Construction of Live Attenuated Vaccine against Vib- rio alginolyticus and the Evaluation on Its Immuno- protection Effect

Vibrio alginolyticus, a gram-negative bacterium has been described to be one of the most common and economically important aquatic pathogens of fish and shellfish. Vaccine immunization is an effective approach preventing V. alginolyticus infection. Attenuated vaccine stimulates systemic immune response in the host, but few attenuated vaccine against V. alginolyticus is available. The type III secretion system （T3SS）, an important pathogenic factor of V. alginolyticus, is used by bacterial pathogens to inject effector proteins into the cytoplasm of their host cells. The T3SS forms a structure called needle complex with a multi-ring base that spans the bacteria and a needle-like extension that protrudes several nanometers from the bacterial surface, vscO locates at the ＂needle＂ site of T3SS, playing the role of escorting the molecular chaperone and effector proteins into host cells and further inducing the death of host cells. In this paper, an in-frame deletion mu- tant of vscO was constructed using overlap PCR and homologous recombination technology combining with chloramphenicol （Cm） and sucrose screening. The LDs0 changes of ZJO3AvscO mutant strains compared with the strain ZJ03 were e^amined in grouper （ Epinephelus coioides）. The ZJO3AvscO mutant showed about 150 times decrease in virulence in E. coioides compared with wide type ZJ03. After vaccination with ZJO3AvscO in E. coioides through injection and immersion, the spe- cific antibody titers were markedly higher than that in the saline control group （P 〈 0.05 ）. The titers of injection and immersion group on the forth week reached the maximums at 1：2 048 and 1： 128, respectively. The relative percentage survival （RPS） of injection group was 84%, while that in immersion group was 68%. These results indicate that the ZJO3AvscO of V. alginolyticus has a high immunogenicity, and can be used as live attenuated vaccine. In addition, RPS may be affected by vaccination and infection methods. This study can provide technical support for controlling fish diseases caused by V. alginolyticus.

Rational design of a DNA-launched live attenuated vaccine against human enterovirus 71

Human Enterovirus 71(EV71)has emerged as one of the predominant causative agents of hand,foot and mouth disease(HFMD)with global impact.Despite the inactivated vaccine being licensed,other vaccine candidates based on advanced technology platforms are under development.In this report,we rationally designed and constructed two DNA-launched live attenuated vaccine candidates(pDL-EV71)under the control of specific promoters.In vitro and in vivo transfection with pDL-EV71 driven by the CMV promoter successfully yielded fully infectious EV71.More importantly,the administration of pDL-EV71 did not cause clinical symptoms following intracranial or intramuscular inoculation in neonatal and IFNα/βR/mice,demonstrating its safety profile.Moreover,a single-dose or two-dose immunization with pDL-EV71 elicited robust neutralizing antibodies against EV71 as well as an antigen-specific cellular response in mice.A single-dose immunization with 10μg of pDL-EV71 conferred complete protection against lethal EV71 infection in neonates born to immunized maternal mice.Overall,our present results demonstrate that pDL-EV71 is a safe and effective vaccine candidate against EV71 for further development.

Intranasal administration of a single dose of a candidate live attenuated vaccine derived from an NSP16-deficient SARS-CoV-2 strain confers sterilizing immunity in animals

Live attenuated vaccines might elicit mucosal and sterilizing immunity against SARS-CoV-2 that the existing mRNA,adenoviral vector and inactivated vaccines fail to induce.Here,we describe a candidate live attenuated vaccine strain of SARS-CoV-2 in which the NSP16 gene,which encodes 2′-O-methyltransferase,is catalytically disrupted by a point mutation.This virus,designated d16,was severely attenuated in hamsters and transgenic mice,causing only asymptomatic and nonpathogenic infection.A single dose of d16 administered intranasally resulted in sterilizing immunity in both the upper and lower respiratory tracts of hamsters,thus preventing viral spread in a contact-based transmission model.It also robustly stimulated humoral and cell-mediated immune responses,thus conferring full protection against lethal challenge with SARS-CoV-2 in a transgenic mouse model.The neutralizing antibodies elicited by d16 effectively cross-reacted with several SARS-CoV-2 variants.Secretory immunoglobulin A was detected in the blood and nasal wash of vaccinated mice.Our work provides proof-of-principle evidence for harnessing NSP16-deficient SARS-CoV-2 for the development of live attenuated vaccines and paves the way for further preclinical studies of d16 as a prototypic vaccine strain,to which new features might be introduced to improve safety,transmissibility,immunogenicity and efficacy.

