Shifting the Immune Memory Paradigm: Trained Immunity in Viral Infections

Superior protective efficacy of genotype IVa-based single-cycle viral hemorrhagic septicemia virus (VHSV) vaccine compared to formalin-killed VHSV vaccine against VHSV genotype Ia in rainbow trout (Oncorhynchus mykiss)

Current viral vaccine strategies for aquaculture primarily target homologous viral infections through adaptive immune responses. However, the emergence of diverse genetic variants of viral hemorrhagic septicemia virus (VHSV) poses a significant challenge to aquaculture, necessitating vaccines capable of providing broad-spectrum cross-protection. This study aimed to compare the protective efficacy of a formalin-killed virus (FKC) vaccine and a single-cycle VHSV (rVHSV-ΔG) vaccine, both based on VHSV genotype IVa, against a heterologous VHSV genotype Ia challenge in rainbow trout (Oncorhynchus mykiss). Upon heterologous challenge with VHSV genotype Ia, the rVHSV-ΔG vaccine demonstrated superior protective efficacy relative to the FKC vaccine. Despite comparable levels of cross-reactive antibody titers and Type I interferon responses among the experimental groups, the rVHSV-ΔG group exhibited significantly elevated expression of pro-inflammatory cytokines (tnf-α, il-1β, and il-6) and the chemokine cxcl8 following challenge, suggesting an important role of innate immune mechanisms in mediating the enhanced protective effect. Notably, elevated levels of histone modifications (H3K4me3, H3K27ac) at the promoter regions of these cytokine genes suggest that rVHSV-ΔG may induce trained immunity. These results indicate that live VHSV vaccines may leverage innate immune memory to promote strong pro-inflammatory responses, representing a promising strategy for cross-protection against diverse VHSV variants.

Boosting effect of high-dose influenza vaccination on innate immunity among elderly

BACKGROUNDThe high-dose quadrivalent influenza vaccine (QIV-HD) showed superior efficacy against laboratory-confirmed illness compared with the standard-dose quadrivalent influenza vaccine (QIV-SD) in randomized controlled trials with the elderly. However, specific underlying mechanism remains unclear.METHODSThis phase IV randomized controlled trial compared early innate responses induced by QIV-HD and QIV-SD in 59 individuals aged > 65 years. Systemic innate cells and gene signatures at day 0 (D0) and D1 as well as hemagglutinin inhibition antibody (HIA) titers at D0 and D21 after vaccination were assessed.RESULTSQIV-HD elicited robust humoral response with significantly higher antibody titers and seroconversion rates than QIV-SD. At D1 after vaccination, QIV-HD recipients showed significant reduction in innate cells, including conventional DCs and NK cells, compared with QIV-SD, correlating with significantly increased HIA titers at D21. Blood transcriptomic analysis revealed greater amplitude of gene expression in the QIV-HD arm, encompassing genes related to innate immune response, IFNs, and antigen processing and presentation, and correlated with humoral responses. Interestingly, comparative analysis with a literature dataset from young adults vaccinated with influenza standard-dose vaccine highlighted strong similarities in gene expression patterns and biological pathways with the elderly vaccinated with QIV-HD.CONCLUSIONQIV-HD induces higher HIA titers than QIV-SD, a youthful boost of the innate gene expression significantly associated with high HIA titers.TRIAL REGISTRATIONEudraCT no. 2021-004573-32.

Infection-induced trained immunity: a twist in paradigm of innate host defense and generation of immunological memory

In contrast to adaptive immunity, which relies on memory T and B cells for long-term pathogen-specific responses, trained immunity involves the enhancement of innate immune responses through cellular reprogramming. Experimental evidence from animal models and human studies supports the concept of trained immunity and its potential therapeutic applications in the development of personalized medicine. However, there remains a huge gap in understanding the mechanisms, identifying specific microbial triggers responsible for the induction of trained immunity. This underscores the importance of investigating the potential role of trained immunity in redefining host defense and highlights future research directions. This minireview will provide a comprehensive summary of the new paradigm of trained immunity or innate memory pathways. It will shed light on infection-induced pathways through non-specific stimulation within macrophages and natural killer cells, which will be further elaborated in multiple disease perspectives caused by infectious agents such as bacteria, fungi, and viruses. The article further elaborates on the biochemical and cellular basis of trained immunity and its impact on disease status during recurrent exposures. The review concludes with a perspective segment discussing potential therapeutic benefits, limitations, and future challenges in this area of study. The review also sheds light upon potential risks involved in the induction of trained immunity.

