Rapid recall and de novo T cell responses during SARS-CoV-2 breakthrough infection

While the protective role of neutralising antibodies against COVID-19 is well-established, questions remain about the relative importance of cellular immunity. Using 6 pMHC-multimers in a cohort with early and frequent sampling we define the phenotype and kinetics of recalled and primary T cell responses following Delta or Omicron breakthrough infection. Recall of spike-specific CD4+ T cells was rapid, with cellular proliferation and extensive activation evident as early as 1 day post-symptom onset. Similarly, spike-specific CD8+ T cells were rapidly activated but showed variable levels of expansion. Strikingly, high levels of SARS-CoV-2-specific CD8+ T cell activation at baseline and peak were strongly correlated with reduced peak SARS-CoV-2 RNA levels in nasal swabs and accelerated clearance of virus. Our study demonstrates rapid and extensive recall of memory T cell populations occurs early after breakthrough infection and suggests that CD8+ T cells contribute to the control of viral replication in breakthrough SARS-CoV-2 infections.

Anti-PEG antibodies boosted in humans by SARS-CoV-2 lipid nanoparticle mRNA vaccine

Humans commonly have low level antibodies to poly(ethylene) glycol (PEG) due to environmental exposure. Lipid nanoparticle (LNP) mRNA vaccines for SARS-CoV-2 contain small amounts of PEG but it is not known whether PEG antibodies are enhanced by vaccination and what their impact is on particle-immune cell interactions in human blood. We studied plasma from 130 adults receiving either the BNT162b2 (Pfizer-BioNTech) or mRNA-1273 (Moderna) mRNA vaccines, or no SARS-CoV-2 vaccine for PEG-specific antibodies. Anti-PEG IgG was commonly detected prior to vaccination and was significantly boosted a mean of 13.1-fold (range 1.0 to 70.9) following mRNA-1273 vaccination and a mean of 1.78-fold (range 0.68 to 16.6) following BNT162b2 vaccination. Anti-PEG IgM increased 68.5-fold (range 0.9 to 377.1) and 2.64-fold (0.76 to 12.84) following mRNA-1273 and BNT162b2 vaccination, respectively. The rise in PEG-specific antibodies following mRNA-1273 vaccination was associated with a significant increase in the association of clinically relevant PEGylated LNPs with blood phagocytes ex vivo. PEG antibodies did not impact the SARS-CoV-2 specific neutralizing antibody response to vaccination. However, the elevated levels of vaccine-induced anti-PEG antibodies correlated with increased systemic reactogenicity following two doses of vaccination. We conclude that PEG-specific antibodies can be boosted by LNP mRNA-vaccination and that the rise in PEG-specific antibodies is associated with systemic reactogenicity and an increase of PEG particle-leukocyte association in human blood. The longer-term clinical impact of the increase in PEG-specific antibodies induced by lipid nanoparticle mRNA-vaccines should be monitored.

SARS-CoV-2 mRNA vaccination elicits robust and persistent T follicular helper cell response in humans

SARS-CoV-2 mRNA vaccines induce robust anti-spike (S) antibody and CD4+ T cell responses. It is not yet clear whether vaccine-induced follicular helper CD4+ T (TFH) cell responses contribute to this outstanding immunogenicity. Using fine needle aspiration of draining axillary lymph nodes from individuals who received the BNT162b2 mRNA vaccine, we show that frequency of TFH correlates with that of S-binding germinal center B cells. Mining of the responding TFH T cell receptor repertoire revealed a strikingly immunodominant HLADPB1* 04-restricted response to S167-180 in individuals with this allele, which is among the most common HLA alleles in humans. Paired blood and lymph node specimens show that while circulating S-specific TFH cells peak one week after the second immunization, S-specific TFH persist at nearly constant frequencies for at least six months. Collectively, our results underscore the key role that robust TFH cell responses play in establishing long-term immunity by this efficacious human vaccine.

