Interpatient mutational spectrum of human coronavirus-OC43 revealed by illumina sequencing

Comparison of mutations in human parainfluenza viruses during passage in primary human bronchial/tracheal epithelial air-liquid interface cultures and cell lines

Human parainfluenza virus (HPIV) causes respiratory infections, which are exacerbated in children and older people. Correct evaluation of viral characteristics is essential for the study of countermeasures. However, adaptation of viruses to cultured cells during isolation or propagation might select laboratory passage-associated mutations that modify the characteristics of the virus. It was previously reported that adaptation of HPIV3, but not other HPIVs, was avoided in human airway epithelia. To examine the influence of laboratory passage on the genomes of HPIV1-HPIV4, we evaluated the occurrence of mutations after passage in primary human bronchial/tracheal epithelial cell air-liquid interface (HBTEC-ALI) culture and conventional cultured cells (Vero cells expressing the transmembrane protease, serine 2, and normal Vero cells). The occurrence of mutations was significantly lower in HBTEC-ALI than in conventional culture. In HBTEC-ALI culture, most of the mutations were silent or remained at low variant frequency, resulting in less impact on the viral consensus sequence. In contrast, passage in conventional culture induced or selected genetic mutations at high frequency with passage-associated unique substitutions. High mutagenesis of hemagglutinin-neuraminidase was commonly observed in all four HPIVs, and mutations even occurred in a single passage. In addition, in HPIV1 and HPIV2, mutations in the large protein were more frequent. These results indicate that passage in HBTEC-ALI culture is more suitable than conventional culture for maintaining the original characteristics of clinical isolates in all four HPIVs, which can help with the understanding of viral pathogenesis.

IMPORTANCE

Adaptation of viruses to cultured cells can increase the risk of misinterpretation in virological characterization of clinical isolates. In human parainfluenza virus (HPIV) 3, it has been reported that the human airway epithelial and lung organoid models are preferable for the study of viral characteristics of clinical strains without mutations. Therefore, we analyzed clinical isolates of all four HPIVs for the occurrence of mutations after five laboratory passages in human bronchial/tracheal epithelial cell air-liquid interface (HBTEC-ALI) or conventional culture. We found a high risk of hemagglutinin-neuraminidase mutagenesis in all four HPIVs in conventional cultured cells. In addition, in HPIV1 and HPIV2, mutations of the large protein were also more frequent in conventional cultured cells than in HBTEC-ALI culture. HBTEC-ALI culture was useful for maintaining the original sequence and characteristics of clinical isolates in all four HPIVs. The present study contributes to the understanding of HPIV pathogenesis and antiviral strategies.

From viral democratic genomes to viral wild bunch of quasispecies

The tremendous majority of RNA genomes from pathogenic viruses analyzed and deposited in databases are consensus or "democratic" genomes. They represent the genomes most frequently found in the clinical samples of patients but do not account for the huge genetic diversity of coexisting genomes, which is better described as quasispecies. A viral quasispecies is defined as the dynamic distribution of nonidentical but closely related mutants, variants, recombinant, or reassortant viral genomes. Viral quasispecies have collective behavior and dynamics and are the subject of internal interactions that comprise interference, complementation, or cooperation. In the setting of SARS-CoV-2 infection, intrahost SARS-CoV-2 genetic diversity was recently notably reported for immunocompromised, chronically infected patients, for patients treated with monoclonal antibodies targeting the viral spike protein, and for different body compartments of a single patient. A question that deserves attention is whether such diversity is generated postinfection from a clonal genome in response to selection pressure or is already present at the time of infection as a quasispecies. In the present review, we summarize the data supporting that hosts are infected by a "wild bunch" of viruses rather than by multiple virions sharing the same genome. Each virion in the "wild bunch" may have different virulence and tissue tropisms. As the number of viruses replicated during host infections is huge, a viral quasispecies at any time of infection is wide and is also influenced by host-specific selection pressure after infection, which accounts for the difficulty in deciphering and predicting the appearance of more fit variants and the evolution of epidemics of novel RNA viruses.

