Does the BCG vaccine protect infants from severe forms of childhood tuberculosis by trained innate and humoral immune mechanisms?

点击翻译按钮获取中文摘要

Tuberculosis (TB) is a significant global health burden, with 1.8 million TB-related deaths(0.2 million in children) in 2015, as reported by the WHO. Recent research suggested thatinfant immune responses may be suboptimal, predisposing them to TB and itscomplications. However, the current anti-TB vaccine, Mycobacterium bovis BCG, protectsthem from TB complications and may exert non-specific effects, reducing overall infantmortality from other, unrelated infections.The mechanisms mediating these properties are yet unknown; however, one candidate maybe a recently discovered monocyte immune memory (or training), regulated throughepigenetic and metabolic modifications. This phenomenon was shown to improve monocyteactivation and the inflammatory cytokine production in BCG vaccinated adult monocytes forup to 3 months post-vaccination in response to stimuli other than BCG. This mechanismmay contribute to infant protection from TB, possibly improving monocyte function and soenhancing T-cell (a major effector of anti-TB immunity) activation or proinflammatoryresponses.Anti-BCG antibodies may also contribute to protecting infants from severe TB forms. Recentresearch associated anti-mycobacterial antibodies with reduced infant TB risk, and theearlier studies suggested that such antibodies could improve BCG phagocytosis, control ofits growth and even T-cell responses. As the innate immune cells express receptors for thecrystallisable antibody domains, they may possibly act synergistically protecting infants fromTB complications.As neither BCG-trained innate immunity, nor the anti-mycobacterial antibody responseshave been extensively studied in infants, this study aims to fill the gap in the currentunderstanding on the role of these mechanisms in infant TB and BCG immunobiology,potentially contributing to novel TB vaccine design strategies. To do so, the study willcombine a mixture of immunology, cell and molecular biology, metabolic and quantitative 2approaches characterising the multi-layered effects of BCG humoral immunity and trainingin monocytes.First, infant monocyte surface activation marker and cytokine profiles will be determined byflow cytometry/Luminex/intracellular staining to associate monocyte surface and functionalphenotypes with their training status in infants prior to and post the BCG vaccination. Theepigenetic histone modification and DNA methylation analyses will then be applied todetermine which gene regulation changes correlate with monocyte phenotypes induced byBCG training upon vaccination. In addition, monocyte metabolic phenotypes prior to andpost the infant BCG vaccination will be determined. Computational analysis via R/Matlabwill be used to test the relationship between the surface, functional, epigenetic andmetabolic markers detected and BCG-induced monocyte training.This study will also test the anti-BCG antibody role in infant protection from TB. Pre- andpost-BCG vaccination infant blood sample anti-mycobacterial antibody titres will bemeasured by ELISA/Luminex. To test their functional contribution to anti-TB immunity,cellular infant phagocyte and sera assays from the pre- or post-vaccination samples will beused to characterise their activation marker and cytokine profiles. In addition, their ability toactivate anti-mycobacterial T-cells will be measured by flow cytometry and ELISA/Luminexassays. To study their clinical implications in anti-TB immunity, the pre- and post-BCGvaccination sera antimicrobial effect on mycobacterial growth will be tested. ComputationalR/Matlab analysis will be used to determine the correlation between serological markersand other immune compartment component activation.