High-affinity, neutralizing antibodies to SARS-CoV-2 can be made without T follicular helper cells

T-cell-derived IFN-γ suppresses T follicular helper cell differentiation and antibody responses

CD4+ T cells play a critical role in antiviral humoral and cellular immune responses. We have previously reported that subcutaneous lymphocytic choriomeningitis virus (s.c. LCMV) infection is characterized by a stark compartmentalization of CD4+ T cells, leading to strong TH1 cell polarization but virtually absent T follicular helper (TFH) cells, key drivers of humoral immunity. Here, we investigate the mechanisms responsible for this impaired TFH differentiation. We show that T-bet+ cells induced by LCMV infection encompass a TH1 cell subset expressing granzyme B (GzmB), and a Tcf-1+ cell subset that retains the potential for TFH differentiation without expressing mature TFH markers. Notably, IFN-γ blockade enables full differentiation of Tcf-1+ cells into TFH cells, formation of germinal centers, and increased antibody production. Suppression of TFH cells by IFN-γ is not directly mediated by CD4+ T cells but rather involves another cell type, likely dendritic cells (DCs). Our study provides novel insights into the mechanisms underlying early CD4+ T-cell polarization and humoral responses to viruses, with the potential to facilitate the development of effective vaccine strategies.

Shielding the immunocompromised: COVID-19 prevention strategies for patients with primary and secondary immunodeficiencies

The COVID-19 pandemic has significantly impacted immunocompromised patients, particularly those with inborn errors of immunity (IEI), transplant recipients, hematologic malignancies, and those undergoing treatment with immunosuppressive biologics and medications. These patients face an elevated risk of experiencing severe or even fatal consequences following SARS-CoV-2 infections. Vaccination is the primary defense against COVID-19; however, immune responses following immunization are often suboptimal in these patients, with variable specific humoral response rates. Despite the expedited regulatory approval and the widespread implementation of COVID-19 vaccines, the efficacy and safety for immunocompromised populations require thorough investigation. In future pandemics, including vulnerable populations (VPs) in vaccine and monoclonal antibody (mAb) trials is crucial to develop safe, effective immunization strategies, address gaps in vaccine efficacy and safety data, and create tailored guidelines for at-risk groups. This review provides a comprehensive examination of the efficacy of COVID-19 vaccines and mAbs in patients with primary and secondary immunodeficiency, with a specific focus on individuals with IEI, considering previous regulatory aspects and the necessity of including VPs in vaccine trials to enhance the quality of patient care and promote equitable health outcomes in future pandemics.

mRNA vaccine-induced SARS-CoV-2 spike-specific IFN-γ and IL-2 T-cell responses are predictive of serological neutralization and are transiently enhanced by pre-existing cross-reactive immunity

The contributions of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific T cells to vaccine efficacy and durability are unclear. We investigated relationships between mRNA vaccine-induced spike-specific interferon- gamma (IFN-γ) and interleukin-2 (IL-2) T-cell responses and neutralizing antibody development in long-term care home staff doubly vaccinated with BNT162b2 or mRNA-1273. The impacts of pre-existing cross-reactive T-cell immunity on cellular and humoral responses to vaccination were additionally assessed. Mathematical modeling of the kinetics of spike-specific IFN-γ and IL-2 T-cell responses over 6 months post-second dose was bifurcated into recipients who exhibited gradual increases with doubling times of 155 and 167 days or decreases with half-lives of 165 and 132 days, respectively. Differences in kinetics did not correlate with clinical phenotypes. Serological anti-spike IgG, anti-receptor binding domain (RBD) IgG, anti-spike IgA, and anti-RBD IgA antibody levels otherwise decayed in all participants with half-lives of 63, 57, 79, and 46 days, respectively, alongside waning neutralizing capacity (t1/2 = 408 days). Spike-specific T-cell responses induced at 2-6 weeks positively correlated with live viral neutralization at 6 months post-second dose, especially in hybrid immune individuals. Participants with pre-existing cross-reactive T-cell immunity to SARS-CoV-2 exhibited greater spike-specific T-cell responses, reduced anti-RBD IgA antibody levels, and a trending increase in neutralization at 2-6 weeks post-second dose. Non-spike-specific T-cells predominantly targeted SARS-CoV-2 non-structural protein at 6 months post-second dose in cross-reactive participants. mRNA vaccination was lastly shown to induce off-target T-cell responses against unrelated antigens. In summary, vaccine-induced spike-specific T-cell immunity appeared to influence serological neutralizing capacity, with only a modest effect induced by pre-existing cross-reactivity.

IMPORTANCE

Our findings provide valuable insights into the potential contributions of mRNA vaccine-induced spike-specific T-cell responses to the durability of neutralizing antibody levels in both uninfected and hybrid immune recipients. Our study additionally sheds light on the precise impacts of pre-existing cross-reactive T-cell immunity to severe acute respiratory syndrome coronavirus 2 on the magnitude and kinetics of cellular and humoral responses to vaccination. Accordingly, our data will help optimize the development of next-generation T cell-based coronavirus vaccines and vaccine regimens to maximize efficacy and durability.

