A recombinant receptor-binding domain in trimeric form generates completely protective immunity against SARS-CoV-2 infection in nonhuman primates

Safe and effective vaccination is critical to combatting the COVID-19 pandemic. Here, we developed a trimeric SARS-CoV-2 receptor-binding domain (RBD) subunit vaccine candidate that simulates the natural structure of the spike (S) trimer glycoprotein. Immunization with RBD-trimer induced robust humoral and cellular immune responses and a high level of neutralizing antibodies that were maintained for at least 4 months. Moreover, the antibodies that were produced in response to the vaccine effectively neutralized the SARS-CoV-2 501Y.V2 variant. Of note, when the titers of the antibodies dropped to a sufficiently low level, only one boost quickly activated the anamnestic immune response, resulting in complete protection against the SARS-CoV-2 challenge in rhesus macaques without typical histopathological changes or viral replication in the lungs and other respiratory tissues. Our results indicated that immunization with SARS-CoV-2 RBD-trimer could raise long-term and broad immunity protection in nonhuman primates, thereby offering an optimal vaccination strategy against COVID-19.

A rapid and quantitative fluorescent microsphere immunochromatographic strip test for detection of antibodies to porcine reproductive and respiratory syndrome virus

A fluorescent microsphere-based immunochromatographic strip test (FICT) was developed for the rapid, sensitive, and quantitative detection of porcine reproductive and respiratory syndrome virus (PRRSV) antibodies at the pen-side. The assay was based on the formation of a sandwich immune-complex (anti-pig IgG-PRRSV antibodies-NSP7/N), which was validated by a comparison with IDEXX-ELISA using 3325 clinical specimens. The diagnostic specificity, sensitivity, and accuracy of FICT were 97.28, 93.41, and 94.95%, respectively. FICT showed a good correlation with the virus neutralization assay. Overall, a promising pen-side diagnostic tool was developed for the rapid and quantitative detection of PRRSV antibodies within 15 min.

Strategies for vaccine development of COVID-19 / 生物工程学报

An epidemic of acute respiratory syndrome in humans, which appeared in Wuhan, China in December 2019, was caused by a novel coronavirus (SARS-CoV-2). This disease was named as "Coronavirus Disease 2019" (COVID-19). SARS-CoV-2 was first identified as an etiological pathogen of COVID-19, belonging to the species of severe acute respiratory syndrome-related coronaviruses (SARSr-CoV). The speed of both the geographical transmission and the sudden increase in numbers of cases is much faster than SARS and Middle East respiratory syndrome (MERS). COVID-19 is the first global pandemic caused by a coronavirus, which outbreaks in 211 countries/territories/areas. The vaccine against COVID-19, regarded as an effective prophylactic strategy for control and prevention, is being developed in about 90 institutions worldwide. The experiences and lessons encountered in the previous SARS and MERS vaccine research can be used for reference in the development of COVID-19 vaccine. The present paper hopes to provide some insights for COVID-19 vaccines researchers.

Pullulanase Is Necessary for the Efficient Intracellular Growth of Francisella tularensis.

Pullulanase, an enzyme that catalyzes the hydrolysis of polysaccharides, has been identified in a broad range of organisms, including bacteria, yeasts, fungi, and animals. The pullulanase (pulB; FTT_0412c) of F. tularensis subspecies tularensis Schu S4 is considered to be a homologue of the type I pullulanase (pulA) of the other Francisella subspecies. The significance of Francisella pullulanase has been obscure until now. In the present study, we characterized a recombinant PulB of F. tularensis SCHU P9, which was expressed as a his-tagged protein in Escherichia coli. The recombinant PulB was confirmed to be a type I pullulanase by its enzymatic activity in vitro. A pulB gene knockout mutant of F. tularensis SCHU P9 (ΔpulB) was constructed using the TargeTron Knockout system and plasmid pKEK1140 to clarify the function of PulB during the growth of F. tularensis in macrophages. The intracellular growth of the ΔpulB mutant in murine macrophage J774.1 cells was significantly reduced compared with that of the parental strain SCHU P9. Expression of PulB in ΔpulB, using an expression plasmid, resulted in the complementation of the reduced growth in macrophages, suggesting that PulB is necessary for the efficient growth of F. tularensis in macrophages. To assess the role of PulB in virulence, the knockout and parent bacterial strains were used to infect C57BL/6J mice. Histopathological analyses showed that tissues from ΔpulB-infected mice showed milder lesions compared to those from SCHU P9-infected mice. However, all mice infected with SCHU P9 and ΔpulB showed the similar levels of bacterial loads in their tissues. The results suggest that PulB plays a significant role in bacterial growth within murine macrophage but does not contribute to bacterial virulence in vivo.