Integrated immune networks in SARS-CoV-2 infected pregnant women reveal differential NK cell and unconventional T cell activation

Although pregnancy poses a greater risk for severe COVID-19, the underlying immunological changes associated with SARS-CoV-2 infection during pregnancy are poorly understood. We defined immune responses to SARS-CoV-2 in pregnant and non-pregnant women during acute and convalescent COVID-19 up to 258 days post symptom onset, quantifying 217 immunological parameters. Additionally, matched maternal and cord blood were collected from COVID-19 convalescent pregnancies. Although serological responses to SARS-CoV-2 were similar in pregnant and non-pregnant women, cellular immune analyses revealed marked differences in key NK cell and unconventional T cell responses during COVID-19 in pregnant women. While NK cells, {gamma}{delta} T cells and MAIT cells displayed pre-activated phenotypes in healthy pregnant women when compared to non-pregnant age-matched women, activation profiles of these pre-activated NK and unconventional T cells remained unchanged at acute and convalescent COVID-19 in pregnancy. Conversely, activation dynamics of NK and unconventional T cells were prototypical in non-pregnant women in COVID-19. In contrast, activation of {beta} CD4+ and CD8+ T cells, T follicular helper cells and antibody-secreting cells was similar in pregnant and non-pregnant women with COVID-19. Elevated levels of IL-1{beta}, IFN-{gamma}, IL-8, IL-18 and IL-33 were also found in pregnant women in their healthy state, and these cytokine levels remained elevated during acute and convalescent COVID-19. Collectively, our study provides the first comprehensive map of longitudinal immunological responses to SARS-CoV-2 infection in pregnant women, providing insights into patient management and education during COVID-19 pregnancy.

A point-of-care lateral flow assay for neutralising antibodies against SARS-CoV-2

As vaccines against SARS-CoV-2 are now being rolled out, a better understanding of immunity to the virus; whether through infection, or passive or active immunisation, and the durability of this protection is required. This will benefit from the ability to measure SARS-CoV-2 immunity, ideally with rapid turnaround and without the need for laboratory-based testing. Current rapid point-of-care (POC) tests measure antibodies (Ab) against the SARS-CoV-2 virus, however, these tests provide no information on whether the antibodies can neutralise virus infectivity and are potentially protective, especially against newly emerging variants of the virus. Neutralising Antibodies (NAb) are emerging as a strong correlate of protection, but most current NAb assays require many hours or days, samples of venous blood, and access to laboratory facilities, which is especially problematic in resource-limited settings. We have developed a lateral flow POC test that can measure levels of RBD-ACE2 neutralising antibodies from whole blood, with a result that can be determined by eye (semi-quantitative) or on a small instrument (quantitative), and results show high correlation with microneutralisation assays. This assay also provides a measure of total anti-RBD antibody, thereby providing evidence of exposure to SARS-CoV-2, regardless of whether NAb are present in the sample. By testing samples from immunised macaques, we demonstrate that this test is equally applicable for use with animal samples, and we show that this assay is readily adaptable to test for immunity to newly emerging SARS-CoV-2 variants. Accordingly, the COVID-19 NAb-test test described here can provide a rapid readout of immunity to SARS-CoV-2 at the point of care.

Suboptimal SARS-CoV-2-specific CD8+ T-cell response associated with the prominent HLA-A*02:01 phenotype

