Modulation of immune responses to vaccination by the microbiota: implications and potential mechanisms

The gut microbiota modifies antibody durability and booster responses after SARS-CoV-2 vaccination

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines are pivotal in combating coronavirus disease 2019 (COVID-19); however, the declining antibody titers postvaccination pose challenges for sustained protection and herd immunity. Although gut microbiome is reported to affect the early antibody response after vaccination, its impact on the longevity of vaccine-induced antibodies remains unexplored.

METHODS

A prospective cohort study was conducted involving 44 healthy adults who received two doses of either the BNT162b2 or ChAdOx1 vaccine, followed by a BNT162b2 booster at six months. The gut microbiome was serially analyzed using 16S rRNA and shotgun sequencing, while humoral immune response was assessed using a SARS-CoV-2 spike protein immunoassay.

RESULTS

Faecalibacterium prausnitzii was associated with robust and persistent antibody responses post-BNT162b2 vaccination. In comparison, Escherichia coli was associated with a slower antibody decay following ChAdOx1 vaccination. The booster immune response was correlated with metabolic pathways involving cellular functions and aromatic amino acid synthesis.

CONCLUSIONS

The findings of this study underscored the potential interaction between the gut microbiome and the longevity/boosting effect of antibodies following vaccination against SARS-CoV-2. The identification of specific microbial associations suggests the prospect of microbiome-based strategies for enhancing vaccine efficacy.

Systems vaccinology studies - achievements and future potential

Human immune responses to vaccination are variable both within and between populations. Systems vaccinology, which is the application of multi-omics technologies to vaccine studies, seeks to understand such variation and predict responses to optimise vaccine strategies. Here, we outline new approaches to systems vaccinology, focusing on the incorporation of additional cohorts, endpoints and technologies.

Exploring the associations between gut microbiota composition and SARS-CoV-2 inactivated vaccine response in mice with type 2 diabetes mellitus

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination is crucial for protecting vulnerable individuals, yet individuals with type 2 diabetes mellitus (T2DM) often exhibit impaired vaccine responses. Emerging evidence suggests that the composition of the host microbiota, crucial in immune regulation and development, influences vaccine efficacy. This study aimed to characterize the relationships between the SARS-CoV-2 inactivated vaccine and the host microbiota (specifically, gut and lung microbiota) of C57BL/6 mice with T2DM. Employing 16S rRNA metagenomic sequencing and ultra-high-performance liquid chromatography-mass spectrometry, we observed lower alpha diversity and distinct beta diversity in fecal microbiota before vaccination and in gut microbiota 28 days post-vaccination between T2DM mice and healthy mice. Compared with healthy mice, T2DM mice showed a higher Firmicutes/Bacteroidetes ratio 28 days post-vaccination. Significant alterations in gut microbiota composition were detected following vaccination, while lung microbiota remained unchanged. T2DM was associated with a diminished initial IgG antibody response against the spike protein, which subsequently normalized after 28 days. Notably, the initial IgG response positively correlated with fecal microbiota alpha diversity pre-vaccination. Furthermore, after 28 days, increased relative abundance of gut probiotics (Bifidobacterium and Lactobacillus) and higher levels of the gut bacterial tryptophan metabolite, indole acrylic acid, were positively associated with IgG levels. These findings suggest a potential link between vaccine efficacy and gut microbiota composition. Nonetheless, further research is warranted to elucidate the precise mechanisms underlying the impact of the gut microbiome on vaccine response. Overall, this study enhances our understanding of the intricate relationships among host microbiota, SARS-CoV-2 vaccination, and T2DM, with potential implications for improving vaccine efficacy.

IMPORTANCE

Over 7 million deaths attributed to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by 6 May 2024 underscore the urgent need for effective vaccination strategies. However, individuals with type 2 diabetes mellitus (T2DM) have been identified as particularly vulnerable and display compromised immune responses to vaccines. Concurrently, increasing evidence suggests that the composition and diversity of gut microbiota, crucial regulators of immune function, may influence the efficacy of vaccines. Against this backdrop, our study explores the complex interplay among SARS-CoV-2 inactivated vaccination, T2DM, and host microbiota. We discover that T2DM compromises the initial immune response to the SARS-CoV-2 inactivated vaccine, and this response is positively correlated with specific features of the gut microbiota, such as alpha diversity. We also demonstrate that the vaccination itself induces alterations in the composition and structure of the gut microbiota. These findings illuminate potential links between the gut microbiota and vaccine efficacy in individuals with T2DM, offering valuable insights that could enhance vaccine responses in this high-risk population.

Therapeutic potential of probiotics in gut microbial homeostasis and Rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by inflammation and joint damage. Existing treatment options primarily focus on managing symptoms and slowing disease progression, often with side effects and limitations. The gut microbiome, a vast community of microorganisms present in the gastrointestinal tract, plays a crucial role in health and disease. Recent research suggests a bidirectional relationship between the gut microbiome and RA, highlighting its potential as a therapeutic option. This review focuses on the interaction between the gut microbiome and RA development, by discussing how dysbiosis, an imbalance in gut bacteria, can contribute to RA through multiple mechanisms such as molecular mimicry, leaky gut, and metabolic dysregulation. Probiotics, live microorganisms with health benefits, are emerging as promising tools for managing RA. They can prevent the negative effects of dysbiosis by displacing harmful bacteria, producing anti-inflammatory metabolites like short-chain fatty acids (SCFA), Directly influencing immune cells, and modifying host metabolism. animal and clinical studies demonstrate the potential of probiotics in improving RA symptoms and disease outcomes. However, further research is needed to optimize probiotic strains, dosages, and treatment protocols for personalized and effective management of RA. This review summarizes the current understanding of the gut microbiome and its role in RA and discusses future research directions. In addition to the established role of gut dysbiosis in RA, emerging strategies like fecal microbiota transplantation, prebiotics, and postbiotics offer exciting possibilities. However, individual variations in gut composition necessitate personalized treatment plans. Long-term effects and clear regulations need to be established. Future research focusing on metagenomic analysis, combination therapies, and mechanistic understanding will unlock the full potential of gut microbiome modulation for effective RA management.

Effect of metabolic dysfunction-associated steatotic liver disease on BNT162b2 immunogenicity against the severe acute respiratory syndrome coronavirus 2 omicron variant

BACKGROUND AND AIM

We aimed to investigate the effect of metabolic dysfunction-associated steatotic liver disease (MASLD) on three-dose BNT162b2 immunogenicity to the omicron variant.

METHODS

Adult recipients of three doses of BNT162b2 were prospectively recruited between May and December 2021. The serology of the neutralizing antibody by live virus microneutralization (vMN) to the omicron variant was measured at baseline, day 180, and day 360 after the first dose. The primary outcome was seroconversion (vMN titer ≥ 10) at day 360. Exposure of interest was MASLD, defined as hepatic steatosis (controlled attenuation parameter ≥ 248 dB/m on transient elastography) plus at least one of five cardiometabolic risk factors. Subjects with prior COVID-19 were excluded. A multivariable logistic regression model was used to derive the adjusted odds ratio of seroconversion with MASLD by adjusting for age, sex, antibiotic use, and proton pump inhibitor use.

