Distinctive Dynamics and Functions of the CD4+CD25+FOXP3+ Regulatory T Cell Population in Patients with Severe and Mild COVID-19.

Although CD4+CD25+FOXP3+ regulatory T (TREG) cells have been studied in patients with COVID-19, changes in the TREG cell population have not been longitudinally examined during the course of COVID-19. In this study, we longitudinally investigated the quantitative and qualitative changes in the TREG cell population in patients with COVID-19. We found that the frequencies of total TREG cells and CD45RA-FOXP3hi activated TREG cells were significantly increased 15-28 d postsymptom onset in severe patients, but not in mild patients. TREG cells from severe patients exhibited not only increased proliferation but also enhanced apoptosis, suggesting functional derangement of the TREG cell population during severe COVID-19. The suppressive functions of the TREG cell population did not differ between patients with severe versus mild COVID-19. The frequency of TREG cells inversely correlated with SARS-CoV-2-specific cytokine production by CD4+ T cells and their polyfunctionality in patients with mild disease, suggesting that TREG cells are major regulators of virus-specific CD4+ T cell responses during mild COVID-19. However, such correlations were not observed in patients with severe disease. Thus, in this study, we describe distinctive changes in the TREG cell population in patients with severe and mild COVID-19. Our study provides a deep understanding of host immune responses upon SARS-CoV-2 infection in regard to TREG cells.

Corticosteroids reduce pathologic interferon responses by downregulating STAT1 in patients with high-risk COVID-19.

We do not yet understand exactly how corticosteroids attenuate hyperinflammatory responses and alleviate high-risk coronavirus disease 2019 (COVID-19). We aimed to reveal the molecular mechanisms of hyperinflammation in COVID-19 and the anti-inflammatory effects of corticosteroids in patients with high-risk COVID-19. We performed single-cell RNA sequencing of peripheral blood mononuclear cells (PBMCs) from three independent COVID-19 cohorts: cohort 1 was used for comparative analysis of high-risk and low-risk COVID-19 (47 PBMC samples from 28 patients), cohort 2 for longitudinal analysis during COVID-19 (57 PBMC samples from 15 patients), and cohort 3 for investigating the effects of corticosteroid treatment in patients with high-risk COVID-19 (55 PBMC samples from 13 patients). PBMC samples from healthy donors (12 PBMC samples from 12 donors) were also included. Cohort 1 revealed a significant increase in the proportion of monocytes expressing the long noncoding RNAs NEAT1 and MALAT1 in high-risk patients. Cohort 2 showed that genes encoding inflammatory chemokines and their receptors were upregulated during aggravation, whereas genes related to angiogenesis were upregulated during improvement. Cohort 3 demonstrated downregulation of interferon-stimulated genes (ISGs), including STAT1, in monocytes after corticosteroid treatment. In particular, unphosphorylated STAT-dependent ISGs enriched in monocytes from lupus patients were selectively downregulated by corticosteroid treatment in patients with high-risk COVID-19. Corticosteroid treatment suppresses pathologic interferon responses in monocytes by downregulating STAT1 in patients with high-risk COVID-19. Our study provides insights into the mechanisms underlying COVID-19 aggravation and improvement and the effects of corticosteroid treatment.

A heterologous AZD1222 priming and BNT162b2 boosting regimen more efficiently elicits neutralizing antibodies, but not memory T cells, than the homologous BNT162b2 regimen.

BACKGROUND: Comparative analyses of SARS-CoV-2-specific immune responses elicited by diverse prime-boost regimens are required to establish efficient regimens for the control of COVID-19. METHOD: In this prospective observational cohort study, spike-specific immunoglobulin G (IgG) and neutralizing antibodies (nAbs) alongside spike-specific T-cell responses in age-matched groups of homologous BNT162b2/BNT162b2 or AZD1222/AZD1222 vaccination, heterologous AZD1222/BNT162b2 vaccination, and prior wild-type SARS-CoV-2 infection/vaccination were evaluated. RESULTS: Peak immune responses were achieved after the second vaccine dose in the naïve vaccinated groups and after the first dose in the prior infection/vaccination group. Peak titers of anti-spike IgG and nAb were significantly higher in the AZD1222/BNT162b2 vaccination and prior infection/vaccination groups than in the BNT162b2/BNT162b2 or AZD1222/AZD1222 groups. However, the frequency of interferon-γ-producing CD4+ T cells was highest in the BNT162b2/BNT162b2 vaccination group. Similar results were observed in the analysis of polyfunctional T cells. When nAb and CD4+T-cell responses against the Delta variant were analyzed, the prior infection/vaccination group exhibited higher responses than the groups of other homologous or heterologous vaccination regimens. CONCLUSION: nAbs are efficiently elicited by heterologous AZD1222/BNT162b2 vaccination, as well as prior infection/vaccination, whereas spike-specific CD4+T-cell responses are efficiently elicited by homologous BNT162b2 vaccination. Variant-recognizing immunity is more efficiently generated by prior infection/vaccination than the other homologous or heterologous vaccination regimens.

