Objective:To construct a nanoparticle vaccine displaying the prefusion F (preF) protein of respiratory syncytial virus (RSV) using the I53-50 protein nanoparticle platform, and to systematically evaluate its immunogenicity and protective efficacy.Methods:The RSV preF trimer antigen was genetically fused to I53-50A and assembled in vitro with I53-50B to form preF-I53-50 nanoparticles, theoretically displaying 20 preF antigens per particle. The structure and purity were characterized by size-exclusion chromatography, SDS-PAGE, and negative-stain electron microscopy. BALB/c mice were intramuscularly immunized with varying doses (1 μg or 5 μg) of preF antigen or an equimolar amount of preF-I53-50 nanoparticles. Humoral immunity, B-cell responses, and protective efficacy were assessed following intranasal viral challenge.Results:The preF-I53-50 nanoparticles self-assembled into spherical structures (50-60 nm in diameter) with uniformly arrayed antigens. The nanoparticle vaccine enhanced RSV-specific IgG1 and IgG2a antibody responses, promoting a Th1-biased immune profile. At equimolar preF doses, the neutralizing antibody titers induced by 1 μg and 5 μg nanoparticle formulations were 2.8-fold and 2.3-fold higher, respectively, than those elicited by preF alone ( P<0.05). Notably, even the low-dose nanoparticle group outperformed the high-dose preF group (1.6-fold increase). Viral challenge experiments demonstrated that preF-I53-50 effectively suppressed pulmonary viral replication, mitigated pathological damage, and induced stronger germinal center and memory B-cell responses, suggesting enhanced B-cell affinity maturation and long-term immune memory. Conclusion:The preF-I53-50 vaccine improves the immunogenicity and protective efficacy of RSV preF through multivalent antigen display.

Objective:To analyze the epidemiological characteristics of mumps in China under the immunization strategies of different doses of mumps-containing vaccines(MuCV) by analyzing the national mumps surveillance data from 2020 to 2023.Methods:Based on the national mumps surveillance data from 2020 to 2023, a comparative analysis was conducted on the mumps incidence and the distribution characteristics of mumps cases in time, region and population in the three different periods of 2004-2007 (without MuCV implementation), 2008-2019 (one-dose MuCV implementation) and 2020-2023 (two-dose MuCV implementation) in China.Results:From 2020 to 2023, the annual incidence rate of mumps was 6.48-9.20/100 000, and the annual number of reported cases was 91 303-129 120 cases. After the implementation of the 2-dose MuCV immunization strategy, the epidemiological characteristics of mumps in China have changed to some extent. Compared with the period of 2004-2007 and 2008-2019, the traditional seasonal epidemic pattern of mumps disappeared from 2020 to 2023, with no obvious epidemic peak throughout the year. There was no significant regional difference in the incidence of mumps. Children and adolescents under 15 years of age were the main population of mumps (accounting for 85.46%), of which children aged 5-9 years accounted for 45.07%. Compared with the period of 2004-2007 and 2008-2019, the proportion of mumps cases in the 0-4 years old group showed an increasing trend, the proportion of mumps cases in the 10-14 years old group showed a decreasing trend, and the proportion of adult cases over 40 years old also increased from 2020 to 2023. The age group with the highest incidence of mumps was found to have shifted from 7 years old to 4 years old.Conclusions:The 2-dose MuCV immunization strategy has effectively reduced the incidence of mumps in China. It is necessary to strengthen the surveillance of mumps in kindergartens and primary school children.

Objective:A monoclonal cell line that stably expresses transmembrane protease serine 2 (TMPRSS2) was constructed using the PiggyBac (PB) transposon system to establish a technique for isolating human parainfluenza viruses (HPIVs) without rely on exogenous trypsin.Methods:The pB513B/TMPRSS2 recombinant expression plasmid was synthetized based on the principle of PB transposition, and co-transfected into LLC-MK2, HEp-2, and Vero cells, together with the helper plasmid. Positive cells were then identified using the puromycin resistance and limiting dilution method. Stable TMPRSS2 expression was verified by PCR and western blot (WB). Furthermore, the viral replication capacity of the cell lines was evaluated using digital PCR and immunostaining plaque assays.Results:The successful construction of the recombinant plasmid pB513B/TMPRSS2 was confirmed through restriction enzyme digestion and DNA sequencing. Following transfection, the LLC-MK2/TMPRSS2 cell survival rate was higher than those of the HEp-2/TMPRSS2 and Vero/TMPRSS2 cells. Subsequent PCR and WB analysis results revealed that the LLC-MK2/TMPRSS2 cells maintained stable TMPRSS2 expression after 20 successive passages. Cell counting kit-8 (CCK-8) assays confirmed that there was no significant difference in proliferative activity between LLC-MK2/TMPRSS2 cells and LLC-MK2 cells. Viral replication capability testing showed that the laboratory-adapted strain of HPIV3 (ATCC strain) exhibited exponential growth in both LLC-MK2 and LLC-MK2/TMPRSS2 cells in culture without exogenous trypsin. Notably, LLC-MK2/TMPRSS2 cells significantly supported the replication of clinical HPIV3 isolates (circulating strain), whereas LLC-MK2 cells failed to sustain their infectivity effectively.Conclusions:In this study, we successfully generated the LLC-MK2/TMPRSS2 cell line using the PB transposon system to stably express TMPRSS2. Our TMPRSS2-transfected cell line enables the efficient isolation and propagation of HPIVs in vitro, eliminating the need for exogenous trypsin and providing a vital technical platform for isolating HPIVs and studying their pathogenicity.

