Circulating Tfh cell and subsets distribution are associated with low-responsiveness to hepatitis B vaccination

Role of circulating T follicular helper subsets following Ty21a immunization and oral challenge with wild type S. Typhi in humans

Despite decades of intense research, our understanding of the correlates of protection against Salmonella Typhi (S. Typhi) infection and disease remains incomplete. T follicular helper cells (TFH), an important link between cellular and humoral immunity, play an important role in the development and production of high affinity antibodies. While traditional TFH cells reside in germinal centers, circulating TFH (cTFH) (a memory subset of TFH) are present in blood. We used specimens from a typhoid controlled human infection model whereby participants were immunized with Ty21a live attenuated S. Typhi vaccine and then challenged with virulent S. Typhi. Some participants developed typhoid disease (TD) and some did not (NoTD), which allowed us to assess the association of cTFH subsets in the development and prevention of typhoid disease. Of note, the frequencies of cTFH were higher in NoTD than in TD participants, particularly 7 days after challenge. Furthermore, the frequencies of cTFH2 and cTFH17, but not cTFH1 subsets were higher in NoTD than TD participants. However, we observed that ex-vivo expression of activation and homing markers were higher in TD than in NoTD participants, particularly after challenge. Moreover, cTFH subsets produced higher levels of S. Typhi-specific responses (cytokines/chemokines) in both the immunization and challenge phases. Interestingly, unsupervised analysis revealed unique clusters with distinct signatures for each cTFH subset that may play a role in either the development or prevention of typhoid disease. Importantly, we observed associations between frequencies of defined cTFH subsets and anti-S. Typhi antibodies. Taken together, our results suggest that circulating TFH2 and TFH17 subsets might play an important role in the development or prevention of typhoid disease. The contribution of these clusters was found to be distinct in the immunization and/or challenge phases. These results have important implications for vaccines aimed at inducing long-lived protective T cell and antibody responses.

Investigation of the Hepatitis-B Vaccine's Immune Response in a Non-Alcoholic Fatty Liver Disease Mouse Model

This study aimed to investigate the immunogenicity of the hepatitis B virus (HBV) vaccine by applying a normal and high-dose hepatitis B virus vaccination program in the mice modeling of non-alcoholic fatty liver disease (NAFLD). NAFLD was induced in mouse livers via diet. At the 10-week mark, both groups were divided into 3 subgroups. While the standard dose vaccination program was applied on days 0, 7, and 21, two high-dose programs were applied: one was applied on days 0 and 7, and the other was applied on days 0, 7, and 21. All mice were euthanized. Blood samples from anti-HB titers; T follicular helper, T follicular regulatory, CD27+, and CD38+ cells; and the liver, spleen, and thymus were taken for histopathologic evaluation. NAFLD subgroups receiving high doses showed higher hepatocyte ballooning scores than normal-dose subgroup. There were differences in CD27+ and CD27+CD38+ cells in animals fed on different diets, without any differences or interactions in terms of vaccine protocols. In the NAFLD group, a negative correlation was observed between anti-HB titers and T helper and CD27+ cells, while a positive correlation was observed with CD38+ cells. NAFLD induced changes in immune parameters in mice, but there was no difference in vaccine efficacy among the applied vaccine protocols. Based on this study's results, high-dose vaccination protocols are not recommended in cases of NAFLD, as they do not enhance efficacy and may lead to increased liver damage.

Activation and induction of antigen-specific T follicular helper cells play a critical role in recombinant SARS-CoV-2 RBD vaccine-induced humoral responses

The role of follicular T helper (Tfh) cells in humoral response has been considered essential in recent years. Understanding how Tfh cells control complex humoral immunity is critical to developing strategies to improve the efficacy of vaccines against SARS-CoV-2 and other emerging pathogens. However, the immunologic mechanism of Tfh cells in SARS-CoV-2 receptor binding domain (RBD) vaccine strategy is limited. In this study, we expressed and purified recombinant SARS-CoV-2 RBD protein in Drosophila S2 cells for the first time and explored the mechanism of Tfh cells induced by RBD vaccine in humoral immune response. We mapped the dynamic of Tfh cell in lymph node and spleen following RBD vaccination and revealed the relationship between Tfh cells and humoral immune response induced by SARS-CoV-2 RBD vaccine through correlation analysis, blocking of IL-21 signaling pathway, and co-culture of Tfh with memory B cells. Recombinant RBD protein elicited a predominant Tfh1 and Tfh1-17 subset response and strong GC responses in spleen and lymph nodes, especially to enhanced vaccination. IL-21 secreted by Tfh cells affected the development and differentiation of B cells and played a key role in the humoral immune response. These observations will help us further understand the mechanism of protective immune response induced by COVID-19 vaccine and has guiding significance for the development of vaccines against newly emerging mutants.