Distinct Requirements for CD4+ T Cell Help for Immune Responses Induced by mRNA and Adenovirus-Vector SARS-CoV-2 Vaccines

CD4+ T cells have been established as central orchestrators of cellular and humoral immune responses to infection or vaccination. However, the need for CD4+ T cell help to generate primary CD8+ T cell responses is variable depending on the infectious agent or vaccine and yet consistently required for the recall of CD8+ T cell memory responses or antibody responses. Given the deployment of new vaccine platforms such as nucleoside-modified mRNA vaccines, we sought to elucidate the requirement for CD4+ T cell help in the induction of cellular and antibody responses to mRNA and adenovirus (Ad)-vectored vaccines against SARS-CoV-2. Using antibody-mediated depletion of CD4+ T cells in a mouse immunization model, we observed that CD4+ T cell help was dispensable for both primary and secondary CD8+ T cell responses to the BNT162b2 and mRNA-1273 mRNA vaccines but required for the AZD1222 Ad-vectored vaccine. Nonetheless, CD4+ T cell help was needed by both mRNA and Ad-vectored vaccine platforms for the generation of antibodies, demonstrating the centrality of CD4+ T cells in vaccine-induced protective immunity against SARS-CoV-2. Ultimately, this highlights the shared and distinct regulation of humoral and cellular responses induced by these vaccine platforms.

RSV Vaccine with Nanoparticle-Based Poly-Sorbitol Transporter (PST) Adjuvant Improves Respiratory Protection Against RSV Through Inducing Both Systemic and Mucosal Humoral Immunity

Background/Objectives: Respiratory syncytial virus (RSV) causes symptoms similar to a mild cold for adults, but in case of infants, it causes bronchitis and/or pneumonia, and in some cases, mortality. Mucosal immunity within the respiratory tract includes tissue-resident memory T (TRM) cells and tissue-resident memory B (BRM) cells, which provides rapid and efficient protection against RSV re-infection. Therefore, vaccine strategies should aim to generate mucosal immune responses. However, the interactions between RSV vaccines and mucosal immune responses within the respiratory tract are poorly understood. We evaluated a mucosal immune system following immunization by RSV vaccine with poly-sorbitol transporter (RSV-PST), a nanoparticle adjuvant. Methods: We intranasally immunized the RSV-PST and identified the systemic and mucosal immune responses. Furthermore, we challenged with RSV A2 strain after immunization and investigated the protective effects. Results: Consequently, antigen-specific CD8+ TRM cells were markedly elevated in the lung parenchyma, yet exhibited impaired cytokine expression. In contrast, humoral immunity, with systemic antibody production from serum, but not in the respiratory tract, was significantly increased by RSV-PST immunization. Interestingly, the production of respiratory mucosal antigen-specific IgG after RSV A2 challenge dramatically increased in the bronchoalveolar lavage fluid (BALF) of the RSV-PST immunized group in the presence of FTY720, and the lung-infected RSV titer was significantly lower in this group. Furthermore, after RSV A2 challenge, CD69+ IgG+ BRM cells were significantly increased in lung tissues in the RSV-PST group. Conclusions: The RSV-PST vaccine has protective effects against RSV infection by promoting both systemic and local humoral immunity rather than cellular immunity.

An Integrated Signaling Threshold Initiates IgG Response toward Virus-like Immunogens

Class-switched neutralizing Ab (nAb) production is rapidly induced upon many viral infections. However, due to the presence of multiple components in virions, the precise biochemical and biophysical signals from viral infections that initiate nAb responses remain inadequately defined. Using a reductionist system of synthetic virus-like structures, in this study, we show that a foreign protein on a virion-sized liposome can serve as a stand-alone danger signal to initiate class-switched nAb responses without T cell help or TLR but requires CD19. Introduction of internal nucleic acids (iNAs) obviates the need for CD19, lowers the epitope density (ED) required to elicit the Ab response, and transforms these structures into highly potent immunogens that rival conventional virus-like particles in their ability to elicit strong Ag-specific IgG. As early as day 5 after immunization, structures harboring iNAs and decorated with just a few molecules of surface Ag at doses as low as 100 ng induced all IgG subclasses of Ab in mice and reproduced the IgG2a/2c restriction that is long observed in live viral infections. These findings reveal a shared mechanism for the nAb response in mice. High ED is capable but not necessary for driving Ab secretion. Instead, even a few molecules of surface Ag, when combined with nucleic acids within these structures, can trigger strong IgG production. As a result, the signaling threshold for induction of IgG in individual B cells is set by dual signals originating from both ED on the surface and the presence of iNAs within viral particulate immunogens.