An improved understanding of human T-cell-mediated immunity in COVID-19 is important if we are to optimize therapeutic and vaccine strategies. Experience with influenza shows that infection primes CD8+ T-cell memory to shared peptides presented by common HLA types like HLA-A2. Following re-infection, cross-reactive CD8+ T-cells enhance recovery and diminish clinical severity. Stimulating peripheral blood mononuclear cells from COVID-19 convalescent patients with overlapping peptides from SARS-CoV-2 Spike, Nucleocapsid and Membrane proteins led to the clonal expansion of SARS-CoV-2-specific CD8+ and CD4+ T-cells in vitro, with CD4+ sets being typically robust. For CD8+ T-cells taken directly ex vivo, we identified two HLA-A*02:01-restricted SARS-CoV-2 epitopes, A2/S269-277 and A2/Orf1ab3183-3191. Using peptide-HLA tetramer enrichment, direct ex vivo assessment of the A2/S269+CD8+ and A2/Orf1ab3183+CD8+ populations indicated that the more prominent A2/S269+CD8+ set was detected at comparable frequency ([~]1.3x10-5) in acute and convalescent HLA-A*02:01+ patients. But, while the numbers were higher than those found in uninfected HLA-A*02:01+ donors ([~]2.5x10-6), they were low when compared with frequencies for influenza-specific (A2/M158) and EBV-specific (A2/BMLF1280) ([~]1.38x10-4) populations. Phenotypic analysis ex vivo of A2/S269+CD8+ T-cells from COVID-19 convalescents showed that A2/S269+CD8+ T-cells were predominantly negative for the CD38, HLA-DR, PD-1 and CD71 activation markers, although the majority of total CD8+ T-cells were granzyme and/or perforin-positive. Furthermore, the bias towards naive, stem cell memory and central memory A2/S269+CD8+ T-cells rather than effector memory populations suggests that SARS-CoV2 infection may be compromising CD8+ T-cell activation. Priming with an appropriate vaccine may thus have great value for optimizing protective CD8+ T-cell immunity in COVID-19.

Distinct systems serology features in children, elderly and COVID patients

SARS-CoV-2, the pandemic coronavirus that causes COVID-19, has infected millions worldwide, causing unparalleled social and economic disruptions. COVID-19 results in higher pathogenicity and mortality in the elderly compared to children. Examining baseline SARS-CoV-2 cross-reactive coronavirus immunological responses, induced by circulating human coronaviruses, is critical to understand such divergent clinical outcomes. The cross-reactivity of coronavirus antibody responses of healthy children (n=89), adults (n=98), elderly (n=57), and COVID-19 patients (n=19) were analysed by systems serology. While moderate levels of cross-reactive SARS-CoV-2 IgG, IgM, and IgA were detected in healthy individuals, we identified serological signatures associated with SARS-CoV-2 antigen-specific Fc{gamma} receptor binding, which accurately distinguished COVID-19 patients from healthy individuals and suggested that SARS-CoV-2 induces qualitative changes to antibody Fc upon infection, enhancing Fc{gamma} receptor engagement. Vastly different serological signatures were observed between healthy children and elderly, with markedly higher cross-reactive SARS-CoV-2 IgA and IgG observed in elderly, whereas children displayed elevated SARS-CoV-2 IgM, including receptor binding domain-specific IgM with higher avidity. These results suggest that less-experienced humoral immunity associated with higher IgM, as observed in children, may have the potential to induce more potent antibodies upon SARS-CoV-2 infection. These key insights will inform COVID-19 vaccination strategies, improved serological diagnostics and therapeutics.

Innate and adaptive T cells in influenza disease / 医学前沿

Influenza is a major global health problem, causing infections of the respiratory tract, often leading to acute pneumonia, life-threatening complications and even deaths. Over the last seven decades, vaccination strategies have been utilized to protect people from complications of influenza, especially groups at high risk of severe disease. While current vaccination regimens elicit strain-specific antibody responses, they fail to generate cross-protection against seasonal, pandemic and avian viruses. Moreover, vaccines designed to generate influenza-specific T-cell responses are yet to be optimized. During natural infection, viral replication is initially controlled by innate immunity before adaptive immune responses (T cells and antibody-producing B cells) achieve viral clearance and host recovery. Adaptive T and B cells maintain immunological memory and provide protection against subsequent infections with related influenza viruses. Recent studies also shed light on the role of innate T-cells (MAIT cells, γδ cells, and NKT cells) in controlling influenza and linking innate and adaptive immune mechanisms, thus making them attractive targets for vaccination strategies. We summarize the current knowledge on influenza-specific innate MAIT and γδ T cells as well as adaptive CD8 and CD4 T cells, and discuss how these responses can be harnessed by novel vaccine strategies to elicit cross-protective immunity against different influenza strains and subtypes.