Johns Hopkins Researchers Develop Experimental Intranasal DNA Vaccine Targeting Drug-Tolerant Tuberculosis Bacteria

Researchers at Johns Hopkins Medicine and the Johns Hopkins Bloomberg School of Public Health have unveiled a groundbreaking experimental therapeutic DNA vaccine for tuberculosis (TB), delivered non-invasively through the nose. This innovative vaccine is meticulously engineered to bolster the immune system’s capacity to recognize and combat "persisters" – drug-tolerant TB bacteria notoriously capable of surviving prolonged antibiotic regimens and subsequently triggering disease relapse. The findings, which represent a significant stride in the ongoing global battle against one of humanity’s oldest and deadliest infectious diseases, were published in the esteemed Journal of Clinical Investigation.

The Enduring Scourge of Tuberculosis: A Global Health Crisis

Tuberculosis, caused by the bacterium Mycobacterium tuberculosis, has plagued humanity for millennia, with archaeological evidence tracing its presence back at least 6,000 years. Despite advancements in modern medicine, it remains an intractable global health crisis. According to the World Health Organization (WHO), TB continues to be the leading cause of death from a single infectious pathogen worldwide. In 2024 alone, over 10 million individuals developed active TB, and a staggering 1.2 million succumbed to the disease. The sheer scale of its impact is further underscored by the fact that roughly one-quarter of the global population, approximately 2 billion people, carry latent TB infections, meaning they are infected with the bacteria but do not yet have active disease symptoms. While latent TB carriers are not contagious, they face a 5-10% lifetime risk of developing active TB, a risk that significantly increases for individuals with weakened immune systems, such as those living with HIV, malnutrition, or diabetes.

The economic ramifications of TB are also profound, particularly in low- and middle-income countries, where the disease disproportionately affects young adults in their most productive years. This leads to substantial losses in income, productivity, and national economic development, creating a vicious cycle of poverty and disease. The long and arduous treatment regimens, often lasting six months or more for drug-sensitive TB and up to 24 months for drug-resistant forms, impose immense burdens on patients, healthcare systems, and national economies. Adherence to these complex multi-drug therapies is a major challenge, frequently leading to incomplete treatment, treatment failure, and the emergence of drug-resistant strains, which further complicate global control efforts.

The Urgent Need for Novel Therapeutic Approaches

The current primary tool for TB prevention, the Bacillus Calmette-Guérin (BCG) vaccine, developed nearly a century ago, offers variable protection. While effective against severe forms of TB in infants and young children, such as TB meningitis and disseminated TB, its efficacy against pulmonary TB in adolescents and adults, the most common and transmissible form of the disease, is limited. This significant gap in protection underscores the critical need for more effective vaccines, especially those that can complement existing drug treatments. The WHO has consistently emphasized the development of therapeutic vaccines as a cornerstone of its End TB Strategy, aiming to drastically reduce TB incidence and mortality by 2035. Such vaccines could revolutionize TB management by potentially shortening lengthy treatment regimens, improving patient outcomes, and mitigating the spread of increasingly prevalent drug-resistant forms of TB.

The emergence and spread of multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) represent a dire public health threat. These strains are resistant to the most potent first-line anti-TB drugs, making treatment exponentially more difficult, toxic, and expensive. Patients with drug-resistant TB often face grim prognoses, highlighting the urgent imperative for innovative tools that can either prevent the disease more effectively or enhance the power of existing and new drug combinations.

Targeting the Elusive "Persisters": A Paradigm Shift

The Johns Hopkins study specifically addresses one of the most challenging aspects of TB treatment: the persistence of drug-tolerant bacteria. These so-called "persisters" are a subpopulation of M. tuberculosis that enter a dormant or quiescent state in response to stress factors like antibiotic exposure, low oxygen, or nutrient limitation. In this state, their metabolic activity slows down significantly, rendering them largely impervious to antibiotics designed to target rapidly dividing cells. While they don’t actively multiply, they remain viable and can re-emerge to cause relapse once antibiotic treatment ceases, even if the patient initially appeared cured. This phenomenon is a primary reason why TB treatment regimens are so prolonged, aimed at eradicating every last bacterium, including these resilient persisters.