Within-Host Diversity of SARS-CoV-2 in COVID-19 Patients With Variable Disease Severities

Background: The ongoing pandemic of SARS-COV-2 has already infected more than eight million people worldwide. The majority of COVID-19 patients either are asymptomatic or have mild symptoms. Yet, about 15% of the cases experience severe complications and require intensive care. Factors determining disease severity are not yet fully characterized. Aim: Here, we investigated the within-host virus diversity in COVID-19 patients with different clinical manifestations. Methods: We compared SARS-COV-2 genetic diversity in 19 mild and 27 severe cases. Viral RNA was extracted from nasopharyngeal samples and sequenced using the Illumina MiSeq platform. This was followed by deep-sequencing analyses of SARS-CoV-2 genomes at both consensus and sub-consensus sequence levels. Results: Consensus sequences of all viruses were very similar, showing more than 99.8% sequence identity regardless of the disease severity. However, the sub-consensus analysis revealed significant differences in within-host diversity between mild and severe cases. Patients with severe symptoms exhibited a significantly (p-value 0.001) higher number of variants in coding and non-coding regions compared to mild cases. Analysis also revealed higher prevalence of some variants among severe cases. Most importantly, severe cases exhibited significantly higher within-host diversity (mean = 13) compared to mild cases (mean = 6). Further, higher within-host diversity was observed in patients above the age of 60 compared to the younger age group. Conclusion: These observations provided evidence that within-host diversity might play a role in the development of severe disease outcomes in COVID-19 patients; however, further investigations are required to elucidate this association.

A novel target enrichment strategy in next-generation sequencing through 7-deaza-dGTP-resistant enzymatic digestion

Objective

Owing to the overwhelming dominance of human and commensal microbe sequences, low efficiency is a major concern in clinical viral sequencing using next-generation sequencing. DNA composed of 7-deaza-2′-deoxyguanosine 5′-triphosphate (c⁷dGTP), an analog of deoxyguanosine triphosphate (dGTP), is resistant to selective restriction enzymes. This characteristic has been utilized to develop a novel strategy for target enrichment in next-generation sequencing.

Results

The new enrichment strategy is named target enrichment via enzymatic digestion in next-generation sequencing (TEEDseq). It combined 7-deaza-2′-deoxyguanosine 5′-triphosphate (c⁷dGTP)-involved primer extension, splinter-assisted intracellular cyclization, c⁷dGTP)-resistant enzymatic digestion, and two-phase rolling cycle amplification. We first estimated c7dGTP for its efficiency in PCR amplification and its resistance to three restriction enzymes, AluI, HaeIII, and HpyCH4V. We then evaluated TEEDseq using a serum sample spiked with a 1311-bp hepatitis B virus (HBV) fragment. TEEDseq achieved an HBV on-target rate of 3.31 ± 0.39%, which was equivalent to 454× the enrichment of direct Illumina sequencing. Therefore, the current study has provided a concept proof for TEEDseq as an alternative option for clinical viral sequencing that requires an enrichment in next-generation sequencing.

Longitudinal epidemiology of human coronavirus OC43 in Yamagata, Japan, 2010-2017: Two groups based on spike gene appear one after another

Human coronavirus OC43 (HCoV-OC43) is divided into genotypes A to H based on genetic recombination including the spike (S) gene. To investigate the longitudinal transition of the phylogenetic feature of the HCoV-OC43 S gene in a community, phylogenetic analysis of the S1 region of the S gene was conducted using 208 strains detected in Yamagata during 2010 to 2017 with reference strains of the genotype. The S1 sequences were divisible into four groups: A to D. All Yamagata strains belonged to either group B or group D. In group B, 46 (90.2%) out of 51 Yamagata strains were clustered with those of genotype E reference strains (cluster E). In group D, 28 (17.8%) and 122 (77.7%) out of 157 Yamagata strains were clustered, respectively, with genotype F and genotype G reference strains. In cluster G, 28 strains formed a distinct cluster. Monthly distributions of HCoV-OC43 in Yamagata in 2010 to 2017 revealed that group B and group D appeared one after another. In group B, the cluster E strains were prevalent recurrently. In conclusion, epidemics of HCoV-OC43 in Yamagata, Japan might be attributable to two genetically different groups: group B showed a recurrent epidemic of strains belonging to a single phylogenetic cluster and group D showed epidemic strains belonging to multiple clusters.