Development of T follicular helper cell-independent nanoparticle vaccines for SARS-CoV-2 or HIV-1 by targeting ICOSL

T helper cells, particularly T follicular helper (TFH) cells, are essential for the neutralizing antibody production elicited by pathogens or vaccines. However, in immunocompromised individuals, the inefficient support from TFH cells could lead to limited protection after vaccine inoculation. Here we showed that the conjugation of inducible T cell costimulatory (ICOS) onto the nanoparticle, together with immunogen, significantly enhanced the immune response of the vaccines specific for SARS-CoV-2 or human immunodeficiency virus type-1 (HIV-1) in TFH-deficient mice. Further studies indicated that ICOSL on B cells was triggered by ICOS binding, subsequently activated the PKCβ signaling pathway, and enhanced the survival and proliferation of B cells. Our findings revealed that the stimulation of ICOS-ICOSL interaction by adding ICOS on the nanoparticle vaccine significantly substitutes the function of TFH cells to support B cell response, which is significant for the immunocompromised people, such as the elderly or HIV-1-infected individuals.

Antibody Fc receptor binding and T cell responses to homologous and heterologous immunization with inactivated or mRNA vaccines against SARS-CoV-2

Whole virion inactivated vaccine CoronaVac (C) and Spike (S) mRNA BNT162b2 (B) vaccines differ greatly in their ability to elicit neutralizing antibodies but have somewhat comparable effectiveness in protecting from severe COVID-19. We conducted further analyses for a randomized trial (Cobovax study, NCT05057169) of third dose homologous and heterologous booster vaccination, i.e. four interventions CC-C, CC-B, BB-C and BB-B. Here, we assess vaccine immunogenicity beyond neutralizing function, including S and non-S antibodies with Fc receptor (FcR) binding, antibody avidity and T cell specificity to 6 months post-vaccination. Ancestral and Omicron S-specific IgG and FcR binding are significantly higher by BNT162b2 booster than CoronaVac, regardless of first doses. Nucleocapsid (N) antibodies are only increased in homologous boosted CoronaVac participants (CC-C). CoronaVac primed participants have lower baseline S-specific CD4+ IFNγ+ cells, but are significantly increased by either CoronaVac or BNT162b2 boosters. Priming vaccine content defined T cell peptide specificity preference, with S-specific T cells dominating B primed groups and non-S structural peptides contributing more in C primed groups, regardless of booster type. S-specific CD4+ T cell responses, N-specific antibodies, and antibody effector functions via Fc receptor binding may contribute to protection and compensate for less potent neutralizing responses in CoronaVac recipients.

T-B Collaboration in Autoimmunity, Infection, and Transplantation

We have attempted here to provide an up-to-date review of the collaboration between helper T cells and B cells in response to protein and glycoprotein antigens. This collaboration is essential as it not only protects from many pathogens but also contributes to a litany of autoimmune and immune-mediated diseases.

An integrated signaling threshold initiates IgG response towards virus-like immunogens

Class-switched neutralizing antibody (nAb) production is rapidly induced upon many viral infections. However, due to the presence of multiple components in typical virions, the precise biochemical and biophysical signals from viral infections that initiate nAb responses remain inadequately defined. Using a reductionist system of synthetic virus-like structures (SVLS) containing minimal, highly purified biochemical components commonly found in enveloped viruses, here we show that a foreign protein on a virion-sized liposome can serve as a stand-alone danger signal to initiate class-switched nAb responses in the absence of cognate T cell help or Toll-like receptor signaling but requires CD19, the antigen (Ag) coreceptor on B cells. Introduction of internal nucleic acids (iNAs) obviates the need for CD19, lowers the epitope density (ED) required to elicit the Ab response and transforms these structures into highly potent immunogens that rival conventional virus-like particles in their ability to elicit strong Ag-specific IgG. As early as day 5 after immunization, structures harbouring iNAs and decorated with just a few molecules of surface Ag at doses as low as 100 ng induced all IgG subclasses of Ab known in mice and reproduced the IgG2a/2c restriction that has been long observed in live viral infections. These findings reveal a shared mechanism for nAb response upon viral infection. High ED is capable but not necessary for driving Ab secretion in vivo . Instead, even a few molecules of surface Ag, when combined with nucleic acids within these structures, can trigger strong antiviral IgG production. As a result, the signaling threshold for the induction of neutralizing IgG is set by dual signals originating from both ED on the surface and the presence of iNAs within viral particulate immunogens.

One-sentence summary

Reconstitution of minimal viral signals necessary to initiate antiviral IgG.