Role of Trained Immunity in Heath and Disease

PURPOSE OF REVIEW

This review aims to explore the role of immune memory and trained immunity, focusing on how innate immune cells like monocytes, macrophages, and natural killer cells undergo long-term epigenetic and metabolic rewiring. Specifically, it examines the mechanisms by which trained immunity, often triggered by infection or vaccination, could impact cardiac processes and contribute to both protective and pathological responses within the cardiovascular system.

RECENT FINDINGS

Recent research demonstrates that vaccination and infection not only activate immune responses in circulating monocytes and tissue macrophages but also affect immune progenitor cells within the bone marrow environment, conferring lasting protection against heterologous infections. These protective effects are attributed to epigenetic and metabolic reprogramming, which enable a heightened immune response upon subsequent encounters with pathogens. However, while trained immunity is beneficial in combating infections, it has been linked to exacerbated inflammation, which may increase susceptibility to cardiovascular diseases, including atherosclerosis and heart failure. Our review highlights the dual nature of trained immunity: while it offers protective advantages against infections, it also poses potential risks for cardiovascular health by promoting chronic inflammation. Understanding the molecular mechanisms underlying immune memory's impact on cardiac processes could lead to new therapeutic strategies to mitigate cardiovascular diseases, such as atherosclerosis, heart failure, and diabetes. These insights build the grounds for future research to balance the benefits of trained immunity with its potential risks in cardiovascular disease management.

Spatially resolved single-cell atlas unveils a distinct cellular signature of fatal lung COVID-19 in a Malawian population

Postmortem single-cell studies have transformed understanding of lower respiratory tract diseases (LRTDs), including coronavirus disease 2019 (COVID-19), but there are minimal data from African settings where HIV, malaria and other environmental exposures may affect disease pathobiology and treatment targets. In this study, we used histology and high-dimensional imaging to characterize fatal lung disease in Malawian adults with (n = 9) and without (n = 7) COVID-19, and we generated single-cell transcriptomics data from lung, blood and nasal cells. Data integration with other cohorts showed a conserved COVID-19 histopathological signature, driven by contrasting immune and inflammatory mechanisms: in US, European and Asian cohorts, by type I/III interferon (IFN) responses, particularly in blood-derived monocytes, and in the Malawian cohort, by response to IFN-γ in lung-resident macrophages. HIV status had minimal impact on histology or immunopathology. Our study provides a data resource and highlights the importance of studying the cellular mechanisms of disease in underrepresented populations, indicating shared and distinct targets for treatment.

Integrating genetic and immune factors to uncover pathogenetic mechanisms of viral-associated pulmonary aspergillosis

Invasive pulmonary aspergillosis is a severe fungal infection primarily affecting immunocompromised patients. Individuals with severe viral infections have recently been identified as vulnerable to developing invasive fungal infections. Both influenza-associated pulmonary aspergillosis (IAPA) and COVID-19-associated pulmonary aspergillosis (CAPA) are linked to high mortality rates, emphasizing the urgent need for an improved understanding of disease pathogenesis to unveil new molecular targets with diagnostic and therapeutic potential. The recent establishment of animal models replicating the co-infection context has offered crucial insights into the mechanisms that underlie susceptibility to disease. However, the development and progression of human viral-fungal co-infections exhibit a significant degree of interindividual variability, even among patients with similar clinical conditions. This observation implies a significant role for host genetics, but information regarding the genetic basis for viral-fungal co-infections is currently limited. In this review, we discuss how genetic factors known to affect either antiviral or antifungal immunity could potentially reveal pathogenetic mechanisms that predispose to IAPA or CAPA and influence the overall disease course. These insights are anticipated to foster further research in both pre-clinical models and human patients, aiming to elucidate the complex pathophysiology of viral-associated pulmonary aspergillosis and contributing to the identification of new diagnostic and therapeutic targets to improve the management of these co-infections.

