Courtney M. Yuen

Opposing effects of Tcf3 and Tcf1 control Wnt stimulation of embryonic stem cell self-renewal

The co-occupancy of Tcf3 with Oct4, Sox2 and Nanog on embryonic stem cell (ESC) chromatin indicated that Tcf3 has been suggested to play an integral role in a poorly understood mechanism underlying Wnt-dependent stimulation of mouse ESC self-renewal of mouse ESCs. Although the conventional view of Tcf proteins as the β-catenin-binding effectors of Wnt signalling suggested Tcf3–β-catenin activation of target genes would stimulate self-renewal, here we show that an antagonistic relationship between Wnt3a and Tcf3 on gene expression regulates ESC self-renewal. Genetic ablation of Tcf3 replaced the requirement for exogenous Wnt3a or GSK3 inhibition for ESC self-renewal, demonstrating that inhibition of Tcf3 repressor is the necessary downstream effect of Wnt signalling. Interestingly, both Tcf3–β-catenin and Tcf1–β-catenin interactions contributed to Wnt stimulation of self-renewal and gene expression, and the combination of Tcf3 and Tcf1 recruited Wnt-stabilized β-catenin to Oct4 binding sites on ESC chromatin. This work elucidates the molecular link between the effects of Wnt and the regulation of the Oct4/Sox2/Nanog network.

Incidence of multidrug-resistant tuberculosis disease in children: systematic review and global estimates.

BACKGROUND Multidrug-resistant tuberculosis threatens to reverse recent reductions in global tuberculosis incidence. Although children younger than 15 years constitute more than 25% of the worldwide population, the global incidence of multidrug-resistant tuberculosis disease in children has never been quantified. We aimed to estimate the regional and global annual incidence of multidrug-resistant tuberculosis in children. METHODS We developed two models: one to estimate the setting-specific risk of multidrug-resistant tuberculosis among child cases of tuberculosis, and a second to estimate the setting-specific incidence of tuberculosis disease in children. The model for risk of multidrug-resistant tuberculosis among children with tuberculosis needed a systematic literature review. We multiplied the setting-specific estimates of multidrug-resistant tuberculosis risk and tuberculosis incidence to estimate regional and global incidence of multidrug-resistant tuberculosis disease in children in 2010. FINDINGS We identified 3403 papers, of which 97 studies met inclusion criteria for the systematic review of risk of multidrug-resistant tuberculosis. 31 studies reported the risk of multidrug-resistant tuberculosis in both children and treatment-naive adults with tuberculosis and were used for evaluation of the linear association between multidrug-resistant disease risk in these two patient groups. We identified that the setting-specific risk of multidrug-resistant tuberculosis was nearly identical in children and treatment-naive adults with tuberculosis, consistent with the assertion that multidrug-resistant disease in both groups reflects the local risk of transmitted multidrug-resistant tuberculosis. After application of these calculated risks, we estimated that around 999,792 (95% CI 937,877-1,055,414) children developed tuberculosis disease in 2010, of whom 31,948 (25,594-38,663) had multidrug-resistant disease. INTERPRETATION Our estimates underscore that many cases of tuberculosis and multidrug-resistant tuberculosis disease are not being detected in children. Future estimates can be refined as more and better tuberculosis data and new diagnostic instruments become available. FUNDING US National Institutes of Health, the Helmut Wolfgang Schumann Fellowship in Preventive Medicine at Harvard Medical School, the Norman E Zinberg Fellowship at Harvard Medical School, and the Doris and Howard Hiatt Residency in Global Health Equity and Internal Medicine at the Brigham and Womens Hospital.

