Characterization of a pangolin SARS-CoV-2-related virus isolate that uses the human ACE2 receptor.

Various SARS-CoV-2-related coronaviruses have been increasingly identified in pangolins, showing a potential threat to humans. Here we report the infectivity and pathogenicity of the SARS-CoV-2-related virus, PCoV-GX/P2V, which was isolated from a Malayan pangolin (Manis javanica). PCoV-GX/P2V could grow in human hepatoma, colorectal adenocarcinoma cells, and human primary nasal epithelial cells. It replicated more efficiently in cells expressing human angiotensin-converting enzyme 2 (hACE2) as SARS-CoV-2 did. After intranasal inoculation to the hACE2-transgenic mice, PCoV-GX/P2V not only replicated in nasal turbinate and lungs, but also caused interstitial pneumonia, characterized by infiltration of mixed inflammatory cells and multifocal alveolar hemorrhage. Existing population immunity established by SARS-CoV-2 infection and vaccination may not protect people from PCoV-GX/P2V infection. These findings further verify the hACE2 utility of PCoV-GX/P2V by in vivo experiments using authentic viruses and highlight the importance for intensive surveillance to prevent possible cross-species transmission.

A variant-proof SARS-CoV-2 vaccine targeting HR1 domain in S2 subunit of spike protein.

The emerging SARS-CoV-2 variants, commonly with many mutations in S1 subunit of spike (S) protein are weakening the efficacy of the current vaccines and antibody therapeutics. This calls for the variant-proof SARS-CoV-2 vaccines targeting the more conserved regions in S protein. Here, we designed a recombinant subunit vaccine, HR121, targeting the conserved HR1 domain in S2 subunit of S protein. HR121 consisting of HR1-linker1-HR2-linker2-HR1, is conformationally and functionally analogous to the HR1 domain present in the fusion intermediate conformation of S2 subunit. Immunization with HR121 in rabbits and rhesus macaques elicited highly potent cross-neutralizing antibodies against SARS-CoV-2 and its variants, particularly Omicron sublineages. Vaccination with HR121 achieved near-full protections against prototype SARS-CoV-2 infection in hACE2 transgenic mice, Syrian golden hamsters and rhesus macaques, and effective protection against Omicron BA.2 infection in Syrian golden hamsters. This study demonstrates that HR121 is a promising candidate of variant-proof SARS-CoV-2 vaccine with a novel conserved target in the S2 subunit for application against current and future SARS-CoV-2 variants.

Double lock of a potent human therapeutic monoclonal antibody against SARS-CoV-2.

Receptor recognition and subsequent membrane fusion are essential for the establishment of successful infection by SARS-CoV-2. Halting these steps can cure COVID-19. Here we have identified and characterized a potent human monoclonal antibody, HB27, that blocks SARS-CoV-2 attachment to its cellular receptor at sub-nM concentrations. Remarkably, HB27 can also prevent SARS-CoV-2 membrane fusion. Consequently, a single dose of HB27 conferred effective protection against SARS-CoV-2 in two established mouse models. Rhesus macaques showed no obvious adverse events when administrated with 10 times the effective dose of HB27. Cryo-EM studies on complex of SARS-CoV-2 trimeric S with HB27 Fab reveal that three Fab fragments work synergistically to occlude SARS-CoV-2 from binding to the ACE2 receptor. Binding of the antibody also restrains any further conformational changes of the receptor binding domain, possibly interfering with progression from the prefusion to the postfusion stage. These results suggest that HB27 is a promising candidate for immuno-therapies against COVID-19.

Cathepsin L plays a key role in SARS-CoV-2 infection in humans and humanized mice and is a promising target for new drug development.

To discover new drugs to combat COVID-19, an understanding of the molecular basis of SARS-CoV-2 infection is urgently needed. Here, for the first time, we report the crucial role of cathepsin L (CTSL) in patients with COVID-19. The circulating level of CTSL was elevated after SARS-CoV-2 infection and was positively correlated with disease course and severity. Correspondingly, SARS-CoV-2 pseudovirus infection increased CTSL expression in human cells in vitro and human ACE2 transgenic mice in vivo, while CTSL overexpression, in turn, enhanced pseudovirus infection in human cells. CTSL functionally cleaved the SARS-CoV-2 spike protein and enhanced virus entry, as evidenced by CTSL overexpression and knockdown in vitro and application of CTSL inhibitor drugs in vivo. Furthermore, amantadine, a licensed anti-influenza drug, significantly inhibited CTSL activity after SARS-CoV-2 pseudovirus infection and prevented infection both in vitro and in vivo. Therefore, CTSL is a promising target for new anti-COVID-19 drug development.

A Mouse Model of SARS-CoV-2 Infection and Pathogenesis.

Since December 2019, a novel coronavirus SARS-CoV-2 has emerged and rapidly spread throughout the world, resulting in a global public health emergency. The lack of vaccine and antivirals has brought an urgent need for an animal model. Human angiotensin-converting enzyme II (ACE2) has been identified as a functional receptor for SARS-CoV-2. In this study, we generated a mouse model expressing human ACE2 (hACE2) by using CRISPR/Cas9 knockin technology. In comparison with wild-type C57BL/6 mice, both young and aged hACE2 mice sustained high viral loads in lung, trachea, and brain upon intranasal infection. Although fatalities were not observed, interstitial pneumonia and elevated cytokines were seen in SARS-CoV-2 infected-aged hACE2 mice. Interestingly, intragastric inoculation of SARS-CoV-2 was seen to cause productive infection and lead to pulmonary pathological changes in hACE2 mice. Overall, this animal model described here provides a useful tool for studying SARS-CoV-2 transmission and pathogenesis and evaluating COVID-19 vaccines and therapeutics.