T follicular helper cell responses to SARS-CoV-2 vaccination among healthy and immunocompromised adults

The worldwide rollout of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccinations in the last 2 years has produced a multitude of studies investigating T-cell responses in the peripheral blood and a limited number in secondary lymphoid tissues. As a key component to an effective immune response, vaccine-specific T follicular helper (Tfh) cells are localized in the draining lymph node (LN) and assist in the selection of highly specific B-cell clones for the production of neutralizing antibodies. While these cells have been noted in the blood as circulating Tfh (cTfh) cells, they are not often taken into consideration when examining effective CD4+ T-cell responses, particularly in immunocompromised groups. Furthermore, site-specific analyses in locations such as the LN have recently become an attractive area of investigation. This is mainly a result of improved sampling methods via ultrasound-guided fine-needle biopsy (FNB)/fine-needle aspiration (FNA), which are less invasive than LN excision and able to be performed longitudinally. While these studies have been undertaken in healthy individuals, data from immunocompromised groups are lacking. This review will focus on both Tfh and cTfh responses after SARS-CoV-2 vaccination in healthy and immunocompromised individuals. This area of investigation could identify key characteristics of a successful LN response required for the prevention of infection and viral clearance. This furthermore may highlight responses that could be fine-tuned to improve vaccine efficacy within immunocompromised groups that are at a risk of more severe disease.

Schistosoma mansoni infection alters the host pre-vaccination environment resulting in blunted Hepatitis B vaccination immune responses

Schistosomiasis is a disease caused by parasitic flatworms of the Schistosoma spp., and is increasingly recognized to alter the immune system, and the potential to respond to vaccines. The impact of endemic infections on protective immunity is critical to inform vaccination strategies globally. We assessed the influence of Schistosoma mansoni worm burden on multiple host vaccine-related immune parameters in a Ugandan fishing cohort (n = 75) given three doses of a Hepatitis B (HepB) vaccine at baseline and multiple timepoints post-vaccination. We observed distinct differences in immune responses in instances of higher worm burden, compared to low worm burden or non-infected. Concentrations of pre-vaccination serum schistosome-specific circulating anodic antigen (CAA), linked to worm burden, showed a significant bimodal distribution associated with HepB titers, which was lower in individuals with higher CAA values at month 7 post-vaccination (M7). Comparative chemokine/cytokine responses revealed significant upregulation of CCL19, CXCL9 and CCL17 known to be involved in T cell activation and recruitment, in higher CAA individuals, and CCL17 correlated negatively with HepB titers at month 12 post-vaccination. We show that HepB-specific CD4+ T cell memory responses correlated positively with HepB titers at M7. We further established that those participants with high CAA had significantly lower frequencies of circulating T follicular helper (cTfh) subpopulations pre- and post-vaccination, but higher regulatory T cells (Tregs) post-vaccination, suggesting changes in the immune microenvironment in high CAA could favor Treg recruitment and activation. Additionally, we found that changes in the levels of innate-related cytokines/chemokines CXCL10, IL-1β, and CCL26, involved in driving T helper responses, were associated with increasing CAA concentration. This study provides further insight on pre-vaccination host responses to Schistosoma worm burden which will support our understanding of vaccine responses altered by pathogenic host immune mechanisms and memory function and explain abrogated vaccine responses in communities with endemic infections.

Schistosoma mansoni infection alters the host pre-vaccination environment resulting in blunted Hepatitis B vaccination immune responses

The impact of endemic infections on protective immunity is critical to inform vaccination strategies. In this study, we assessed the influence of Schistosoma mansoni infection on host responses in a Ugandan fishing cohort given a Hepatitis B (HepB) vaccine. Concentrations of schistosome-specific circulating anodic antigen (CAA) pre-vaccination showed a significant bimodal distribution associated with HepB titers, which were lower in individuals with high CAA. We established that participants with high CAA had significantly lower frequencies of circulating T follicular helper (cTfh) subpopulations pre- and post-vaccination and higher regulatory T cells (Tregs) post-vaccination. Polarization towards higher frequencies of Tregs: cTfh cells can be mediated by changes in the cytokine environment favoring Treg differentiation. In fact, we observed higher levels of CCL17 and soluble IL-2R pre-vaccination (important for Treg recruitment and development), in individuals with high CAA that negatively associated with HepB titers. Additionally, alterations in pre-vaccination monocyte function correlated with HepB titers, and changes in innate-related cytokines/chemokine production were associated with increasing CAA concentration. We report, that by influencing the immune landscape, schistosomiasis has the potential to modulate immune responses to HepB vaccination. These findings highlight multiple Schistosoma -related immune associations that could explain abrogated vaccine responses in communities with endemic infections.

