Point-of-care detection of SARS-CoV-2 in nasopharyngeal swab samples using an integrated smartphone-based centrifugal microfluidic platform (preprint)

With its origin estimated around December 2019 in Wuhan, China, the ongoing 2020 SARS-CoV-2 pandemic is a major global health challenge, resulting in more than 45 million infections and 1.2 million deaths. The demand for scalable, rapid and sensitive viral diagnostics is thus particularly pressing at present to help contain the rapid spread of infection and prevent overwhelming the capacity of health systems. While high-income countries have managed to rapidly expand diagnostic capacities, such is not the case in resource-limited settings of low- to medium-income countries. Aiming at developing cost-effective viral load detection systems for point-of-care COVID-19 diagnostics in resource-limited and resource-rich settings alike, we report the development of an integrated modular centrifugal microfluidic platform to perform loop-mediated isothermal amplification (LAMP) of viral RNA directly from heat-inactivated nasopharyngeal swab samples. The discs were pre-packed with dried n-benzyl-n-methylethanolamine modified agarose beads used as a versatile post-nucleic acid amplification signal enhancement strategy, allowing fluorescence detection via a smartphone camera and simple optics. The platform provided sample-to-answer analysis within 1 hour from sample collection and a detection limit between 100 and 1000 RNA copies in 10 L reaction volume. Furthermore, direct detection of non-extracted SARS-CoV-2 RNA in nasopharyngeal swab samples from patients with Ct values below 26 (n=25 plus 6 PCR negative samples) was achieved with ~94% sensitivity and 100% specificity, thus being fit-for-purpose to diagnose patients with a high risk of viral transmission. These results show significant promise towards bringing routine point-of-care COVID-19 diagnostics closer to resource-limited settings.

SARS-CoV-2 detection by extraction-free qRT-PCR for massive and rapid COVID-19 diagnosis during a pandemic (preprint)

COVID-19 pandemic severely impacted the healthcare and economy on a global scale. It is widely recognized that mass testing is an efficient way to contain the infection spread as well as the development of informed policies for disease management. However, the current COVID-19 worldwide infection rates increased demand in the rapid and reliable screening of SARS-CoV-2 infection. We compared the performance of qRT-PCR in direct heat-inactivated, heat-inactivated/pelleted samples against RNA in a group of 74 subjects (44 positive and 30 negative). In addition, we compared the sensitivity of heat-inactivated/pelleted in another group of 196 COVID-19 positive samples. Our study suggests that swab sample heat-inactivation and pelleting show higher accuracy for SARS-CoV-2 detection PCR assay compared to heat-inactivation only (89% vs 83% of the detection in RNA). The accuracy of detection using direct samples varied depending on the sample transport and storage media as well as the concentration of viral particles. Our study suggests that purified RNA provides more accurate results, however, direct qRT-PCR may help to significantly increase testing capacity. Switching to the direct sample testing is justified if the number of tests is doubled at least.

Detection of SARS-CoV-2 using non-commercial RT-LAMP regents and raw samples. (preprint)

Abstract RT-LAMP detection of SARS-CoV-2 has been shown as a valuable approach to scale up COVID-19 diagnostics and thus contribute to limiting the spread of the disease. Here we present the optimization of highly cost-effective in-house produced enzymes, and we benchmark their performance against commercial alternatives. We explore the compatibility between multiple DNA polymerases with high strand-displacement activity and thermostable reverse transcriptases required for RT-LAMP. We optimize reaction conditions and demonstrate their applicability using both synthetic RNA and clinical patient samples. Finally, we validated the optimized RT-LAMP assay for the detection of SARS-CoV-2 in raw nasopharyngeal samples from 184 patients. We anticipate that optimized and affordable reagents for RT-LAMP will facilitate the expansion of SARS-CoV-2 testing globally, especially in sites and settings with limited economic resources.

Engineered human mesenchymal stem cells as new vaccine platform for COVID-19 (preprint)

Recently, there are several routes for COVID-19 vaccine research, yet their weaknesses lie in low efficiency, tolerability, immune adaptability and safety. We describe a new approach to COVID-19 based on engineered human mesenchymal stem cells(hu-MSC), which is like a small protein antigen response device, but will be gradually cleared and degraded by bodys immune system among recognization process. The antibody response results show that this is effective and fast. Furthermore, after several antibody response tests, we obtained an injection of a set of cocktail-like modified human mesenchymal stem cell line. This strategy opened a new avenue for vaccine design against COVID-19.

Structure of SARS-CoV-2 main protease in the apo state reveals the inactive conformation (preprint)

Mpro is of considerable interest as a drug target in the treatment of COVID-19 since the proteolytic activity of this viral protease is essential for viral replication. Here we report the first insight of the structure Mpro for SARS-CoV-2 in the inactive conformation under conditions close to the physiological state (pH 7.5) to an overall resolution of 1.9 [A]. The comparisons of Mpro in different states reveal that substrate binding site and the active site are more flexible in the inactive conformation than that in the active conformations. Notably, compared with the active conformation of the apo state structure in pH7.6 of SARS, the SARS-CoV-2 apo state is in the inactive conformation under condition close to physiological state (pH7.5). Two water molecules are present in the oxyanion hole in our apo state structure, whereas in the ligand-bound structure, water molecular is absence in the same region. This structure provides novel and important insights that have broad implications for understanding the structural basis underlying enzyme activity, and can facilitate rational, structure-based, approaches for the design of specific SARS-CoV-2 ligands as new therapeutic agents.

Rapid colorimetric detection of COVID-19 coronavirus using a reverse tran-scriptional loop-mediated isothermal amplification (RT-LAMP) diagnostic plat-form: iLACO (preprint)

The recent outbreak of a novel coronavirus SARS-CoV-2 (also known as 2019-nCoV) threatens global health, given serious cause for concern. SARS-CoV-2 is a human-to-human pathogen that caused fever, severe respiratory disease and pneumonia (known as COVID-19). By press time, more than 70,000 infected people had been confirmed worldwide. SARS-CoV-2 is very similar to the severe acute respiratory syndrome (SARS) coronavirus broke out 17 years ago. However, it has increased transmissibility as compared with the SARS-CoV, e.g. very often infected individuals without any symptoms could still transfer the virus to others. It is thus urgent to develop a rapid, accurate and onsite diagnosis methods in order to effectively identify these early infects, treat them on time and control the disease spreading. Here we developed an isothermal LAMP based method-iLACO (isothermal LAMP based method for COVID-19) to amplify a fragment of the ORF1ab gene using 6 primers. We assured the species-specificity of iLACO by comparing the sequences of 11 related viruses by BLAST (including 7 similar coronaviruses, 2 influenza viruses and 2 normal coronaviruses). The sensitivity is comparable to Taqman based qPCR detection method, detecting synthesized RNA equivalent to 10 copies of 2019-nCoV virus. Reaction time varied from 15-40 minutes, depending on the loading of virus in the collected samples. The accuracy, simplicity and versatility of the new developed method suggests that iLACO assays can be conveniently applied with for 2019-nCoV threat control, even in those cases where specialized molecular biology equipment is not available.