Influence of advanced age on Mycobacterium bovis BCG vaccination in guinea pigs aerogenically infected with Mycobacterium tuberculosis

Tuberculosis in an Aging World

Tuberculosis (TB) is one of the leading causes of death due to its being an infectious disease, caused by the airborne pathogen Mycobacterium tuberculosis (M.tb). Approximately one-fourth of the world’s population is infected with latent M.tb, and TB is considered a global threat killing over 4000 people every day. The risk of TB susceptibility and mortality is significantly increased in individuals aged 65 and older, confirming that the elderly represent one of the largest reservoirs for M.tb infection. The elderly population faces many challenges that increase their risk of developing respiratory diseases, including TB. The challenges the elderly face in this regard include the following: decreased lung function, immuno-senescence, inflammaging, adverse drug effects, low tolerance to anti-TB drugs, lack of suitable diagnoses/interventions, and age-associated comorbidities. In order to find new therapeutic strategies to maintain lung homeostasis and resistance to respiratory infections as we age, it is necessary to understand the molecular and cellular mechanisms behind natural lung aging. This review focuses primarily on why the elderly are more susceptible to TB disease and death, with a focus on pulmonary function and comorbidities.

A prospective cross-sectional study of tuberculosis in elderly Hispanics reveals that BCG vaccination at birth is protective whereas diabetes is not a risk factor

BACKGROUND

Aging increases the risk of tuberculosis (TB) and its adverse outcomes, but most studies are based on secondary analyses, and few are in Hispanics. Diabetes is a risk factor for TB in adults, but its contribution in the elderly is unknown. We aimed to identify the role of diabetes and other risk factors for TB in elderly Hispanics.

METHODS

Cross-sectional study among newly-diagnosed TB patients, recent contacts (ReC), or community controls (CoC) totaling 646 participants, including 183 elderly (>60 years; 43 TB, 80 ReC, 60 CoC) and 463 adults (18 to 50 years; 80 TB, 301 ReC and 82 CoC). Host characteristics associated with TB and latent Mycobacterium tuberculosis infection (LTBI) were identified in the elderly by univariable and confirmed by multivariable logistic regression.

RESULTS

LTBI was more prevalent among the elderly CoC (55% vs. 23.2% in adults; p<0.001), but not in ReC (elderly 71.3% vs. adult 63.8%); p = 0.213). Risk factors for TB in the elderly included male sex (adj-OR 4.33, 95% CI 1.76, 10.65), smoking (adj-OR 2.55, 95% CI 1.01, 6.45) and low BMI (adj-OR 12.34, 95% CI 4.44, 34.33). Unexpectedly, type 2 diabetes was not associated with TB despite its high prevalence (adj-OR 0.38, 95% CI 0.06, 2.38), and BCG vaccination at birth was protective (adj-OR 0.16, 95% CI 0.06, 0.45).

CONCLUSIONS

We report novel distinctions in TB risk factors in the elderly vs. adults, notably in diabetes and BCG vaccination at birth. Further studies are warranted to address disparities in this vulnerable, understudied population.

BCG as a game-changer to prevent the infection and severity of COVID-19 pandemic?

The impact of COVID-19 is changing with country wise and depend on universal immunization policies. COVID-19 badly affects countries that did not have universal immunization policies or having them only for the selective population of countries (highly prominent population) like Italy, USA, UK, Netherland, etc. Universal immunization of BCG can provide great protection against the COVID-19 infection because the BCG vaccine gives broad protection against respiratory infections. BCG vaccine induces expressions of the gene that are involved in the antiviral innate immune response against viral infections with long-term maintenance of BCG vaccine-induced cellular immunity. COVID-19 cases are reported very much less in the countries with universal BCG vaccination policies such as India, Afghanistan, Nepal, Bhutan, Bangladesh, Israel, Japan, etc. as compared to without BCG implemented countries such as the USA, Italy, Spain, Canada, UK, etc. BCG vaccine provides protection for 50–60 years of immunization, so the elderly population needs to be revaccinated with BCG. Several countries started clinical trials of the BCG vaccine for health care workers and elderly people. BCG can be uses as a prophylactic treatment until the availability of the COVID-19 vaccine.

Attrition of T-cell functions and simultaneous upregulation of inhibitory markers correspond with the waning of BCG-induced protection against tuberculosis in mice

Mycobacterium bovis bacille Calmette-Guérin (BCG) is the most widely used live attenuated vaccine. However, the correlates of protection and waning of its immunity against tuberculosis is poorly understood. In this study, we correlated the longitudinal changes in the magnitude and functional quality of CD4⁺ and CD8⁺ T-cell response over a period of two years after mucosal or parenteral BCG vaccination with the strength of protection against Mycobacterium tuberculosis in mice. The BCG vaccination-induced CD4⁺ and CD8⁺ T cells exhibited comparable response kinetics but distinct functional attributes in-terms of IFN-γ, IL-2 and TNF-α co-production and CD62L memory marker expression. Despite a near life-long BCG persistence and the induction of enduring CD4⁺ T-cell responses characterized by IFN-γ and/or TNF-α production with comparable protection, the protective efficacy waned regardless of the route of vaccination. The progressive decline in the multifactorial functional abilities of CD4⁺ and CD8⁺ T cells in-terms of type-1 cytokine production, proliferation and cytolytic potential corresponded with the waning of protection against M. tuberculosis infection. In addition, simultaneous increase in the dysfunctional and terminally-differentiated T cells expressing CTLA-4, KLRG-1 and IL-10 during the contraction phase of BCG-induced response coincided with the loss of protection. Our results question the empirical development of BCG-booster vaccines and emphasize the pursuit of strategies that maintain superior T-cell functional capacity. Furthermore, our results underscore the importance of understanding the comprehensive functional dynamics of antigen-specific T-cell responses in addition to cytokine polyfunctionality in BCG-vaccinated hosts while optimizing novel vaccination strategies against tuberculosis.

Method for assessing IFN-γ responses in guinea pigs during TB vaccine trials

AIMS

We sought to develop a new method that enables the assessment of the immune response of guinea pigs during TB vaccine evaluation studies, without the need to cull or anaesthetize animals.

METHOD AND RESULTS

Guinea pigs were vaccinated with five different formulations of oral BCG. One week prior to challenge with Mycobacterium bovis, blood (50-200 μl) was taken from the ears of vaccinated subjects. Host RNA was isolated and amplified following antigenic restimulation of PBMCs for 24 h with 30 μg of bovine PPD. The up- or down-regulation of γ-interferon (IFN-γ), a key cytokine involved in protection against tuberculosis, was assessed using real-time PCR. The relative expression of prechallenge IFN-γ mRNA in the vaccinated groups (n=5) correlated (P<0·001) with protection against M. bovis challenge.

CONCLUSION

We have demonstrated that it is possible to take blood samples and track IFN-γ responses in guinea pigs that then go on to be exposed to M. bovis, thus providing prechallenge vaccine uptake information.

SIGNIFICANCE AND IMPACT OF THE STUDY

This methodology will also be applicable for tracking the immune responses of vaccinated guinea pigs over time that then go on to be challenged with M. tuberculosis during human TB vaccine evaluation studies.