Low pre-existing endemic human coronavirus (HCoV-NL63)-specific T cell frequencies are associated with impaired SARS-CoV-2-specific T cell responses in people living with HIV

Background

Understanding how HIV affects SARS-CoV-2 immunity is crucial for managing COVID-19 in sub-Saharan populations due to frequent coinfections. Our previous research showed that unsuppressed HIV is associated with weaker immune responses to SARS-CoV-2, but the underlying mechanisms are unclear. We investigated how pre-existing T cell immunity against an endemic human coronavirus HCoV-NL63 impacts SARS-CoV-2 T cell responses in people living with HIV (PLWH) compared to uninfected individuals, and how HIV-related T cell dysfunction influences responses to SARS-CoV-2 variants.

Methods

We used flow cytometry to measure T cell responses following PBMC stimulation with peptide pools representing beta, delta, wild-type, and HCoV-NL63 spike proteins. Luminex bead assay was used to measure circulating plasma chemokine and cytokine levels. ELISA and MSD V-PLEX COVID-19 Serology and ACE2 Neutralization assays were used to measure humoral responses.

Results

Regardless of HIV status, we found a strong positive correlation between responses to HCoV-NL63 and SARS-CoV-2. However, PLWH exhibited weaker CD4+ T cell responses to both HCoV-NL63 and SARS-CoV-2 than HIV-uninfected individuals. PLWH also had higher proportions of functionally exhausted (PD-1high) CD4+ T cells producing fewer proinflammatory cytokines (IFNγ and TNFα) and had elevated plasma IL-2 and IL-12(p70) levels compared to HIV-uninfected individuals. HIV status didn't significantly affect IgG antibody levels against SARS-CoV-2 antigens or ACE2 binding inhibition activity.

Conclusion

Our results indicate that the decrease in SARS-CoV-2 specific T cell responses in PLWH may be attributable to reduced frequencies of pre-existing cross-reactive responses. However, HIV infection minimally affected the quality and magnitude of humoral responses, and this could explain why the risk of severe COVID-19 in PLWH is highly heterogeneous.

Vaccine-elicited B- and T-cell immunity to SARS-CoV-2 is impaired in chronic lung disease patients

Background

While vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) provides significant protection from coronavirus disease 2019, the protection afforded to individuals with chronic lung disease is less well established. This study seeks to understand how chronic lung disease impacts SARS-CoV-2 vaccine-elicited immunity.

Methods

Deep immune phenotyping of humoral and cell-mediated responses to the SARS-CoV-2 vaccine was performed in patients with asthma, COPD and interstitial lung disease (ILD) compared to healthy controls.

Results

48% of vaccinated patients with chronic lung diseases had reduced antibody titres to the SARS-CoV-2 vaccine antigen relative to healthy controls. Vaccine antibody titres were significantly reduced among asthma (p<0.035), COPD (p<0.022) and a subset of ILD patients as early as 3-4 months after vaccination, correlating with decreased vaccine-specific memory B-cells in circulation. Vaccine-specific memory T-cells were significantly reduced in patients with asthma (CD8+ p<0.004; CD4+ p<0.023) and COPD (CD8+ p<0.008) compared to healthy controls. Impaired T-cell responsiveness was also observed in a subset of ILD patients (CD8+ 21.4%; CD4+ 42.9%). Additional heterogeneity between healthy and disease cohorts was observed among bulk and vaccine-specific follicular T-helper cells.

Conclusions

Deep immune phenotyping of the SARS-CoV-2 vaccine response revealed the complex nature of vaccine-elicited immunity and highlights the need for more personalised vaccination schemes in patients with underlying lung conditions.

Investigating the impact of prior COVID-19 on IgG antibody and interferon γ responses after BBIBP-CorV vaccination in a disease endemic population: A prospective observational study

Background and Aims

COVID-19 vaccinations have reduced morbidity and mortality from the disease. Antibodies against severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) have been associated with immune protection. Seroprevalence studies revealed high immunoglobulin G (IgG) antibody levels to SARS-CoV-2 in the Pakistani population before vaccinations. We investigated the effect of BBIBP-CorV vaccination on circulating IgG antibodies and interferon (IFN)-γ from T cells measured in a cohort of healthy individuals, with respect to age, gender, and history of COVID-19.

Methods

The study was conducted between April and October 2021. BBIBP-CorV vaccinated participants were followed up to 24 weeks. Antibodies to SARS-CoV-2 Spike protein and its receptor-binding domain (RBD) were measured. IFNγ secreted by whole blood stimulation of Spike protein and extended genome antigens was determined.

Results

Study participants with a history of prior COVID-19 displayed a higher magnitude of IgG antibodies to Spike and RBD. IgG seropositivity was greater in those with prior COVID-19, aged 50 years or younger and in females. At 24 weeks after vaccination, 37.4% of participants showed IFN-γ responses to SARS-CoV-2 antigens. T cell IFN-γ release was higher in those with prior COVID-19 and those aged 50 years or less. Highest IFN-γ release was observed to extended genome antigens in individuals both with and without prior COVID-19.

