Post-entry, spike-dependent replication advantage of B.1.1.7 and B.1.617.2 over B.1 SARS-CoV-2 in an ACE2-deficient human lung cell line (preprint)

Epidemiological data demonstrate that B.1.1.7, and even more, B.1.617.2 SARS-CoV-2 are more transmissible and infections are associated with a higher mortality than B.1 virus infection. Intrinsic properties underlying their enhanced spread in the human population remain unknown. B.1.1.7 virus isolates displayed inferior or equivalent spread in most cell lines and primary cells compared to B.1 SARS-CoV-2, and were outcompeted by the latter. Lower infectivity and delayed entry kinetics of B.1.1.7 viruses were accompanied by inefficient proteolytic processing of spike. B.1.1.7 viruses failed to escape from neutralizing antibodies, but slightly dampened induction of innate immunity. The lung cell line NCI-H1299 supported 24- and 595-fold increased growth of B.1.1.7 and B.1.617.2 viruses, respectively, in the absence of detectable ACE2 expression and in a spike-determined fashion. Superior spread in ACE2-deficient NCI-H1299 cells suggests that variants of concern employ a distinct set of cellular cofactors that may be unavailable in standard cell culture lines.

Cross-reactive CD4+ T cells enhance SARS-CoV-2 immune responses upon infection and vaccination (preprint)

While evidence for pre-existing SARS-CoV-2-cross-reactive CD4+ T cells in unexposed individuals is increasing, their functional significance remains unclear. Here, we comprehensively determined SARS-CoV-2-cross-reactivity and human coronavirus-reactivity in unexposed individuals. SARS-CoV-2-cross-reactive CD4+ T cells were ubiquitous, but their presence decreased with age. Within the spike glycoprotein fusion domain, we identified a universal immunodominant coronavirus-specific peptide epitope (iCope). Pre-existing spike- and iCope-reactive memory T cells were efficiently recruited into mild SARS-CoV-2 infections and their abundance correlated with higher IgG titers. Importantly, the cells were also reactivated after primary BNT162b2 COVID-19 mRNA vaccination in which their kinetics resembled that of secondary immune responses. Our results highlight the functional importance of pre-existing spike-cross-reactive T cells in SARS-CoV-2 infection and vaccination. Abundant spike-specific cross-immunity may be responsible for the unexpectedly high efficacy of current vaccines even with single doses and the high rate of asymptomatic/mild infection courses.

Comparison of seven commercial SARS-CoV-2 rapid Point-of-Care Antigen tests (preprint)

BackgroundAntigen point of care tests (AgPOCT) can accelerate SARS-CoV-2 testing. As first AgPOCT are becoming available, there is a growing interest in their utility and performance. MethodsHere we compare AgPOCT products by seven suppliers: the Abbott Panbio COVID-19 Ag Rapid Test; the RapiGEN BIOCREDIT COVID-19 Ag; the Healgen(R) Coronavirus Ag Rapid Test Cassette (Swab); the Coris Bioconcept Covid.19 Ag Respi-Strip; the R-Biopharm RIDA(R)QUICK SARS-CoV-2 Antigen; the NAL von minden NADAL COVID19-Ag Test; and the Roche/SD Biosensor SARS-CoV Rapid Antigen Test. Tests were evaluated on recombinant nucleoprotein, cultured endemic and emerging coronaviruses, stored clinical samples with known SARS-CoV-2 viral loads (n=138), stored samples from patients with respiratory agents other than SARS-CoV-2 (n=100), as well as self-sampled swabs from healthy volunteers (n=35). FindingsLimits of detection in six of seven tested products ranged between 2.08 x 106 and 2.88 x 107 copies per swab, the outlier at 1.58 x 1010 copies per swab. Specificities ranged between 98.53% and 100% in five products, with two outliers at 94.85% and 88.24%. False positive results were not associated with any specific respiratory agent. As some of the tested AgPOCT were early production lots, the observed issues with specificity are unlikely to persist. InterpretationThe sensitivity range of most AgPOCT overlaps with viral load figures typically observed during the first week of symptoms, which marks the infectious period in the majority patients. AgPOCTs with a limit of detection that approximates the virus concentration above which patients are infectious may enable shortcuts in decision-making in various areas of healthcare and public health.

Presence of SARS-CoV-2 reactive T cells in COVID-19 patients and healthy donors (preprint)