Objective:To construct a nanoparticle vaccine displaying the prefusion F (preF) protein of respiratory syncytial virus (RSV) using the I53-50 protein nanoparticle platform, and to systematically evaluate its immunogenicity and protective efficacy.Methods:The RSV preF trimer antigen was genetically fused to I53-50A and assembled in vitro with I53-50B to form preF-I53-50 nanoparticles, theoretically displaying 20 preF antigens per particle. The structure and purity were characterized by size-exclusion chromatography, SDS-PAGE, and negative-stain electron microscopy. BALB/c mice were intramuscularly immunized with varying doses (1 μg or 5 μg) of preF antigen or an equimolar amount of preF-I53-50 nanoparticles. Humoral immunity, B-cell responses, and protective efficacy were assessed following intranasal viral challenge.Results:The preF-I53-50 nanoparticles self-assembled into spherical structures (50-60 nm in diameter) with uniformly arrayed antigens. The nanoparticle vaccine enhanced RSV-specific IgG1 and IgG2a antibody responses, promoting a Th1-biased immune profile. At equimolar preF doses, the neutralizing antibody titers induced by 1 μg and 5 μg nanoparticle formulations were 2.8-fold and 2.3-fold higher, respectively, than those elicited by preF alone ( P<0.05). Notably, even the low-dose nanoparticle group outperformed the high-dose preF group (1.6-fold increase). Viral challenge experiments demonstrated that preF-I53-50 effectively suppressed pulmonary viral replication, mitigated pathological damage, and induced stronger germinal center and memory B-cell responses, suggesting enhanced B-cell affinity maturation and long-term immune memory. Conclusion:The preF-I53-50 vaccine improves the immunogenicity and protective efficacy of RSV preF through multivalent antigen display.

Objective:To analyze the epidemiological characteristics of mumps in China under the immunization strategies of different doses of mumps-containing vaccines(MuCV) by analyzing the national mumps surveillance data from 2020 to 2023.Methods:Based on the national mumps surveillance data from 2020 to 2023, a comparative analysis was conducted on the mumps incidence and the distribution characteristics of mumps cases in time, region and population in the three different periods of 2004-2007 (without MuCV implementation), 2008-2019 (one-dose MuCV implementation) and 2020-2023 (two-dose MuCV implementation) in China.Results:From 2020 to 2023, the annual incidence rate of mumps was 6.48-9.20/100 000, and the annual number of reported cases was 91 303-129 120 cases. After the implementation of the 2-dose MuCV immunization strategy, the epidemiological characteristics of mumps in China have changed to some extent. Compared with the period of 2004-2007 and 2008-2019, the traditional seasonal epidemic pattern of mumps disappeared from 2020 to 2023, with no obvious epidemic peak throughout the year. There was no significant regional difference in the incidence of mumps. Children and adolescents under 15 years of age were the main population of mumps (accounting for 85.46%), of which children aged 5-9 years accounted for 45.07%. Compared with the period of 2004-2007 and 2008-2019, the proportion of mumps cases in the 0-4 years old group showed an increasing trend, the proportion of mumps cases in the 10-14 years old group showed a decreasing trend, and the proportion of adult cases over 40 years old also increased from 2020 to 2023. The age group with the highest incidence of mumps was found to have shifted from 7 years old to 4 years old.Conclusions:The 2-dose MuCV immunization strategy has effectively reduced the incidence of mumps in China. It is necessary to strengthen the surveillance of mumps in kindergartens and primary school children.

