.7- and 1.3-fold for the moderately radiosensitive small cell lung carcinoma 54A and the highly radioresistant glioblastoma multiforme U87, respectively. In contrast to tumors, no increase in skin radiation reaction by the antibody was detected. Surprisingly, 44% of mice bearing 54A tumor developed clear ascites after DC101 treatment at its highest dose; this was fatal to 20% of mice. This adverse effect was seen only in mice that received whole-body irradiation 1 day before tumor implantation. The encouraging results on two human tumor xenografts suggest that vascular endothelial growth factor receptor-2 blockade merits further investigation to assess its potential as an enhancer of radiation therapy in the clinic.

Interleukin-7 mediates the homeostasis of naïve and memory CD8 T cells in vivo

The naïve and memory T lymphocyte pools are maintained through poorly understood homeostatic mechanisms that may include signaling via cytokine receptors. We show that interleukin-7 (IL-7) plays multiple roles in regulating homeostasis of CD8+ T cells. We found that IL-7 was required for homeostatic expansion of naïve CD8+ and CD4+ T cells in lymphopenic hosts and for CD8+ T cell survival in normal hosts. In contrast, IL-7 was not necessary for growth of CD8+ T cells in response to a virus infection but was critical for generating T cell memory. Up-regulation of Bcl-2 in the absence of IL-7 signaling was impaired after activation in vivo. Homeostatic proliferation of memory cells was also partially dependent on IL-7. These results point to IL-7 as a pivotal cytokine in T cell homeostasis.

NOD/LtSz-Rag1null mice: an immunodeficient and radioresistant model for engraftment of human hematolymphoid cells, HIV infection, and adoptive transfer of NOD mouse diabetogenic T cells

Development of a small animal model for the in vivo study of human immunity and infectious disease remains an important goal, particularly for investigations of HIV vaccine development. NOD/Lt mice homozygous for the severe combined immunodeficiency (Prkdcscid) mutation readily support engraftment with high levels of human hematolymphoid cells. However, NOD/LtSz-scid mice are highly radiosensitive, have short life spans, and a small number develop functional lymphocytes with age. To overcome these limitations, we have backcrossed the null allele of the recombination-activating gene (Rag1) for 10 generations onto the NOD/LtSz strain background. Mice deficient in RAG1 activity are unable to initiate V(D)J recombination in Ig and TCR genes and lack functional T and B lymphocytes. NOD/LtSz-Rag1null mice have an increased mean life span compared with NOD/LtSz-scid mice due to a later onset of lymphoma development, are radioresistant, and lack serum Ig throughout life. NOD/LtSz-Rag1null mice were devoid of mature T or B cells. Cytotoxic assays demonstrated low NK cell activity. NOD/LtSz-Rag1null mice supported high levels of engraftment with human lymphoid cells and human hemopoietic stem cells. The engrafted human T cells were readily infected with HIV. Finally, NOD/LtSz-Rag1null recipients of adoptively transferred spleen cells from diabetic NOD/Lt+/+ mice rapidly developed diabetes. These data demonstrate the advantages of NOD/LtSz-Rag1null mice as a radiation and lymphoma-resistant model for long-term analyses of engrafted human hematolymphoid cells or diabetogenic NOD lymphoid cells.

CD8(+), radiosensitive T cells of parental origin, oppose cells capable of down-regulating cytotoxicity in murine acute lethal graft-versus-host disease

Murine graft-versus-host (GVH) disease takes two forms depending upon the parental/F1 strain combination employed. Anemia, lymphopenia, hypogammaglobulinemia, profound anti-F1 cytotoxicity, and the loss of cytotoxic potential against third party alloantigen is seen in acute lethal GVH disease. In contrast to this, in chronic GVH disease there is polyclonal B cell activation, auto-antibody production, no anti-F1 cytotoxicity, and retained cytotoxicity against allotargets. We have previously reported that this marked disparity in disease expression results from a radiosensitive host veto cell which protects the F1 mouse from parental anti-F1 cytotoxicity in mice undergoing CGVH disease. This cell could be induced in vitro or in vivo in CGVH disease. Using an in vitro system, we now demonstrate that a CD4(+), radiation-sensitive, T cell does emerge in acute lethal GVH disease which is capable of down-regulating cytotoxicity. The cell does not appear to be a veto cell in that it attenuates cytotoxicity directed against nonself alloantigen. The function of this cell does not appear to be influenced by minor lymphocyte stimulatory gene products. We further report that, in ALGVH disease, regulation by this cell is not readily apparent due to the emergence of a CD8(+) T cell of parental (B6) origin, which opposes its action.

