Specific T cell frequency and cytokine expression profile do not correlate with protection against tuberculosis after bacillus Calmette-Guérin vaccination of newborns.

RATIONALE: Immunogenicity of new tuberculosis (TB) vaccines is commonly assessed by measuring the frequency and cytokine expression profile of T cells. OBJECTIVES: We tested whether this outcome correlates with protection against childhood TB disease after newborn vaccination with bacillus Calmette-Guérin (BCG). METHODS: Whole blood from 10-week-old infants, routinely vaccinated with BCG at birth, was incubated with BCG for 12 hours, followed by cryopreservation for intracellular cytokine analysis. Infants were followed for 2 years to identify those who developed culture-positive TB-these infants were regarded as not protected against TB. Infants who did not develop TB disease despite exposure to TB in the household, and another group of randomly selected infants who were never evaluated for TB, were also identified-these groups were regarded as protected against TB. Cells from these groups were thawed, and CD4, CD8, and γδ T cell-specific expression of IFN-γ, TNF-α, IL-2, and IL-17 measured by flow cytometry. MEASUREMENTS AND MAIN RESULTS: A total of 5,662 infants were enrolled; 29 unprotected and two groups of 55 protected infants were identified. There was no difference in frequencies of BCG-specific CD4, CD8, and γδ T cells between the three groups of infants. Although BCG induced complex patterns of intracellular cytokine expression, there were no differences between protected and unprotected infants. CONCLUSIONS: The frequency and cytokine profile of mycobacteria-specific T cells did not correlate with protection against TB. Critical components of immunity against Mycobacterium tuberculosis, such as CD4 T cell IFN-γ production, may not necessarily translate into immune correlates of protection against TB disease.

Risk of Disease After Isoniazid Preventive Therapy for Mycobacterium tuberculosis Exposure in Young HIV-uninfected Children.

BACKGROUND: The risk of developing tuberculosis (TB) disease in HIV-uninfected children after isoniazid preventive therapy (IPT) for a positive QuantiFERON-TB Gold In-Tube test (QFT-GIT) is unknown. The aim of this study was to evaluate risk of TB disease after IPT in young HIV-uninfected children with a positive QFT-GIT result, or household TB contact. METHODS: HIV-uninfected South African infants aged 4-6 months were screened for enrolment in a TB vaccine trial. Baseline household TB contact and positive QFT-GIT result were exclusion criteria, and these infants were referred for IPT. Outcome data are reported for 36 months after IPT referral. RESULTS: Four thousand seven hundred forty-nine infants were screened. Household TB contact was reported in 131 (2.8%) infants; 279 (6.0%) were QFT-GIT positive, and 138 of these 410 infants (34.0%) started IPT. Forty-four cases of TB disease (11.0%) were recorded within 991 child years of observation. TB disease incidence was 4.8 versus 3.6 per 100 child years in household exposed versus QFT-GIT-positive children [incidence rate ratio: 1.35; 95% confidence interval (CI): 0.67-2.88] and 2.4 versus 5.5 per 100 child years in children who received versus did not receive IPT, respectively (incidence rate ratio: 0.44; 95% CI: 0.17-0.96). Adjusted hazard ratio (Cox regression) for TB disease was 0.48 (95% CI: 0.21-1.05) for those who received IPT. CONCLUSION: In young HIV-uninfected children, the effect of IPT on risk of TB disease is similar, whether TB exposure was defined by household contact history or by positive QFT-GIT result. International IPT guidelines for HIV-uninfected children with a positive QFT-GIT result should be updated.

Neonatal mycobacterial specific cytotoxic T-lymphocyte and cytokine profiles in response to distinct BCG vaccination strategies.

This study evaluated whether different bacillus Calmette-Guérin (BCG) strains, routes of administration, vaccination age and percutaneous tools influenced immune responses to BCG vaccination in infants. Proliferative responses, cytokine production and cell-mediated cytotoxicity obtained in post-vaccinated children were compared to baseline cord bloods and unvaccinated 10-week-old infants. BCG vaccination generally induced strong lymphoproliferative and T helper type 1 (Th1)-type cytokine responses. There was a trend for greater responsiveness following the intradermal route of vaccination, with Japanese-172 strain and with delaying vaccination until 10 weeks. Cord mononuclear cells differentially stimulated the Th2-type cytokines interleukin-5 (IL-5) and IL-10 selectively in response to BCG, as compared to H37Rv or purified protein derivative stimulation. We document for the first time the generation of mycobacterium-specific cytotoxic T lymphocytes in neonates, following BCG vaccination. Cytotoxic activity correlated with the ratio of interferon-gamma to IL-5, aside from a single instance where use of the Biovac tool resulted in a striking dissociation selectively against H37Rv targets. These data have implications for correlates of protective immunity in design of vaccine studies.