Conclusion

We found that IgG seropositivity to both Spike and RBD was affected by prior COVID-19, age and gender. Importantly, seropositive responses persisted up to 24 weeks after vaccination. Persistence of vaccine induced IgG antibodies may be linked to the high seroprevalence observed earlier in unvaccinated individuals. Increased T cell reactivity to Spike and extended genome antigens reflects cellular activation induced by BBIBP-CorV. COVID-19 vaccination may have longer lasting immune responses in populations with a higher seroprevalence. These data inform on vaccination booster policies for high-risk groups.

Age-dependent changes in T follicular helper cells shape the humoral immune response to vaccination

Vaccination is an excellent strategy to limit the morbidity and mortality associated with infectious disease. Vaccination creates protective, long-lived antibody-mediated immunity by inducing the germinal centre response, an intricate immune reaction that produces memory B cells and long-lived antibody-secreting plasma cells that provide protection against (re)infection. The magnitude and quality of the germinal centre response declines with age, contributing to poor vaccine-induced immunity in older individuals. T follicular helper cells are essential for the formation and function of the germinal centre response. This review will discuss how age-dependent changes in T follicular helper cells influence the germinal centre response, and the evidence that age-dependent changes need not be a barrier to successful vaccination in the later years of life.

SARS-CoV-2-specific immune responses and clinical outcomes after COVID-19 vaccination in patients with immune-suppressive disease

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immune responses and infection outcomes were evaluated in 2,686 patients with varying immune-suppressive disease states after administration of two Coronavirus Disease 2019 (COVID-19) vaccines. Overall, 255 of 2,204 (12%) patients failed to develop anti-spike antibodies, with an additional 600 of 2,204 (27%) patients generating low levels (<380 AU ml-1). Vaccine failure rates were highest in ANCA-associated vasculitis on rituximab (21/29, 72%), hemodialysis on immunosuppressive therapy (6/30, 20%) and solid organ transplant recipients (20/81, 25% and 141/458, 31%). SARS-CoV-2-specific T cell responses were detected in 513 of 580 (88%) patients, with lower T cell magnitude or proportion in hemodialysis, allogeneic hematopoietic stem cell transplantation and liver transplant recipients (versus healthy controls). Humoral responses against Omicron (BA.1) were reduced, although cross-reactive T cell responses were sustained in all participants for whom these data were available. BNT162b2 was associated with higher antibody but lower cellular responses compared to ChAdOx1 nCoV-19 vaccination. We report 474 SARS-CoV-2 infection episodes, including 48 individuals with hospitalization or death from COVID-19. Decreased magnitude of both the serological and the T cell response was associated with severe COVID-19. Overall, we identified clinical phenotypes that may benefit from targeted COVID-19 therapeutic strategies.

Intrinsic B cell TLR-BCR linked coengagement induces class-switched, hypermutated, neutralizing antibody responses in absence of T cells

Maturation of antibody responses entails somatic hypermutation (SHM), class-switch DNA recombination (CSR), plasma cell differentiation, and generation of memory B cells, and it is thought to require T cell help. We showed that B cell Toll-like receptor 4 (TLR4)-B cell receptor (BCR) (receptor for antigen) coengagement by 4-hydroxy-3-nitrophenyl acetyl (NP)-lipopolysaccharide (LPS) (Escherichia coli lipid A polysaccharide O-antigen) or TLR5-BCR coengagement by Salmonella flagellin induces mature antibody responses to NP and flagellin in Tcrβ-/-Tcrδ-/- and NSG/B mice. TLR-BCR coengagement required linkage of TLR and BCR ligands, "linked coengagement." This induced B cell CSR/SHM, germinal center-like differentiation, clonal expansion, intraconal diversification, plasma cell differentiation, and an anamnestic antibody response. In Tcrβ-/-Tcrδ-/- mice, linked coengagement of TLR4-BCR by LPS or TLR5-BCR by flagellin induced protective antibodies against E. coli or Salmonella Typhimurium. Our findings unveiled a critical role of B cell TLRs in inducing neutralizing antibody responses, including those to microbial pathogens, without T cell help.

Comparable cellular and humoral immunity upon homologous and heterologous COVID-19 vaccination regimens in kidney transplant recipients

Background

Kidney transplant recipients (KTRs) are at high risk for a severe course of coronavirus disease 2019 (COVID-19); thus, effective vaccination is critical. However, the achievement of protective immunogenicity is hampered by immunosuppressive therapies. We assessed cellular and humoral immunity and breakthrough infection rates in KTRs vaccinated with homologous and heterologous COVID-19 vaccination regimens.

Method

We performed a comparative in-depth analysis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)–specific T-cell responses using multiplex Fluorospot assays and SARS-CoV-2-specific neutralizing antibodies (NAbs) between three-times homologously (n = 18) and heterologously (n = 8) vaccinated KTRs.