Yield of Contact Investigations in Households of Patients With Drug-Resistant Tuberculosis: Systematic Review and Meta-Analysis

Contact investigations among individuals living with drug-susceptible tuberculosis patients (source cases) have shown a high yield of tuberculosis disease and latent tuberculosis, but the yield of such investigations in households of drug-resistant tuberculosis source cases is unknown. In this systematic review and meta-analysis, we found 25 studies that evaluated a median of 111 (interquartile range, 21-302) household contacts of drug-resistant tuberculosis source cases. The pooled yield was 7.8% (95% CI, 5.6%-10.0%) for active tuberculosis and 47.2% (95% CI, 30.0%-61.4%) for latent tuberculosis, although there was significant statistical heterogeneity (P < .0001). More than 50% of secondary cases with drug susceptibility test results were concordant with those of the source case. Among studies that followed household members, the majority of secondary cases were detected within 1 year of the source cases diagnosis. Household contact investigation around drug-resistant tuberculosis patients is a high-yield intervention for detection of drug-resistant tuberculosis and prevention of ongoing transmission.

Turning off the tap: stopping tuberculosis transmission through active case-finding and prompt effective treatment

Summary To halt the global tuberculosis epidemic, transmission must be stopped to prevent new infections and new cases. Identification of individuals with tuberculosis and prompt initiation of effective treatment to rapidly render them non-infectious is crucial to this task. However, in settings of high tuberculosis burden, active case-finding is often not implemented, resulting in long delays in diagnosis and treatment. A range of strategies to find cases and ensure prompt and correct treatment have been shown to be effective in high tuberculosis-burden settings. The population-level effect of targeted active case-finding on reducing tuberculosis incidence has been shown by studies and projected by mathematical modelling. The inclusion of targeted active case-finding in a comprehensive epidemic-control strategy for tuberculosis should contribute substantially to a decrease in tuberculosis incidence.

Dissecting protein structure and function using directed evolution.

To characterize the contributions of individual amino acids to the structure or function of a protein, researchers have adopted directed evolution approaches, which use iterated cycles of mutagenesis and selection or screening to search vast areas of sequence space for sets of mutations that provide insights into the protein of interest.

Mortality in children diagnosed with tuberculosis: a systematic review and meta-analysis

BACKGROUND Case fatality ratios in children with tuberculosis are poorly understood-particularly those among children with HIV and children not receiving tuberculosis treatment. We did a systematic review of published work to identify studies of population-representative samples of paediatric (ie, <15 years) tuberculosis cases. METHODS We searched PubMed and Embase for reports published in English, French, Portuguese, or Spanish before Aug 12, 2016, that included terms related to tuberculosis, children, mortality, and population representativeness. We also reviewed our own files and reference lists of articles identified by this search. We screened titles and abstracts for inclusion, excluding studies in which outcomes were unknown for 10% or more of the children and publications detailing non-representative samples. We used random-effects meta-analysis to produce pooled estimates of case fatality ratios from the included studies, which we divided into three eras: the pre-treatment era (ie, studies before 1946), the middle era (1946-80), and the recent era (after 1980). We stratified our analyses by whether or not children received tuberculosis treatment, age (0-4 years, 5-14 years), and HIV status. FINDINGS We identified 31 papers comprising 35 datasets representing 82 436 children with tuberculosis disease, of whom 9274 died. Among children with tuberculosis included in studies in the pre-treatment era, the pooled case fatality ratio was 21·9% (95% CI 18·1-26·4) overall. The pooled case fatality ratio was significantly higher in children aged 0-4 years (43·6%, 95% CI 36·8-50·6) than in those aged 5-14 years (14·9%, 11·5-19·1). In studies in the recent era, when most children had tuberculosis treatment, the pooled case fatality ratio was 0·9% (95% CI 0·5-1·6). US surveillance data suggest that the case fatality ratio is substantially higher in children with HIV receiving treatment for tuberculosis (especially without antiretroviral therapy) than in those without HIV. INTERPRETATION Without adequate treatment, children with tuberculosis, especially those younger than 5 years, are at high risk of death. Children with HIV have an increased mortality risk, even when receiving tuberculosis treatment. FUNDING US National Institutes of Health, Janssen Global Public Health.

Recent Transmission of Tuberculosis - United States, 2011-2014.

