Serial T-SPOT.TB responses in Tanzanian adolescents: Transient, persistent and irregular conversions.

BACKGROUND: Prospective studies of interferon-gamma release assays (IGRA) on healthy subjects in tuberculosis-endemic regions have not examined the long-term variability of serial assays. This issue is relevant to the interpretation of tuberculosis (TB) vaccine trials based on prevention of infection. METHODS: T-SPOT.TB assays were performed manually on healthy adolescents during a tuberculosis vaccine trial in Tanzania at 5 intervals over 3 years. Assay results were defined as negative, positive, borderline or invalid. Subsequently, microtiter plates were analyzed by an automated reader to obtain quantitative counts of spot forming cells (SFCs) for the present analysis. RESULTS: 3387 T-SPOT.TB samples were analyzed from 928 adolescents; manual and automated assay results were 97% concordant. Based on the quantitative results 143 (15%) participants were prevalent IGRA-positives at baseline, were ineligible for further study. Among the remaining IGRA-negative participants, the annual rate of IGRA conversion was 2·9%. Among 43 IGRA converters with repeat assays 12 (28%) were persistent converters, 16 (37%) were transient converters, and 15 (35%) comprised a new category defined as irregular converters (≥2 different subsequent results). ESAT-6 and CFP-10 responses were higher in prevalent than incident positives: 53 vs 36 for CFP-10 (p < 0·007); 44 vs 34 for ESAT-6 (p = 0·12). CONCLUSIONS: Definitions of IGRA conversion, reversion, and persistence depend critically on the frequency of testing. Multiple shifts in categories among adolescents in a TB-endemic country may represent multiple infections, variable host responses in subclinical infection, or assay variation. These findings should to be considered in the design and interpretation of TB vaccine trials based on prevention of infection. Household contact studies could determine whether even transient IGRA conversion might represent exposure to an active case of M. tuberculosis disease.

DAR-901 vaccine for the prevention of infection with Mycobacterium tuberculosis among BCG-immunized adolescents in Tanzania: A randomized controlled, double-blind phase 2b trial.

BACKGROUND: SRL172 prevented disease due to Mycobacterium tuberculosis in a Phase 3 trial. DAR-901 represents a scalable manufacturing process for SRL172. We sought to determine if DAR-901 would prevent infection with M. tuberculosis among BCG-primed adolescents age 13-15 years in Tanzania. METHODS: Adolescents with a negative T- SPOT.TBR interferon gamma release assay (IGRA) were randomized 1:1 to three intradermal injections of DAR-901 or saline placebo at 0, 2 and 4 months. Repeat IGRAs were performed at 2 months, and at 1, 2, and 3 years. The primary efficacy outcome was time to new TB infection (IGRA conversion to positive); the secondary outcome was time to persistent TB infection (IGRA conversion with repeat positive IGRA). RESULTS: Among 936 participants screened 667 were eligible and randomized to their first dose of vaccine or placebo (safety cohort). At 2 months, 625 participants remained IGRA-negative and were scheduled for the additional two doses (efficacy cohort). DAR-901 was safe and well-tolerated. One DAR-901 recipient developed a vaccine site abscess. Neither the primary nor secondary endpoints differed between the two treatment arms (p = 0.90 and p = 0.20, respectively). DAR-901 IGRA converters had median responses to ESAT-6 of 50.1 spot-forming cells (SFCs) vs. 19.6 SFCs in placebo IGRA converters (p = 0.03). CONCLUSIONS: A three-dose series of 1 mg DAR-901 was safe and well-tolerated but did not prevent initial or persistent IGRA conversion. DAR-901 recipients with IGRA conversion demonstrated enhanced immune responses to ESAT-6. Since protection against disease may require different immunologic responses than protection against infection a trial of DAR-901 to prevent TB disease is warranted. TRIAL REGISTRATION: The trial is registered at ClinicalTrials.gov as NCT02712424.

The potential of CBC-derived ratios (monocyte-to-lymphocyte, neutrophil-to-lymphocyte, and platelet-to-lymphocyte) to predict or diagnose incident TB infection in Tanzanian adolescents.

BACKGROUND: Ratios of different immune cell populations (i.e., monocyte-to-lymphocyte, neutrophil-to-lymphocyte, and platelet-to-lymphocyte ratios) have been studied as a means of predicting future tuberculosis (TB) disease risk or to assist in the diagnosis of incident TB disease. No studies to-date, however, have evaluated the potential of these ratios to predict or assist in the diagnosis of incident TB infection - the first step in the natural history of TB disease. METHODS: In this prospective study, we evaluated the complete blood count (CBC)-derived metrics of monocyte-to-lymphocyte ratio (MLR), neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR) as predictors of future TB infection risk or aids in the diagnosis of TB infection among 145 Tanzanian adolescents enrolled in the DAR-901 vaccine trial, using paired CBCs and interferon-gamma release assays (IGRAs) obtained at 0, 60 and 720 days after study enrollment. RESULTS: At baseline, there were no significant differences between study participants who remained persistently IGRA negative throughout the study period and those who subsequently converted to IGRA positive with respect to MLR (0.18 vs 0.17, p = 0.10), NLR (0.88 vs 1.02, p = 0.08), or PLR (115 vs 120, p = 0.28). Similarly, no significant differences were noted with respect to MLR, NLR, and PLR between IGRA converters and time-matched negative controls at the time of IGRA conversion. With respect to other blood cell measures, however, there were modest but significant differences between IGRA negatives and IGRA converters with respect to red blood cell count (4.8 vs 4.6 ×  106 cells/mcL, p = 0.008), hemoglobin (12.6 vs 12.3 g/dL, p = 0.01), and hematocrit (38.8 vs 37.8%, p = 0.005). CONCLUSIONS: In contrast to prior studies that have suggested that the ratios of different immune cell populations are associated with development of TB disease, our present findings do not demonstrate an association between these ratios and the development of TB infection. However, decreased red blood cell measures were associated with the subsequent development of TB infection, suggesting either that dysregulation of iron metabolism may play a role in TB pathogenesis or that following TB infection, iron dysregulation may precede IGRA positivity. TRIAL REGISTRATION: Clinicaltrials.gov NCT02712424 . Date of registration: March 14, 2016.