Modulation of Mycobacterial-Specific Th1 and Th17 Cells in Latent Tuberculosis by Coincident Hookworm Infection

Hookworm infections and tuberculosis are co-endemic in many parts of the world. It has been suggested that infection with helminth parasites could suppress the predominant Th1 (IFN-γ-mediated) response needed to control Mycobacterium tuberculosis (Mtb) infection and enhance susceptibility to infection and/or disease. To determine the role of coincident hookworm infection on responses at steady state and on Mtb – specific immune responses in latent tuberculosis (TB), we examined the cellular responses in individuals with latent TB with or without concomitant hookworm infection. By analyzing the expression of Th1, Th2 and Th17 subsets of CD4(+) T cells, we were able to demonstrate that the presence of coincident hookworm infection significantly diminished both spontaneously expressed and Mtb – specific mono – and dual – functional Th1 and Th17 cells. Hookworm infection, in contrast, was associated with expanded frequencies of mono – and dual – functional Th2 cells at both steady state and upon antigen – stimulation. This differential induction of CD4(+) T cell subsets was abrogated upon mitogen stimulation. In addition, coincident hookworm infection was associated with increased adaptive T regulatory (aTreg) cells but not natural regulatory T cells (nTregs) in latent TB. Finally, the CD4(+) T cell cytokine expression pattern was also associated with alterations in the systemic levels of Th1 and Th2 cytokines. Thus, coincident hookworm infection exerts a profound inhibitory effect on protective Th1 and Th17 responses in latent tuberculosis and may predispose toward the development of active tuberculosis in humans

Revisiting the Chingleput BCG vaccination trial for the impact of BCG revaccination on the incidence of tuberculosis disease

Background & objectives: Vaccines play a crucial role in the prevention of tuberculosis (TB). Revaccination with Bacille Calmette–Guerin (BCG) for the prevention of TB is an important strategy that is currently gaining interest. The objective of this study was to reanalyze the community-based Chingleput BCG vaccination trial for protective efficacy of BCG revaccination against incident TB disease. Methods: A retrospective analysis of the Chingleput BCG vaccination trial (conducted in 1968) data was carried out. Data on participants with evidence of prior BCG vaccination at trial intake and randomized to BCG vaccine [low dose (0.01 mg), high dose (0.1 mg)] and placebo arms were analyzed. The incidence of TB disease, which was based on sputum culture and/or chest X-ray was compared between the BCG and placebo arms over a 15 yr follow up period. Results: Of the 269,727 individuals randomized in the trial; 263,158 had no evidence of TB at baseline, of which 4436 (1.68%) had evidence of BCG vaccination at trial intake (2890 in the BCG vaccine and 1546 in the placebo arms, respectively). There were 77 (190 per 100,000) and 64 (296 per 100,000) incident TB cases in the BCG and placebo arm, respectively, at 15 yr post-vaccination. The incidence of TB disease was significantly lower in the BCG arm [Hazard ratio of BCG arm (95% confidence interval): 0.64 (0.46-0.89)]. Interpretation & conclusions: Retrospective data analysis of this community-based trial revealed that BCG revaccination in a community offered modest protection against the development of TB disease at the end of 15 years which, however, requires further evaluation