Role of the complement system in Long COVID (preprint)

Long COVID, or Post-Acute COVID Syndrome (PACS), may develop following SARS-CoV-2 infection, posing a substantial burden to society. Recently, PACS has been linked to a persistent activation of the complement system (CS), offering hope for both a diagnostic tool and targeted therapy. However, our findings indicate that, after adjusting proteomics data for age, body mass index and sex imbalances, the evidence of complement system activation disappears. Furthermore, proteomic analysis of two orthogonal cohorts-one addressing PACS following severe acute phase and another after a mild acute phase-fails to support the notion of persistent CS activation. Instead, we identify a proteomic signature indicative of either ongoing infections or sustained immune activation similar to that observed in acute COVID-19, particularly within the mild-PACS cohort.

Pharmacokinetics of nirmatrelvir and ritonavir in COVID-19 patients with end stage renal disease on intermittent haemodialysis (preprint)

Background: Nirmatrelvir/ritonavir is an effective therapy against SARS-CoV-2. Patients with end-stage renal disease (ESRD) are at high risk for severe COVID-19 and show impaired vaccine responses underlining the importance of antiviral therapy. However, use of nirmatrelvir/ritonavir is not recommended in these patients due to lack of clinical and pharmacokinetic data. Objective: To investigate pharmacokinetics and hepatic tolerance of nirmatrelvir/ritonavir in patients with ESRD and haemodialysis (HD). Patients and methods: Four patients diagnosed with SARS-CoV-2 infection received nirmatrelvir/ritonavir 150/100mg twice daily as recommended for renal impairment; HD ran in two- to three-day intervals. Plasma and serum samples were drawn before and after each HD during the 5-day treatment and for ensuing 3-5 days. Results: Median peak levels of nirmatrelvir obtained two hours after medication pre-HD in three patients were 7745ng/mL on day 3 and 6653ng/mL on day 5; median post-HD levels (C6h) declined to 5765ng/mL (74%) and 5521ng/mL (83%), on days 3 and 5 of treatment, respectively. Three days after end of treatment, median levels were 365ng/mL pre-HD and 30ng/mL post-HD. Measurements of the fourth patient, six hours after drug intake pre-HD showed nirmatrelvir-levels of 3704ng/mL on treatment day 3 which fell to 2308ng/mL post-HD, at one hour before intake of the next dose (Cmin). Conclusion: Use of nirmatrelvir/ritonavir in patients with ESRD results in high nirmatrelvir blood concentrations, which are still within the range known from patients without renal failure. No accumulation of nirmatrelvir took place and levels declined to zero within few days after end of treatment.

Neutralization sensitivity of the SARS-CoV-2 Omicron BA.2.75 sublineage (preprint)

The recently emerged BA.2.75 Omicron sublineage of SARS-CoV-2 identified in numerous countries is rapidly increasing in prevalence in regions of India. Compared with BA.2, the spike protein of BA.2.75 differs in nine amino acid residues. To determine the impact of the spike mutations on polyclonal and monoclonal antibody activity, we investigated the neutralization sensitivity of BA.2.75 in comparison with B.1, BA.2, BA.2.12.1, and BA.4/5. Analysis of post-boost samples from 30 vaccinated individuals revealed significantly lower serum neutralizing activity against BA.2.75 than against BA.2. However, BA.2.75 was more sensitive to serum neutralization than the widely circulating BA.4/5 sublineages. Moreover, evaluation of 17 clinical-stage monoclonal antibodies demonstrated individual differences in Omicron sublineage activity. Notably, some authorized antibodies with low activity against other Omicron sublineages demonstrated high BA.2.75 neutralizing potency. Our results indicate a less pronounced degree of antibody evasion of BA.2.75 compared with BA.4/5 and suggest that factors beyond immune evasion may be required for an expansion of BA.2.75 over BA.4/5.

