Early Detection of Severe Acute Respiratory Syndrome Coronavirus 2 Antibodies as a Serologic Marker of Infection in Patients With Coronavirus Disease 2019.

BACKGROUND: Thousands of medical staff have been infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with hundreds of deaths reported. Such loss could be prevented if there were a serologic assay for SARS-CoV-2-specific antibodies for serological surveillance of its infection at the early stage of disease. METHODS: Using Chinese hamster ovarian (CHO) cell-expressed full-length SARS-CoV-2 S1 protein as capturing antigen, a coronavirus disease 2019 (COVID-19)/SARS-CoV-2 S1 serology enzyme-linked immunosorbent assay (ELISA) kit was developed and validated with negative samples collected prior to the outbreak or during the outbreak and positive samples from patients confirmed with COVID-19. RESULTS: The specificity of the ELISA kit was 97.5%, as examined against total 412 normal human samples. The sensitivity was 97.1% by testing against 69 samples from hospitalized and/or recovered COVID-19 patients. The overall accuracy rate reached 97.3%. The assay was able to detect SARS-CoV-2 antibody on day 1 after the onset of COVID-19 disease. The average antibody levels increased during hospitalization and 14 days after discharge. SARS-CoV-2 antibodies were detected in 28 of 276 asymptomatic medical staff and 1 of 5 nucleic acid test-negative "close contacts" of COVID-19 patients. CONCLUSIONS: With the assays developed here, we can screen medical staff, incoming patients, passengers, and people who are in close contact with the confirmed patients to identify the "innocent viral spreaders," protect the medical staff, and stop further spread of the virus.

Novel strategy for expression and characterization of rabies virus glycoprotein.

Rabies is a fatal zoonosis which could affect all mammals. Glycoprotein (G protein) from the rabies virus plays an important role in the binding of virus to target cells. However, expression of the G protein with native conformation has been a great challenge for many years. In this study, we solved this problem by replacing the original signal peptide of rabies virus G protein with the one from the heavy chain of human IgG. The expression levels of recombinant G protein dramatically increased from a few µg/L to 50 mg/L in the culture supernatants. The identity of the recombinant G protein was confirmed by western blotting using both 6XHis mAb 6E2 and rabies G protein mAb 7G3. The correct conformation of the recombinant G protein was shown by using rabies virus neutralizing antibodies. In addition, the recombinant G protein had immune-reactivities with mice sera raised against rabies vaccines and vice versa. Taken together, our data suggested that by replacing the signal peptide, the expression level of the G protein with native conformation could be significantly improved. This would help the development of a rabies subunit vaccine, structural studies of rabies G protein, elucidation of the signal pathway of RABV infection.

Recombinant SARS-CoV-2 spike S1-Fc fusion protein induced high levels of neutralizing responses in nonhuman primates.

The COVID-19 outbreak has become a global pandemic responsible for over 2,000,000 confirmed cases and over 126,000 deaths worldwide. In this study, we examined the immunogenicity of CHO-expressed recombinant SARS-CoV-2 S1-Fc fusion protein in mice, rabbits, and monkeys as a potential candidate for a COVID-19 vaccine. We demonstrate that the S1-Fc fusion protein is extremely immunogenic, as evidenced by strong antibody titers observed by day 7. Strong virus neutralizing activity was observed on day 14 in rabbits immunized with the S1-Fc fusion protein using a pseudovirus neutralization assay. Most importantly, in <20 days and three injections of the S1-Fc fusion protein, two monkeys developed higher virus neutralizing titers than a recovered COVID-19 patient in a live SARS-CoV-2 infection assay. Our data strongly suggests that the CHO-expressed SARS-CoV-2 S1-Fc recombinant protein could be a strong candidate for vaccine development against COVID-19.