The potency of hematopoietic stem cell reprogramming for changing immune tone

Innate immune memory endows innate immune cells with antigen independent heightened responsiveness to subsequent challenges. The durability of this response can be mediated by inflammation induced epigenetic and metabolic reprogramming in hematopoietic stem and progenitor cells (HSPCs) that are maintained through differentiation to mature immune progeny. Understanding the mechanisms and extent of trained immunity induction by pathogens and vaccines, such as BCG, in HSPC remains a critical area of exploration with important implications for health and disease. Here we review these concepts and present new analysis to highlight how inflammatory reprogramming of HSPC can potently alter immune tone, including to enhance specific anti-tumor responses. New findings in the field pave the way for novel HSPC targeting therapeutic strategies in cancer and other contexts of immune modulation. Future studies are expected to unravel diverse and extensive effects of infections, vaccines, microbiota, and sterile inflammation on hematopoietic progenitor cells and begin to illuminate the broad spectrum of immunologic tuning that can be established through altering HSPC phenotypes. The purpose of this review is to draw attention to emerging and speculative topics in this field where we posit that focused study of HSPC in the framework of trained immunity holds significant promise.

(Henri)11van de WijgertJanneke H.H.119)Noordwest Ziekenhuis, Alkmaar, the Netherlands10)Catharina Ziekenhuis, Eindhoven, the Netherlands11)University Medical Center Utrecht, Utrecht, the Netherlands12)OLVG, Amsterdam, the Netherlands13)Radboud University Medical Center, Nijmegen, the Netherlands14)Medisch Spectrum Twente, Enschede, the Netherlands15)Canisius-Wilhelmina Hospital, Nijmegen16)Amsterdam UMC, Amsterdam, the Netherlands17)Leiden University Medical Center, Leiden, the Netherlands18)Rijnstate Hospital, Arnhem, the Netherlands19)Erasmus Medical Center, Rotterdam, the Netherlands20)Meander Medisch Centrum, Amersfoort, the Netherlands21)University Medical Center Amsterdam, Amsterdam, the Netherlands22)Santeon Bureau of Research & Innovation, Utrecht, the Netherlands23)Martini Hospital, Groningen, the Netherlands24)Ikazia Hospital, Rotterdam, the Netherlands25)University Medical Center Groningen, Groningen, the Netherlands26)University Medical Center Maastricht, Maastricht, the Netherlands27)St. Antonius Hospital, Nieuwegein, the Netherlands28)Haga Teaching Hospital, The Hague, the Netherlands29)Anticoagulation Clinic Leiden, Leiden, the Netherlands30)Bernhoven Hospital, Uden, the Netherlands31)Maasstad Hospital, Rotterdam, the Netherlands, Werkhoven C(HV, BCG-PRIME study group. Bacillus Calmette-Guérin vaccine for prevention of COVID-19 and other respiratory tract infections in older adults with comorbidities: a randomized controlled trial

OBJECTIVES

To test whether Bacillus Calmette-Guérin (BCG) vaccination would reduce the incidence of COVID-19 and other respiratory tract infections (RTIs) in older adults with one or more comorbidities.

METHODS

Community-dwelling adults aged 60 years or older with one or more underlying comorbidities and no contraindications to BCG vaccination were randomized 1:1 to BCG or placebo vaccination and followed for 6 months. The primary endpoint was a self-reported, test-confirmed COVID-19 incidence. Secondary endpoints included COVID-19 hospital admissions and clinically relevant RTIs (i.e. RTIs including but not limited to COVID-19 requiring medical intervention). COVID-19 and clinically relevant RTI episodes were adjudicated. Incidences were compared using Fine-Gray regression, accounting for competing events.