The human host response to monkeypox infection: a proteomic case series study (preprint)

Monkeypox (MPX) is caused by the homonymous orthopoxvirus (MPXV) known since the 1970s to occur at low frequency in West and Central Africa. Recently, the disease has been spreading quickly in Europe and the US. The rapid rise of MPX cases outside previously endemic areas and the different clinical presentation prompt for a better understanding of the disease, including the development of clinical tests for rapid diagnosis and monitoring. Here, using Zeno SWATH MS - a latest-generation proteomic technology - we studied the plasma proteome of a group of MPX patients with a similar infection history and clinical severity typical for the current outbreak. Moreover, we compared their proteomes to those of healthy volunteers and COVID-19 patients. We report that MPX is associated with a strong and characteristic plasma proteomic response and describe MPXV infection biomarkers among nutritional and acute phase response proteins. Moreover, we report a correlation between plasma protein markers and disease severity, approximated by the degree of skin manifestation. Contrasting the MPX host response with that of COVID-19, we find a range of similarities, but also important differences. For instance, Complement factor H-related protein 1 (CFHR1) is induced in COVID-19, but suppressed in MPX, reflecting the different role of the complement system in the two infectious diseases. However, the partial overlap between MPX and COVID-19 host response proteins allowed us to explore the repurposing of a clinically applicable COVID-19 biomarker panel assay, resulting in the successful classification of MPX patients. Hence, our results provide a first proteomic characterization of the MPX human host response based on a case series. The results obtained highlight that proteomics is a promising technology for the timely identification of disease biomarkers in studies with moderate cohorts, and we reveal a thus far untapped potential for accelerating the response to disease outbreaks through the repurposing of multiplex biomarker assays.

90K/LGALS3BP Expression is Upregulated in COVID-19 but Does Not Restrict SARS-CoV-2 Infection (preprint)

Glycoprotein 90K, encoded by the interferon-stimulated gene LGALS3BP, displays broad antiviral activity. It reduces HIV-1 infectivity by interfering with Env maturation and virion incorporation, and increases survival of Influenza A virus-infected mice via antiviral innate immune signaling. Here, we analyzed the expression of 90K/LGALS3BP in 44 hospitalized COVID-19 patients. 90K protein serum levels were significantly elevated in COVID-19 patients compared to uninfected sex- and age-matched controls. Furthermore, PBMC-associated concentrations of 90K protein were overall reduced by SARS-CoV-2 infection in vivo, suggesting enhanced secretion into the extracellular space. Mining of published PBMC scRNA-seq datasets uncovered monocyte-specific induction of LGALS3BP mRNA expression in COVID-19 patients. In functional assays, neither 90K overexpression in susceptible cell lines nor exogenous addition of purified 90K consistently inhibited SARS-CoV-2 infection. Our data suggests that 90K/LGALS3BP contributes to the global type I IFN response during SARS-CoV-2 infection in vivo without displaying detectable antiviral properties.

Impaired Neutralization of SARS-CoV-2 Including Omicron Variants after COVID-19 mRNA Booster Immunization under Methotrexate Therapy (preprint)

ABSTRACT Objective To determine the immediate need for a fourth COVID-19 vaccination based on the neutralizing capacity in patients on methotrexate (MTX) therapy after mRNA booster immunization. Methods In this observational cohort study, neutralizing serum activity against SARS-CoV-2 wildtype (Wu01) and variant of concern (VOC) Omicron BA.1 and BA.2 were assessed by pseudovirus neutralization assay before, 4 and 12 weeks after mRNA booster immunization in 50 rheumatic patients on MTX, 26 of whom paused the medication. 44 non-immunosuppressed persons (NIP) served as control group. Results While the neutralizing serum activity against SARS-CoV-2 Wu01 and Omicron variants increased 67-to 73-fold in the NIP after booster vaccination, the serum activity in patients receiving MTX increased only 20-to 23-fold. As a result, significantly lower neutralizing capacities were measured in patients on MTX compared to the NIP at week 4. Patients who continued MTX treatment during vaccination had significantly lower neutralizing serum titres against all three virus strains at week 4 and 12 compared to patients who paused MTX and the control group, except for BA.2 at week 12. Patients who paused MTX reached comparably high neutralization titres as the NIP, except for Wu01 at week 12. Neutralization of omicron variants was significantly lower in comparison to wildtype in both groups. Conclusion Patients pausing MTX showed a similar vaccine response to NIP. Patients who continued MTX demonstrated an impaired booster response indicating a potential benefit of a second booster vaccination.