RESULTS

One hundred forty-eight BNT162b2 recipients (male: 48 [32.4%]; median age: 51.0 years [interquartile range, IQR: 44.5-57.3]) were recruited. The median time from the first dose to the third dose was 8.5 months (IQR: 7.9-8.9). MASLD subjects had a lower seroconversion rate than non-MASLD ones (89.6% vs 99.0%; P = 0.007). MASLD was the only independent risk factor for seroconversion (adjusted odds ratio: 0.051, 95% confidence interval: 0.002-0.440). Subgroup analysis of immunogenicity at 4 months after the third dose shows significantly lower vMN titer (13.06 [IQR: 7.69-22.20] vs 33.49 [IQR: 24.05-46.53]; P = 0.004) and seroconversion rate (76.9% vs 97.4%; P = 0.016) in MASLD than non-MASLD subjects, but not within 4 months from the third dose (vMN titer: 46.87 [IQR: 33.12-66.02] vs 41.86 [IQR: 34.47-50.91], P = 0.240; seroconversion rate: 94.3% vs 100%, P = 0.131).

CONCLUSION

Metabolic dysfunction-associated steatotic liver disease was a risk factor for poorer immunogenicity to the omicron variant, with a more pronounced waning effect compared among three-dose BNT162b2 recipients.

Baseline Gut Microbiota Was Associated with Long-Term Immune Response at One Year Following Three Doses of BNT162b2

BACKGROUND

This study explored neutralizing IgG antibody levels against COVID-19 decline over time post-vaccination. We conducted this prospective cohort study to investigate the function of gut microbiota in the host immune response following three doses of BNT162b2.

METHODS

Subjects who received three doses of BNT162b2 were recruited from three centers in Hong Kong. Blood samples were obtained before the first dose and at the one-year timepoint for IgG ELISA to determine the level of neutralizing antibody (NAb). The primary outcome was a high immune response (NAb > 600 AU/mL). We performed shotgun DNA metagenomic sequencing on baseline fecal samples to identify bacterial species and metabolic pathways associated with high immune response using linear discriminant analysis effect size analysis.

RESULTS

A total of 125 subjects were recruited (median age: 52 years [IQR: 46.2-59.0]; male: 43 [34.4%]), and 20 were regarded as low responders at the one-year timepoint. Streptococcus parasanguinis (log10LDA score = 2.38, p = 0.003; relative abundance of 2.97 × 10-5 vs. 0.03%, p = 0.001), Bacteroides stercoris (log10LDA score = 4.29, p = 0.024; relative abundance of 0.14% vs. 2.40%, p = 0.014) and Haemophilus parainfluenzae (log10LDA score = 2.15, p = 0.022; relative abundance of 0.01% vs. 0, p = 0.010) were enriched in low responders. Bifidobacterium pseudocatenulatum (log10LDA score = 2.99, p = 0.048; relative abundance of 0.09% vs. 0.36%, p = 0.049) and Clostridium leptum (log10LDA score = 2.38, p = 0.014; relative abundance of 1.2 × 10-5% vs. 0, p = 0.044) were enriched in high responders. S. parasanguinis was negatively correlated with the superpathway of pyrimidine ribonucleotides de novo biosynthesis (log10LDA score = 2.63), which contributes to inflammation and antibody production. H. parainfluenzae was positively correlated with pathways related to anti-inflammatory processes, including the superpathway of histidine, purine, and pyrimidine biosynthesis (log10LDA score = 2.14).

CONCLUSION

Among three-dose BNT162b2 recipients, S. parasanguinis, B. stercoris and H. parainfluenzae were associated with poorer immunogenicity at one year, while B. pseudocatenulatum and C. leptum was associated with a better response.

Integrated analyses of the intestinal microbiome and transcriptome in Ningxiang piglets

Ningxiang (NX) pig has been recognized as one of the most famous Chinese indigenous breeds due to its characteristics in stress resistance. However, intestinal microbial feature and gene profiling in NX piglets have not been studied. Here, we compared the intestinal microbiome and transcriptome between NX and Duroc × Landrace × Large white (DLY) piglets and found the high enrichment of several colonic Bacteroides, Prevotella and Clostridium species in NX piglets. Further functional analyses revealed their predominant function in methane, glycolysis and gluconeogenesis metabolism. Our mRNA-sequencing data unraveled the distinct colonic gene expression between these two breeds. In particular, we showed that the improved intestinal function in NX piglets may be determined by enhanced intestinal barrier gene expression and varied immune gene expression through modulating the composition of the gut microbes. Together, our study revealed the intestinal characteristics of NX piglets, providing their potential application in improving breeding strategies and developing dietary interventions.

The role of the gut microbiota in regulating responses to vaccination: current knowledge and future directions

Antigen-specific B and T cell responses play a critical role in vaccine-mediated protection against infectious diseases, but these responses are highly variable between individuals and vaccine immunogenicity is frequently sub-optimal in infants, the elderly and in people living in low- and middle-income countries. Although many factors such as nutrition, age, sex, genetics, environmental exposures, and infections may all contribute to variable vaccine immunogenicity, mounting evidence indicates that the gut microbiota is an important and targetable factor shaping optimal immune responses to vaccination. In this review, we discuss evidence from human, preclinical and experimental studies supporting a role for a healthy gut microbiota in mediating optimal vaccine immunogenicity, including the immunogenicity of COVID-19 vaccines. Furthermore, we provide an overview of the potential mechanisms through which this could occur and discuss strategies that could be used to target the microbiota to boost vaccine immunogenicity where it is currently sub-optimal.

From Womb to World: Exploring the Immunological Connections between Mother and Child

Mother and child are immunologically interconnected by mechanisms that we are only beginning to understand. During pregnancy, multiple molecular and cellular factors of maternal origin are transferred across the placenta and influence the development and function of the fetal and newborn immune system. Altered maternal immune states arising from pregnancy-associated infections or immunizations have the potential to program offspring immune function in ways that may have long-term health consequences. In this study, we review current literature on the impact of prenatal infection and vaccination on the developing immune system, highlight knowledge gaps, and look to the horizon to envision maternal interventions that could benefit both the mother and her child.

Pediococcus pentosaceus MIANGUAN Enhances the Immune Response to Vaccination in Mice

Increasing evidence shows that some probiotics can improve vaccine responses as adjuvants. This study aimed to evaluate the effect of Pediococcus pentosaceus MIANGUAN (PPM) on SARS-CoV-2 vaccine-elicited immune response in mice. Six-week-old female ICR mice were primed and boosted with SARS-CoV-2 vaccine intramuscularly at weeks 0 and 4, respectively. Mice were gavaged with PPM (5 × 109 CFU/mouse) or PBS (control) for 3 days immediately after boosting vaccination. Compared to the control, oral PPM administration resulted in significantly higher levels of RBD-specific IgG binding antibodies (> 2.3-fold) and RBD-specific IgG1 binding antibodies (> 4-fold) in the serum. Additionally, PPM-treated mice had higher titers of RBD-specific IgG binding antibodies (> 2.29-fold) and neutralization antibodies (> 1.6-fold) in the lung compared to the control mice. The transcriptional analyses showed that the B cell receptor (BCR) signaling pathway was upregulated in both splenocytes and BAL cells in the PPM group vs. the control group. In addition, the number of IFN-γ-producing splenocytes (mainly in CD4 + T cells as determined by flow cytometry) in response to restimulation of RBD peptides was significantly increased in the PPM group. RNA sequencing showed that the genes associated with T cell activation and maturation and MHC class II pathway (CD4, H2-DMa, H2-DMb1, H2-Oa, Ctss) were upregulated, suggesting that oral administration of PPM may enhance CD4 + T cell responses through MHC class II pathway. Furthermore, PPM administration could downregulate the expression level of proinflammatory genes. To conclude, oral administration of PPM could boost SARS-CoV-2 vaccine efficacy through enhancing the specific humoral and cellular immunity response and decrease the expression of inflammation pathways.

