SARS-CoV-2 transmission in educational settings during an early summer epidemic wave in Luxembourg, 2020.

BACKGROUND: Following a first wave in spring and gradual easing of lockdown, Luxembourg experienced an early second epidemic wave of SARS-CoV-2 before the start of summer school holidays on 15th July. This provided the opportunity to investigate the role of school-age children and school settings for transmission. METHODS: We compared the incidence of SARS-CoV-2 in school-age children, teachers and the general working population in Luxembourg during two epidemic waves: a spring wave from March-April 2020 corresponding to general lockdown with schools being closed and May-July 2020 corresponding to schools being open. We assessed the number of secondary transmissions occurring in schools between May and July 2020 using routine contact tracing data. RESULTS: During the first wave in March-April 2020 when schools were closed, the incidence in pupils peaked at 28 per 100,000, while during the second wave in May-July 2020 when schools were open, incidence peaked 100 per 100,000. While incidence of SARS-CoV-2 was higher in adults than in children during the first spring wave, no significant difference was observed during the second wave in early summer. Between May and July 2020, we identified a total of 390 and 34 confirmed COVID-19 cases among 90,150 school-age children and 11,667 teachers, respectively. We further estimate that 179 primary cases caused 49 secondary cases in schools. While some small clusters of mainly student-to-student transmission within the same class were identified, we did not observe any large outbreaks with multiple generations of infection. CONCLUSIONS: Transmission of SARS-CoV-2 within Luxembourg schools was limited during an early summer epidemic wave in 2020. Precautionary measures including physical distancing as well as easy access to testing, systematic contact tracing appears to have been successful in mitigating transmission within educational settings.

Comparison study of in vivo dose response to laser-driven versus conventional electron beam.

The long-term goal to integrate laser-based particle accelerators into radiotherapy clinics not only requires technological development of high-intensity lasers and new techniques for beam detection and dose delivery, but also characterization of the biological consequences of this new particle beam quality, i.e. ultra-short, ultra-intense pulses. In the present work, we describe successful in vivo experiments with laser-driven electron pulses by utilization of a small tumour model on the mouse ear for the human squamous cell carcinoma model FaDu. The already established in vitro irradiation technology at the laser system JETI was further enhanced for 3D tumour irradiation in vivo in terms of beam transport, beam monitoring, dose delivery and dosimetry in order to precisely apply a prescribed dose to each tumour in full-scale radiobiological experiments. Tumour growth delay was determined after irradiation with doses of 3 and 6 Gy by laser-accelerated electrons. Reference irradiation was performed with continuous electron beams at a clinical linear accelerator in order to both validate the dedicated dosimetry employed for laser-accelerated JETI electrons and above all review the biological results. No significant difference in radiation-induced tumour growth delay was revealed for the two investigated electron beams. These data provide evidence that the ultra-high dose rate generated by laser acceleration does not impact the biological effectiveness of the particles.

Antibodies against potassium channel interacting protein 2 induce necrosis in isolated rat cardiomyocytes.

Auto-antibodies against cardiac proteins have been described in patients with dilated cardiomyopathy. Antibodies against the C-terminal part of KChIP2 (anti-KChIP2 [C-12]) enhance cell death of rat cardiomyocytes. The underlying mechanisms are not fully understood. Therefore, we wanted to explore the mechanisms responsible for anti-KChIP2-mediated cell death. Rat cardiomyocytes were treated with anti-KChIP2 (C-12). KChIP2 RNA and protein expressions, nuclear NF-κB, mitochondrial membrane potential Δψm, caspase-3 and -9 activities, necrotic and apoptotic cells, total Ca(2+) and K(+) concentrations, and the effects on L-type Ca(2+) channels were quantified. Anti-KChIP2 (C-12) induced nuclear translocation of NF-κB. Anti-KChIP2 (C-12)-treatment for 2 h significantly reduced KChIP2 mRNA and protein expression. Anti-KChIP2 (C-12) induced nuclear translocation of NF-κB after 1 h. After 6 h, Δψm and caspase-3 and -9 activities were not significantly changed. After 24 h, anti-KChIP2 (C-12)-treated cells were 75 ± 3% necrotic, 2 ± 1% apoptotic, and 13 ± 2% viable. Eighty-six ± 1% of experimental buffer-treated cells were viable. Anti-KChIP2 (C-12) induced significant increases in total Ca(2+) (plus 11 ± 2%) and K(+) (plus 18 ± 2%) concentrations after 5 min. Anti-KChIP2 (C-12) resulted in an increased Ca(2+) influx through L-type Ca(2+) channels. In conclusion, our results suggest that anti-KChIP2 (C-12) enhances cell death of rat cardiomyocytes probably due to necrosis.

