Minimal Sex-Differential Modulation of Reactivity to Pathogens and Toll-Like Receptor Ligands following Infant Bacillus Calmette-Guérin Russia Vaccination

Genetic and hormonal mechanisms underlying sex-specific immune responses in tuberculosis

Tuberculosis (TB), the world's deadliest bacterial infection, afflicts more human males than females, with a male/female (M/F) ratio of 1.7. Sex disparities in TB prevalence, pathophysiology, and clinical manifestations are widely reported, but the underlying biological mechanisms remain largely undefined. This review assesses epidemiological data on sex disparity in TB, as well as possible underlying hormonal and genetic mechanisms that might differentially modulate innate and adaptive immune responses in males and females, leading to sex differences in disease susceptibility. We consider whether this sex disparity can be extended to the efficacy of vaccines and discuss novel animal models which may offer mechanistic insights. A better understanding of the biological factors underpinning sex-related immune responses in TB may enable sex-specific personalized therapies for TB.

Can what have we learnt about BCG vaccination in the last 20 years help us to design a better tuberculosis vaccine?

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The BCG vaccine provides variable protection against tuberculosis.

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Correlates of protection remain elusive, but IFNγ can measure immunogenicity.

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BCG vaccination induces innate immune training as well as antigen-specific immunity.

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Many factors may contribute to the variable responses to BCG vaccination.

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Prior BCG vaccination or factors modulating its efficacy may affect new TB vaccines.

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Innate training may also provide non-specific protection against infectious diseases.

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New TB vaccines should not lose BCG's beneficial non-specific effects.

The BCG vaccine will, in 2021, have been in use for 100 years. Much remains to be understood, including the reasons for its variable efficacy against pulmonary tuberculosis in adults. This review will discuss what has been learnt about the BCG vaccine in the last two decades, and whether this new information can be exploited to improve its efficacy, by enhancing its ability to induce either antigen-specific and/or non-specific effects. Many factors affect both the immunogenicity of BCG and its protective efficacy, highlighting the challenges of working with a live vaccine in man, but new insights may enable us to exploit better what BCG can do.

Gene expression pattern analysis using dual-color RT-MLPA and integrative genome-wide association studies of eQTL for tuberculosis suscepitibility

Background

When infected with Mycobacterium tuberculosis, only a small proportion of the population will develop active TB, and the role of host genetic factors in different TB infection status was not fully understood.

Methods

Forty-three patients with active tuberculosis and 49 with latent tuberculosis were enrolled in the prospective cohort. Expressing levels of 27 candidate mRNAs, which were previously demonstrated to differentially expressed in latent and active TB, were measured by dual color reverse transcription multiplex ligation dependent probe amplification assay (dcRT-MLPA). Using expression levels of these mRNAs as quantitative traits, associations between expression abundance and genome-wild single nucleotide polymorphisms (SNPs) were calculated. Finally, identified candidate SNPs were further assessed for their associations with TB infection status in a validation cohort with 313 Chinese Han cases.

Results

We identified 9 differentially expressed mRNAs including il7r, il4, il8, tnfrsf1b, pgm5, ccl19, il2ra, marco and fpr1 in the prospective cohort. Through expression quantitative trait loci mapping, we screened out 8 SNPs associated with these mRNAs. Then, CG genotype of the SNP rs62292160 was finally verified to be significantly associated with higher transcription levels of IL4 in LTBI than in TB patients.

Conclusion

We reported that the SNP rs62292160 in Chinese Han population may link to higher expression of il4 in latent tuberculosis. Our findings provided a new genetic variation locus for further exploration of the mechanisms of TB and a possible target for TB genetic susceptibility studies, which might aid the clinical decision to precision treatment of TB.

The impact of vaccines on heterologous adaptive immunity

BACKGROUND

Vaccines induce antigen-specific memory in adaptive immune cells that enables long-lived protection against the target pathogen. In addition to this, several vaccines have beneficial effects greater than protection against their target pathogen. These non-specific effects are proposed to be the result of vaccine-induced immunomodulation. In the case of bacille Calmette-Guérin (BCG) vaccine, this involves induction of innate immune memory, termed 'trained immunity', in monocytes and natural killer cells.

OBJECTIVES

This review discusses current evidence for vaccine-induced immunomodulation of adaptive immune cells and heterologous adaptive immune responses.

CONTENT

The three vaccines that have been associated with changes in all-cause infant mortality: BCG, diphtheria-tetanus-pertussis (DTP) and measles-containing vaccines (MCV) alter T-cell and B-cell immunity. The majority of studies that investigated non-specific effects of these vaccines on the adaptive immune system report changes in numbers or proportions of adaptive immune cell populations. However, there is also evidence for effects of these vaccines on adaptive immune cell function and responses to heterologous stimuli. There is some evidence that, in addition to BCG, DTP and MCV, other vaccines (that have not been associated with changes in all-cause mortality) may alter adaptive immune responses to unrelated stimuli.

IMPLICATIONS

This review concludes that vaccines alter adaptive immune cell populations and heterologous immune responses. The non-specific effects differ between various vaccines and their effects on heterologous adaptive immune responses may also involve bystander activation, cross-reactivity and other as yet undefined mechanisms. This has major implications for future vaccine design and vaccination scheduling.

Heterologous effects of infant BCG vaccination: potential mechanisms of immunity

The current antituberculosis vaccine, BCG, was derived in the 1920s, yet the mechanisms of BCG-induced protective immunity and the variability of protective efficacy among populations are still not fully understood. BCG challenges the concept of vaccine specificity, as there is evidence that BCG may protect immunized infants from pathogens other than Mycobacterium tuberculosis – resulting in heterologous or nonspecific protection. This review summarizes the up-to-date evidence for this phenomenon, potential immunological mechanisms and implications for improved childhood vaccine design. BCG induces functional changes in infant innate and adaptive immune compartments, encouraging their collaboration in the first year of life. Understanding biological mechanisms beyond heterologous BCG effects is crucial to improve infant protection from infectious diseases.

Non-specific effects of vaccines: Current evidence and potential implications

Besides protection against specific microorganisms, vaccines can induce heterologous or non-specific effects (NSE). Epidemiological data suggest that vaccination with live-attenuated vaccines such as Bacillus Calmette-Guérin (BCG), measles vaccine, and oral polio vaccine results in increased overall childhood survival, and several of these observations have been confirmed in randomized trials. Immunological mechanisms mediating NSE include heterologous lymphocyte effects and induction of innate immune memory (trained immunity). Trained immunity induces long-term functional upregulation of innate immune cells through epigenetic and metabolic reprogramming. An overview of the epidemiological evidence of non-specific effects of vaccines and the latest insights regarding the biological mechanisms behind this phenomenon is presented, and future research priorities and potential implications are discussed.

Effect of sex on vaccination outcomes: important but frequently overlooked

It is well established that vaccination does not affect males and females equally. For example, females generally mount greater antibody responses to vaccination than males, but also suffer more adverse events following vaccination, probably as a result of more robust immunity. Despite this, most researchers in the field of vaccinology do not take biological sex into account when conducting their studies. This omission is likely to lead to a loss of important information in terms of both reactogenicity and immunogenicity following vaccination as well as those suffering adverse events. It also suggests that the vaccine dose in males and females may need to be different in order to achieve the same outcome of protective immunity while minimising reactogenicity.