Groundbreaking Developments in Tuberculosis Vaccination Research[1]In a significant stride towards more effective tuberculosis (TB) vaccination strategies, researchers at Weill Cornell Medicine have engineered two innovative strains of mycobacteria equipped with “kill switches.” These strains are designed to halt bacterial growth once they have elicited an immune response, addressing key challenges in developing safe and effective TB vaccines.[2]TB remains a persistent global health threat, claiming over a million lives annually. Although the disease is under control in many developed countries, its resurgence and drug-resistant strains pose ongoing concerns. Mycobacterium tuberculosis, the bacterium responsible for TB, infects the lungs and can cause a lethal respiratory disease. The Bacille Calmette-Guérin (BCG) vaccine, derived from a weakened strain of the closely related mycobacterium bovis, has limited efficacy, particularly in protecting adults from pulmonary TB. As Dr. Dirk Schnappinger, a professor of microbiology and immunology at Weill Cornell Medicine, notes, “BCG protects children from tuberculosis meningitis, but it doesn’t effectively protect adults from pulmonary tuberculosis, which is why it’s only used in high-incidence countries.”

Researchers have long sought to overcome these limitations. Previous studies by collaborators at the University of Pittsburgh and the National Institutes of Health’s Vaccine Research Center discovered that administering high doses of the BCG vaccine intravenously, rather than the traditional subcutaneous route, enhanced protection in adult macaque monkeys. However, the high-dose intravenous method poses safety concerns. To mitigate these risks, Dr. Schnappinger’s team developed a modified version of BCG that triggers an immune response while allowing for a controlled halt to bacterial growth.

Dr. Schnappinger elaborates: “We needed a version of BCG that triggers an immune response, but then you can flip a switch to eliminate the bacteria.”

After experimenting with numerous strategies, the researchers successfully employed lysins, enzymes encoded by viruses that infect BCG, to initiate self-destruction in the bacteria. By placing these lysin genes under the control of gene regulators responsive to antibiotics, the team could activate or deactivate the kill switch. According to Dr. Sabine Ehrt, professor of microbiology and immunology at Weill Cornell Medicine, “The lysins were known, but I don’t think they have been utilized as kill switches previously.” The modified BCG strains were then tested on antibiotic-treated macaques, resulting in a robust immune response when the kill switch was activated, effectively protecting the animals from subsequent lung infections with M. tuberculosis.

While these preclinical results are promising, the efficiency of such vaccines necessitates extensive, lengthy, and costly clinical trials. Dr. Schnappinger emphasizes the practical challenges: “Despite the promising preclinical results, evaluating if the vaccination actually works takes a long time and many people to test it. Tuberculosis doesn’t develop quickly and only in a small fraction of the people who are infected.” Such trials can cost hundreds of millions of dollars, forming a substantial barrier to the introduction of new vaccines.

Evaluating if the vaccination actually works takes a long time and many people to test it. Tuberculosis doesn’t develop quickly and only in a small fraction of the people who are infected.
Dr. Dirk Schnappinger, Professor of Microbiology and Immunology at Weill Cornwall Medicine.

Despite the promising preclinical results, evaluating if the vaccination actually works takes a long time and many people to test it. Tuberculosis doesn’t develop quickly and only in a small fraction of the people who are infected. – Dr. Dirk Schnappinger.”

Innovatively, the researchers also developed a strain of M. tuberculosis featuring a triple kill switch, employing three molecular mechanisms to ensure bacterial destruction. This strain can be employed in controlled human infection studies, significantly increasing the feasibility of such trials. Currently, the team is conducting additional tests in mice and non-human primates to validate the system’s effectiveness, aiming to use this strain in human challenge trials.

TB’s lethality can be seen in urban areas of the U.S. Similar to other major U.S. cities, New York City faces challenges with TB outbreaks, particularly among high-risk populations such as migrants living in crowded communities. Implementing a stable third-generation vaccination within the next five to ten years could drastically lower disease prevalence in these populations.

Though several humanitarian organizations have started putting pressure on federal agencies to expand investment and clinical research for a modern and effective vaccine strategy, stringent follow-up periods and regulatory oversight of new formulations are essential. These advancements mark a significant progress in battling TB, potentially reducing the worldwide TB burden and enhancing public health in the United States. Anti-TB conduction protocols need to be continually updated as new TB strains emerge due to antibiotic resistance.