Enhanced antibody responses in fully vaccinated individuals against pan-SARS-CoV-2 variants following Omicron breakthrough infection.

Omicron has become the globally dominant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant, creating additional challenges due to its ability to evade neutralization. Here, we report that neutralizing antibodies against Omicron variants are undetected following COVID-19 infection with ancestral or past SARS-CoV-2 variant viruses or after two-dose mRNA vaccination. Compared with two-dose vaccination, a three-dose vaccination course induces broad neutralizing antibody responses with improved durability against different SARS-CoV-2 variants, although neutralizing antibody titers against Omicron remain low. Intriguingly, among individuals with three-dose vaccination, Omicron breakthrough infection substantially augments serum neutralizing activity against a broad spectrum of SARS-CoV-2 variants, including Omicron variants BA.1, BA.2, and BA.5. Additionally, after Omicron breakthrough infection, memory T cells respond to the spike proteins of both ancestral and Omicron SARS-CoV-2 by producing cytokines with polyfunctionality. These results suggest that Omicron breakthrough infection following three-dose mRNA vaccination induces pan-SARS-CoV-2 immunity that may protect against emerging SARS-CoV-2 variants of concern.

The generation of stem cell-like memory cells early after BNT162b2 vaccination is associated with durability of memory CD8+ T cell responses.

COVID-19 vaccines elicit humoral and cellular immune responses. Durable maintenance of vaccine-induced immunity is required for long-term protection of the host. Here, we examine activation and differentiation of vaccine-induced CD8+ T cells using MHC class I (MHC-I) multimers and correlations between early differentiation and the durability of CD8+ T cell responses among healthcare workers immunized with two doses of BNT162b2. The frequency of MHC-I multimer+ cells is robustly increased by BNT162b2 but decreases 6 months post-second vaccination to 2.4%-65.6% (23.0% on average) of the peak. MHC-I multimer+ cells dominantly exhibit phenotypes of activated effector cells 1-2 weeks post-second vaccination and gradually acquire phenotypes of long-term memory cells, including stem cell-like memory T (TSCM) cells. Importantly, the frequency of TSCM cells 1-2 weeks post-second vaccination significantly correlates with the 6-month durability of CD8+ T cells, indicating that early generation of TSCM cells determines the longevity of vaccine-induced memory CD8+ T cell responses.

Modeling Incorporating the Severity-Reducing Long-term Immunity: Higher Viral Transmission Paradoxically Reduces Severe COVID-19 During Endemic Transition.

Natural infection with severe acute respiratory syndrome-coronavirus-2 or vaccination induces virus-specific immunity protecting hosts from infection and severe disease. While the infection-preventing immunity gradually declines, the severity-reducing immunity is relatively well preserved. Here, based on the different longevity of these distinct immunities, we develop a mathematical model to estimate courses of endemic transition of coronavirus disease 2019 (COVID-19). Our analysis demonstrates that high viral transmission unexpectedly reduces the rates of progression to severe COVID-19 during the course of endemic transition despite increased numbers of infection cases. Our study also shows that high viral transmission amongst populations with high vaccination coverages paradoxically accelerates the endemic transition of COVID-19 with reduced numbers of severe cases. These results provide critical insights for driving public health policies in the era of 'living with COVID-19.'

Safety and immunogenicity of two recombinant DNA COVID-19 vaccines containing the coding regions of the spike or spike and nucleocapsid proteins: an interim analysis of two open-label, non-randomised, phase 1 trials in healthy adults.