Objective:A monoclonal cell line that stably expresses transmembrane protease serine 2 (TMPRSS2) was constructed using the PiggyBac (PB) transposon system to establish a technique for isolating human parainfluenza viruses (HPIVs) without rely on exogenous trypsin.Methods:The pB513B/TMPRSS2 recombinant expression plasmid was synthetized based on the principle of PB transposition, and co-transfected into LLC-MK2, HEp-2, and Vero cells, together with the helper plasmid. Positive cells were then identified using the puromycin resistance and limiting dilution method. Stable TMPRSS2 expression was verified by PCR and western blot (WB). Furthermore, the viral replication capacity of the cell lines was evaluated using digital PCR and immunostaining plaque assays.Results:The successful construction of the recombinant plasmid pB513B/TMPRSS2 was confirmed through restriction enzyme digestion and DNA sequencing. Following transfection, the LLC-MK2/TMPRSS2 cell survival rate was higher than those of the HEp-2/TMPRSS2 and Vero/TMPRSS2 cells. Subsequent PCR and WB analysis results revealed that the LLC-MK2/TMPRSS2 cells maintained stable TMPRSS2 expression after 20 successive passages. Cell counting kit-8 (CCK-8) assays confirmed that there was no significant difference in proliferative activity between LLC-MK2/TMPRSS2 cells and LLC-MK2 cells. Viral replication capability testing showed that the laboratory-adapted strain of HPIV3 (ATCC strain) exhibited exponential growth in both LLC-MK2 and LLC-MK2/TMPRSS2 cells in culture without exogenous trypsin. Notably, LLC-MK2/TMPRSS2 cells significantly supported the replication of clinical HPIV3 isolates (circulating strain), whereas LLC-MK2 cells failed to sustain their infectivity effectively.Conclusions:In this study, we successfully generated the LLC-MK2/TMPRSS2 cell line using the PB transposon system to stably express TMPRSS2. Our TMPRSS2-transfected cell line enables the efficient isolation and propagation of HPIVs in vitro, eliminating the need for exogenous trypsin and providing a vital technical platform for isolating HPIVs and studying their pathogenicity.

Objective:To understand the epidemiology of rubella and the genetic characteristics of the virus circulating during the period 2021-2022, providing basic scientific data for rubella prevention and control in China.Methods:National rubella incidence data for the period 2021-2022 were obtained from the Infectious Disease Surveillance System module and the Surveillance Report Management module of the China′s Disease Prevention and Control Information System. Positive rubella virus(RuV)isolates were obtained from the National Measles/Rubella Laboratory Network. Two nucleotide (nt) fragments [F1-480 (8 633-9 112 nt) and F2-633 (8 945-9 577 nt)] located in the E1 gene were amplified and determined by reverse transcription polymerase chain reaction (RT-PCR), and the target gene (E1-739) was obtained after collating and splicing. The sequences obtained in this study were used to construct a phylogenetic tree with the reported reference strains for genotype and lineage identification. Additionally, the phylogenetic analysis was performed to assess their genetic relatedness of RuV strains prevalent in China during 2018-2020 from GenBank database.Results:In 2021-2022, the rubella incidence in China was 0.06/100, 000 (2021: 840 cases; 2022: 784 cases), with cases primarily concentrated in the western and southern provinces. Age distribution analysis showed that rubella cases in 2021-2022 was mainly in children under 5 years of age (2021: 34.17%, 287/840; 2022: 42.09%, 330/784), with the highest proportion in children aged 0-2 years. Further analysis of the immunization history of cases revealed that in the 8-23 months age group, a significant proportion of cases had received only one dose of rubella containing vaccine (RCV); cases in the 2-14 years age group were mainly among children who had received two or more doses of RCV; however, cases over 15 years of age were primarily found in individuals who had not received RCV or had unknown immunization history. National virological surveillance data showed that totally 22 RuV virus isolates were obtained, from 6 provinces in China during 2021-2022, which belonged to lineage 1E-L2 (11 strains) and 2B-L2c (11 strains). And these viruses displayed high genetic homology with RuV prevalent from 2018 to 2020.Conclusions:The incidence of rubella in China was maintained at a low level during 2021-2022, and the prevalent RuV strains were lineage 1E-L2 and 2B-L2c.

Objective:To establish a Plaque-reduction Neutralization Test (PRNT) for the detection of neutralizing antibody titers of Human Respiratory Syncytial Virus (HRSV) and optimize the conditions for preliminary application.Methods:The CHO expression system was used to produce palivizumab monoclonal antibody (palivizumab) and the influencing factors such as cell type, cell culture duration, fixation and permeabilization protocols, and blocking agents. The reproducibility of the method was verified and its correlation was verified with conventional PRNT. Finally, the optimized PRNT assay was further used to determine neutralizing antibody titers against HRSV subtypes A and B in BALB/c mouse serum (immunized by intramuscular injection of HRSV fusion proteins).Results:Palivizumab was expressed at approximately 50 mg/L. The optimal working conditions for PRNT were as follows: culturing HEp-2 cells for 2 days, fixing with 4% (V/V) paraformaldehyde at room temperature for 15 min followed by 0.2% (V/V) Triton X-100 permeabilization for 15 minutes as the optimal fixation-permeabilization and removing the blocking step. The overall coefficient of variation (CV) for the reproducibility validation of this method was <15%, showing a good linear relationship with the conventional PRNT. The Spearman correlation coefficient r s was 0.983. This method was used to detect neutralizing antibody titers in mouse sera against HRSV subtype A strain long and subtype B strain 9320, and the fusion proteins combined with AlOH and CpG adjuvant induced the highest neutralizing antibody titers in mice. Conclusion:The HRSV neutralizing antibody assay established in this study is rapid, reproducible, high-throughput, and can be used to detect neutralizing antibodies to HRSV subtypes A and B.