Extending the German Corona Consensus Dataset (GECCO) to the immunization, pediatrics, and cardiology domains (preprint)

Background The COVID-19 pandemic has spurred large-scale, inter-institutional research efforts. To enable these efforts, the German Corona Consensus (GECCO) dataset has been developed previously as a harmonized, interoperable collection of the most relevant data elements for COVID-19-related patient research. As GECCO has been developed as a compact core dataset across all medical fields, the focused research within particular medical domains demanded the definition of extension modules that include those data elements that are most relevant to the research performed in these individual medical specialties. Main body We created GECCO extension modules for the immunization, pediatrics , and cardiology domains with respect to the pandemic requests. The data elements included in each of these modules were selected in a consensus-based process by working groups of medical experts from the respective specialty to ensure that the contents are aligned with the research needs of the specialty. The selected data elements were mapped to international standardized vocabularies and data exchange specifications were created using HL7 FHIR profiles on the appropriate resources. All steps were performed in close interdisciplinary collaboration between medical domain experts, medical information scientists and FHIR developers. The profiles and vocabulary mappings were syntactically and semantically validated in a two-stage process. In that way, we defined dataset specifications for a total number of 23 ( immunization ), 59 ( pediatrics ), and 50 ( cardiology ) data elements that augment the GECCO core dataset. We created and published implementation guides and example implementations as well as dataset annotations for each extension module. Conclusions We here present extension modules for the GECCO core dataset that contain data elements most relevant to COVID-19-related patient research in immunization, pediatrics and cardiology . These extension modules were defined in an interdisciplinary, iterative, consensus-based approach that may serve as a blueprint for the development of further dataset definitions and GECCO extension modules. The here developed GECCO extension modules provide a standardized and harmonized definition of specialty-related datasets that can help to enable inter-institutional and cross-country COVID-19 research in these specialties.

Delineating antibody escape from Omicron variants (preprint)

SARS-CoV-2-neutralizing antibodies play a critical role for protection and treatment of COVID-19. Viral antibody evasion therefore threatens essential prophylactic and therapeutic measures. The high number of mutations in the Omicron BA.1 sublineage results in markedly reduced neutralization susceptibility. Consistently, Omicron is associated with lower vaccine effectiveness and a high re-infection rate. Notably, newly emerging Omicron sublineages (BA.1.1, BA.2) have rapidly become dominant. Here, we determine polyclonal serum activity against BA.1, BA.1.1 and BA.2 in 50 convalescent or vaccinated individuals as well as delineate antibody sensitivities on a monoclonal level using 163 antibodies. Our study reveals a significant but comparable reduction of serum activity against Omicron sublineages which markedly increases after booster immunization. However, notable differences in sensitivity to individual antibodies demonstrate distinct escape patterns of BA.1 and BA.2 that also affect antibodies in clinical use. The results have strong implications for vaccination strategies and antibody use in prophylaxis and therapy.

Local CCL18 and CCL21 expand lung fibrovascular niches and recruit lymphocytes, leading to tertiary lymphoid structure formation in prolonged COVID-19 (preprint)

Post-acute lung sequelae of COVID-19 are challenging many survivors across the world, yet the mechanisms behind are poorly understood. Our results delineate an inflammatory cascade of events occurring along disease progression within fibrovascular niches. It is initiated by endothelial dysfunction, followed by heme scavenging of CD163+ macrophages and production of CCL18. This chemokine synergizes with local CCL21 upregulation to influence the stromal composition favoring endothelial to mesenchymal transition. The local immune response is further modulated via recruitment of CCR7+ T cells into the expanding fibrovascular niche and imprinting an exhausted, T follicular helper like phenotype in these cells. Eventually, this culminates in the formation of tertiary lymphoid structures, further perpetuating chronic inflammation. Thus, our work presents misdirected immune-stromal interaction mechanisms promoting a self-sustained and non-resolving local immune response that extends beyond active viral infection and leads to profound tissue repurposing and chronic inflammation.