Exploratory application of a cannulation model in recently weaned pigs to monitor longitudinal changes in the enteric microbiome across varied porcine reproductive and respiratory syndrome virus (PRRSV) infection statuses

Introduction

The enteric microbiome and its possible modulation to improve feed conversion or vaccine efficacy is gaining more attention in pigs. Weaning pigs from their dam, along with many routine procedures, is stressful. A better understanding of the impact of this process on the microbiome may be important for improving pig production. The objective of this study was to develop a weaner pig cannulation model, thus allowing ileum content collection from the same pig over time for 16S rRNA sequencing under different porcine reproductive and respiratory syndrome virus (PRRSV) infection statuses.

Methods

A total of 15 3-week-old pigs underwent abdominal surgery and were fitted with an ileum cannula, with ileum contents collected over time. In this pilot study, treatment groups included a NEG-CONTROL group (no vaccination, no PRRSV challenge), a POS-CONTROL group (no vaccination, challenged with PRRSV), a VAC-PRRSV group (vaccinated, challenged with PRRSV), a VAC-PRO-PRRSV group (vaccinated, supplemented with a probiotic, challenged with PRRSV), and a VAC-ANTI-PRRSV group (vaccinated, administered an antibiotic, challenged with PRRSV). We assessed the microbiome over time and measured anti-PRRSV serum antibodies, PRRSV load in serum and nasal samples, and the severity of lung lesions.

Results

Vaccination was protective against PRRSV challenge, irrespective of other treatments. All vaccinated pigs mounted an immune response to PRRSV within 1 week after vaccination. A discernible impact of treatment on the diversity, structure, and taxonomic abundance of the enteric microbiome among the groups was not observed. Instead, significant influences on the ileum microbiome were observed in relation to time and treatment.

Discussion

The cannulation model described in this pilot study has the potential to be useful in studying the impact of weaning, vaccination, disease challenge, and antimicrobial administration on the enteric microbiome and its impact on pig health and production. Remarkably, despite the cannulation procedures, all vaccinated pigs exhibited robust immune responses and remained protected against PRRSV challenge, as evidenced by the development of anti-PRRSV serum antibodies and viral shedding data.

From dysbiosis to defense: harnessing the gut microbiome in HIV/SIV therapy

BACKGROUND

Although the microbiota has been extensively associated with HIV pathogenesis, the majority of studies, particularly those using omics techniques, are largely correlative and serve primarily as a basis for hypothesis generation. Furthermore, most have focused on characterizing the taxonomic composition of the bacterial component, often overlooking other levels of the microbiome. The intricate mechanisms by which the microbiota influences immune responses to HIV are still poorly understood. Interventional studies on gut microbiota provide a powerful tool to test the hypothesis of whether we can harness the microbiota to improve health outcomes in people with HIV.

RESULTS

Here, we review the multifaceted role of the gut microbiome in HIV/SIV disease progression and its potential as a therapeutic target. We explore the complex interplay between gut microbial dysbiosis and systemic inflammation, highlighting the potential for microbiome-based therapeutics to open new avenues in HIV management. These include exploring the efficacy of probiotics, prebiotics, fecal microbiota transplantation, and targeted dietary modifications. We also address the challenges inherent in this research area, such as the difficulty in inducing long-lasting microbiome alterations and the complexities of study designs, including variations in probiotic strains, donor selection for FMT, antibiotic conditioning regimens, and the hurdles in translating findings into clinical practice. Finally, we speculate on future directions for this rapidly evolving field, emphasizing the need for a more granular understanding of microbiome-immune interactions, the development of personalized microbiome-based therapies, and the application of novel technologies to identify potential therapeutic agents.

CONCLUSIONS

Our review underscores the importance of the gut microbiome in HIV/SIV disease and its potential as a target for innovative therapeutic strategies.

Host Functional Response to a Prototypic Orally Delivered Self-Replicating Vaccine Platform

The development of mucosal vaccines has been limited and could be aided by a systems vaccinology approach to identify platforms and adjuvant strategies that induce protective immune responses. The induction of local immune responses by mucosal-delivered vaccines has been difficult to evaluate from peripheral samples, as systemic responses often do not correlate with the mucosal response. Here, we utilized transcriptomics in combination with Gene Set Enrichment Analysis (GSEA) to assess innate immune activation by an oral probiotic Lactobacillus acidophilus-based vaccine platform in mice. The goal was to explore the earliest immune responses elicited after oral immunization at the Peyer's patch. Twenty-four hours after oral delivery of the L. acidophilus vaccine platform, we found an abundance of L. acidophilus at Peyer's patches and detected expression of the vaccine viral proteins and adjuvants, confirming in vivo vaccine delivery. Compared to mice orally dosed with buffer or wild-type L. acidophilus, we identified enhanced responses in immune pathways related to cytokine and gene signaling, T and B cell activation, phagocytosis, and humoral responses. While more work is needed to correlate these pathways with protection from infection and/or disease, they indicate this method's potential to evaluate and aid in the iterative development of next-generation mucosal vaccines.

Immuno-Microbial Signature of Vaccine-Induced Immunity against SARS-CoV-2

Although vaccines address critical public health needs, inter-individual differences in responses are not always considered in their development. Understanding the underlying basis for these differences is needed to optimize vaccine effectiveness and ultimately improve disease control. In this pilot study, pre- and post-antiviral immunological and gut microbiota features were characterized to examine inter-individual differences in SARS-CoV-2 mRNA vaccine response. Blood and stool samples were collected before administration of the vaccine and at 2-to-4-week intervals after the first dose. A cohort of 14 adults was separated post hoc into two groups based on neutralizing antibody levels (high [HN] or low [LN]) at 10 weeks following vaccination. Bivariate correlation analysis was performed to examine associations between gut microbiota, inflammation, and neutralization capacity at that timepoint. These analyses revealed significant differences in gut microbiome composition and inflammation states pre-vaccination, which predicted later viral neutralization capacity, with certain bacterial taxa, such as those in the genus Prevotella, found at higher abundance in the LN vs HN group that were also negatively correlated with a panel of inflammatory factors such as IL-17, yet positively correlated with plasma levels of the high mobility group box 1 (HMGB-1) protein at pre-vaccination. In particular, we observed a significant inverse relationship (Pearson = -0.54, p = 0.03) between HMGB-1 pre-vaccination and neutralization capacity at 10 weeks post-vaccination. Consistent with known roles as mediators of inflammation, our results altogether implicate HMGB-1 and related gut microbial signatures as potential biomarkers in predicting SARS-CoV-2 mRNA vaccine effectiveness measured by the production of viral neutralization antibodies.

Dietary Inulin to Improve SARS-CoV-2 Vaccine Response in Kidney Transplant Recipients: The RIVASTIM-Inulin Randomised Controlled Trial

Kidney transplant recipients are at an increased risk of hospitalisation and death from SARS-CoV-2 infection, and standard two-dose vaccination schedules are typically inadequate to generate protective immunity. Gut dysbiosis, which is common among kidney transplant recipients and known to effect systemic immunity, may be a contributing factor to a lack of vaccine immunogenicity in this at-risk cohort. The gut microbiota modulates vaccine responses, with the production of immunomodulatory short-chain fatty acids by bacteria such as Bifidobacterium associated with heightened vaccine responses in both observational and experimental studies. As SCFA-producing populations in the gut microbiota are enhanced by diets rich in non-digestible fibre, dietary supplementation with prebiotic fibre emerges as a potential adjuvant strategy to correct dysbiosis and improve vaccine-induced immunity. In a randomised, double-bind, placebo-controlled trial of 72 kidney transplant recipients, we found dietary supplementation with prebiotic inulin for 4 weeks before and after a third SARS-CoV2 mRNA vaccine to be feasible, tolerable, and safe. Inulin supplementation resulted in an increase in gut Bifidobacterium, as determined by 16S RNA sequencing, but did not increase in vitro neutralisation of live SARS-CoV-2 virus at 4 weeks following a third vaccination. Dietary fibre supplementation is a feasible strategy with the potential to enhance vaccine-induced immunity and warrants further investigation.