Equal distribution of competitive long-term repopulating stem cells in the CD34+ and CD34- fractions of Thy-1lowLin-/lowSca-1+ bone marrow cells

CD34 antigen is present on most, if not all, human hematopoietic stem cells (HSCs). Consistent with this pattern of expression, we recently reported that primitive murine HSCs defined as competitive long-term repopulating units (CRUs) are highly enriched among CD34+ bone marrow (BM) cells (one CRU/2500 cells). However, in agreement with one recent report that some murine HSCs do not express CD34 (Science 273:242), we observed that 15% of phenotypically defined Thy-1lowLin-/lowSca-1+ (TLS) stem cells were CD34- by fluorescence-activated cell sorting. To examine further the nature of CD34 expression on murine hematopoietic cells, we separated TLS cells into CD34+ (0.022% of BM cells) and CD34- (0.005% of BM cells) fractions, confirmed their phenotype by reverse transcriptase-polymerase chain reaction analysis of CD34 transcripts, and evaluated them in a variety of in vitro and in vivo assays. The CD34+ TLS population contained most (93-95%) of the day 12 spleen colony-forming units (CFU-S) and in vitro colony-forming cells (CFCs). Cobblestone area-forming cells (CAFCs) able to proliferate on a murine bone marrow stromal cell line (SyS-1) represented one of every 5 CD34+ TLS and one of every 31 CD34 TLS cells. When lethally irradiated mice were injected with 100 CD34+ TLS cells, all animals survived and began to recover circulating leukocytes, platelets, and erythrocytes by 15 days. In contrast, only 40% of mice injected with 100 CD34- TLS cells were radioprotected, and hematopoietic reconstitution in surviving mice was not apparent until 21 days. The frequency of CRUs in CD34+ and CD34 TLS cells was determined by injecting limiting numbers of cells into lethally irradiated Ly-5 congenic hosts together with 10(5) "compromised" BM cells to provide radioprotection. CRUs able to regenerate and maintain lymphoid and myeloid cells for at least 6 months in primary and 5 months in secondary hosts represented one of every 156 CD34+ TLS and one of every 35 CD34- TLS cells. However, when normalized for the proportion of TLS cells that were CD34+ or CD34-, it was determined that the recovery of CRU among CD34+ and CD34- TLS cells was equivalent (46% and 54%, respectively). These data are consistent with the previous description of repopulating HSCs among CD34-c-kit+Sca-1+Lin- cells (Science 273:242, 1996) and provide additional evidence that TLS cells are functionally heterogeneous and can be further fractionated on the basis of CD34 expression. Overall, approximately 95% of CFCs, CFU-S, and CAFCs in the TLS population were found to be CD34+, whereas more primitive CRU were distributed equally among CD34+ and CD34 TLS cells. These results should enable better characterization of the most primitive stem cells in murine BM.

Cellular radiosensitivity in human severe-combined-immunodeficiency (SCID) syndromes

PURPOSE

The aim of the work was to establish to what extent a variety of human severe-combined-immunodeficiency (SCID) disorders are associated with in vitro cellular hypersensitivity to ionizing radiation.

MATERIALS AND METHODS

A study was made of fibroblast strains established from individuals with adenosine deaminase deficiency, T(-)B(-) SCID, Omenn's syndrome and a SCID heterozygote. For comparison, an assessment was also made of the radiosensitivity of a series of fibroblast strains derived from: normal donors, a patients with ataxia-telangiectasia (A-T) and an A-T heterozygote. Radiosensitivity was determined using a clonogenic assay following both high (HDR) and low (LDR) dose-rate irradiation.

RESULTS

Following HDR irradiation, the fibroblast strains derived from the different human SCID disorders displayed a wide range of radiosensitivity: the adenosine deaminase deficiency cells were similar in radiosensitivity to normal fibroblasts, T(-)B(-) cells were as hypersensitive to radiation as A-T cells and the Omenn's syndrome cells showed intermediate radiosensitivity. However, whereas all four normal cell strains studied showed significant LDR sparing, none of the SCID fibroblasts did.

CONCLUSIONS

These data indicate that human SCID is variable in terms of radiosensitivity depending on the particular defect. In addition, the lack of LDR sparing of radiation-induced damage suggests the involvement of some form(s) of DNA repair defect in all the human SCID syndromes.

The effect of ionizing radiation on signal transduction: antibodies to EGF receptor sensitize A431 cells to radiation

What determines the degree of cell-resistance or sensitivity to ionizing radiation is not yet known. As a corollary to the ability of ceramide to induce apoptosis, some questions arise as to whether malignant cells escape apoptosis because of their inability to mount a ceramide response to inducers of apoptosis. To shed more light on the molecular mechanisms of tumor cell response to radiation, we tested whether exposure to ionizing radiation (of 200-1000 cGy) is associated with changes in ceramide levels in A431 tumor epithelial cells and whether the ability of ceramide to induce apoptosis is inhibited by protein kinase C (PKC) activation. Our studies demonstrate an immediate decrease in cellular levels of ceramide in response to radiation, while sphingosine levels increase. Under the same conditions the cellular 1,2-diacylglycerol (DAG) levels decrease as well, being accompanied by the translocation of PKC alpha from the membrane to the cytoplasm. Elevation of membrane PKC levels by 12-O-tetradecanoylphorbol 13-acetate (TPA) treatment had no effect on cell survival after irradiation, while treatment with EGF during and after irradiation augmented cell survival. Moreover, monoclonal antibodies to the EGF receptor (EGFR) sensitize cells to radiation by facilitating radiation-induced apoptosis. It is thus plausible that in human Squamous carcinoma cells, radiation activates predominantly the EGFR to induce resistance, while both sphingomyelin and PKC signal transduction pathways are deactivated and demonstrate no significant role in the modulation of the sensitivity or the resistance of A431 cells to ionizing radiation.