ELF5 is a respiratory epithelial cell-specific risk gene for severe COVID-19 (preprint)

Despite two years of intense global research activity, host genetic factors that predispose to a poorer prognosis and severe course of COVID-19 infection remain poorly understood. Here, we identified eight candidate protein mediators of COVID-19 outcomes by establishing a shared genetic architecture at protein-coding loci using large-scale human genetic studies. The transcription factor ELF5 (ELF5) showed robust and directionally consistent associations across different outcome definitions, including a >4-fold higher risk (odds ratio: 4.85; 95%-CI: 2.65-8.89; p-value<3.1x10-7) for severe COVID-19 per 1 s.d. higher genetically predicted plasma ELF5. We show that ELF5 is specifically expressed in epithelial cells of the respiratory system, such as secretory and alveolar type 2 cells, using single-cell RNA sequencing and immunohistochemistry. These cells are also likely targets of SARS-CoV-2 by colocalisation with key host factors, including ACE2 and TMPRSS2. We also observed a 25% reduced risk of severe COVID-19 per 1 s.d. higher genetically predicted plasma G-CSF, a finding corroborated by a clinical trial of recombinant human G-CSF in COVID-19 patients with lymphopenia reporting a lower number of patients developing critical illness and death. In summary, large-scale human genetic studies together with gene expression at single-cell resolution highlight ELF5 as a novel risk gene for COVID-19 prognosis, supporting a role of epithelial cells of the respiratory system in the adverse host response to SARS-CoV-2.

mRNA booster immunization elicits potent neutralizing serum activity against the SARS-CoV-2 Omicron variant (preprint)

The Omicron variant of SARS-CoV-2 is causing a rapid increase in infections in various countries. This new variant of concern carries an unusually high number of mutations in key epitopes of neutralizing antibodies on the spike glycoprotein, suggesting potential immune evasion. Here we assessed serum neutralizing capacity in longitudinal cohorts of vaccinated and convalescent individuals, as well as monoclonal antibody activity against Omicron using pseudovirus neutralization assays. We report a near-complete lack of neutralizing activity against Omicron in polyclonal sera after two doses of the BNT162b2 vaccine, in convalescent individuals, as well as resistance to different monoclonal antibodies in clinical use. However, mRNA booster immunizations in vaccinated and convalescent individuals resulted in a significant increase of serum neutralizing activity against Omicron. Our study demonstrates that booster immunizations will be critical to substantially improve the humoral immune response against the Omicron variant.

Nachhaltige Strategien gegen die COVID-19-Pandemie in Deutschland im Winter 2021/2022 (preprint)

In this position paper, a large group of interdisciplinary experts outlines response strategies against the spread of SARS-CoV-2 in the winter of 2021/2022 in Germany. We review the current state of the COVID-19 pandemic, from incidence and vaccination efficacy to hospital capacity. Building on this situation assessment, we illustrate various possible scenarios for the winter, and detail the mechanisms and effectiveness of the non-pharmaceutical interventions, vaccination, and booster. With this assessment, we want to provide orientation for decision makers about the progress and mitigation of COVID-19.

Severity of respiratory failure and computed chest tomography in acute COVID-19 correlates with pulmonary function and respiratory symptoms after infection with SARS-CoV-2: an observational longitudinal study over 12 months (preprint)

Background Prospective and longitudinal data on pulmonary injury over one year after acute coronavirus disease 2019 (COVID-19) are sparse. Research question With this study, we aim to investigate pulmonary outcome following SARS-CoV-2 infection including pulmonary function, computed chest tomography, respiratory symptoms and quality of life over 12 months. Study design and Methods 180 patients after acute COVID-19 were enrolled into a single-centre, prospective observational study and examined 6 weeks, 3, 6 and 12 months after onset of COVID-19 symptoms. Chest CT-scans, pulmonary function and symptoms assessed by St. Georges Respiratory Questionnaire were used to evaluate objective and subjective respiratory limitations. Patients were stratified according to acute COVID-19 disease severity. Results Of 180 patients enrolled, 42/180 were not hospitalized during acute SARS-CoV-2 infection, 29/180 were hospitalized without need for oxygen, 43/180 with need for low-flow and 24/180 with high-flow oxygen, 26/180 required invasive mechanical ventilation and 16/180 were treated with ECMO. After acute COVID-19, pulmonary restriction and reduced carbon monoxide diffusion capacity was associated with disease severity after the acute phase and improved over 12 months except for those requiring ECMO treatment. Patients with milder disease showed a predominant reduction of ventilated area instead of simple restriction. The CT score of lung involvement in the acute phase increased significantly with COVID-19 severity and was associated with restriction and reduction in diffusion capacity in follow-up. Respiratory symptoms improved for patients in higher severity groups during follow-up, but not for patients with mild initially disease. Interpretation Severity of respiratory failure during COVID-19 correlates with the degree of pulmonary function impairment and respiratory quality of life in the year after acute infection. Patients with mild vs. severe disease show different patterns of lung involvement and symptom resolution. Clinical Trial Registration The study is registered at the German registry for clinical studies (DRKS00021688)