Optical control of hard X-ray polarization by electron injection in a laser wakefield accelerator.

Laser-plasma particle accelerators could provide more compact sources of high-energy radiation than conventional accelerators. Moreover, because they deliver radiation in femtosecond pulses, they could improve the time resolution of X-ray absorption techniques. Here we show that we can measure and control the polarization of ultra-short, broad-band keV photon pulses emitted from a laser-plasma-based betatron source. The electron trajectories and hence the polarization of the emitted X-rays are experimentally controlled by the pulse-front tilt of the driving laser pulses. Particle-in-cell simulations show that an asymmetric plasma wave can be driven by a tilted pulse front and a non-symmetric intensity distribution of the focal spot. Both lead to a notable off-axis electron injection followed by collective electron-betatron oscillations. We expect that our method for an all-optical steering is not only useful for plasma-based X-ray sources but also has significance for future laser-based particle accelerators.

Deducing the electron-beam diameter in a laser-plasma accelerator using x-ray betatron radiation.

We investigate the properties of a laser-plasma electron accelerator as a bright source of keV x-ray radiation. During the interaction, the electrons undergo betatron oscillations and from the carefully measured x-ray spectrum the oscillation amplitude of the electrons can be deduced which decreases with increasing electron energies. From the oscillation amplitude and the independently measured x-ray source size of (1.8±0.3) µm we are able to estimate the electron bunch diameter to be (1.6±0.3) µm.

High resolution 3D gas-jet characterization.

We present a tomographic characterization of gas jets employed for high-intensity laser-plasma interaction experiments where the shape can be non-symmetrically. With a Mach-Zehnder interferometer we measured the phase shift for different directions through the neutral density distribution of the gas jet. From the recorded interferograms it is possible to retrieve 3-dimensional neutral density distributions by tomographic reconstruction based on the filtered back projections. We report on criteria for the smallest number of recorded interferograms as well as a comparison with the widely used phase retrieval based on an Abel inversion. As an example for the performance of our approach, we present the characterization of nozzles with rectangular openings or gas jets with shock waves. With our setup we obtained a spatial resolution of less than 60 µm for an Argon density as low as 2 × 10(17) cm(-3).

Long-term pharmacologically regulated expression of erythropoietin in primates following AAV-mediated gene transfer.

Gene therapy is a potential route for the delivery of secreted therapeutic proteins, but pharmacologic control of expression will generally be required for optimal safety and efficacy. Previous attempts to achieve regulated expression in large animal models have been thwarted by transient expression or immune responses to regulatory proteins. We evaluated the ability of the dimerizer-regulated gene expression system to achieve controlled, long-term production of erythropoietin (Epo) following intramuscular administration of adeno-associated virus (AAV) vectors to 16 primates. All animals showed dose-responsive and completely reversible elevation of Epo and hematocrit in response to the dimerizer rapamycin, or analogs with reduced immunosuppressive activity, administered intravenously or orally. Animals that received optimized dual vectors showed persistent regulated expression for the duration of the study, with no apparent immune response to Epo or the regulatory proteins. Similar results were obtained with single vectors incorporating both the Epo and regulatory genes, including those packaged into serotype 1 AAV vectors to allow use of lower viral doses. For the longest-studied animal, regulated expression has persisted for more than 6 years and 26 induction cycles. These data indicate that one-time or infrequent gene transfer followed by dimerizer regulation is a promising approach for delivery of therapeutic proteins.