Evaluation of the Safety and Immune Efficacy of Recombinant Human Respiratory Syncytial Virus Strain Long Live Attenuated Vaccine Candidates

Human respiratory syncytial virus(RSV)infection is the leading cause of lower respiratory tract illness(LRTI),and no vaccine against LRTI has proven to be safe and effective in infants.Our study assessed attenuated recombinant RSVs as vaccine candidates to prevent RSV infection in mice.The constructed recombinant plasmids harbored(5′to 3′)a T7 promoter,hammerhead ribozyme,RSV Long strain antigenomic cDNA with cold-passaged(cp)mutations or cp combined with temperature-sensitive attenuated mutations from the A2 strain(A2cpts)or further combined with SH gene deletion(A2cptsΔSH),HDV ribozyme(δ),and a T7 terminator.These vectors were subsequently co-transfected with four helper plasmids encoding N,P,L,and M2-1 viral proteins into BHK/T7-9 cells,and the recovered viruses were then passaged in Vero cells.The rescued recombinant RSVs(rRSVs)were named rRSV-Long/A2cp,rRSV-Long/A2cpts,and rRSV-Long/A2cptsΔSH,respectively,and stably passaged in vitro,without reversion to wild type(wt)at sites containing introduced mutations or deletion.Although rRSV-Long/A2cpts and rRSV-Long/A2cptsΔSH displayed temperature-sensitive(ts)phenotype in vitro and in vivo,all rRSVs were significantly attenuated in vivo.Furthermore,BALB/c mice immunized with rRSVs produced Th1-biased immune response,resisted wtRSV infection,and were free from enhanced respiratory disease.We showed that the combination ofΔSH with attenuation(att)mutations of cpts contributed to improving att phenotype,efficacy,and gene stability of rRSV.By successfully introducing att mutations and SH gene deletion into the RSV Long parent and producing three rRSV strains,we have laid an important foundation for the development of RSV live attenuated vaccines.

Current efforts towards safe and effective live attenuated vaccines against African swine fever: challenges and prospects

Background: African swine fever (ASF) is a fatal hemorrhagic disease in domestic pigs and wild boar caused by African swine fever virus (ASFV). Since ASF has been introduced into Europe and Asia, the major pig-raising areas, posing a huge threat to the pork industry worldwide. Currently, prevention and control of ASF are basically dependent on strict biosecurity measures and stamping-out policy once ASF occurs.Main text: The major risks of ASF spread are insufficient biosecurity measures and human behaviors. Therefore, a safe and effective vaccine seems to be a reasonable demand for the prevention and control of ASF. Due to the efficacy advantage over other types of vaccines, live attenuated vaccines (LAVs), especially virulence-associated genes deleted vaccines, are likely to be put into emergency and conditional use in restricted areas if ASF is out of control in a country with a huge pig population and pork consumption, like China. However, the safety, efficacy, and genetic stability of current candidate ASF LAVs require comprehensive clinical evaluations prior to country-wide field application. Several critical issues need to be addressed to commercialize an ideal ASF LAV, including a stable cell line for manufacturing vaccines, differentiation of infected from vaccinated animals (DIVA), and cross-protection from different genotypes.Conclusion: A safe and effective DIVA vaccine and an accompanying diagnostic assay will facilitate the prevention, control, and eradication of ASF, which is quite challenging in the near future.

HUMAN PAPILLOMAVIRUS TYPE 16 L1 PROTEIN CAN BE EXPRESSED IN LIVE ATTENUATED SHIGELLA FLEXNERI 5A STRAIN SH42

Objective Attenuated strains of Shigella are attractive live vaccine candidates for eliciting mucosal immune responses which is a suitable carrier for the prophylactic human papillomaviruses (HPV) vaccine development, To examine the potential of a live Shigella based prophylactic HPV vaccine, HPV16L1should be expressed in attenuated shigella strain. Methods A Shigella large invasive plasmid (icsA/virG) based prokaryotic expression plasmid pHS3199 was constructed. HPV16L1 gene was inserted into plasmid pHS3199 to form pHS3199-HPV16 L1 construct, and pHS3199-hpv16L1 was electroporated into a live attenuated shigella strain sh42. The expression of HPV16L1 protein was demonstrated by Western blotting with monoclonal antibody to HPV16L1, The genetic stability of recombinant strain sh42-HPV16 L1 was monitored by consecutive passage culture. Invasive ability of sh42-HPV16L1 was evaluated by Hela cell infection assay. Results HPV16 L1 protein can be expressed in recombinant strain sh42-HPV16 L1, and the protein stably expressed over 140 generations. The invasive ability of sh42-HPV16L1 was diminished dramatically compared to its parent strain, but not abolished completely. Conclusion HPV16L1 protein was constitutively expressed in the attenuated strain of shigella flexneri sh42, and maintained partial invasive ability. Our strategy may represent a promising vaccine candidate against genital HPV16 infection.