BACKGROUND: We assessed the safety and immunogenicity of two recombinant DNA vaccines for COVID-19: GX-19 containing plasmid DNA encoding the SARS-CoV-2 spike protein, and GX-19N containing plasmid DNA encoding the SARS-CoV-2 receptor-binding domain (RBD) foldon, nucleocapsid protein, and plasmid DNA encoding the spike protein. METHODS: Two open-label non-randomised phase 1 trials, one of GX-19 and the other of GX-19N were done at two hospitals in South Korea. We enrolled healthy adults aged 19-49 years for the GX-19 trial and healthy adults aged 19-54 years for the GX-19N trial. Participants who tested positive by serological testing for SARS-CoV-2 were excluded. At 4-week intervals, the GX-19 trial participants received two vaccine doses (either 1·5 mg or 3·0 mg), and the GX-19N trial participants received two 3·0 mg doses. The vaccines were delivered intramuscularly using an electroporator. The participants were followed up for 52 weeks after first vaccination. Data collected up to day 57 after first vaccination were analysed in this interim analysis. The primary outcome was safety within 28 days after each vaccination measured in the intention-to-treat population. The secondary outcome was vaccine immunogenicity using blood samples collected on day 43 or 57 after first vaccination measured in the intention-to-treat population. The GX-19 (NCT044445389) and GX-19N (NCT04715997) trials are registered with ClinicalTrials.gov. FINDINGS: Between June 17 and July 30, 2020, we screened 97 individuals, of whom 40 (41%) participants were enrolled in the GX-19 trial (20 [50%] in the 1·5 mg group and 20 [50%] in the 3·0 mg group). Between Dec 28 and 31, 2020, we screened 23 participants, of whom 21 (91%) participants were enrolled on the GX-19N trial. 32 (52%) of 61 participants reported 80 treatment-emergent adverse events after vaccination. All solicited adverse events were mild except one (2%) case of moderate fatigue in the 1·5 mg GX-19 group; no serious vaccine-related adverse events were detected. Binding antibody responses increased after second dose of vaccination in all groups (p=0·0002 in the 1·5 mg GX-19 group; p<0·0001 in the 3·0 mg GX-19; and p=0·0004 for the spike protein and p=0·0001 for the RBD in the 3·0 mg GX-19N group). INTERPRETATION: GX-19 and GX-19N are safe and well tolerated. GX-19N induces humoral and broad SARS-CoV-2-specific T-cell responses. GX-19N shows lower neutralising antibody responses and needs improvement to enhance immunogenicity. FUNDING: The Korea Drug Development Fund, funded by the Ministry of Science and ICT, Ministry of Trade, Industry, and Energy, and Ministry of Health and Welfare.

Comparative safety of mRNA COVID-19 vaccines to influenza vaccines: A pharmacovigilance analysis using WHO international database.

Two messenger RNA (mRNA) vaccines developed by Pfizer-BioNTech and Moderna are being rolled out. Despite the high volume of emerging evidence regarding adverse events (AEs) associated with the COVID-19 mRNA vaccines, previous studies have thus far been largely based on the comparison between vaccinated and unvaccinated control, possibly highlighting the AE risks with COVID-19 mRNA vaccination. Comparing the safety profile of mRNA vaccinated individuals with otherwise vaccinated individuals would enable a more relevant assessment for the safety of mRNA vaccination. We designed a comparative safety study between 18 755 and 27 895 individuals who reported to VigiBase for adverse events following immunization (AEFI) with mRNA COVID-19 and influenza vaccines, respectively, from January 1, 2020, to January 17, 2021. We employed disproportionality analysis to rapidly detect relevant safety signals and compared comparative risks of a diverse span of AEFIs for the vaccines. The safety profile of novel mRNA vaccines was divergent from that of influenza vaccines. The overall pattern suggested that systematic reactions like chill, myalgia, fatigue were more noticeable with the mRNA COVID-19 vaccine, while injection site reactogenicity events were more prevalent with the influenza vaccine. Compared to the influenza vaccine, mRNA COVID-19 vaccines demonstrated a significantly higher risk for a few manageable cardiovascular complications, such as hypertensive crisis (adjusted reporting odds ratio [ROR], 12.72; 95% confidence interval [CI], 2.47-65.54), and supraventricular tachycardia (adjusted ROR, 7.94; 95% CI, 2.62-24.00), but lower risk of neurological complications such as syncope, neuralgia, loss of consciousness, Guillain-Barre syndrome, gait disturbance, visual impairment, and dyskinesia. This study has not identified significant safety concerns regarding mRNA vaccination in real-world settings. The overall safety profile patterned a lower risk of serious AEFI following mRNA vaccines compared to influenza vaccines.