Long Prime-Boost Interval and Heightened Anti-GD2 Antibody Response to Carbohydrate Cancer Vaccine

The carbohydrate ganglioside GD2/GD3 cancer vaccine adjuvanted by β-glucan stimulates anti-GD2 IgG1 antibodies that strongly correlate with improved progression-free survival (PFS) and overall survival (OS) among patients with high-risk neuroblastoma. Thirty-two patients who relapsed on the vaccine (first enrollment) were re-treated on the same vaccine protocol (re-enrollment). Titers during the first enrollment peaked by week 32 at 751 ± 270 ng/mL, which plateaued despite vaccine boosts at 1.2-4.5 month intervals. After a median wash-out interval of 16.1 months from the last vaccine dose during the first enrollment to the first vaccine dose during re-enrollment, the anti-GD2 IgG1 antibody rose to a peak of 4066 ± 813 ng/mL by week 3 following re-enrollment (p < 0.0001 by the Wilcoxon matched-pairs signed-rank test). Yet, these peaks dropped sharply and continually despite repeated boosts at 1.2-4.5 month intervals, before leveling off by week 20 to the first enrollment peak levels. Despite higher antibody titers, patients experienced no pain or neuropathic side effects, which were typically associated with immunotherapy using monoclonal anti-GD2 antibodies. By the Kaplan-Meier method, PFS was estimated to be 51%, and OS was 81%. The association between IgG1 titer during re-enrollment and β-glucan receptor dectin-1 SNP rs3901533 was significant (p = 0.01). A longer prime-boost interval could significantly improve antibody responses in patients treated with ganglioside conjugate cancer vaccines.

Update on Early-Life T Cells: Impact on Oral Rotavirus Vaccines

Rotavirus infection continues to be a significant public health problem in developing countries, despite the availability of several vaccines. The efficacy of oral rotavirus vaccines in young children may be affected by significant immunological differences between individuals in early life and adults. Therefore, understanding the dynamics of early-life systemic and mucosal immune responses and the factors that affect them is essential to improve the current rotavirus vaccines and develop the next generation of mucosal vaccines. This review focuses on the advances in T-cell development during early life in mice and humans, discussing how immune homeostasis and response to pathogens is established in this period compared to adults. Finally, the review explores how this knowledge of early-life T-cell immunity could be utilized to enhance current and novel rotavirus vaccines.

Proton pump inhibitors associated with severe COVID-19 among two-dose but not three-dose vaccine recipients

BACKGROUND AND AIM

Proton pump inhibitors (PPIs) may increase the risk of COVID-19 among non-vaccinated subjects via various mechanisms, including gut dysbiosis. We aimed to investigate whether PPIs also affect the clinical outcomes of COVID-19 among vaccine recipients.

METHODS

This was a territory-wide cohort study of 3 272 286 vaccine recipients (aged ≥ 18 years) of ≥ 2 doses of either BNT162b2 or CoronaVac. Exclusion criteria included prior gastrointestinal surgery, immunocompromised status, and prior COVID-19. The primary outcome was COVID-19, and secondary outcomes included COVID-19-related hospitalization and severe infection (composite of intensive care unit admission, ventilatory support, and/or death). Covariates include age, sex, the Charlson Comorbidity Index, comorbidities, and concomitant medication use. Subjects were followed from index date (first dose of vaccination) until outcome occurrence, death, additional dose of vaccination, or March 31, 2022. Exposure was pre-vaccination PPI use (any prescription within 90 days before the index date). Propensity score (PS) matching and a Poisson regression model were used to estimate the adjusted incidence rate ratio (aIRR) of outcomes with PPI use.

RESULTS

Among 439 154 PS-matched two-dose vaccine recipients (mean age: 65.3 years; male: 45.7%) with a median follow-up of 6.8 months (interquartile range: 2.6-7.9), PPI exposure was associated with a higher risk of COVID-19 (aIRR: 1.08; 95% confidence interval [95% CI]: 1.05-1.10), hospitalization (aIRR: 1.20; 95% CI: 1.08-1.33), and severe infection (aIRR: 1.57; 95% CI: 1.24-1.98). Among 188 360 PS-matched three-dose vaccine recipients (mean age: 62.5 years; male: 49.0%; median follow-up: 9.1 months [interquartile range: 8.0-10.9]), PPIs were associated with higher infection risk (aIRR: 1.11; 95% CI: 1.08-1.15) but not other outcomes.

CONCLUSIONS

Although PPI use was associated with a higher COVID-19 risk, severe infection was limited to two-dose but not three-dose vaccine recipients.

Live-attenuated virus vaccine defective in RNAi suppression induces rapid protection in neonatal and adult mice lacking mature B and T cells

Global control of infectious diseases depends on the continuous development and deployment of diverse vaccination strategies. Currently available live-attenuated and killed virus vaccines typically take a week or longer to activate specific protection by the adaptive immunity. The mosquito-transmitted Nodamura virus (NoV) is attenuated in mice by mutations that prevent expression of the B2 viral suppressor of RNA interference (VSR) and consequently, drastically enhance in vivo production of the virus-targeting small-interfering RNAs. We reported recently that 2 d after immunization with live-attenuated VSR-disabled NoV (NoVΔB2), neonatal mice become fully protected against lethal NoV challenge and develop no detectable infection. Using Rag1-/- mice that produce no mature B and T lymphocytes as a model, here we examined the hypothesis that adaptive immunity is dispensable for the RNAi-based protective immunity activated by NoVΔB2 immunization. We show that immunization of both neonatal and adult Rag1-/- mice with live but not killed NoVΔB2 induces full protection against NoV challenge at 2 or 14 d postimmunization. Moreover, NoVΔB2-induced protective antiviral immunity is virus-specific and remains effective in adult Rag1-/- mice 42 and 90 d after a single-shot immunization. We conclude that immunization with the live-attenuated VSR-disabled RNA virus vaccine activates rapid and long-lasting protective immunity against lethal challenges by a distinct mechanism independent of the adaptive immunity mediated by B and T cells. Future studies are warranted to determine whether additional animal and human viruses attenuated by VSR inactivation induce similar protective immunity in healthy and adaptive immunity-compromised individuals.

Longitudinal profiling of the microbiome at four body sites reveals core stability and individualized dynamics during health and disease

To understand the dynamic interplay between the human microbiome and host during health and disease, we analyzed the microbial composition, temporal dynamics, and associations with host multi-omics, immune, and clinical markers of microbiomes from four body sites in 86 participants over 6 years. We found that microbiome stability and individuality are body-site specific and heavily influenced by the host. The stool and oral microbiome are more stable than the skin and nasal microbiomes, possibly due to their interaction with the host and environment. We identify individual-specific and commonly shared bacterial taxa, with individualized taxa showing greater stability. Interestingly, microbiome dynamics correlate across body sites, suggesting systemic dynamics influenced by host-microbial-environment interactions. Notably, insulin-resistant individuals show altered microbial stability and associations among microbiome, molecular markers, and clinical features, suggesting their disrupted interaction in metabolic disease. Our study offers comprehensive views of multi-site microbial dynamics and their relationship with host health and disease.