A live attenuated RHΔompdcΔuprt mutant of Toxoplasma gondii induces strong protective immunity against toxoplasmosis in mice and cats

Background Toxoplasma gondii is an obligate intracellular apicomplexan parasite and is responsible for zoonotic toxoplasmosis.It is essential to develop an effective anti-T.gondii vaccine for the control of toxoplasmosis,and this study is to explore the immunoprotective effects of a live attenuated vaccine in mice and cats.Methods First,theompdc anduprt genes of T.gondii were deleted through the CRISPR-Cas9 system.Then,the intracellular proliferation and virulence of this mutant strain were evaluated.Subsequently,the immune responses induced by this mutant in mice and cats were detected,including antibody titers,cytokine levels,and subsets of T lymphocytes.Finally,the immunoprotective effects were evaluated by challenge with tachyzoites of different strains in mice or cysts of the ME49 strain in cats.Furthermore,to discover the effective immune element against toxoplasmosis,passive immunizations were carried out.GraphPad Prism software was used to conduct the log-rank(Mantel–Cox)test,Student’st test and one-way ANOVA.Results The RHΔompdcΔuprt were constructed by the CRISPR-Cas9 system.Compared with the wild-type strain,the mutant notably reduced proliferation(P<0.05).In addition,the mutant exhibited virulence attenuation in both murine(BALB/c and BALB/c-nu)and cat models.Notably,limited pathological changes were found in tissues from RHΔompdcΔuprt-injected mice.Furthermore,compared with nonimmunized group,high levels of IgG(IgG1 and IgG2a)antibodies and cytokines(IFN-γ,IL-4,IL-10,IL-2 and IL-12)in mice were detected by the mutant(P<0.05).Remarkably,all RHΔompdcΔuprt-vaccinated mice survived a lethal challenge with RHΔku80 and ME49 and WH6 strains.The immunized sera and splenocytes,especially CD8^(+)T cells,could significantly extend(P<0.05)the survival time of mice challenged with the RHΔku80 strain compared with naïve mice.In addition,compared with nonimmunized cats,cats immunized with the mutant produced high levels of antibodies and cytokines(P<0.05),and notably decreased the shedding numbers of oocysts in feces(95.3%).Conclusions The avirulent RHΔompdcΔuprt strain can provide strong anti-T.gondii immune responses,and is a promising candidate for developing a safe and effective live attenuated vaccine.

Attenuation mechanism of Brucella melitensis M5-10,implications for vaccine development and differential diagnosis

Brucellosis is a worldwide zoonosis.Vaccination is the most efficient means to prevent and control brucellosis.The current licensed attenuated vaccines for animal use were developed by sequential passage in nonnatural hosts that decreased virulence in its original hosts.The attenuation mechanism of these strains remains largely unknown.In the present study,we sequenced the genome of Brucella melitensis vaccine strain M5-10.Sequence analysis showed that a large number of genetic changes occurred in the vaccine strains.A total of 2854 genetic polymorphic sites,including 2548 SNP,241 INDEL and 65 MNV were identified.Of the 2074 SNPs in coding regions,1310(63.2%)were non-synonymous SNPs.Gene number,percent and N/S ratios were disproportionally distributed among the cog categories.Genetic polymorphic sites were identified in genes of the virB operon,flagella synthesis,and virulence regulating systems.These data indicate that changes in some cog categories and virulence genes might result in the attenuation.These attenuation mechanisms also have implications for screening and development of new vaccine strains.The genetic changes in the genome represent candidate sites for differential diagnosis between these vaccine strains and other virulence ones.Transcription analysis of virulence genes showed that expression of dnaK,vjbR were reduced in M5-10 strain when compared with that in 16M.A duplex PCR targeting virB6 and dnaK was successfully used to differentiate between M5-10 and the virulent 16M strain.The genome re-sequencing technique represents a strong strategy not only for evaluation of vaccines,but also for development of new vaccines.

Reverse genetics systems for SARS-CoV-2:Development and applications

The recent emergence of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)caused serious harm to human health and struck a blow to global economic development.Research on SARS-CoV-2 has greatly benefited from the use of reverse genetics systems,which have been established to artificially manipulate the viral genome,generating recombinant and reporter infectious viruses or biosafety level 2(BSL-2)-adapted non-infectious replicons with desired modifications.These tools have been instrumental in studying the molecular biological characteristics of the virus,investigating antiviral therapeutics,and facilitating the development of attenuated vaccine candidates.Here,we review the construction strategies,development,and applications of reverse genetics systems for SARS-CoV-2,which may be applied to other CoVs as well.