Antibodies to coronaviruses are higher in older compared with younger adults and binding antibodies are more sensitive than neutralizing antibodies in identifying coronavirus-associated illnesses

Human coronaviruses (HCoV) are common causes of respiratory illnesses (RI) despite preexisting humoral immunity. Sera were obtained near the onset of RI and 3 to 4 weeks later as part of a prospective study of 200 subjects evaluated for RI from 2009 to 2013. Antibodies against common HCoV strains were measured by enzyme‐linked immunosorbent assay and neutralization assay comparing older adults with cardiopulmonary diseases (99 subjects) to younger, healthy adults (101 subjects). Virus shedding was detected in respiratory secretions by polymerase chain reaction. Of 43 HCoV‐associated illnesses, 15 (35%) occurred in 14 older adults (aged ≥60 years) and 28 (65%) in 28 younger adults (aged 21‐40 years). Binding and neutralizing antibodies were higher in older adults. Only 16 (35.7%) of RI with increases in binding antibodies also had increases in neutralizing antibodies to HCoV. Increases in binding antibodies with RI were more frequent than increased neutralizing antibodies and virus shedding, and more frequent in younger compared to older adults. Functional neutralizing antibodies were not stimulated as often as binding antibodies, explaining in part a susceptibility to reinfection with HCoV. Monitoring binding antibodies may be more sensitive for the serologic detection of HCoV infections.

Antibodies to common coronaviruses (HCoV) were higher in older than younger adults.

Antibodies to HCoV can be cross‐reactive between strains.

More HCoV‐related respiratory illnesses were detected in younger than older adults, and binding antibodies to HCoV increased with respiratory illness more frequently than neutralizing antibodies.

There were correlations between binding and neutralizing antibodies, especially to related HCoV strains in convalescent sera.

Pre‐existing antibodies to HCoV may not necessarily be protective against repeated infections and lower rates of neutralizing antibody stimulation may contribute to susceptibility to re‐infection.

Assessment of binding antibodies to HCoV may be useful in seroepidemiologic studies of HCoV infections.

Interpatient mutational spectrum of human coronavirus-OC43 revealed by illumina sequencing

Human coronaviruses (HCoV) are RNA viruses that cause respiratory tract infections with viral replication of limited duration. The host and viral population heterogeneity could influence clinical phenotypes. Employing long RT‐PCR with Illumina sequencing, we quantified the gene mutation load at 0.5% mutation frequency for the 4529 bp‐domain spanning the Spike gene (4086 bp) of HCoV‐OC43 in four upper respiratory clinical specimens obtained during acute illness. There were a total of 121 mutations for all four HCoV samples with the average number of mutations at 30.3 ± 10.2, which is significantly higher than that expected from the Illumina sequencing error rate. There were two mutation peaks, one at the 5′ end and the other near position 1 550 in the S1 subunit. Two coronavirus samples were genotype B and two were genotype D, clustering with HCoV‐OC43 strain AY391777 in neighbor‐joining tree phylogenetic analysis. Nonsynonymous mutations were 76.1 ± 14% of mutation load. Although lower than other RNA viruses such as hepatitis C virus, HCoV‐OC43 did exhibit quasi‐species. The rate of nonsynonymous mutations was higher in the HCoV‐OC43 isolates than in hepatitis C (HCV) virus genotype 1a isolates analyzed for comparison in this study. These characteristics of HCoV‐OC43 may affect viral replication dynamics, receptor binding, antigenicity, evolution, transmission, and clinical illness.