Biotics: An emerging food supplement for health improvement in the era of immune modulation

The involvement of the commensal microbiota in immune function is a multifold process. Biotics, such as probiotics, prebiotics, synbiotics, and paraprobiotics, have been subjected to animal and human trials demonstrating the association between gut microbes and immunity biomarkers leading to improvement in overall health. In recent years, studies on human microbiome interaction have established the multifarious role of biotics in maintaining overall health. The consumption of biotics has been extensively reported to help in maintaining microbial diversity, enhancing gut-associated mucosal immune homeostasis, and providing protection against a wide range of lifestyle disorders. However, the establishment of biotics as an alternative therapy for a range of health conditions is yet to be ascertained. Despite the fact that scientific literature has demonstrated the correlation between biotics and immune modulation, most in vivo and in vitro reports are inconclusive on the dosage required. This review provides valuable insights into the immunomodulatory effects of biotics consumption based on evidence obtained from animal models and clinical trials. Furthermore, we highlight the optimal dosages of biotics that have been reported to deliver maximum health benefits. By identifying critical research gaps, we have suggested a roadmap for future investigations to advance our understanding of the intricate crosstalk between biotics and immune homeostasis.

Immunological factors linked to geographical variation in vaccine responses

Vaccination is one of medicine's greatest achievements; however, its full potential is hampered by considerable variation in efficacy across populations and geographical regions. For example, attenuated malaria vaccines in high-income countries confer almost 100% protection, whereas in low-income regions these same vaccines achieve only 20-50% protection. This trend is also observed for other vaccines, such as bacillus Calmette-Guérin (BCG), rotavirus and yellow fever vaccines, in terms of either immunogenicity or efficacy. Multiple environmental factors affect vaccine responses, including pathogen exposure, microbiota composition and dietary nutrients. However, there has been variable success with interventions that target these individual factors, highlighting the need for a better understanding of their downstream immunological mechanisms to develop new ways of modulating vaccine responses. Here, we review the immunological factors that underlie geographical variation in vaccine responses. Through the identification of causal pathways that link environmental influences to vaccine responsiveness, it might become possible to devise modulatory compounds that can complement vaccines for better outcomes in regions where they are needed most.

Immune Cells, Gut Microbiota, and Vaccines: A Gender Perspective

The development of preventive and therapeutic vaccines has played a crucial role in preventing infections and treating chronic and non-communicable diseases, respectively. For a long time, the influence of sex differences on modifying health and disease has not been addressed in clinical and preclinical studies. The interaction of genetic, epigenetic, and hormonal factors plays a role in the sex-related differences in the epidemiology of diseases, clinical manifestations, and the response to treatment. Moreover, sex is one of the leading factors influencing the gut microbiota composition, which could further explain the different predisposition to diseases in men and women. In the same way, differences between sexes occur also in the immune response to vaccines. This narrative review aims to highlight these differences, focusing on the immune response to vaccines. Comparative data about immune responses, vaccine effectiveness, and side effects are reviewed. Hence, the intricate interplay between sex, immunity, and the gut microbiota will be discussed for its potential role in the response to vaccination. Embracing a sex-oriented perspective in research may improve the efficacy of the immune response and allow the design of tailored vaccine schedules.

Microbiota substances modulate dendritic cells activity: A critical view

Contemporary research in the field of microbiota shows that commensal bacteria influence physiological activity of different organs and systems of a human organism, such as brain, lungs, immune and metabolic systems. This influence is realized by various processes. One of them is trough modulation of immune mechanisms. Interactions between microbiota and the human immune system are known to be complex and ambiguous. Dendritic cells (DCs) are unique cells, which initiate the development and polarization of adaptive immune response. These cells also interconnect native and specific immune reactivity. A large set of biochemical signals from microbiota in the form of different microbiota associated molecular patterns (MAMPs) and bacterial metabolites that act locally and distantly in the human organism. As a result, commensal bacteria influence the maturity and activity of dendritic cells and affect the overall immune reactivity of the human organism. It then determines the response to pathogenic microorganisms, inflammation, associated with different pathological conditions and even affects the effectiveness of vaccination.

Comparison of mouse models of microbial experience reveals differences in microbial diversity and response to vaccination

Specific pathogen-free (SPF) laboratory mice dominate preclinical studies for immunology and vaccinology. Unfortunately, SPF mice often fail to accurately model human responses to vaccination and other immunological perturbations. Several groups have taken different approaches to introduce additional microbial experience to SPF mice to better model human immune experience. How these different models compare is unknown. Here, we directly compare three models: housing SPF mice in a microbe-rich barn-like environment (feralizing), adding wild-caught mice to the barn-like environment (fer-cohoused), or cohousing SPF mice with pet store mice in a barrier facility (pet-cohoused); the two latter representing different murine sources of microbial transmission. Pet-cohousing mice resulted in the greatest microbial exposure. Feralizing alone did not result in the transmission of any pathogens tested, while fer-cohousing resulted in the transmission of several picornaviruses. Murine astrovirus 2, the most common pathogen from pet store mice, was absent from the other two model systems. Previously, we had shown that pet-cohousing reduced the antibody response to vaccination compared with SPF mice. This was not recapitulated in either the feralized or fer-cohoused mice. These data indicate that not all dirty mouse models are equivalent in either microbial experience or immune responses to vaccination. These disparities suggest that more cross model comparisons are needed but also represent opportunities to uncover microbe combination-specific phenotypes and develop more refined experimental models. Given the breadth of microbes encountered by humans across the globe, multiple model systems may be needed to accurately recapitulate heterogenous human immune responses.IMPORTANCEAnimal models are an essential tool for evaluating clinical interventions. Unfortunately, they can often fail to accurately predict outcomes when translated into humans. This failure is due in part to a lack of natural infections experienced by most laboratory animals. To improve the mouse model, we and others have exposed laboratory mice to microbes they would experience in the wild. Although these models have been growing in popularity, these different models have not been specifically compared. Here, we directly compare how three different models of microbial experience impact the immune response to influenza vaccination. We find that these models are not the same and that the degree of microbial exposure affects the magnitude of the response to vaccination. These results provide an opportunity for the field to continue comparing and contrasting these systems to determine which models best recapitulate different aspects of the human condition.

The Predictive Value of Gut Microbiota Composition for Sustained Immunogenicity following Two Doses of CoronaVac

CoronaVac immunogenicity decreases with time, and we aimed to investigate whether gut microbiota associate with longer-term immunogenicity of CoronaVac. This was a prospective cohort study recruiting two-dose CoronaVac recipients from three centres in Hong Kong. We collected blood samples at baseline and day 180 after the first dose and used chemiluminescence immunoassay to test for neutralizing antibodies (NAbs) against the receptor-binding domain (RBD) of wild-type SARS-CoV-2 virus. We performed shotgun metagenomic sequencing performed on baseline stool samples. The primary outcome was the NAb seroconversion rate (seropositivity defined as NAb ≥ 15AU/mL) at day 180. Linear discriminant analysis [LDA] effect size analysis was used to identify putative bacterial species and metabolic pathways. A univariate logistic regression model was used to derive the odds ratio (OR) of seropositivity with bacterial species. Of 119 CoronaVac recipients (median age: 53.4 years [IQR: 47.8-61.3]; male: 39 [32.8%]), only 8 (6.7%) remained seropositive at 6 months after vaccination. Bacteroides uniformis (log10LDA score = 4.39) and Bacteroides eggerthii (log10LDA score = 3.89) were significantly enriched in seropositive than seronegative participants. Seropositivity was associated with B. eggerthii (OR: 5.73; 95% CI: 1.32-29.55; p = 0.022) and B. uniformis with borderline significance (OR: 3.27; 95% CI: 0.73-14.72; p = 0.110). Additionally, B. uniformis was positively correlated with most enriched metabolic pathways in seropositive vaccinees, including the superpathway of adenosine nucleotide de novo biosynthesis I (log10LDA score = 2.88) and II (log10LDA score = 2.91), as well as pathways related to vitamin B biosynthesis, all of which are known to promote immune functions. In conclusion, certain gut bacterial species (B. eggerthii and B. uniformis) and metabolic pathways were associated with longer-term CoronaVac immunogenicity.