Results

We detected SARS-CoV-2-reactive T cells in 100% of KTRs upon third vaccination, with comparable frequencies, T-cell expression profiles, and relative interferon γ and interleukin 2 production per single cell between homologously and heterologously vaccinated KTRs. SARS-CoV-2-specific NAb positivity rates were significantly higher in heterologously (87.5%) compared to homologously vaccinated (50.0%) KTRs (P &lt; 0.0001), whereas the magnitudes of NAb titers were comparable between both subcohorts after third vaccination. SARS-CoV-2 breakthrough infections occurred in equal numbers in homologously (38.9%) and heterologously (37.5%) vaccinated KTRs with mild-to-moderate courses of COVID-19.

Conclusion

Our data support a more comprehensive assessment of not only humoral but also cellular SARS-CoV-2-specific immunity in KTRs to provide an in-depth understanding about the COVID-19 vaccine–induced immune response in a transplant setting.

Type III interferon drives thymic B cell activation and regulatory T cell generation

The activation of thymic B cells is critical for their licensing as antigen presenting cells and resulting ability to mediate T cell central tolerance. The processes leading to licensing are still not fully understood. By comparing thymic B cells to activated Peyer's patch B cells at steady state, we found that thymic B cell activation starts during the neonatal period and is characterized by TCR/CD40-dependent activation, followed by immunoglobulin class switch recombination (CSR) without forming germinal centers. Transcriptional analysis also demonstrated a strong interferon signature, which was not apparent in the periphery. Thymic B cell activation and CSR were primarily dependent on type III IFN signaling, and loss of type III IFN receptor in thymic B cells resulted in reduced thymocyte regulatory T cell (Treg) development. Finally, from TCR deep sequencing, we estimate that licensed B cells induce development of a substantial fraction of the Treg cell repertoire. Together, these findings reveal the importance of steady-state type III IFN in generating licensed thymic B cells that induce T cell tolerance to activated B cells.

PD-1highCXCR5-CD4+ peripheral helper T cells promote CXCR3+ plasmablasts in human acute viral infection

T cell-B cell interaction is the key immune response to protect the host from severe viral infection. However, how T cells support B cells to exert protective humoral immunity in humans is not well understood. Here, we use COVID-19 as a model of acute viral infections and analyze CD4+ T cell subsets associated with plasmablast expansion and clinical outcome. Peripheral helper T cells (Tph cells; denoted as PD-1highCXCR5-CD4+ T cells) are significantly increased, as are plasmablasts. Tph cells exhibit "B cell help" signatures and induce plasmablast differentiation in vitro. Interestingly, expanded plasmablasts show increased CXCR3 expression, which is positively correlated with higher frequency of activated Tph cells and better clinical outcome. Mechanistically, Tph cells help B cell differentiation and produce more interferon γ (IFNγ), which induces CXCR3 expression on plasmablasts. These results elucidate a role for Tph cells in regulating protective B cell response during acute viral infection.

Vaccine-elicited B and T cell immunity to SARS-CoV-2 is impaired in chronic lung disease patients

The protection afforded by vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to individuals with chronic lung disease is not well established. To understand how chronic lung disease impacts SARS-CoV-2 vaccine-elicited immunity we performed deep immunophenotyping of the humoral and cell mediated SARS-CoV-2 vaccine response in an investigative cohort of vaccinated patients with diverse pulmonary conditions including asthma, chronic obstructive pulmonary disease (COPD), and interstitial lung disease (ILD). Compared to healthy controls, 48% of vaccinated patients with chronic lung diseases had reduced antibody titers to the SARS-CoV-2 vaccine antigen as early as 3-4 months after vaccination, correlating with decreased vaccine-specific memory B cells. Vaccine-specific CD4 and CD8 T cells were also significantly reduced in patients with asthma, COPD, and a subset of ILD patients compared to healthy controls. These findings reveal the complex nature of vaccine-elicited immunity in high-risk patients with chronic lung disease.

Tfh cells and the germinal center are required for memory B cell formation & humoral immunity after ChAdOx1 nCoV-19 vaccination

Emergence from the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has been facilitated by the rollout of effective vaccines. Successful vaccines generate high-affinity plasma blasts and long-lived protective memory B cells. Here, we show a requirement for T follicular helper (Tfh) cells and the germinal center reaction for optimal serum antibody and memory B cell formation after ChAdOx1 nCoV-19 vaccination. We found that Tfh cells play an important role in expanding antigen-specific B cells while identifying Tfh-cell-dependent and -independent memory B cell subsets. Upon secondary vaccination, germinal center B cells generated during primary immunizations can be recalled as germinal center B cells again. Likewise, primary immunization GC-Tfh cells can be recalled as either Tfh or Th1 cells, highlighting the pluripotent nature of Tfh cell memory. This study demonstrates that ChAdOx1 nCoV-19-induced germinal centers are a critical source of humoral immunity.

