Editor's Note: World Tuberculosis Day was on March 24, 2015.
By: Jyothi Rengarajan, PhD
It is important to note that studies such as the patient-based translational studies described here, require a real team effort. A very talented scientist in my laboratory, Dr. Toidi Adekambi, spearheaded the immunological studies and Susan and I worked with several other Emory-based clinical collaborators: Dr. Wayne Wang at the Grady Clinical Microbiology Lab, Stephanie Cagle and Dr. Ameeta Kalokhe, who helped us recruit the patients and obtain blood samples, Dr. Yijuan Hu from RSPH who performed the statistical analyses and Dr. Chris Ibegbu at the Emory CFAR Immunology core. This collaborative, interdisciplinary approach to doing science has been a wonderful experience for me personally. In fact, the close interactions between the lab-based and clinical scientists, has also enriched the more basic science projects on host-pathogen interactions that are ongoing in my laboratory. Thinking about TB as a living human disease that affects ordinary people, many of them in our own back door, brings perspective to our day-to-day efforts in the lab and has truly enriched my own scientific experience. Through research on TB, I hope that I can continue to contribute to making connections between science, medicine and public health.
Tuberculosis (TB) is an ancient scourge with a rich cultural, medical and scientific history that is closely tied to the human experience. Evidence of infection with Mycobacterium tuberculosis, the bacterium that causes TB, has been uncovered in human Neolithic remains as well as in Peruvian and Egyptian mummies-- and through the ages, TB has been known by many different names. The debilitating symptoms of coughing, wasting and difficulties with lung function were widely recognized as hallmarks of the disease since antiquity. Many ancient texts describe a disease that closely resembles TB, including yaksma in the Sanskrit Rigveda, xulao bing in classical Chinese medical texts and phthisis in ancient Greece. In Europe, from the Middle Ages to the 18th century, TB was variously known as scrofula, the King’s Evil, Potts disease and consumption and was highly feared as the ‘Captain of Death”. The disease acquired a rather romantic aura and captured the imagination of writers, poets, artists and musicians, many of whom themselves died of the “White Plague”, with its horrifically slow but inexorable progression to death. “ Where youth goes pale, and spectre-thin and dies”, wrote Shelley about John Keats in Ode to a Nightingale, and both Puccini and Verdi had their heroines’ lives cut short by that most operatic of diseases, consumption.
In 1882, Robert Koch identified the “tubercle bacillus” M. tuberculosis as the causative agent of TB; a discovery that revolutionized medical science and paved the way for improved sanitation and public health measures that were critical in reducing the burden of TB and other infectious diseases in Europe and North America. Interestingly, rest, sunlight and good nutrition in sanitoria helped many patients recover from TB, even before the advent of antibiotics. To this day, we still do not understand why some people progress to full-blown, uncontrolled active TB disease after infection, while others contain and limit disease pathology, while still others control infection in an asymptomatic state that we call latent TB infection, or LTBI. These are questions that animate my own research interests. Understanding the molecular mechanisms that define how M. tuberculosis evades the immune system to cause disease as well as understanding how humans control TB are active areas of research in my laboratory at the Emory Vaccine Center. We hope that our studies will provide fundamental insights into how this pathogen interacts with immune cells and lead to identifying new targets that could be developed into better vaccines and therapies for TB.
In 1882, Robert Koch identified the “tubercle bacillus” M. tuberculosis as the causative agent of TB; a discovery that revolutionized medical science and paved the way for improved sanitation and public health measures that were critical in reducing the burden of TB and other infectious diseases in Europe and North America. Interestingly, rest, sunlight and good nutrition in sanitoria helped many patients recover from TB, even before the advent of antibiotics. To this day, we still do not understand why some people progress to full-blown, uncontrolled active TB disease after infection, while others contain and limit disease pathology, while still others control infection in an asymptomatic state that we call latent TB infection, or LTBI. These are questions that animate my own research interests. Understanding the molecular mechanisms that define how M. tuberculosis evades the immune system to cause disease as well as understanding how humans control TB are active areas of research in my laboratory at the Emory Vaccine Center. We hope that our studies will provide fundamental insights into how this pathogen interacts with immune cells and lead to identifying new targets that could be developed into better vaccines and therapies for TB.