Microbiome Dynamics: A Paradigm Shift in Combatting Infectious Diseases

Infectious diseases have long posed a significant threat to global health and require constant innovation in treatment approaches. However, recent groundbreaking research has shed light on a previously overlooked player in the pathogenesis of disease-the human microbiome. This review article addresses the intricate relationship between the microbiome and infectious diseases and unravels its role as a crucial mediator of host-pathogen interactions. We explore the remarkable potential of harnessing this dynamic ecosystem to develop innovative treatment strategies that could revolutionize the management of infectious diseases. By exploring the latest advances and emerging trends, this review aims to provide a new perspective on combating infectious diseases by targeting the microbiome.

Plasma and urine proteomics and gut microbiota analysis reveal potential factors affecting COVID-19 vaccination response

The efficacy of COVID-19 vaccination relies on the induction of neutralizing antibodies, which can vary among vaccine recipients. In this study, we investigated the potential factors affecting the neutralizing antibody response by combining plasma and urine proteomics and gut microbiota analysis. We found that activation of the LXR/FXR pathway in plasma was associated with the production of ACE2-RBD-inhibiting antibodies, while urine proteins related to complement system, acute phase response signaling, LXR/FXR, and STAT3 pathways were correlated with neutralizing antibody production. Moreover, we observed a correlation between the gut microbiota and plasma and urine proteins, as well as the vaccination response. Based on the above data, we built a predictive model for vaccination response (AUC = 0.85). Our study provides insights into characteristic plasma and urine proteins and gut microbiota associated with the ACE2-RBD-inhibiting antibodies, which could benefit our understanding of the host response to COVID-19 vaccination.

Machine-learning-based prediction of a diagnostic model using autophagy-related genes based on RNA sequencing for patients with papillary thyroid carcinoma

Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer and belongs to the category of malignant tumors of the thyroid gland. Autophagy plays an important role in PTC. The purpose of this study is to develop a novel diagnostic model using autophagy-related genes (ARGs) in patients. In this study, RNA sequencing data of PTC samples and normal samples were obtained from GSE33630 and GSE29265. Then, we analyzed GSE33630 datasets and identified 127 DE-ARGs. Functional enrichment analysis suggested that 127 DE-ARGs were mainly enriched in pathways in cancer, protein processing in endoplasmic reticulum, toll-like receptor pathway, MAPK pathway, apoptosis, neurotrophin signaling pathway, and regulation of autophagy. Subsequently, CALCOCO2, DAPK1, and RAC1 among the 127 DE-ARGs were identified as diagnostic genes by support vector machine recursive feature elimination and least absolute shrinkage and selection operator algorithms. Then, we developed a novel diagnostic model using CALCOCO2, DAPK1, and RAC1 and its diagnostic value was confirmed in GSE29265 and our cohorts. Importantly, CALCOCO2 may be a critical regulator involved in immune microenvironment because its expression was related to many types of immune cells. Overall, we developed a novel diagnostic model using CALCOCO2, DAPK1, and RAC1 which can be used as diagnostic markers of PTC.

Longitudinal profiling of the microbiome at four body sites reveals core stability and individualized dynamics during health and disease

To understand dynamic interplay between the human microbiome and host during health and disease, we analyzed the microbial composition, temporal dynamics, and associations with host multi-omics, immune and clinical markers of microbiomes from four body sites in 86 participants over six years. We found that microbiome stability and individuality are body-site-specific and heavily influenced by the host. The stool and oral microbiome were more stable than the skin and nasal microbiomes, possibly due to their interaction with the host and environment. Also, we identified individual-specific and commonly shared bacterial taxa, with individualized taxa showing greater stability. Interestingly, microbiome dynamics correlated across body sites, suggesting systemic coordination influenced by host-microbial-environment interactions. Notably, insulin-resistant individuals showed altered microbial stability and associations between microbiome, molecular markers, and clinical features, suggesting their disrupted interaction in metabolic disease. Our study offers comprehensive views of multi-site microbial dynamics and their relationship with host health and disease.

Study Highlights

The stability of the human microbiome varies among individuals and body sites.Highly individualized microbial genera are more stable over time.At each of the four body sites, systematic interactions between the environment, the host and bacteria can be detected.Individuals with insulin resistance have lower microbiome stability, a more diversified skin microbiome, and significantly altered host-microbiome interactions.

The uncharted territory of host-pathogen interaction in tuberculosis

Mycobacterium tuberculosis (M.tb) effectively manipulates the host processes to establish the deadly respiratory disease, Tuberculosis (TB). M.tb has developed key mechanisms to disrupt the host cell health to combat immune responses and replicate efficaciously. M.tb antigens such as ESAT-6, 19kDa lipoprotein, Hip1, and Hsp70 destroy the integrity of cell organelles (Mitochondria, Endoplasmic Reticulum, Nucleus, Phagosomes) or delay innate/adaptive cell responses. This is followed by the induction of cellular stress responses in the host. Such cells can either undergo various cell death processes such as apoptosis or necrosis, or mount effective immune responses to clear the invading pathogen. Further, to combat the infection progression, the host secretes extracellular vesicles such as exosomes to initiate immune signaling. The exosomes can contain M.tb as well as host cell-derived peptides that can act as a double-edged sword in the immune signaling event. The host-symbiont microbiota produces various metabolites that are beneficial for maintaining healthy tissue microenvironment. In juxtaposition to the above-mentioned mechanisms, M.tb dysregulates the gut and respiratory microbiome to support its replication and dissemination process. The above-mentioned interconnected host cellular processes of Immunometabolism, Cellular stress, Host Microbiome, and Extracellular vesicles are less explored in the realm of exploration of novel Host-directed therapies for TB. Therefore, this review highlights the intertwined host cellular processes to control M.tb survival and showcases the important factors that can be targeted for designing efficacious therapy.

Mechanisms and Clinical Implications of Human Gut Microbiota-Drug Interactions in the Precision Medicine Era

The human gut microbiota, comprising trillions of microorganisms residing in the gastrointestinal tract, has emerged as a pivotal player in modulating various aspects of human health and disease. Recent research has shed light on the intricate relationship between the gut microbiota and pharmaceuticals, uncovering profound implications for drug metabolism, efficacy, and safety. This review depicted the landscape of molecular mechanisms and clinical implications of dynamic human gut Microbiota-Drug Interactions (MDI), with an emphasis on the impact of MDI on drug responses and individual variations. This review also discussed the therapeutic potential of modulating the gut microbiota or harnessing its metabolic capabilities to optimize clinical treatments and advance personalized medicine, as well as the challenges and future directions in this emerging field.

Nutritional regulation of microbiota-derived metabolites: Implications for immunity and inflammation

Nutrition profoundly shapes immunity and inflammation across the lifespan of mammals, from pre- and post-natal periods to later life. Emerging insights into diet-microbiota interactions indicate that nutrition has a dominant influence on the composition-and metabolic output-of the intestinal microbiota, which in turn has major consequences for host immunity and inflammation. Here, we discuss recent findings that support the concept that dietary effects on microbiota-derived metabolites potently alter immune responses in health and disease. We discuss how specific dietary components and metabolites can be either pro-inflammatory or anti-inflammatory in a context- and tissue-dependent manner during infection, chronic inflammation, and cancer. Together, these studies emphasize the influence of diet-microbiota crosstalk on immune regulation that will have a significant impact on precision nutrition approaches and therapeutic interventions for managing inflammation, infection, and cancer immunotherapy.