Preexisting immunity to adenovirus in rhesus monkeys fails to prevent vector-induced toxicity.

In an earlier study we evaluated innate immune responses to a first-generation adenoviral vector infused into the portal vein of rhesus monkeys who had never been exposed to adenovirus previously. In these animals, the systemic administration of E1/E3-deleted adenoviral vectors resulted in immediate activation of innate immunity and serious toxicity caused by targeting of vector to antigen-presenting cells and systemic inflammation. We analyze here how these responses are affected by vector-specific preexisting immunity that was induced by intramuscular immunization 6 months prior to evaluation. Our results show that preexposure to the vector substantially diminishes the transgene expression in most tissues but has little effect on gene transfer. Significantly, preimmunization does not eliminate systemic vector-induced toxicity. These conclusions are based on the presence of clinical features of coagulopathy and elevated levels of proinflammatory cytokine interleukin-6 in the serum of animals treated with vector after intramuscular immunization. Furthermore, preexisting immunity appears to induce a vector-specific inhibitory effect on erythroid progenitor development in the bone marrow that is not found when naive animals are challenged with vector.

Effect of blood collection technique in mice on clinical pathology parameters.

A study was conducted in normal healthy C57BL/6 mice to determine the effect of method of blood collection on clinical pathology parameters and to provide value ranges for these parameters. Males and females were used and were randomly assigned to treatment groups based upon phlebotomy method. The blood was collected using one of four methods: intracardiac (IC), a single attempt at collection from the caudal vena cava (VC), collection from the caudal vena cava with collection of any extravasated blood from the peritoneum (MC), or retroorbital phlebotomy (RO). Evaluation of blood and serum samples was conducted for a number of serum biochemistries including liver function tests and complete blood count with differentials and platelet counts. Female mice demonstrated higher values for red blood cell number, hemoglobin (p < 0.002), hematocrit, alkaline phosphatase, albumin, total protein, and creatinine. Males demonstrated higher values for platelet counts, specific white blood cell numbers (total, neutrophil, lymphocyte, and eosinophil counts), globulin, amylase, and the BUN/creatinine ratio. Overall, the VC method was associated with the least variation in both sexes and appeared slightly better than the IC method for the parameters evaluated. The largest difference between groups was noted for the transaminase levels. While alanine aminotransferase (ALT) values were similar between the IC and VC groups, aspartate aminotransferase (AST) values were associated with less variation for the VC method. Transaminase levels for the MC and RO groups were associated with relatively large ranges and variation. ALT results from the RO method, the only method amenable to repetitive sample collection used in this evaluation, indicate that this is an acceptable method. The results demonstrate the substantial impact that phlebotomy method has on the assay results and that the VC or IC methods provide the most consistent results. The ranges by collection method and sex provided here can be used to select the preferred method of collection when designing a study and for comparison of data obtained with reference ranges. The authors recommend establishment of normal ranges based upon methods employed within an investigator's laboratory.

A New Method to Collect Bile and Access the Duodenum in Conscious Dogs.

A novel, totally implantable catheter system that allows complete bile collection and duodenal access in conscious, freely moving dogs is described. Bile collection catheters remained patent for an average of 417 days (range, 711010 days) in eight animals which were used on study. Three animals have been used to validate the models complete collection of bile via biliary recovery of an intravenous dose of 14C-glycocholic acid, and in selected animals, parameters potentially indicative of liver damage (serum alanine aminotransferase, alkaline phosphatase, gamma glutamyltransferase, and total bilirubin levels) were within normal ranges for as many as 14 months after surgery. The eight study dogs have been used in a total of 29 studies, in which bile was successfully collected for 1248 h. The bile has been collected by using either a tethering system or a protected pouch arrangement. Compared to exteriorized catheter techniques, this system requires less maintenance and is better tolerated by the animals. The potential for a longer functional life span for individual animals, more normal liver enzymes, and the capability to selectively infuse towards the duodenum and flush the entire catheter and bile duct are other advantages of this model.