Robert Koch
The advent of antibiotics in the 1940s, together with the knowledge that TB is an airborne disease, led to the development of anti-TB treatment regimens, and TB dramatically declined in industrialized countries. Unfortunately, despite the availability of effective treatments, 9 million cases of TB are reported each year and about 2 million people worldwide die of TB. The long treatment duration (6 to 9 months with multiple drugs) and the rise of multi- and extensively-drug resistant TB (MDR and XDR-TB), underscores the urgent need for new drugs and shorter treatments for TB. In addition to individuals who develop active TB disease each year, it has been estimated that 2 billion individuals have LTBI. Latently infected individuals can remain asymptomatic for decades but may develop full-blown TB when their immune systems are weakened. This is because the M. tuberculosis bacteria can persist within otherwise healthy individuals without causing disease but can reactivate when immune control is compromised, for example, after HIV infection. Indeed, the risk of developing TB is up to 20 times greater in people living with HIV and one in four of AIDS-related deaths each year are currently due to TB.
Overall, TB remains a disease that is intertwined with poverty and thrives in the overcrowded settings that characterize increasing urbanization around the globe. While the majority of TB cases still occur in resource-limited countries, TB disproportionately affects vulnerable and marginalized populations, including in the U.S., where the Centers for Disease Control (CDC), reported 9,582 new TB cases in 2013. In the metro-Atlanta area, a TB outbreak during the past year has affected several homeless shelters and the state of Georgia reported x TB cases in 2013.
During outbreaks such as this one, as well as for routine diagnosis in parts of the world with high burdens of TB, identifying cases of active TB and initiating treatment is the cornerstone of TB control and public health efforts. Currently, diagnosis of pulmonary TB relies on extensive evaluations of clinical symptoms, X-ray assessments and direct detection of mycobacteria in a patient’s sputum, which is essentially mucus that is coughed up from the lower airways. The most widely used sputum-based test involves direct microscopic detection of bacteria in sputum smears, but the test is poorly sensitive and a high proportion of TB cases are smear-negative. Nucleic acid amplification-based tests are more sensitive for diagnosing TB disease but do not differentiate between live and dead bacteria and therefore are not useful for monitoring clearance of bacteria during and after treatment. Culturing M. tuberculosis from sputum is currently the gold standard for diagnosing TB and for monitoring treatment response, but takes three to six weeks for results due to the slow growth of M. tuberculosis. Sputum samples are also difficult to obtain, particularly in children, elderly and weakened/bed-ridden patients and therefore, blood-based tests are attractive alternatives to sputum-based tests. However, no blood-based tests for diagnosing active TB are currently available.
Overall, TB remains a disease that is intertwined with poverty and thrives in the overcrowded settings that characterize increasing urbanization around the globe. While the majority of TB cases still occur in resource-limited countries, TB disproportionately affects vulnerable and marginalized populations, including in the U.S., where the Centers for Disease Control (CDC), reported 9,582 new TB cases in 2013. In the metro-Atlanta area, a TB outbreak during the past year has affected several homeless shelters and the state of Georgia reported x TB cases in 2013.
During outbreaks such as this one, as well as for routine diagnosis in parts of the world with high burdens of TB, identifying cases of active TB and initiating treatment is the cornerstone of TB control and public health efforts. Currently, diagnosis of pulmonary TB relies on extensive evaluations of clinical symptoms, X-ray assessments and direct detection of mycobacteria in a patient’s sputum, which is essentially mucus that is coughed up from the lower airways. The most widely used sputum-based test involves direct microscopic detection of bacteria in sputum smears, but the test is poorly sensitive and a high proportion of TB cases are smear-negative. Nucleic acid amplification-based tests are more sensitive for diagnosing TB disease but do not differentiate between live and dead bacteria and therefore are not useful for monitoring clearance of bacteria during and after treatment. Culturing M. tuberculosis from sputum is currently the gold standard for diagnosing TB and for monitoring treatment response, but takes three to six weeks for results due to the slow growth of M. tuberculosis. Sputum samples are also difficult to obtain, particularly in children, elderly and weakened/bed-ridden patients and therefore, blood-based tests are attractive alternatives to sputum-based tests. However, no blood-based tests for diagnosing active TB are currently available.
Identifying blood-based biomarkers of TB that could be used to develop blood-based diagnostic tests for TB, is a major interest in my laboratory and I will describe one of our recent projects related to this topic. In collaboration with Susan Ray, MD (Professor of Infectious Diseases and Hospital Epidemiologist at Grady Memorial Hospital), we have established patient-based research studies to study human immunity to latent and active TB in metro Atlanta. While we are very interested in gaining fundamental insights into how the human host controls M. tuberculosis infection—as this is critical for designing a new vaccine that prevents TB—we reasoned that these studies should also point us in the direction of immune-based markers expressed on patients’ T cells that may be useful for improving TB diagnosis and monitoring treatment response. We hypothesized that expression of immune activation markers on M. tuberculosis-specific T cells would be associated with the amount of bacteria present within an infected individual and could thus provide a gauge of M. tuberculosis infection. We reasoned that individuals with active TB would harbor higher frequencies of CD38+/HLA-DR+/Ki-67+ cells in their blood than those with LTBI or those who had cleared their infection after successful treatment.