The new Johns Hopkins vaccine strategy marks a significant departure from traditional approaches by directly targeting these problematic persisters through an immunotherapeutic mechanism. By focusing on boosting the host immune response against these dormant forms, the researchers aim to provide a crucial adjunct to standard antibiotic therapy, potentially leading to more rapid and durable cures.

The Ingenious Design of the Intranasal DNA Fusion Vaccine

The experimental vaccine, as elucidated by study lead author Dr. Styliani Karanika, a faculty member of the Johns Hopkins Center for Tuberculosis Research and assistant professor of medicine at the Johns Hopkins University School of Medicine, combines two specific genes: relMtb and Mip3α. The administration route – intranasal delivery – is not arbitrary but a strategic choice designed to leverage several critical biological mechanisms to amplify immunity against TB.

Dr. Karanika explains the multifaceted mechanism: "First, TB bacteria possess a gene, relMtb, that produces a protein, RelMtb, to help the microbes survive hostile conditions such as antibiotic exposure, low oxygen and nutrient limitation by entering a drug-tolerant persistent state." This RelMtb protein is essentially a survival switch for the bacteria. The brilliance of the vaccine lies in fusing this relMtb gene with the Mip3α gene. "Fusing relMtb with the Mip3α gene produces a signal that attracts immature dendritic cells — key cells that pick up TB proteins and ‘present’ them to T cells, the immune cells that help coordinate a targeted attack on the TB bacteria," Dr. Karanika elaborates. Dendritic cells act as critical sentinels of the immune system, collecting antigens and presenting them to T cells, thereby initiating a robust, antigen-specific immune response. By incorporating the RelMtb protein into this presentation, the vaccine specifically trains the immune system to identify and eliminate the very proteins that enable bacterial persistence.

Furthermore, the choice of intranasal delivery is pivotal. "Finally, intranasal delivery focuses vaccination on the respiratory mucosa in the lungs where TB infection occurs, helping generate long-lasting localized T-cell immunity in the airways and lungs, along with systemic immune responses," Dr. Karanika states. The respiratory mucosa is the primary site of TB infection, and by directly stimulating immune responses there, the vaccine aims to establish a localized protective barrier, akin to a frontline defense, that can immediately confront invading bacteria. This dual action — systemic immunity coupled with robust local mucosal immunity — is a powerful combination against a respiratory pathogen like M. tuberculosis.

Compelling Preclinical Evidence from Animal Studies

The initial preclinical investigations yielded highly encouraging results across multiple animal models. In meticulously designed mouse experiments, the vaccine demonstrated significant efficacy. When administered concurrently with first-line TB drug therapy, the intranasal DNA fusion vaccine facilitated a more rapid clearance of the disease bacteria from infected mice. Crucially, it also led to a significant reduction in lung inflammation, a hallmark of active TB disease, and, most importantly, prevented relapse after the antibiotic treatment concluded. This latter finding is particularly significant, directly addressing the challenge posed by persister bacteria.

Beyond its standalone effect, the vaccine also exhibited a synergistic interaction with powerful TB drug combinations. Dr. Karanika notes, "The vaccine also helped the powerful TB drug combination of bedaquiline, pretomanid and linezolid work better, suggesting it could be used with treatments against drug-resistant TB to help the body fight the disease, even hard-to-treat cases." This finding holds immense promise for patients suffering from drug-resistant TB, for whom treatment options are limited and often accompanied by severe side effects. By enhancing the efficacy of existing and newer drug regimens, the vaccine could shorten treatment durations, improve outcomes, and potentially reduce the incidence of further resistance development.