Adenovirus vector and mRNA vaccines: Mechanisms regulating their immunogenicity

Replication-incompetent adenovirus (Ad) vector and mRNA-lipid nanoparticle (LNP) constructs represent two modular vaccine platforms that have attracted substantial interest over the past two decades. Due to the COVID-19 pandemic and the rapid development of multiple successful vaccines based on these technologies, there is now clear real-world evidence of the utility and efficacy of these platforms. Considerable optimization and refinement efforts underpin the successful application of these technologies. Despite this, our understanding of the specific pathways and processes engaged by these vaccines to stimulate the immune response remains incomplete. This review will synthesize our current knowledge of the specific mechanisms by which CD8⁺ T cell and antibody responses are induced by each of these vaccine platforms, and how this can be impacted by specific vaccine construction techniques. Key gaps in our knowledge are also highlighted, which can hopefully focus future studies.

Antibody and T-Cell Subsets Analysis Unveils an Immune Profile Heterogeneity Mediating Long-term Responses in Individuals Vaccinated Against SARS-CoV-2

BACKGROUND

Based on the fact that coronavirus disease 2019 (COVID-19) is still spreading despite worldwide vaccine administration, there is an imperative need to understand the underlying mechanisms of vaccine-induced interindividual immune response variations.

METHODS

We compared humoral and cellular immune responses in 127 individuals vaccinated with either BNT162b2, mRNA-1273, or ChAdOx1-nCoV-19 vaccine.

RESULTS

Both mRNA vaccines induced faster and stronger humoral responses as assessed by high spike- and RBD-specific antibody titers and neutralizing efficacy in comparison to ChAdOx1-nCoV-19 vaccine. At 7 months postvaccination, a decreasing trend in humoral responses was observed, irrespective of the vaccine administered. Correlation analysis between anti-S1 IgG and interferon- (IFN-) production unveiled a heterogeneous immune profile among BNT162b2-vaccinated individuals. Specifically, vaccination in the high-responder group induced sizable populations of polyfunctional memory CD4 helper T cells (TH1), follicular helper T cells (TFH), and T cells with features of stemness (TSCM), along with high neutralizing antibody production that persisted up to 7 months. In contrast, low responders were characterized by significantly lower antibody titers and memory T cells and a considerably lower capacity for interleukin-2 and IFN- production.

CONCLUSIONS

We identified that long-term humoral responses correlate with the individuals ability to produce antigen-specific persistent memory T-cell populations.

Evolution of antigen-specific follicular helper T cell transcription from effector function to memory

Understanding how follicular helper T cells (TFH) regulate the specialization, maturation, and differentiation of adaptive B cell immunity is crucial for developing durable high-affinity immune protection. Using indexed single-cell molecular strategies, we reveal a skewed intraclonal assortment of higher-affinity T cell receptors and the distinct molecular programming of the localized TFH compartment compared with emigrant conventional effector T_H cells. We find a temporal shift in B cell receptor class switch, which permits identification of inflammatory and anti-inflammatory modules of transcriptional programming that subspecialize TFH function before and during the germinal center (GC) reaction. Late collapse of this local primary GC reaction reveals a persistent post-GC TFH population that discloses a putative memory TFH program. These studies define subspecialized antigen-specific TFH transcriptional programs that progressively change with antibody class-specific evolution of high-affinity B cell immunity and a memory TFH transcriptional program that emerges upon local GC resolution.

Characteristics and Roles of T Follicular Helper Cells in SARS-CoV-2 Vaccine Response

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination is critical to controlling the coronavirus disease 2019 (COVID-19) pandemic. However, a weak response to the vaccine and insufficient persistence of specific antibodies may threaten the global impact of mass vaccination campaigns. This study summarizes the internal factors of the body that affect the effectiveness of the SARS-CoV-2 vaccine. T follicular helper (Tfh) cells support germinal center B cells to produce vaccine-specific immunoglobulins. A reduction in the Tfh cell number and a shift in the subset phenotypes caused by multiple factors may impair the production and persistence of high-affinity antibodies. Besides efficacy differences caused by the different types of vaccines, the factors that affect vaccine effectiveness by intervening in the Tfh cell response also include age-related defects, the polarity of the body microenvironment, repeated immunization, immunodeficiency, and immunosuppressive treatments. Assessing the phenotypic distribution and activation levels of Tfh cell subsets after vaccination is helpful in predicting vaccine responses and may identify potential targets for improving vaccine effectiveness.

