SARS-CoV-2 spike-specific TFH cells exhibit unique responses in infected and vaccinated individuals

Development of Broad-Spectrum Nanobodies for the Therapy and Diagnosis of SARS-CoV-2 and Its Multiple Variants

The continuous evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has evaded the efficacy of previously developed antibodies and vaccines, thus remaining a significant global public health threat. Therefore, it is imperative to develop additional antibodies that are capable of neutralizing emerging variants. Nanobodies, as the smallest functional single-domain antibodies, exhibit enhanced stability and penetration ability, enabling them to recognize numerous concealed epitopes that are inaccessible to conventional antibodies. Herein, we constructed an immune library based on the immunization of alpaca with the S1 subunit of the SARS-CoV-2 spike protein, from which two nanobodies, Nb1 and Nb2, were selected using phage display technology for further characterization. Both nanobodies, with the binding residues residing within the receptor-binding domain (RBD) region of the spike, exhibited high affinity toward the S1 subunit. Moreover, they displayed cross-neutralizing activity against both wild-type SARS-CoV-2 and 10 ο variants, including BA.1, BA.2, BA.3, BA.5, BA.2.75, BF.7, BQ.1, EG.5.1, XBB.1.5, and JN.1. Molecular modeling and dynamics simulations predicted that both nanobodies interacted with the viral RBD through their complementarity determining region 1 (CDR1) and CDR2. These two nanobodies are novel tools for the development of therapeutic and diagnostic countermeasures targeting SARS-CoV-2 variants and potentially emerging coronaviruses.

Heterologous booster vaccination enhances antibody responses to SARS-CoV-2 by improving Tfh function and increasing B-cell clonotype SHM frequency

Heterologous prime-boost has broken the protective immune response bottleneck of the COVID-19 vaccines. however, the underlying mechanisms have not been fully elucidated. Here, we investigated antibody responses and explored the response of germinal center (GC) to priming with inactivated vaccines and boosting with heterologous adenoviral-vectored vaccines or homologous inactivated vaccines in mice. Antibody responses were dramatically enhanced by both boosting regimens. Heterologous immunization induced more robust GC activation, characterized by increased Tfh cell populations and enhanced helper function. Additionally, increased B-cell activation and antibody production were observed in a heterologous regimen. Libra-seq was used to compare the differences of S1-, S2- and NTD-specific B cells between homologous and heterologous vaccination, respectively. S2-specific CD19+ B cells presented increased somatic hypermutations (SHMs), which were mainly enriched in plasma cells. Moreover, a heterologous booster dose promoted the clonal expansion of B cells specific to S2 and NTD regions. In conclusion, the functional role of Tfh and B cells following SARS-CoV-2 heterologous vaccination may be important for modulating antibody responses. These findings provide new insights for the development of SARS-CoV-2 vaccines that induce more robust antibody response.

TIGIT+Tfh show poor B-helper function and negatively correlate with SARS-CoV-2 antibody titre

Circulating follicular helper T cells (cTfh) can show phenotypic alterations in disease settings, including in the context of tissue-damaging autoimmune or anti-viral responses. Using severe COVID-19 as a paradigm of immune dysregulation, we have explored how cTfh phenotype relates to the titre and quality of antibody responses. Severe disease was associated with higher titres of neutralising S1 IgG and evidence of increased T cell activation. ICOS, CD38 and HLA-DR expressing cTfh correlated with serum S1 IgG titres and neutralising strength, and interestingly expression of TIGIT by cTfh showed a negative correlation. TIGIT+cTfh expressed increased IFNγ and decreased IL-17 compared to their TIGIT-cTfh counterparts, and showed reduced capacity to help B cells in vitro. Additionally, TIGIT+cTfh expressed lower levels of CD40L than TIGIT-cTfh, providing a potential explanation for their poor B-helper function. These data identify phenotypic changes in polyclonal cTfh that correlate with specific antibody responses and reveal TIGIT as a marker of cTfh with altered function.

Rise in broadly cross-reactive adaptive immunity against human β-coronaviruses in MERS-recovered patients during the COVID-19 pandemic

To develop a universal coronavirus (CoV) vaccine, long-term immunity against multiple CoVs, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants, Middle East respiratory syndrome (MERS)-CoV, and future CoV strains, is crucial. Following the 2015 Korean MERS outbreak, we conducted a long-term follow-up study and found that although neutralizing antibodies and memory T cells against MERS-CoV declined over 5 years, some recovered patients exhibited increased antibody levels during the COVID-19 pandemic. This likely resulted from cross-reactive immunity induced by SARS-CoV-2 vaccines or infections. A significant correlation in antibody responses across various CoVs indicates shared immunogenic epitopes. Two epitopes-the spike protein's stem helix and intracellular domain-were highly immunogenic after MERS-CoV infection and after SARS-CoV-2 vaccination or infection. In addition, memory T cell responses, especially polyfunctional CD4+ T cells, were enhanced during the pandemic, correlating significantly with MERS-CoV spike-specific antibodies and neutralizing activity. Therefore, incorporating these cross-reactive and immunogenic epitopes into pan-CoV vaccine formulations may facilitate effective vaccine development.

People who use drugs show no increase in pre-existing T-cell cross-reactivity toward SARS-CoV-2 but develop a normal polyfunctional T-cell response after standard mRNA vaccination

People who use drugs (PWUD) are at a high risk of contracting and developing severe coronavirus disease 2019 (COVID-19) and other infectious diseases due to their lifestyle, comorbidities, and the detrimental effects of opioids on cellular immunity. However, there is limited research on vaccine responses in PWUD, particularly regarding the role that T cells play in the immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here, we show that before vaccination, PWUD did not exhibit an increased frequency of preexisting cross-reactive T cells to SARS-CoV-2 and that, despite the inhibitory effects that opioids have on T-cell immunity, standard vaccination can elicit robust polyfunctional CD4+ and CD8+ T-cell responses that were similar to those found in controls. Our findings indicate that vaccination stimulates an effective immune response in PWUD and highlight targeted vaccination as an essential public health instrument for the control of COVID-19 and other infectious diseases in this group of high-risk patients.