RESULTS

A total of 6112 participants with a median age of 69 years (interquartile range, 65-74) and median of 2 (interquartile range, 1-3) comorbidities were randomized to BCG (n = 3058) or placebo (n = 3054) vaccination. COVID-19 infections were reported by 129 BCG recipients compared to 115 placebo recipients [hazard ratio (HR), 1.12; 95% CI, 0.87-1.44]. COVID-19-related hospitalization occurred in 18 BCG and 21 placebo recipients (HR, 0.86; 95% CI, 0.46-1.61). During the study period, 13 BCG recipients died compared with 18 placebo recipients (HR, 0.71; 95% CI, 0.35-1.43), of which 11 deaths (35%) were COVID-19-related: six in the placebo group and five in the BCG group. Clinically relevant RTI was reported by 66 BCG and 72 placebo recipients (HR, 0.92; 95% CI, 0.66-1.28).

DISCUSSION

BCG vaccination does not protect older adults with comorbidities against COVID-19, COVID-19 hospitalization, or clinically relevant RTIs.

The impact of circadian rhythm on Bacillus Calmette-Guérin vaccination effects on SARS-CoV-2 infections

Background and objective

A recent study has suggested that circadian rhythm has an important impact on the immunological effects induced by Bacillus Calmette-Guérin (BCG) vaccination. The objective of this study was to evaluate whether the timing of BCG vaccination (morning or afternoon) affects its impact on severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infections and clinically relevant respiratory tract infections (RTIs).

Methods

This is a post-hoc analysis of the BCG-CORONA-ELDERLY (NCT04417335) multicenter, placebo-controlled trial, in which participants aged 60 years and older were randomly assigned to vaccination with BCG or placebo, and followed for 12 months. The primary endpoint was the cumulative incidence of SARS-CoV-2 infection. To assess the impact of circadian rhythm on the BCG effects, participants were divided into four groups: vaccinated with either BCG or placebo in the morning (between 9:00h and 11:30h) or in the afternoon (between 14:30h and 18:00h).

Results

The subdistribution hazard ratio of SARS-CoV-2 infection in the first six months after vaccination was 2.394 (95% confidence interval [CI], 0.856-6.696) for the morning BCG group and 0.284 (95% CI, 0.055-1.480) for the afternoon BCG group. When comparing those two groups, the interaction hazard ratio was 8.966 (95% CI, 1.366-58.836). In the period from six months until 12 months after vaccination cumulative incidences of SARS-CoV-2 infection were comparable, as well as cumulative incidences of clinically relevant RTI in both periods.

Conclusion

Vaccination with BCG in the afternoon offered better protection against SARS-CoV-2 infections than BCG vaccination in the morning in the first six months after vaccination.

Do bacterial vaccines/adjuvants prevent wheezing episodes in children?

PURPOSE OF REVIEW

To discuss recently discovered mechanisms of action of some bacterial vaccines that may account for their clinical benefit in the prevention of recurrent wheezing and asthma exacerbations in infants and early childhood.

RECENT FINDINGS

Trained immunity has been shown to confer innate immune cells with a quite long-term nonspecific protection against a broad spectrum of pathogens. Inducers of trained immunity include some bacterial vaccines. Trained immunity-based vaccines (TIbV) of bacterial origin have the capability to induce nonspecific responses to a variety of pathogens, including respiratory viruses, in addition to their nominal bacterial antigens. Clinical data, from epidemiological surveys to well designed randomized clinical trials, indicate that TIbV formulated with bacteria prevent respiratory tract infections of viral cause, such as those associated with recurrent wheezing or asthma exacerbation, in children. Administration of these vaccines by the mucosal route may be important for their outcome in respiratory infections.

SUMMARY

Mucosal bacterial immunotherapy, including certain TIbV, confer protection against a broad spectrum of pathogens, such as viruses, through a mechanism mediated by trained immunity. Clinical studies on the use of these preparations against recurrent wheezing reflect these mechanistic effects. These findings open a new avenue for the development of new strategies for this condition.