New susceptibility loci for severe COVID-19 by detailed GWAS analysis in European populations (preprint)

Due to the highly variable clinical phenotype of Coronavirus disease 2019 (COVID-19), deepening the host genetic contribution to severe COVID-19 may further improve our understanding about underlying disease mechanisms. Here, we describe an extended GWAS meta-analysis of 3,260 COVID-19 patients with respiratory failure and 12,483 population controls from Italy, Spain, Norway and Germany, as well as hypothesis-driven targeted analysis of the human leukocyte antigen (HLA) region and chromosome Y haplotypes. We include detailed stratified analyses based on age, sex and disease severity. In addition to already established risk loci, our data identify and replicate two genome-wide significant loci at 17q21.31 and 19q13.33 associated with severe COVID-19 with respiratory failure. These associations implicate a highly pleiotropic ~0.9-Mb 17q21.31 inversion polymorphism, which affects lung function and immune and blood cell counts, and the NAPSA gene, involved in lung surfactant protein production, in COVID-19 pathogenesis.

Pre-activated anti-viral innate immunity in the upper airways controls early SARS-CoV-2 infection in children (preprint)

Children are consistently reported to have reduced SARS-CoV-2 infection rates and a substantially lower risk for developing severe COVID-19. However, the molecular mechanisms underlying protection against COVID-19 in younger age groups remain widely unknown. Here, we systematically characterized the single-cell transcriptional landscape in the upper airways in SARS-CoV-2 negative and age-matched SARS-CoV-2 positive children (n=42) and corresponding samples from adults (n=44), covering an age range of four weeks to 77 years. Children displayed higher basal expression of the relevant pattern recognition receptor (PRR) pathways in upper airway epithelial cells, macrophages, and dendritic cells, resulting in stronger innate antiviral responses upon SARS-CoV-2 infection compared to adults. We further detected distinct immune cell subpopulations with an overall dominance of neutrophils and a population of cytotoxic T cells occurring predominantly in children. Our study provides evidence that the airway epithelial and mucosal immune cells of children are pre-activated and primed for virus sensing, resulting in a stronger early innate antiviral responses to SARS-CoV-2 infection compared to adults.

A proteomic survival predictor for COVID-19 patients in intensive care (preprint)

Global healthcare systems are challenged by the COVID-19 pandemic. There is a need to optimize allocation of treatment and resources in intensive care, as clinically established risk assessments such as SOFA and APACHE II scores show only limited performance for predicting the survival of severely ill COVID-19 patients. Comprehensively capturing the host physiology, we speculated that proteomics in combination with new data-driven analysis strategies could produce a new generation of prognostic discriminators. We studied two independent cohorts of patients with severe COVID-19 who required intensive care and invasive mechanical ventilation. SOFA score, Charlson comorbidity index and APACHE II score were poor predictors of survival. Plasma proteomics instead identified 14 proteins that showed concentration trajectories different between survivors and non-survivors. A proteomic predictor trained on single samples obtained at the first time point at maximum treatment level (i.e. WHO grade 7) and weeks before the outcome, achieved accurate classification of survivors in an exploratory (AUROC 0.81) as well as in the independent validation cohort (AUROC of 1.0). The majority of proteins with high relevance in the prediction model belong to the coagulation system and complement cascade. Our study demonstrates that predictors derived from plasma protein levels have the potential to substantially outperform current prognostic markers in intensive care.

Complement activation induces excessive T cell cytotoxicity in severe COVID-19 (preprint)

Severe COVID-19 is linked to both dysfunctional immune response and unrestrained immunopathogenesis, and it remains unclear if T cells also contribute to disease pathology. Here, we combined single-cell transcriptomics and proteomics with mechanistic studies to assess pathogenic T cell functions and inducing signals. We identified highly activated, CD16+ T cells with increased cytotoxic functions in severe COVID-19. CD16 expression enabled immune complex-mediated, T cell receptor-independent degranulation and cytotoxicity not found in other diseases. CD16+ T cells from COVID-19 patients promoted microvascular endothelial cell injury and release of neutrophil and monocyte chemoattractants. CD16+ T cell clones persisted beyond acute disease maintaining their cytotoxic phenotype. Age-dependent generation of C3a in severe COVID-19 induced activated CD16+ cytotoxic T cells. The proportion of activated CD16+ T cells and plasma levels of complement proteins upstream of C3a correlated with clinical outcome of COVID-19, supporting a pathological role of exacerbated cytotoxicity and complement activation in COVID-19.