[The immunobiological properties of a corpuscular pertussis vaccine inactivated by gamma irradiation]

As a result of the high-dose gamma-irradiation (50 kGy) of corpuscular pertussis vaccine (CPV), pertussis radiovaccine (PRV) was obtained. Compared with CPV, PRV was shown to possess reduced toxicity and higher protective potency. Its adjuvant properties remained at the initial level, while its leukocytosis-promoting and histamine-sensitizing activities drastically decreased. Moreover, PRV produced less pronounced stimulating effect on the proliferation of hematopoietic stem cells, but, in contrast to CPV, was shown to capable of protecting mice from lethal radiation.

Monoclonal anti-tumor necrosis factor antibody renders non-obese diabetic mice hypersensitive to irradiation and enhances insulitis development

In attempt to evaluate biological roles of tumor necrosis factor (TNF), we studied the effects of anti-TNF mAb in non-obese diabetic (NOD) mice. Anti-murine TNF mAb rendered NOD mice hypersensitive to the lethal effects of radiation and prevented the reconstitution of lethally irradiated mice with adoptively transferred lymphocytes. While TNF-alpha reduced the incidence of diabetes development in the adoptive transfer system even when given 6 days post-transfer, mAb to TNF could not reduce or increase the incidence of diabetes compared to control mice. Administration of TNF-alpha for 4 or 8 weeks significantly reduced the incidence of spontaneous insulitis in NOD mice, while anti-TNF mAb given for 8 weeks increased the incidence of insulitis significantly.

Selective radiation resistance of immunologically induced T cells as the basis for irradiation-induced T-cell-mediated regression of immunogenic tumor

Sublethal, whole-body gamma-irradiation of immunocompetent, but not T cell deficient, mice bearing an established immunogenic tumor results in T-cell-mediated complete tumor regression and in long-term host survival. This striking T-cell-dependent immunotherapeutic action of irradiation was paradoxically associated with the destruction of over 90% of host T cells and with a state of severe immunodepression as evidenced by the inability of irradiated mice to reject a tumor allograft. Furthermore, whereas exposure to 500 rads caused regression of a syngeneic tumor implanted 6 days before irradiation, it caused enhanced growth of a different syngeneic tumor growing on the same animal and implanted 1 day before. This ability of irradiation to cause regression of a 6 day tumor, but accelerated growth of a 1 day tumor, was also seen when the tumors were implanted in the reverse order. This means that, between days 1 and 6 of a tumor growth, tumor-specific T cells are converted from a radiosensitive to a highly radioresistant state, almost certainly because of having been activated and inducted into the antitumor immune response. This explanation for the selective radioresistance of effector T cells is based on publications showing that activated, in contrast to resting, T cells are highly radioresistant. Thus irradiation-induced, T-cell-mediated tumor regression depends not only on the destruction of radiosensitive suppressor T cells but also on the selective sparing of radioresistant activated effector T cells that are needed to destroy the tumor in the absence of suppression.

[Various indicators of the immune status of medical roentgenologists]

Study of certain immune status indicators of medical roentgenologists has detected certain immunodeficiency associated with exposure to low doses of ionizing radiation. The number of T-lymphocytes has been noticed to be reduced, while the degree of reduction increases with age, duration of work in the sphere of radiation, and the value of the individual dose of radiation within a year. B-lymphocytes number is susceptible to changes in a smaller degree.

Transplantation resistance to a murine plasmacytoma lacking MHC determinants

A spontaneously arising murine plasmacytoma, HPC-202, derived from a BALB/c.H-2b congenic mouse that lacks any detectable H-2 determinants on its cell surface is described. However, the expression of H-2 determinants is inducible by interferon-gamma. The H-2 negative cell surface phenotype permits the HPC-202 tumor to escape H-2 allospecific cytotoxic cell lysis but not NK cell lysis, as well as to grow, to varying degrees, in some H-2 incompatible hosts. In those strains which exhibit a resistance to HPC-202 growth, resistance does not map to a single gene within the major histocompatibility complex of the mouse. Resistance is also radiosensitive and is therefore presumably due to a rapidly dividing cell population. The utility of this tumor as a model system to study both the non-H-2-restricted natural resistance to tumor growth, and the mechanism by which H-2 genes are regulated by cells is discussed.