We enrolled individuals in the metro Atlanta area who had asymptomatic LTBI and treatment-naive patients who were diagnosed with active TB. We then followed these TB patients during and after their 6-month anti-TB treatment regimens. We were excited to find that the frequencies of M. tuberculosis-specific T cells that expressed immune markers CD38, HLA-DR and Ki-67 accurately identified active TB patients with 100% specificity and greater than 96% sensitivity. Importantly, we were able to validate the ability of these biomarkers to accurately classify active TB and LTBI in an independent cohort from South Africa, in collaboration with our colleague Dr. Cheryl Day. These markers also distinguished individuals with untreated TB from those who had successfully completed anti-TB treatment and correlated with decreasing bacterial loads during treatment. In fact the decrease in expression of our biomarkers during treatment mirrored sputum conversion in all patients. These findings show that blood-based biomarkers have the potential to accurately diagnose TB and discriminate between active and latent TB. Blood-based biomarkers will be particularly useful in situations where sputum-based diagnosis of TB is more difficult. Because these biomarkers provide a gauge of M. tuberculosis load within individuals, they could also have utility as surrogate markers of treatment response and as predictors of treatment efficacy, cure and relapse in patients undergoing treatment for drug-susceptible as well as drug-resistant TB. We are now interested in evaluating these biomarkers in larger studies in TB-endemic areas and across a broader spectrum of M. tuberculosis infection, including extra-pulmonary TB and in HIV-infected populations.
We enrolled individuals in the metro Atlanta area who had asymptomatic LTBI and treatment-naive patients who were diagnosed with active TB. We then followed these TB patients during and after their 6-month anti-TB treatment regimens. We were excited to find that the frequencies of M. tuberculosis-specific T cells that expressed immune markers CD38, HLA-DR and Ki-67 accurately identified active TB patients with 100% specificity and greater than 96% sensitivity. Importantly, we were able to validate the ability of these biomarkers to accurately classify active TB and LTBI in an independent cohort from South Africa, in collaboration with our colleague Dr. Cheryl Day. These markers also distinguished individuals with untreated TB from those who had successfully completed anti-TB treatment and correlated with decreasing bacterial loads during treatment. In fact the decrease in expression of our biomarkers during treatment mirrored sputum conversion in all patients. These findings show that blood-based biomarkers have the potential to accurately diagnose TB and discriminate between active and latent TB. Blood-based biomarkers will be particularly useful in situations where sputum-based diagnosis of TB is more difficult. Because these biomarkers provide a gauge of M. tuberculosis load within individuals, they could also have utility as surrogate markers of treatment response and as predictors of treatment efficacy, cure and relapse in patients undergoing treatment for drug-susceptible as well as drug-resistant TB. We are now interested in evaluating these biomarkers in larger studies in TB-endemic areas and across a broader spectrum of M. tuberculosis infection, including extra-pulmonary TB and in HIV-infected populations.
For a great selection of TB Blues recordings, check out:
https://www.youtube.com/watch?v=pdht6ijnzlY
https://www.youtube.com/watch?v=PI-A2V4Wm74
https://www.youtube.com/watch?v=9M6ybp4IxY8
https://www.youtube.com/watch?v=OoQiZujWKQI
https://www.youtube.com/watch?v=7qdmPKdd_Xc
https://www.youtube.com/watch?v=pdht6ijnzlY
https://www.youtube.com/watch?v=PI-A2V4Wm74
https://www.youtube.com/watch?v=9M6ybp4IxY8
https://www.youtube.com/watch?v=OoQiZujWKQI
https://www.youtube.com/watch?v=7qdmPKdd_Xc
Jyothi Rengarajan is an Assistant Professor in the Division of Infectious Diseases at Emory University and the Emory Vaccine Center. Her research program centers on understanding the mechanisms of tuberculosis (TB) pathogenesis and host immunity to infection in mice and humans. TB remains an enormous global public health challenge and developing new vaccines and immune-therapeutics for TB, are important goals of her research efforts. She also conducts translational patient-based research to study human immunity to latent and active TB in metro Atlanta and aims to identify diagnostic biomarkers of infection and disease. http://www.vaccines.emory.edu/faculty/rengarajan_jyothi.html
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