The research team delved deeper into the immunological mechanisms underlying these observed benefits. They found that the vaccine significantly increased the recruitment and activation of dendritic cells, essential for initiating immune responses. It also improved the spatial organization of dendritic cells and T cells within lung tissue, facilitating more efficient antigen presentation and immune cell interaction. This resulted in the generation of durable, antigen-stimulated T-cell responses, both locally within the lungs and systemically throughout the body. These responses involved both CD4+ (helper T cells), which orchestrate the immune response, and CD8+ (killer T cells), which directly eliminate infected cells, indicating a comprehensive and robust immune activation.

To bridge the gap between mouse models and human physiology, the researchers further evaluated the vaccine in rhesus macaques, an animal model whose immune system more closely resembles that of humans. The intranasally delivered DNA vaccine successfully generated measurable TB-specific immune responses in both the bloodstream and the airways of these primates. These immune responses in macaques strikingly resembled those observed in vaccinated mice that had exhibited reduced bacterial levels in their lungs. Importantly, the researchers observed that these immune responses persisted for at least six months, suggesting the potential for durable protection. However, Dr. Karanika prudently notes that while the primate study confirmed robust immune activation, it did not assess how the animals responded to an actual TB infection, a critical next step for future research.

Translational Promise and Future Directions

The encouraging nonhuman primate data represent a crucial "translational bridge" between initial efficacy studies in mice and the rigorous preclinical work necessary before advancing to human clinical trials. "These nonhuman primate data are encouraging because they show that the Mip3α/relMtb vaccine can generate durable, antigen-stimulated immune responses in an animal model whose immune system more closely resembles that of humans," Dr. Karanika emphasizes. This provides a strong foundation for the additional research that will be required to validate the vaccine’s safety and efficacy in humans.

The researchers firmly believe that their results advocate for a broader, more comprehensive treatment strategy for TB, one that moves beyond an exclusive reliance on antibiotics to kill actively growing bacteria. By incorporating immunotherapy specifically designed to eliminate drug-tolerant TB persisters, this approach offers a novel pathway to achieve more definitive cures and prevent relapse. The inherent characteristics of DNA vaccines—their general stability, ease of production, and adaptability—also suggest practical advantages in terms of manufacturing, storage, and distribution, which are critical considerations for global health interventions, particularly in resource-limited settings.

Before this vaccine can enter human clinical trials, extensive further research will be necessary. This will likely involve detailed toxicology studies, refinement of vaccine dosage and administration schedules, and a deeper understanding of potential immune correlates of protection. Should subsequent studies in humans demonstrate similar benefits, this innovative intranasal DNA vaccine could fundamentally alter the landscape of TB treatment and prevention, offering hope for millions globally.

The research team at Johns Hopkins included a multidisciplinary group of scientists: Tianyin Wang, Addis Yilma, Jennie Ruelas Castillo, James Gordy, Hannah Bailey, Darla Quijada, Kaitlyn Fessler, Rokeya Tasneen, Elisa M. Rouse Salcido, Farah Shamma, Harley Harris, Fengyixin Chen, Rowan Bates, Heemee Ton, Jacob Meza, Yangchen Li, Alannah Taylor, Jean Zheng, Jiaqi Zhang, Theodoros Karantanos, Amanda Maxwell, Eric Nuermberger, J. David Peske, Richard Markham, and Petros Karakousis, alongside Dr. Karanika.

This pivotal research received substantial federal funding from National Institutes of Health grants R01AI148710, K24AI143447, P30AI18436, K08AI174959, and P30CA006973. Additional support was provided by a Gilead HIV Research Scholar Award, a Johns Hopkins University Tuberculosis Research Advancement Center Developmental Award, a Center for HIV/AIDS Developmental Award from the Johns Hopkins University Center for AIDS Research, a Willowcraft Foundation Award, a Johns Hopkins University Clinician Scientist Award, and the Potts Memorial Foundation. Notably, Dr. Karanika, Gordy, Markham, and Karakousis are recognized as inventors on patent PCT/US2023/065584 for the Mip3α/relMtb vaccine, underscoring the innovative nature and potential for real-world application of their work. The authors reported no conflicts of interest.