Modeling human immune responses to vaccination in vitro

The human immune system is a complex network of coordinated components that are crucial for health and disease. Animal models, commonly used to study immunomodulatory agents, are limited by species-specific differences, low throughput, and ethical concerns. In contrast, in vitro modeling of human immune responses can enable species- and population-specific mechanistic studies and translational development within the same study participant. Translational accuracy of in vitro models is enhanced by accounting for genetic, epigenetic, and demographic features such as age, sex, and comorbidity. This review explores various human in vitro immune models, considers evidence that they may resemble human in vivo responses, and assesses their potential to accelerate and de-risk vaccine discovery and development.

Impact of the gut microbiome on immunological responses to COVID-19 vaccination in healthy controls and people living with HIV

Although mRNA SARS-CoV-2 vaccines are generally safe and effective, in certain immunocompromised individuals they can elicit poor immunogenic responses. Among these individuals, people living with HIV (PLWH) have poor immunogenicity to several oral and parenteral vaccines. As the gut microbiome is known to affect vaccine immunogenicity, we investigated whether baseline gut microbiota predicts immune responses to the BNT162b2 mRNA SARS-CoV-2 vaccine in healthy controls and PLWH after two doses of BNT162b2. Individuals with high spike IgG titers and high spike-specific CD4+ T-cell responses against SARS-CoV-2 showed low α-diversity in the gut. Here, we investigated and presented initial evidence that the gut microbial composition influences the response to BNT162b2 in PLWH. From our predictive models, Bifidobacterium and Faecalibacterium appeared to be microbial markers of individuals with higher spike IgG titers, while Cloacibacillus was associated with low spike IgG titers. We therefore propose that microbiome modulation could optimize immunogenicity of SARS-CoV-2 mRNA vaccines.

Oral tolerance to systemic vaccination remains intact without RORγt expression in regulatory T cells

Many promising vaccine candidates and licensed vaccines lead to variable immune responses within humans. Studies suggest that environmental exposures in the gastrointestinal tract could contribute to a reduction in vaccine efficacy via immune tolerance at this site; this is partly achieved by a high abundance of regulatory T cells (Tregs). It is unclear if Treg subsets regulate systemic vaccine responses following oral antigen pre-exposure. Here, we implemented a conditional knock-out mouse model of RORγt+ Tregs to examine the role of these cells in mediating this process. Following oral exposure to the model antigen ovalbumin (OVA) prior to immunization, we found similar induction of vaccine-induced antibody responses in mice lacking RORγt expression in Tregs compared to sufficient controls. Use of various adjuvants led to distinct findings. Our data suggest that expression of RORγt+ within Tregs is not required to regulate tolerance to systemic vaccination following oral antigen exposure.

Development and management of gastrointestinal symptoms in long-term COVID-19

Background

Emerging evidence reveals that SARS-CoV-2 possesses the capability to disrupt the gastrointestinal (GI) homeostasis, resulting in the long-term symptoms such as loss of appetite, diarrhea, gastroesophageal reflux, and nausea. In the current review, we summarized recent reports regarding the long-term effects of COVID-19 (long COVID) on the gastrointestine.

Objective

To provide a narrative review of abundant clinical evidence regarding the development and management of long-term GI symptoms in COVID-19 patients.

Results

Long-term persistent digestive symptoms are exhibited in a majority of long-COVID patients. SARS-CoV-2 infection of intestinal epithelial cells, cytokine storm, gut dysbiosis, therapeutic drugs, psychological factors and exacerbation of primary underlying diseases lead to long-term GI symptoms in COVID-19 patients. Interventions like probiotics, prebiotics, fecal microbiota transplantation, and antibiotics are proved to be beneficial in preserving intestinal microecological homeostasis and alleviating GI symptoms.

Conclusion

Timely diagnosis and treatment of GI symptoms in long-COVID patients hold great significance as they may contribute to the mitigation of severe conditions and ultimately lead to the improvement of outcomes of the patients.

Creation of a non-Western humanized gnotobiotic mouse model through the transplantation of rural African fecal microbiota

IMPORTANCE

There is increasing evidence that microbes residing within the intestines (gut microbiota) play important roles in the well-being of humans. Yet, there are considerable challenges in determining the specific role of gut microbiota in human diseases owing to the complexity of diverse internal and environmental factors that can contribute to diseases. Mice devoid of all microorganisms (germ-free mice) can be colonized with human stool samples to examine the specific contribution of the gut microbiota to a disease. These approaches have been primarily focused on stool samples obtained from individuals in Western countries. Thus, there is limited understanding as to whether the same methods used to colonize germ-free mice with stool from Western individuals would apply to the colonization of germ-free mice with stool from non-Western individuals. Here, we report the results from colonizing germ-free mice with stool samples of Malian children.

Sutterella and its metabolic pathways positively correlate with vaccine-elicited antibody responses in infant rhesus macaques

Introduction

It is becoming clearer that the microbiota helps drive responses to vaccines; however, little is known about the underlying mechanism. In this study, we aimed to identify microbial features that are associated with vaccine immunogenicity in infant rhesus macaques.

Methods

We analyzed 16S rRNA gene sequencing data of 215 fecal samples collected at multiple timepoints from 64 nursery-reared infant macaques that received various HIV vaccine regimens. PERMANOVA tests were performed to determine factors affecting composition of the gut microbiota throughout the first eight months of life in these monkeys. We used DESeq2 to identify differentially abundant bacterial taxa, PICRUSt2 to impute metagenomic information, and mass spectrophotometry to determine levels of fecal short-chain fatty acids and bile acids.

Results

Composition of the early-life gut microbial communities in nursery-reared rhesus macaques from the same animal care facility was driven by age, birth year, and vaccination status. We identified a Sutterella and a Rodentibacter species that positively correlated with vaccine-elicited antibody responses, with the Sutterella species exhibiting more robust findings. Analysis of Sutterella-related metagenomic data revealed five metabolic pathways that significantly correlated with improved antibody responses following HIV vaccination. Given these pathways have been associated with short-chain fatty acids and bile acids, we quantified the fecal concentration of these metabolites and found several that correlated with higher levels of HIV immunogen-elicited plasma IgG.

Discussion

Our findings highlight an intricate bidirectional relationship between the microbiota and vaccines, where multiple aspects of the vaccination regimen modulate the microbiota and specific microbial features facilitate vaccine responses. An improved understanding of this microbiota-vaccine interplay will help develop more effective vaccines, particularly those that are tailored for early life.