T cells in SARS-CoV-2 infection and vaccination

While antibodies garner the lion’s share of attention in SARS-CoV-2 immunity, cellular immunity (T cells) may be equally, if not more important, in controlling infection. Both CD8⁺ and CD4⁺ T cells are elicited earlier and are associated with milder disease, than antibodies, and T-cell activation appears to be necessary for control of infection. Variants of concern (VOCs) such as Omicron have escaped the neutralizing antibody responses after two mRNA vaccine doses, but T-cell immunity is largely intact. The breadth and patient-specific nature of the latter offers a formidable line of defense that can limit the severity of illness, and are likely to be responsible for most of the protection from natural infection or vaccination against VOCs which have evaded the antibody response. Comprehensive searches for T-cell epitopes, T-cell activation from infection and vaccination of specific patient groups, and elicitation of cellular immunity by various alternative vaccine modalities are here reviewed. Development of vaccines that specifically target T cells is called for, to meet the needs of patient groups for whom cellular immunity is weaker, such as the elderly and the immunosuppressed. While VOCs have not yet fully escaped T-cell immunity elicited by natural infection and vaccines, some early reports of partial escape suggest that future VOCs may achieve the dreaded result, dislodging a substantial proportion of cellular immunity, enough to cause a grave public health burden. A proactive, rather than reactive, solution which identifies and targets immutable sequences in SARS-CoV-2, not just those which are conserved, may be the only recourse humankind has to disarm these future VOCs before they disarm us.

T Cell Help in the Autoreactive Germinal Center

The germinal center serves as a site of B cell selection and affinity maturation, critical processes for productive adaptive immunity. In autoimmune disease tolerance is broken in the germinal center reaction, leading to production of autoreactive B cells that may propagate disease. Follicular T cells are crucial regulators of this process, providing signals necessary for B cell survival in the germinal center. Here we review the emerging roles of follicular T cells in the autoreactive germinal center. Recent advances in immunological techniques have allowed study of the gene expression profiles and repertoire of follicular T cells at unprecedented resolution. These studies provide insight into the potential role follicular T cells play in preventing or facilitating germinal center loss of tolerance. Improved understanding of the mechanisms of T cell help in autoreactive germinal centers provides novel therapeutic targets for diseases of germinal center dysfunction.

T peripheral helper cells in autoimmune diseases

Pathologic T cell-B cell interactions underlie many autoimmune diseases. The T cells that help B cells in autoimmune diseases vary in phenotype and include T cells that lack typical features of T follicular helper cells, such as expression of CXCR5 and BCL6. A population of PD-1hi CXCR5- T peripheral helper (Tph) cells has now been recognized in multiple autoantibody-associated diseases. Tph cells display a distinctive set of features, merging the ability to provide B cell help with the capacity to migrate to inflamed peripheral tissues. Here, we review the scope of immune-related conditions in which Tph cells have been implicated and provide a perspective on their potential contributions to pathologic B cell activation in autoimmune diseases. We discuss Tph cells as a promising therapeutic strategy in autoimmunity and consider the utility of tracking Tph cells in blood as a biomarker to quantify aberrant T cell-B cell activation in patients with autoimmune diseases.

Functional analyses and single cell immunoprofiling uncover sex-specific differences in SARS-CoV2 immune memory development

SARS-CoV-2 infection leads to a broad range of outcomes and immune responses, with the development of neutralizing antibodies generally correlated with protection against reinfection. Here, we have characterized both neutralizing activity and T cell responses in a cluster of subjects with mild disease linked to a single spreading event. Surprisingly, we observed sex-specific associations between spike- and particularly nucleoprotein-specific T cell responses and neutralization, with pro-inflammatory cytokines being linked to higher titers only in males. Using single cell immunoprofiling, which provided matched transcriptome and T-cell receptor (TCR) profiles in restimulated CD4 + and CD8 + cells from these subjects, we identified differences in type I IFN signaling that may underlie this difference in antibody generation. Finally, we also identified several TCRs associated with cytokine producing T cells. Altogether, our work maps the breadth of immunological outcomes of SARS-CoV2 infections and highlight the potential role of sex-specific feedback loops during the generation of neutralizing antibodies.

Functional analyses and single cell immunoprofiling uncover sex-specific differences in SARS-CoV2 immune memory development

SARS-CoV-2 infection leads to a broad range of outcomes and immune responses, with the development of neutralizing antibodies generally correlated with protection against reinfection. Here, we have characterized both neutralizing activity and T cell responses in a cluster of subjects with mild disease linked to a single spreading event. Surprisingly, we observed sex-specific associations between spike- and particularly nucleoprotein-specific T cell responses and neutralization, with pro-inflammatory cytokines being linked to higher titers only in males. Using single cell immunoprofiling, which provided matched transcriptome and T-cell receptor (TCR) profiles in restimulated CD4 + and CD8 + cells from these subjects, we identified differences in type I IFN signaling that may underlie this difference in antibody generation. Finally, we also identified several TCRs associated with cytokine producing T cells. Altogether, our work maps the breadth of immunological outcomes of SARS-CoV2 infections and highlight the potential role of sex-specific feedback loops during the generation of neutralizing antibodies.