Induction of balanced immunity in BALB/c mice by vaccination with a recombinant fusion protein containing a respiratory syncytial virus G protein fragment and a CTL epitope.

Respiratory syncytial virus (RSV), an important pathogen of the lower respiratory tract, is responsible for severe illness both in new born and young children and in elderly people. However, development of a RSV vaccine has been hampered by the outcome of the infant trials in the 1960s with a formalin-inactivated RSV (FI-RSV) preparation. Previous studies in mice indicated that G protein immunization resulted in antibody and Th2-type response and failed to induce MHC I-restricted CD8(+) T-cell response. Vaccines designed to induce CD8(+) T-cell along with antibody response might be ideal. In the present report, a fusion protein G1F/M2 containing a RSV-G protein fragment (G: 125-225 amino acid) and a CD8(+) T-cell epitope from RSV-M2 protein was investigated. G1F/M2 was cloned, expressed in E. coli, purified and renaturated. In BALB/c mice, G1F/M2 induced not only humoral immunity but also cellular immunity. In addition, interestedly, G1F/M2 elicited balanced IgG1/IgG2a response. These results suggest that the fusion protein G1F/M2 is potential as a RSV subunit vaccine.

Co-immunization of BALB/c mice with recombinant immunogens containing G protein fragment and chimeric CTL epitope of respiratory syncytial virus induces enhanced cellular immunity and high level of antibody response.

With the goal to develop effective immunogens against infection of respiratory syncytial virus (RSV), vectors co-expressing chimeric CTL epitope or G protein fragment of RSV with carrier protein DsbA (disulfide bond isomerase) were constructed. The capacity of the expressed recombinant immunogens to induce cellular and humoral immunities were evaluated. It was demonstrated that the presence of G protein fragment was able to enhance the CTL activities induced by the chimeric CTL epitope, though G protein fragment alone had no effect on induction of CTL response. In contrast, the level of antibody response to RSV and neutralization titer in co-immunization with G protein fragment plus chimeric CTL epitope was lower than that in immunization with G protein fragment alone. The challenge experiments indicated that co-immunization further reduced RSV titers both in lung tissue and nasal track, indicating the combination of humoral and cellular immunities is more effective. This data imply that the combination of the two protein immunogens would be a viable strategy for a RSV vaccine.

Fusion of DsbA to the N-terminus of CTL chimeric epitope, F/M2:81-95, of respiratory syncytial virus prolongs protein- and virus-specific CTL responses in Balb/c mice.

In an effort to seek a means of inducing long lasting respiratory syncytial virus-specific CTL responses in mice, we constructed a new recombinant protein, DsbA-F/M2:81-95, by fusing carrier protein DsbA (disulfide bond isomerase) to the N-terminus of CTL chimeric epitope F/M2:81-95 of this virus. DsbA-F/M2:81-95 can induce effectively virus-specific CTL responses as well as protective immunity without association with enhanced disease. Furthermore, compared with F/M2:81-95 alone, it increases the longevity of CTL responses in vivo up to 2.93 folds. Our study emphasizes that appropriate stimulation of non-antigen-specific T helper cells is essential to induce long lasting CD8+ CTL, and also implies DsbA-F/M2:81-95 may be a promising candidate for RSV vaccine development since it is an efficacious and safe immunogen.

A simple, efficient, and economical method for recovering DNA from agarose gel.

A simple method of recovering DNA from agarose gel that is fast, inexpensive, and friendly both to operators and environment is described. Two rows of wells are made in an agarose gel, and a DNA sample is loaded into the well nearest to the negative pole for separation by electrophoresis. Recovery is accomplished by pipetting the DNA-containing TAE buffer from the well near the positive pole after target DNA fragments have migrated into the well. A recovery rate of up to 94 +/- 2.3% was observed with this method.

[Sequence variation of the chloroplast gene ndh D region in cytoplasmic male sterile sorghum].

A fragment SAAU-02(700) was amplified specifically from total DNA of seven sorghun varieties with male-fertile cytoplasm (N-cytoplasm). PCR assays indicated that it was amplified from chloroplast (cp) DNA. Sequence analysis revealed this newly cloned fragment contained a portion of chloroplast gene psa C (88 bp) and part of ndh D gene (192 bp). Total DNA, mitochondrial (mt) DNA, and cpDNA were digested with EcoR I + Hind III and probed with fragment SAAU-02(700). The Southern hybridization patterns displayed a 0.74 kb band both in total DNA and cpDNA, but an additional faint band 0.45 kb in size was found only in the latter. No polymorphic hybridization signal between the N-cytoplasm and male-sterile cytoplasm (S-cytoplasm) was observed. Southern hybridization of total DNA of CMS line A1 Tx623 and fertile line Tx623 digested with Hae III gave a band 4.9 kb in size in the former and a 4.45 kb band in the latter. This revealed that the sequence of ndh D from CMS line was likely altered. Further studies designed to determine whether or not the variation has some effect on the metabolism of mitochondria and chloroplast, even on the occurrence of male sterility in sorghum are underway.