Phenotypes and Functions of SARS-CoV-2-Reactive T Cells.

Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19), which is an ongoing pandemic disease. SARS-CoV-2-specific CD4+ and CD8+ T-cell responses have been detected and characterized not only in COVID-19 patients and convalescents, but also unexposed individuals. Here, we review the phenotypes and functions of SARS-CoV-2-specific T cells in COVID-19 patients and the relationships between SARS-CoV-2-specific T-cell responses and COVID-19 severity. In addition, we describe the phenotypes and functions of SARS-CoV-2-specific memory T cells after recovery from COVID-19 and discuss the presence of SARS-CoV-2-reactive T cells in unexposed individuals and SARS-CoV-2-specific T-cell responses elicited by COVID-19 vaccines. A better understanding of T-cell responses is important for effective control of the current COVID-19 pandemic.

Longitudinal Assessment of Antisevere Acute Respiratory Syndrome Coronavirus 2 Immune Responses for Six Months Based on the Clinical Severity of Coronavirus Disease 2019.

BACKGROUND: There is insufficient data on the longevity of immunity acquired after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. METHODS: We aimed to evaluate the duration of SARS-CoV-2-specific humoral and cellular immunity according to the clinical severity of coronavirus disease 2019 (COVID-19). The study population comprised asymptomatic (n = 14), symptomatic/nonpneumonic (n = 42), and pneumonic (n = 41) patients. RESULTS: The anti-SARS-CoV-2 immunoglobulin class G and neutralizing antibody (NAb) titers lasted until 6 months after diagnosis, with positivity rates of 66.7% and 86.9%, respectively. Older age, prolonged viral shedding, and accompanying pneumonia were more frequently found in patients with sustained humoral immunity. Severe acute respiratory syndrome coronavirus 2-specific T-cell response was strongly observed in pneumonic patients and prominent in individuals with sustained humoral immunity. CONCLUSIONS: In conclusion, most (>85%) patients carry NAb until 6 months after diagnosis of SARS-CoV-2 infection, providing insights for establishing vaccination strategies against COVID-19.

SARS-CoV-2-Specific Antibody and T Cell Response Kinetics According to Symptom Severity.

Data on the longevity of humoral and cell-mediated immune responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in patients with coronavirus disease 2019 (COVID-19) are limited. We evaluated the detailed kinetics of antibody and T-cell responses at the acute, convalescent, and post-convalescent phases in COVID-19 patients with a wide range of severity. We enrolled patients with COVID-19 prospectively from four hospitals and one community treatment center between February 2020 and January 2021. symptom severity was classified as mild, moderate, or severe/critical. Patient blood samples were collected at 1 week (acute), 1 month (convalescent), and 2 months after symptom onset (post-convalescent). Human SARS-CoV-2 IgG and IgM antibodies were measured using in-house-developed ELISA. The SARS-CoV-2-specific T-cell responses against overlapping peptides of spike proteins and nucleoprotein were measured by interferon-γ enzyme-linked immunospot assays. Twenty-five COVID-19 patients were analyzed (mild, n = 5; moderate, n = 9; severe/critical, n = 11). IgM and IgG antibody responses peaked at 1 month after symptom onset and decreased at 2 months. IgG response levels were significantly greater in the severe/critical group compared with other groups. Interferon-γ-producing T-cell responses increased between 1 week and 1 month after symptom onset, and had a trend toward decreasing at 2 months, but did not show significant differences according to severity. Our data indicate that SARS-CoV-2-specific antibody responses were greater in those with severe symptoms and waned after reaching a peak around 1 month after symptom onset. However, SARS-CoV-2-specific T-cell responses were not significantly different according to symptom severity, and decreased slowly during the post-convalescent phase.