Rapid High-Yield Production of Functional SARS-CoV-2 Receptor Binding Domain by Viral and Non-Viral Transient Expression for Pre-Clinical Evaluation

Vaccine design strategies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are focused on the Spike protein or its subunits as the main antigen target of neutralizing antibodies. In this work, we propose rapid production methods of an extended segment of the Spike Receptor Binding Domain (RBD) in HEK293SF cells cultured in suspension, in serum-free media, as a major component of a COVID-19 subunit vaccine under development. The expression of RBD, engineered with a sortase-recognition motif for protein-based carrier coupling, was achieved at high yields by plasmid transient transfection or human type-5-adenoviral infection of the cells, in a period of only two and three weeks, respectively. Both production methods were evaluated in 3L-controlled bioreactors with upstream and downstream bioprocess improvements, resulting in a product recovery with over 95% purity. Adenoviral infection led to over 100 µg/mL of RBD in culture supernatants, which was around 7-fold higher than levels obtained in transfected cultures. The monosaccharide and sialic acid content was similar in the RBD protein from the two production approaches. It also exhibited a proper conformational structure as recognized by monoclonal antibodies directed against key native Spike epitopes. Efficient direct binding to ACE2 was also demonstrated at similar levels in RBD obtained from both methods and from different production lots. Overall, we provide bioprocess-related data for the rapid, scalable manufacturing of low cost RBD based vaccines against SARS-CoV-2, with the added value of making a functional antigen available to support further research on uncovering mechanisms of virus binding and entry as well as screening for potential COVID-19 therapeutics.

Validity and reliability of the session-RPE method for quantifying training load in karate athletes

AIM

To test the construct validity and reliability of the session rating of perceived exertion (sRPE) method by examining the relationship between RPE and physiological parameters (heart rate: HR and blood lactate concentration: [La --] ) and the correlations between sRPE and two HR--based methods for quantifying internal training load (Banister's method and Edwards's method) during karate training camp.

METHODS

Eighteen elite karate athletes: ten men (age: 24.2 ± 2.3 y, body mass: 71.2 ± 9.0 kg, body fat: 8.2 ± 1.3% and height: 178 ± 7 cm) and eight women (age: 22.6 ± 1.2 y, body mass: 59.8 ± 8.4 kg, body fat: 20.2 ± 4.4%, height: 169 ± 4 cm) were included in the study. During training camp, subjects participated in eight karate--training sessions including three training modes (4 tactical--technical, 2 technical--development, and 2 randori training), during which RPE, HR, and [La -- ] were recorded.

RESULTS

Significant correlations were found between RPE and physiological parameters (percentage of maximal HR: r = 0.75, 95% CI = 0.64--0.86; [La --] : r = 0.62, 95% CI = 0.49--0.75; P < 0.001). Moreover, individual sRPE was significantly correlated with two HR--based methods for quantifying internal training load ( r = 0.65--0.95; P < 0.001). The sRPE method showed the high reliability of the same intensity across training sessions (Cronbach's α = 0.81, 95% CI = 0.61--0.92).

CONCLUSION

This study demonstrates that the sRPE method is valid for quantifying internal training load and intensity in karate.

Investigation of exciton photodissociation, charge transport and photovoltaic response of poly(N-vinyl carbazole):TiO(2) nanocomposites for solar cell applications

The photogeneration of charge carriers in spin-coated thin films of nanocrystalline (nc-)TiO(2) particles dispersed in a semiconducting polymer, poly(N-vinylcarbazole) (PVK), has been studied by photoluminescence and charge transport measurements. The solvent and the TiO(2) particle concentration have been selected to optimize the composite morphology. A large number of small domains leading to a large interface and an improved exciton dissociation could be obtained with tetrahydrofuran (THF). The charge transport mechanism and trap distribution at low and high voltage in ITO/nc-TiO(2):PVK/Al diodes in the dark could be identified by current-voltage measurements and impedance spectroscopy. The transport mechanism is space charge limited with an exponential trap distribution in the high voltage regime (1-4 V), whereas a Schottky process with a barrier height of about 0.9 eV is observed at low bias voltages (<1 V). The current-voltage characteristics under white illumination have shown a dramatic increase of the short circuit current density J(sc) and open circuit voltage V(oc) for a 30% TiO(2) volume content corresponding to the morphology exhibiting the best dispersion of TiO(2) particles. A degradation of the photovoltaic properties is induced at higher compositions by the formation of larger TiO(2) aggregates. A procedure has been developed to extract the physical parameters from the J-V characteristics in the dark and under illumination on the basis of an equivalent circuit. The variation of the solar cell parameters with the TiO(2) composition confirms that the photovoltaic response is optimum for 30% TiO(2) volume content. It is concluded that the photovoltaic properties of nc-TiO(2):PVK nanocomposites are controlled by the interfacial area between the donor and the acceptor material and are limited by the dispersion of the TiO(2) nanoparticles in the polymer.

Reference phase-shifter for measuring high power microwave impedance by using a phase modulation method

A basic mechanical phase-shifter is described and proposed for use as a reference circuit for impedance measurements with a phase modulation method. It consists of a section of a curved rectangular waveguide, the length of which is mechanically varied with a stepper motor. The phase-shifter functions without gears. It can be used successfully in industrial set-ups with a pulsed or CW generator which are of low stability in frequency and in amplitude.