Tuberculosis is an infectious disease that may result from recent transmission or from an infection acquired many years in the past; there is no diagnostic test to distinguish the two causes. Cases resulting from recent transmission are particularly concerning from a public health standpoint. To describe recent tuberculosis transmission in the United States, we used a field-validated plausible source-case method to estimate cases likely resulting from recent transmission during January 2011–September 2014. We classified cases as resulting from either limited or extensive recent transmission based on transmission cluster size. We used logistic regression to analyze patient characteristics associated with recent transmission. Of 26,586 genotyped cases, 14% were attributable to recent transmission, 39% of which were attributable to extensive recent transmission. The burden of cases attributed to recent transmission was geographically heterogeneous and poorly predicted by tuberculosis incidence. Extensive recent transmission was positively associated with American Indian/Alaska Native (adjusted prevalence ratio [aPR] = 3.6 (95% confidence interval [CI] 2.9–4.4), Native Hawaiian/Pacific Islander (aPR = 3.2, 95% CI 2.3–4.5), and black (aPR = 3.0, 95% CI 2.6–3.5) race, and homelessness (aPR = 2.3, 95% CI 2.0–2.5). Extensive recent transmission was negatively associated with foreign birth (aPR = 0.2, 95% CI 0.2–0.2). Tuberculosis control efforts should prioritize reducing transmission among higher-risk populations.

Association between Regimen Composition and Treatment Response in Patients with Multidrug-Resistant Tuberculosis: A Prospective Cohort Study.

Background For treating multidrug-resistant tuberculosis (MDR TB), the World Health Organization (WHO) recommends a regimen of at least four second-line drugs that are likely to be effective as well as pyrazinamide. WHO guidelines indicate only marginal benefit for regimens based directly on drug susceptibility testing (DST) results. Recent evidence from isolated cohorts suggests that regimens containing more drugs may be beneficial, and that DST results are predictive of regimen effectiveness. The objective of our study was to gain insight into how regimen design affects treatment response by analyzing the association between time to sputum culture conversion and both the number of potentially effective drugs included in a regimen and the DST results of the drugs in the regimen. Methods and Findings We analyzed data from the Preserving Effective Tuberculosis Treatment Study (PETTS), a prospective observational study of 1,659 adults treated for MDR TB during 2005–2010 in nine countries: Estonia, Latvia, Peru, Philippines, Russian Federation, South Africa, South Korea, Thailand, and Taiwan. For all patients, monthly sputum samples were collected, and DST was performed on baseline isolates at the US Centers for Disease Control and Prevention. We included 1,137 patients in our analysis based on their having known baseline DST results for at least fluoroquinolones and second-line injectable drugs, and not having extensively drug-resistant TB. These patients were followed for a median of 20 mo (interquartile range 16–23 mo) after MDR TB treatment initiation. The primary outcome of interest was initial sputum culture conversion. We used Cox proportional hazards regression, stratifying by country to control for setting-associated confounders, and adjusting for the number of drugs to which patients’ baseline isolates were resistant, baseline resistance pattern, previous treatment history, sputum smear result, and extent of disease on chest radiograph. In multivariable analysis, receiving an average of at least six potentially effective drugs (defined as drugs without a DST result indicating resistance) per day was associated with a 36% greater likelihood of sputum culture conversion than receiving an average of at least five but fewer than six potentially effective drugs per day (adjusted hazard ratio [aHR] 1.36, 95% CI 1.09–1.69). Inclusion of pyrazinamide (aHR 2.00, 95% CI 1.65–2.41) or more drugs to which baseline DST indicated susceptibility (aHR 1.65, 95% CI 1.48–1.84, per drug) in regimens was associated with greater increases in the likelihood of sputum culture conversion than including more drugs to which baseline DST indicated resistance (aHR 1.33, 95% CI 1.18–1.51, per drug). Including in the regimen more drugs for which DST was not performed was beneficial only if a minimum of three effective drugs was present in the regimen (aHR 1.39, 95% CI 1.09–1.76, per drug when three effective drugs present in regimen). The main limitation of this analysis is that it is based on observational data, not a randomized trial, and drug regimens varied across sites. However, PETTS was a uniquely large and rigorous observational study in terms of both the number of patients enrolled and the standardization of laboratory testing. Other limitations include the assumption of equivalent efficacy across drugs in a category, incomplete data on adherence, and the fact that the analysis considers only initial sputum culture conversion, not reversion or long-term relapse. Conclusions MDR TB regimens including more potentially effective drugs than the minimum of five currently recommended by WHO may encourage improved response to treatment in patients with MDR TB. Rapid access to high-quality DST results could facilitate the design of more effective individualized regimens. Randomized controlled trials are necessary to confirm whether individualized regimens with more than five drugs can indeed achieve better cure rates than current recommended regimens.