Objective:To establish a Plaque-reduction Neutralization Test (PRNT) for the detection of neutralizing antibody titers of Human Respiratory Syncytial Virus (HRSV) and optimize the conditions for preliminary application.Methods:The CHO expression system was used to produce palivizumab monoclonal antibody (palivizumab) and the influencing factors such as cell type, cell culture duration, fixation and permeabilization protocols, and blocking agents. The reproducibility of the method was verified and its correlation was verified with conventional PRNT. Finally, the optimized PRNT assay was further used to determine neutralizing antibody titers against HRSV subtypes A and B in BALB/c mouse serum (immunized by intramuscular injection of HRSV fusion proteins).Results:Palivizumab was expressed at approximately 50 mg/L. The optimal working conditions for PRNT were as follows: culturing HEp-2 cells for 2 days, fixing with 4% (V/V) paraformaldehyde at room temperature for 15 min followed by 0.2% (V/V) Triton X-100 permeabilization for 15 minutes as the optimal fixation-permeabilization and removing the blocking step. The overall coefficient of variation (CV) for the reproducibility validation of this method was <15%, showing a good linear relationship with the conventional PRNT. The Spearman correlation coefficient r s was 0.983. This method was used to detect neutralizing antibody titers in mouse sera against HRSV subtype A strain long and subtype B strain 9320, and the fusion proteins combined with AlOH and CpG adjuvant induced the highest neutralizing antibody titers in mice. Conclusion:The HRSV neutralizing antibody assay established in this study is rapid, reproducible, high-throughput, and can be used to detect neutralizing antibodies to HRSV subtypes A and B.

Objective:This study comprehensively analyzed the genomic characterizations of human parainfluenza virus type 3 (HPIV3) strains circulating in six provinces and cities of China (Beijing, Henan, Jilin, Anhui, Gansu, and Shandong) during the period of 2019-2020. The aim was to elucidate the intricate genetic variations and molecular evolutionary trends within the HPIV3 genome.Methods:Based on genotypic differentiation, genetic divergence, and spatial and temporal distribution, 12 representative HPIV3 strains (including 7 of C3a subtype, 2 of C3b subtype and 3 of C3f subtype) were selected from the aforementioned provinces, and the complete genome sequence was successfully obtained by overlapping amplification of fragments using nested RT-PCR. Subsequently, a complete genome database of global representative HPIV3 strains was constructed and analyzed using bioinformatics tools.Results:The length of complete genome of the 12 HPIV3 strains in the present study varied between 15 227 bp and 15 370 bp, the G+ C content ranged from 35.1% to 35.3% and the nucleotide identity intermediated from 97.6% to 99.6%. Compared with the prototype strain (GenBank accession number: NC_001796.2), the nucleotide identity of 12 HPIV3 strains ranged from 94.2% to 94.5%. Analysis of the complete genome of HPIV3 available in China and globally showed that the genomic variation of HPIV3 was mainly shaped by substitution mutations, and no base deletions or gene recombination were observed.Only a six-base insertion (ATTAAA) was found in the F gene’s 3′UTR region of a representative strain originating from Jilin province (CHN/Jilin036/2019/C3b) in this study, and its potential pathogenic significance needs to be further investigated. Amino acid analysis of the encoded proteins revealed that the C3a lineage of HPIV3, widely prevalent both in China and worldwide, exhibits lineage-specific mutation sites in the N, P and L proteins. Furthermore, within the Chinese prevalent C3a strains, a distinctive mutation site (N216S) in L protein was also identified. Notably, specific variant sites have not been found in Chinese C3b and C3f branch strains. Based on the complete genome, the comprehensive evolutionary analysis showed that the time to the most recent common ancestor (tMRCA) of global HPIV3 strains was estimated to 1927 (95% HPD: 1901-1945), with an average molecular evolutionary rate of 5.29 × 10 -4 substitutions/site/year, while the average molecular evolutionary rate of HPIV3 strains in China is 5.24 × 10 -4 substitutions/site/year. In addition, each gene of HPIV3 was subjected to negative selection pressure, with the P, HN and F genes showing the most significant nucleotide variation and higher rates of molecular evolution than the other genes. Conclusions:This study reveals that the complete genome of HPIV3 strains circulating in six provinces and cities of China tend to evolve conservatively. Moreover, substitution emerge as the main driving force for molecular evolution of HPIV3.