Author Summary

Schistosomiasis drives host immune responses for optimal pathogen survival, potentially altering host responses to vaccine-related antigen. Chronic schistosomiasis and co-infection with hepatotropic viruses are common in countries where schistosomiasis is endemic. We explored the impact of Schistosoma mansoni ( S. mansoni ) infection on Hepatitis B (HepB) vaccination of individuals from a fishing community in Uganda. We demonstrate that high schistosome-specific antigen (circulating anodic antigen, CAA) concentration pre-vaccination, is associated with lower HepB antibody titers post-vaccination. We show higher pre-vaccination levels of cellular and soluble factors in instances of high CAA that are negatively associated with HepB antibody titers post-vaccination, which coincided with lower frequencies of circulating T follicular helper cell populations (cTfh), proliferating antibody secreting cells (ASCs), and higher frequencies of regulatory T cells (Tregs). We also show that monocyte function is important in HepB vaccine responses, and that high CAA is associated with alterations in the early innate cytokine/chemokine microenvironment. Our findings suggest that in individuals with high CAA and likely high worm burden, schistosomiasis creates and sustains an environment that is polarized against optimal host immune responses to the vaccine, which puts many endemic communities at risk for infection against HepB and other diseases that are preventable by vaccines.

Effects of hepatitis B virus infection and strategies for preventing mother-to-child transmission on maternal and fetal T-cell immunity

One of the most common routes of chronic hepatitis B virus (HBV) infection is mother-to-child transmission (MTCT). Approximately 6.4 million children under the age of five have chronic HBV infections worldwide. HBV DNA high level, HBeAg positivity, placental barrier failure, and immaturity of the fetal immune are the possible causes of chronic HBV infection. The passive-active immune program for children, which consists of the hepatitis B vaccine and hepatitis B immunoglobulin, and antiviral therapy for pregnant women who have a high HBV DNA load (greater than 2 × 10⁵ IU/ml), are currently two of the most important ways to prevent the transmission of HBV from mother to child. Unfortunately, some infants still have chronic HBV infections. Some studies have also found that some supplementation during pregnancy can increase cytokine levels and then affect the level of HBsAb in infants. For example, IL-4 can mediate the beneficial effect on infants' HBsAb levels when maternal folic acid supplementation. In addition, new research has indicated that HBV infection in the mother may also be linked to unfavorable outcomes such as gestational diabetes mellitus, intrahepatic cholestasis of pregnancy, and premature rupture of membranes. The changes in the immune environment during pregnancy and the hepatotropic nature of HBV may be the main reasons for the adverse maternal outcomes. It is interesting to note that after delivery, the women who had a chronic HBV infection may spontaneously achieve HBeAg seroconversion and HBsAg seroclearance. The maternal and fetal T-cell immunity in HBV infection is important because adaptive immune responses, especially virus-specific CD8 T-cell responses, are largely responsible for viral clearance and disease pathogenesis during HBV infection. Meanwhile, HBV humoral and T-cell responses are important for the durability of protection after fetal vaccination. This article reviews the literature on immunological characteristics of chronic HBV-infected patients during pregnancy and postpartum, blocking mother-to-child transmissions and related immune mechanisms, hoping to provide new insights for the prevention of HBV MTCT and antiviral intervention during pregnancy and postpartum.

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.

An old problem with new solutions: Strategies to improve vaccine efficacy in the elderly

Vaccination is the most effective measure to protect against infections. However, with increasing age, there is a progressive decline in the ability of the immune system to both protect against infection and develop protective immunity from vaccination. This age-related decline of the immune system is due to age-related changes in both the innate and adaptive immune systems. With an aging world population and increased risk of pandemics, there is a need to continue to develop strategies to increase vaccine responses in the elderly. Here, the major age-related changes that occur in both the innate and adaptive immune responses that impair the response to vaccination in the elderly will be highlighted. Existing and future strategies to improve vaccine efficacy in the elderly will then be discussed, including adjuvants, delivery methods, and formulation. These strategies provide mechanisms to improve the efficacy of existing vaccines and develop novel vaccines for the elderly.

Long-Term Analysis of Pertussis Vaccine Immunity to Identify Potential Markers of Vaccine-Induced Memory Associated With Whole Cell But Not Acellular Pertussis Immunization in Mice

Over two decades ago acellular pertussis vaccines (aP) replaced whole cell pertussis vaccines (wP) in several countries. Since then, a resurgence in pertussis has been observed, which is hypothesized to be linked, in part, to waning immunity. To better understand why waning immunity occurs, we developed a long-term outbred CD1 mouse model to conduct the longest murine pertussis vaccine studies to date, spanning out to 532 days post primary immunization. Vaccine-induced memory results from follicular responses and germinal center formation; therefore, cell populations and cytokines involved with memory were measured alongside protection from challenge. Both aP and wP immunization elicit protection from intranasal challenge by decreasing bacterial burden in both the upper and lower airways, and by generation of pertussis specific antibody responses in mice. Responses to wP vaccination were characterized by a significant increase in T follicular helper cells in the draining lymph nodes and CXCL13 levels in sera compared to aP mice. In addition, a population of B. pertussis⁺ memory B cells was found to be unique to wP vaccinated mice. This population peaked post-boost, and was measurable out to day 365 post-vaccination. Anti-B. pertussis and anti-pertussis toxoid antibody secreting cells increased one day after boost and remained high at day 532. The data suggest that follicular responses, and in particular CXCL13 levels in sera, could be monitored in pre-clinical and clinical studies for the development of the next-generation pertussis vaccines.