Isoniazid-Resistant Tuberculosis in Children: A Systematic Review

Background: Isoniazid resistance is an obstacle to the treatment of tuberculosis disease and latent tuberculosis infection in children. We aim to summarize the literature describing the risk of isoniazid-resistant tuberculosis among children with tuberculosis disease. Methods: We did a systematic review of published reports of children with tuberculosis disease who had isolates tested for susceptibility to isoniazid. We searched PubMed, Embase and LILACS online databases up to January 12, 2012. Results: Our search identified 3403 citations, of which 95 studies met inclusion criteria. These studies evaluated 8351 children with tuberculosis disease for resistance to isoniazid. The median proportion of children found to have isoniazid-resistant strains was 8%; the distribution was right-skewed (25th percentile: 0% and 75th percentile: 18%). Conclusions: High proportions of isoniazid resistance among pediatric tuberculosis patients have been reported in many settings suggesting that diagnostics detecting only rifampin resistance are insufficient to guide appropriate treatment in this population. Many children are likely receiving substandard tuberculosis treatment with empirical isoniazid-based regimens, and treating latent tuberculosis infection with isoniazid may not be effective in large numbers of children. Work is needed urgently to identify effective regimens for the treatment of children sick with or exposed to isoniazid-resistant tuberculosis and to better understand the scope of this problem.

The global burden of tuberculosis mortality in children: a mathematical modelling study

Summary Background Tuberculosis in children is increasingly recognised as an important component of the global tuberculosis burden, with an estimated 1 million cases in 2015. Although younger children are vulnerable to severe forms of tuberculosis disease, no age-disaggregated estimates of paediatric tuberculosis mortality exist, and tuberculosis has never been included in official estimates of under-5 child mortality. We aimed to produce a global mortality burden estimate in children using a complementary approach not dependent on vital registration data. Methods In this mathematical modelling study, we estimated deaths in children younger than 5 years and those aged 5–14 years for 217 countries and territories using a case-fatality-based approach. We used paediatric tuberculosis notification data and HIV and antiretroviral treatment estimates to disaggregate the WHO paediatric tuberculosis incidence estimates by age, HIV, and treatment status. We then applied systematic review evidence on corresponding case-fatality ratios. Findings We estimated that 239 000 (95% uncertainty interval [UI] 194 000–298 000) children younger than 15 years died from tuberculosis worldwide in 2015; 80% (191 000, 95% UI 132 000–257 000) of these deaths were in children younger than 5 years. More than 70% (182 000, 140 000–239 000) of deaths occurred in the WHO southeast Asia and Africa regions. We estimated that 39 000 (17%, 23 000–73 000) paediatric tuberculosis deaths worldwide were in children with HIV infections, with 31 000 (36%, 19 000–59 000) in the WHO Africa region. More than 96% (230 000, 185 000–289 000) of all tuberculosis deaths occurred in children not receiving tuberculosis treatment. Interpretation Tuberculosis is a top ten cause of death in children worldwide and a key omission from previous analyses of under-5 mortality. Almost all these deaths occur in children not on tuberculosis treatment, implying substantial scope to reduce this burden. Funding UNITAID, National Institutes of Health, and National Institute for Health Research.