The effect of dosage on the protective efficacy of whole-sporozoite formulations for immunization against malaria

Immunization with Plasmodium sporozoites, either attenuated or administered under the cover of an antimalarial drug, can induce strong protection against malaria in pre-clinical murine models, as well as in human trials. Previous studies have suggested that whole-sporozoite (WSpz) formulations based on parasites with longer liver stage development induce higher protection, but a comparative analysis of four different WSpz formulations has not been reported. We employed a rodent model of malaria to analyze the effect of immunization dosage on the protective efficacy of WSpz formulations consisting of (i) early liver arresting genetically attenuated parasites (EA-GAP) or (ii) radiation-attenuated sporozoites (RAS), (iii) late arresting GAP (LA-GAP), and (iv) sporozoites administered under chemoprophylaxis, that are eliminated upon release into the bloodstream (CPS). Our results show that, unlike all other WSpz formulations, EA-GAP fails to confer complete protection against an infectious challenge at any immunization dosage employed, suggesting that a minimum threshold of liver development is required to elicit fully effective immune responses. Moreover, while immunization with RAS, LA-GAP and CPS WSpz yields comparable, dosage-dependent protection, protection by EA-GAP WSpz peaks at an intermediate dosage and markedly decreases thereafter. In-depth immunological analyses suggest that effector CD8+ T cells elicited by EA-GAP WSpz immunization have limited developmental plasticity, with a potential negative impact on the functional versatility of memory cells and, thus, on protective immunity. Our findings point towards dismissing EA-GAP from prioritization for WSpz malaria vaccination and enhance our understanding of the complexity of the protection elicited by these WSpz vaccine candidates, guiding their future optimization.

Cross-regulation of antibody responses against the SARS-CoV-2 Spike protein and commensal microbiota via molecular mimicry

The commensal microflora provides a repertoire of antigens that illicit mucosal antibodies. In some cases, these antibodies can cross-react with host proteins, inducing autoimmunity, or with other microbial antigens. We demonstrate that the oral microbiota can induce salivary anti-SARS-CoV-2 Spike IgG antibodies via molecular mimicry. Anti-Spike IgG antibodies in the saliva correlated with enhanced abundance of Streptococcus salivarius 1 month after anti-SARS-CoV-2 vaccination. Several human commensal bacteria, including S. salivarius, were recognized by SARS-CoV-2-neutralizing monoclonal antibodies and induced cross-reactive anti-Spike antibodies in mice, facilitating SARS-CoV-2 clearance. A specific S. salivarius protein, RSSL-01370, contains regions with homology to the Spike receptor-binding domain, and immunization of mice with RSSL-01370 elicited anti-Spike IgG antibodies in the serum. Additionally, oral S. salivarius supplementation enhanced salivary anti-Spike antibodies in vaccinated individuals. Altogether, these data show that distinct species of the human microbiota can express molecular mimics of SARS-CoV-2 Spike protein, potentially enhancing protective immunity.

Baseline immune states (BIS) associated with vaccine responsiveness and factors that shape the BIS

Vaccines are among the greatest inventions in medicine, leading to the elimination or control of numerous diseases, including smallpox, polio, measles, rubella, and, most recently, COVID-19. Yet, the effectiveness of vaccines varies among individuals. In fact, while some recipients mount a robust response to vaccination that protects them from the disease, others fail to respond. Multiple clinical and epidemiological factors contribute to this heterogeneity in responsiveness. Systems immunology studies fueled by advances in single-cell biology have been instrumental in uncovering pre-vaccination immune cell types and genomic features (i.e., the baseline immune state, BIS) that have been associated with vaccine responsiveness. Here, we review clinical factors that shape the BIS, and the characteristics of the BIS associated with responsiveness to frequently studied vaccines (i.e., influenza, COVID-19, bacterial pneumonia, malaria). Finally, we discuss potential strategies to enhance vaccine responsiveness in high-risk groups, focusing specifically on older adults.

Variability of vaccine responsiveness in early life

Vaccinations in early life elicit variable antibody and cellular immune responses, sometimes leaving fully vaccinated children unprotected against life-threatening infectious diseases. Specific immune cell populations and immune networks may have a critical period of development and calibration in a window of opportunity occurring during the first 100 days of early life. Among the early life determinants of vaccine responses, this review will focus on modifiable factors involving development of the infant microbiota and metabolome: antibiotic exposure, breast versus formula feeding, and Caesarian section versus vaginal delivery of newborns. How microbiota may serve as natural adjuvants for vaccine responses and how microbiota-derived metabolites influence vaccine responses are also reviewed. Early life poor vaccine responsiveness can be linked to increased infection susceptibility because both phenotypes share similar immunity dysregulation profiles. An early life pre-vaccination endotype, when interventions have the highest potential for success, should be sought that predicts vaccine response trajectories.

Vaccination with an HIV T-Cell Immunogen (HTI) Using DNA Primes Followed by a ChAdOx1-MVA Boost Is Immunogenic in Gut Microbiota-Depleted Mice despite Low IL-22 Serum Levels

Despite the important role of gut microbiota in the maturation of the immune system, little is known about its impact on the development of T-cell responses to vaccination. Here, we immunized C57BL/6 mice with a prime-boost regimen using DNA plasmid, the Chimpanzee Adenovirus, and the modified Vaccinia Ankara virus expressing a candidate HIV T-cell immunogen and compared the T-cell responses between individuals with an intact or antibiotic-depleted microbiota. Overall, the depletion of the gut microbiota did not result in significant differences in the magnitude or breadth of the immunogen-specific IFNγ T-cell response after vaccination. However, we observed marked changes in the serum levels of four cytokines after vaccinating microbiota-depleted animals, particularly a significant reduction in IL-22 levels. Interestingly, the level of IL-22 in serum correlated with the abundance of Roseburia in the large intestine of mice in the mock and vaccinated groups with intact microbiota. This short-chain fatty acid (SCFA)-producing bacterium was significantly reduced in the vaccinated, microbiota-depleted group. Therefore, our results indicate that, although microbiota depletion reduces serum levels of IL-22, the powerful vaccine regime used could have overcome the impact of microbiota depletion on IFNγ-producing T-cell responses.

Factors Influencing Microbiota in Modulating Vaccine Immune Response: A Long Way to Go

Vaccine immunogenicity still represents an unmet need in specific populations, such as people from developing countries and "edge populations". Both intrinsic and extrinsic factors, such as the environment, age, and dietary habits, influence cellular and humoral immune responses. The human microbiota represents a potential key to understanding how these factors impact the immune response to vaccination, with its modulation being a potential step to address vaccine immunogenicity. The aim of this narrative review is to explore the intricate interactions between the microbiota and the immune system in response to vaccines, highlighting the state of the art in gut microbiota modulation as a novel therapeutic approach to enhancing vaccine immunogenicity and laying the foundation for future, more solid data for its translation to the clinical practice.

Carbohydrates as putative pattern recognition receptor agonists in vaccine development

Adjuvants are essential components of modern vaccines. One general mechanism underlying their immunostimulatory functions is the activation of pattern recognition receptors (PRRs) of innate immune cells. Carbohydrates - as essential signaling molecules on microbial surfaces - are potent PRR agonists and candidate materials for adjuvant design. Here, we summarize the latest trends in developing carbohydrate-containing adjuvants, with fresh opinions on how the physicochemical characteristics of the glycans (e.g., molecular size, assembly status, monosaccharide components, and functional group patterns) affect their adjuvant activities in aiding antigen transport, regulating antigen processing, and enhancing adaptive immune responses. From a translational perspective, we also discuss potential technologies for solving long-lasting challenges in carbohydrate adjuvant design.

Mechanistic insights into the interaction between the host gut microbiome and malaria

Malaria is a devastating infectious disease and significant global health burden caused by the bite of a Plasmodium-infected female Anopheles mosquito. Gut microbiota was recently discovered as a risk factor of severe malaria. This review entails the recent advances on the impact of gut microbiota composition on malaria severity and consequence of malaria infection on gut microbiota in mammalian hosts. Additionally, this review provides mechanistic insight into interactions that might occur between gut microbiota and host immunity which in turn can modulate malaria severity. Finally, approaches to modulate gut microbiota composition are discussed. We anticipate this review will facilitate novel hypotheses to move the malaria-gut microbiome field forward.