Reactogenicity of homologous and heterologous prime-boost immunization with BNT162b2 and ChAdOx1-nCoV19: a prospective cohort study (preprint)

Heterologous prime-boost vaccination is of increasing interest for COVID-19 vaccines. Evidence of rare thrombotic events associated with ChAdOx1-nCoV19 (Vaxzevria, ChAdOx) has lead several European countries to recommend a heterologous booster with mRNA vaccines for certain age groups (e.g. persons <60years in Germany), who have already received one dose of ChAdOx, although data on reactogenicity and safety of this vaccination regimen are still missing. Here we report reactogenicity data of homologous BNT162b2 (Comirnaty, BNT) or heterologous ChAdOx/BNT prime-boost immunisations in a prospective observational cohort study of 326 healthcare workers. Reactogenicity of heterologous ChAdOx/BNT booster vaccination was largely comparable to homologous BNT/BNT vaccination and overall well-tolerated. No major differences were observed in the frequency or severity of local reactions after either of the vaccinations. In contrast, notable differences between the regimens were observed for systemic reactions, which were most frequent after prime immunisation with ChAdOx (86%, 95CI: 79-91), and less frequent after homologous BNT/BNT (65%, 95CI: 56-72), or heterologous ChAdOx/BNT boosters (48%, 95CI: 36-59). This interim analysis supports the safety of currently recommended heterologous ChAdOx/BNT prime-boost immunisations with 12-week intervals.

Immunogenicity of COVID-19 Tozinameran Vaccination in Patients on Chronic Dialysis (preprint)

ObjectivePatients with kidney failure have notoriously weak responses to common vaccines. Thus, immunogenicity of novel SARS-CoV-2 vaccines might be impaired in this group. To determine immunogenicity of SARS-CoV-2 vaccination in patients with chronic dialysis, we analyzed the humoral and T-cell response after two doses of mRNA vaccine Tozinameran (BNT162b2 BioNTech/Pfizer). Design, Settings, and ParticipantsThis observational study included 43 patients on dialysis before vaccination with two doses of Tozinameran 21 days apart. Overall, 36 patients completed the observation period. Serum samples were analyzed by SARS-CoV-2 specific antibodies [~]1 and [~]3-4 weeks after the second vaccination. In addition, SARS-CoV-2-specific T-cell responses were assessed at the later time point by an interferon-gamma release assay (IGRA). Outcomes at later timepoints were compared to a group of 44 elderly patients with no dialysis after immunization with Tozinameran. ExposuresBlood drawings during regular laboratory routine assessment right before start of dialysis therapy or at the time of vaccination and at follow-up study visits. Main Outcomes and MeasuresAssessment of immunogenicity after vaccination against SARS-CoV-2 in patients on and without dialysis. ResultsMedian age of patients on chronic dialysis was 74.0 years (IQR 66.0, 82.0). The proportion of males was higher (69.4%) than females. Only 20/36 patients (55.6%, 95%CI: 38.29-71.67) developed SARS-CoV-2-IgG antibodies at first sampling, whereas 32/36 patients (88.9%, 95%CI:73.00-96.38) demonstrated seropositivity at the second sampling. Seroconversion rates and antibody titers were significantly lower compared to a cohort of vaccinees with similar age but no chronic dialysis (>90% seropositivity). SARS-CoV-2-specific T-cell responses 3 weeks after second vaccination were detected in 21/31 vaccinated dialysis patients (67.7%, 95%CI: 48.53-82.68) compared to 42/44 (93.3%, 95%CI: 76.49-98.84) in controls of similar age. Conclusion and RelevancePatients on dialysis demonstrate a delayed, but robust immune response three weeks after the second dose, which indicates effective vaccination of this vulnerable group. However, the lower immunogenicity of Tozinameran in these patients needs further attention to develop potential countermeasures such as an additional booster vaccination.

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.