The fusion of viral and cellular membranes is an important step in infections caused by enveloped viruses. Safe and rapid cell-based assay systems have been developed to identify inhibitors of various infections caused by enveloped viruses. In this review, we have described a cell-based membrane fusion assay and its application in drug screening. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Middle East respiratory syndrome coronavirus (MERS-CoV) induce membrane fusion by cleavage of the N-terminal region of the fusion peptide in the Spike protein by cellular proteases. To quantify the membrane fusion mediated by SARS-CoV-2 and MERS-CoV, effector cells expressing the Spike protein and target cells expressing the receptor and host protease TMRPSS2 were used. Cell fusion caused by co-culture was measured by monitoring the signals from dual split proteins (DSPs) as the reporter. Using this assay system, nafamostat was identified as a potential inhibitor of the membrane fusion caused by MERS-CoV and SARS-CoV-2. Clinical trials of nafamostat are underway. Cell-based membrane fusion assays using DSPs are expected to be useful for the discovery of viral infection inhibitors and for the evaluation of neutralizing antibodies.

Human-induced pluripotent stem (iPS) cells are expected to be used in regenerative medicine and drug toxicity tests. Earlier, human iPS cells were cryopreserved by the vitrification method because the slow freezing of human iPS cells resulted in low recovery following thawing. However, the vitrification method requires a high level of skill to rapidly prepare many frozen cell stocks. Furthermore, a dry shipper is necessary to transport the stocks of vitrified human iPS cells because simple transport of vitrified cell stocks on dry ice was impossible. Transportation using dry shippers is logistically cumbersome and expensive. In this study, we developed a new slow-freezing medium to prepare cell stocks that can be transported on dry ice without a dry shipper. This medium allowed the preparation of several stocks of frozen cells of the same lot simultaneously and their transportation on dry ice. Using human peripheral blood mononuclear cells (PBMCs) and human iPS cells, we investigated the optimal slow preservation solution. We found that a slow freezing medium containing 10% (v/v) dimethyl sulfoxide (DMSO) and 1% (v/v) human serum albumin (HSA) was optimal for cryopreservation of human PBMCs and iPS cells. This xeno-free freezing medium was shown to have the potential for application in the cryopreservation of cells used in regenerative medicine.

To evaluate the effects of antiviral drugs against coronavirus disease (COVID-19), we calculated the sample size needed to detect significant differences in daily viral load in randomized controlled trials. While calculating sample sizes, simulated viral loads that mimicked longitudinal clinical data were used. The sample size computed from the viral load was the smallest 2 to 4 days after trial participation, while the smallest sample size computed from the positive rate was 4 to 7 days after clinical trial participation.

Simple, rapid, and accurate diagnosis is indispensable for broadercontrol measures, search for routes of infection, and understanding treatment status of emerging infectious diseases. Although PCR and LAMP are commonly used, in cases where the pathogen is an RNA virus, there are issues in terms of simplicity and speed, as multi-step operations including reverse transcription (RT) and many reagents, as well as time and expertise in optimizing primers and probes, are required. To solve these issues, we propose the artificial chaperone-enhanced MNAzyme (ACEzyme), which combines the functions of the multicomponent nucleic acid enzyme (MNAzyme) and cationic copolymers. PLL-g-Dex has artificial nucleic acid chaperone activity and can act as a molecular sensing system. ACEzyme resulted in an approximately 2,700-fold increase in MNAzyme activity. In this study, we showed that ACEzyme was also useful when working with RNA targets with robust high-order structures, and had high selectivity for single nucleotide mutation detection.

There is currently an outbreak of respiratory disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and many vaccines have been rapidly developed using different technologies. We have challenged to develop DNA vaccines for SARS-CoV-2. After the basic and preclinical experiments, AnGes, Inc. conducted a randomized, open-label, non-controlled Phase I/II Study to assess safety and immunogenicity of intramuscular DNA vaccine (AG0302-COVID19) in Osaka University Hospital. Thirty healthy volunteers, male or female, aged 20–65, will be randomized to one of the following three groups, 1) 2.0 mg of AG0302-COVID19 twice at 2-week intervals, 2) 2.0 mg of AG0302-COVID19 twice at 4-week intervals, 3) 2.0 mg of AG0302-COVID19 three times at 2-week intervals. This study will assess the safety and immunogenicity of AG0302-COVID19. The primary endpoint about the safety and tolerability has been assessed by the incidence of treatment emergent adverse events from week 1 through week 9, and frequency and severity of each adverse event, including solicited local and systemic adverse events through 8 weeks after the first vaccination. The immunogenicity has been also assessed by the change in geometric mean titer (GMT) of serum anti-SARS-CoV-2 Spike glycoprotein specific antibody. This study has been registered at the ClinicalTrials.gov.as NCT04527081.

Sendai virus (SeV) vectors are able to infect a diverse range of cells. They have a high affinity for epithelial cells in the respiratory tract, which provides advantageous properties for intranasal inoculation. Vaccination of the respiratory tract, the main route of infection for Coronavirus (COVID-19), can strongly induce mucosal immunity, which is difficult to induce through injected vaccines, in addition to systemic immunity in a manner similar to innate immunity. A SeV vector vaccine carrying part of the SARS-CoV-2 spike-protein gene showed high immunogenicity in pharmacological studies using intranasally inoculated rodents and is a promising next-generation vaccine.