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a rapidly unfolding pandemic, overwhelming health care systems worldwide1. Clinical manifestations of Corona-virus-disease 2019 (COVID-19) vary broadly, ranging from asymptomatic infection to acute respiratory failure and death2, yet the underlying physiological conditions and mechanisms for this high variability are still unknown. Also, the role of host immune responses in viral clearance and its involvement in pathogenesis remains unresolved. For SARS-CoV (2002/03), however, CD4+ T cell responses are generally associated with positive outcomes3,4, while cellular immune responses to SARS-CoV-2 have not yet been investigated. Here we describe an assay that allows direct detection and characterization of SARS-CoV-2 spike glycoprotein (S)-reactive CD4+ T cells in peripheral blood. We demonstrate the presence of S-reactive CD4+ T cells in 83% of COVID-19 patients, as well as in 34% of SARS-CoV-2 seronegative healthy donors, albeit at lower frequencies. Strikingly, in COVID-19 patients S-reactive CD4+ T cells equally targeted both N-terminal and C-terminal parts of S whereas in healthy donors S-reactive CD4+ T cells reacted almost exclusively to the Cterminal part that is a) characterized by higher homology to spike glycoprotein of human endemic "common cold" coronaviruses, and b) contains the S2 subunit of S with the cytoplasmic peptide (CP), the fusion peptide (FP), and the transmembrane domain (TM) but not the receptor-binding domain (RBD). S-reactive CD4+ T cells from COVID-19 patients were further distinct to those from healthy donors as they co-expressed higher levels of CD38 and HLA-DR, indicating their recent in vivo activation. Our study is the first to directly measure SARS-CoV-2-reactive T cell responses providing critical tools for large scale testing, in depth epitope mapping and characterization of potential cross-reactive cellular immunity to SARS-CoV-2. The presence of pre-existing SARS-CoV-2-reactive T cells in healthy donors is of high interest but larger scale prospective cohort studies are needed to assess whether their presence is a correlate of protection or pathology. Results of such studies will be key for a mechanistic understanding of the SARS-CoV-2 pandemic, adaptation of containment methods and to support vaccine development.

Clinical presentation and virological assessment of hospitalized cases of coronavirus disease 2019 in a travel-associated transmission cluster (preprint)

Background: In coronavirus disease 2019 (COVID-19), current case definitions presume mainly lower respiratory tract infection. However, cases seen outside the epicenter of the epidemic may differ in their overall clinical appearance due to more sensitive case finding. Methods: We studied viral load courses by RT-PCR in oro- and nasopharyngeal swabs, sputum, stool, blood, and urine in nine hospitalized cases. Infectious virus was detected by cell culture. Active replication was demonstrated by analysis of viral subgenomic replicative intermediates. Serology including neutralization testing was done to characterize immune response. Results: Seven cases had upper respiratory tract disease. Lower respiratory tract symptoms seen in two cases were limited. Clinical sensitivity of RT-PCR on swabs taken on days 1-5 of symptoms was 100%, with no differences comparing swab and sputum samples taken simultaneously. Average viral load was 6.76x10E5 copies per swab during the first 5 days. Live virus isolates were obtained from swabs during the first week of illness. Proof of active viral replication in upper respiratory tract tissues was obtained by detection of subgenomic viral RNA. Shedding of viral RNA from sputum outlasted the end of symptoms. Seroconversion occurred after about one week. Conclusions: The present study shows that COVID-19 can often present as a common cold-like illness. SARS-CoV-2 can actively replicate in the upper respiratory tract, and is shed for a prolonged time after symptoms end, including in stool. These findings suggest adjustments of current case definitions and re-evaluation of the prospects of outbreak containment.

Rapid reconstruction of SARS-CoV-2 using a synthetic genomics platform (preprint)

Reverse genetics has been an indispensable tool revolutionising our insights into viral pathogenesis and vaccine development. Large RNA virus genomes, such as from Coronaviruses, are cumbersome to clone and to manipulate in E. coli hosts due to size and occasional instability1-3. Therefore, an alternative rapid and robust reverse genetics platform for RNA viruses would benefit the research community. Here we show the full functionality of a yeast-based synthetic genomics platform for the genetic reconstruction of diverse RNA viruses, including members of the Coronaviridae, Flaviviridae and Paramyxoviridae families. Viral subgenomic fragments were generated using viral isolates, cloned viral DNA, clinical samples, or synthetic DNA, and reassembled in one step in Saccharomyces cerevisiae using transformation associated recombination (TAR) cloning to maintain the genome as a yeast artificial chromosome (YAC). T7-RNA polymerase has been used to generate infectious RNA, which was then used to rescue viable virus. Based on this platform we have been able to engineer and resurrect chemically-synthetized clones of the recent epidemic SARS-CoV-24 in only a week after receipt of the synthetic DNA fragments. The technical advance we describe here allows to rapidly responding to emerging viruses as it enables the generation and functional characterization of evolving RNA virus variants - in real-time - during an outbreak.

The novel coronavirus 2019 (2019-nCoV) uses the SARS-coronavirus receptor ACE2 and the cellular protease TMPRSS2 for entry into target cells (preprint)

The emergence of a novel, highly pathogenic coronavirus, 2019-nCoV, in China, and its rapid national and international spread pose a global health emergency. Coronaviruses use their spike proteins to select and enter target cells and insights into nCoV-2019 spike (S)-driven entry might facilitate assessment of pandemic potential and reveal therapeutic targets. Here, we demonstrate that 2019-nCoV-S uses the SARS-coronavirus receptor, ACE2, for entry and the cellular protease TMPRSS2 for 2019-nCoV-S priming. A TMPRSS2 inhibitor blocked entry and might constitute a treatment option. Finally, we show that the serum form a convalescent SARS patient neutralized 2019-nCoV-S-driven entry. Our results reveal important commonalities between 2019-nCoV and SARS-coronavirus infection, which might translate into similar transmissibility and disease pathogenesis. Moreover, they identify a target for antiviral intervention. One sentence summaryThe novel 2019 coronavirus and the SARS-coronavirus share central biological properties which can guide risk assessment and intervention.