Bacillus Calmette-Guérin (BCG) vaccine has failed to control the global tuberculosis (TB) epidemic, and there is a lack of safe and effective mucosal vaccines capable of potent protection against pulmonary TB. A recombinant replication-deficient adenoviral-based vaccine expressing an immunogenic Mycobacterium tuberculosis Ag Ag85A (AdAg85A) was engineered and evaluated for its potential to be used as a respiratory mucosal TB vaccine in a murine model of pulmonary TB. A single intranasal, but not i.m., immunization with AdAg85A provided potent protection against airway Mycobacterium tuberculosis challenge at an improved level over that by cutaneous BCG vaccination. Systemic priming with an Ag85A DNA vaccine and mucosal boosting with AdAg85A conferred a further enhanced immune protection which was remarkably better than BCG vaccination. Such superior protection triggered by AdAg85 mucosal immunization was correlated with much greater retention of Ag-specific T cells, particularly CD4 T cells, in the lung and was shown to be mediated by both CD4 and CD8 T cells. Thus, adenoviral TB vaccine represents a promising novel vaccine platform capable of potent mucosal immune protection against TB. Our study also lends strong evidence that respiratory mucosal vaccination is critically advantageous over systemic routes of vaccination against TB.

The emerging SARS-CoV-2 variants of concern (VOC) threaten the effectiveness of current COVID-19 vaccines administered intramuscularly and designed to only target the spike protein. There is a pressing need to develop next-generation vaccine strategies for broader and long-lasting protection. Using adenoviral vectors (Ad) of human and chimpanzee origin, we evaluated Ad-vectored trivalent COVID-19 vaccines expressing Spike-1, Nucleocapsid and RdRp antigens in murine models. We show that single-dose intranasal immunization, particularly with chimpanzee Ad-vectored vaccine, is superior to intramuscular immunization in induction of the tripartite protective immunity consisting of local and systemic antibody responses, mucosal tissue-resident memory T cells and mucosal trained innate immunity. We further show that intranasal immunization provides protection against both the ancestral SARS-CoV-2 and two VOC, B.1.1.7 and B.1.351. Our findings indicate that respiratory mucosal delivery of Ad-vectored multivalent vaccine represents an effective next-generation COVID-19 vaccine strategy to induce all-around mucosal immunity against current and future VOC.

There is an urgent need to develop new tuberculosis (TB) vaccines to safely and effectively boost Bacille Calmette-Guérin (BCG)-triggered T cell immunity in humans. AdHu5Ag85A is a recombinant human type 5 adenovirus (AdHu5)-based TB vaccine with demonstrated efficacy in a number of animal species, yet it remains to be translated to human applications. In this phase 1 study, we evaluated the safety and immunogenicity of AdHu5Ag85A in both BCG-naïve and previously BCG-immunized healthy adults. Intramuscular immunization of AdHu5Ag85A was safe and well tolerated in both trial volunteer groups. Moreover, although AdHu5Ag85A was immunogenic in both trial volunteer groups, it much more potently boosted polyfunctional CD4(+) and CD8(+) T cell immunity in previously BCG-vaccinated volunteers. Furthermore, despite prevalent preexisting anti-AdHu5 humoral immunity in most of the trial volunteers, we found little evidence that such preexisting anti-AdHu5 immunity significantly dampened the potency of AdHu5Ag85A vaccine. This study supports further clinical investigations of the AdHu5Ag85A vaccine for human applications. It also suggests that the widely perceived negative effect of preexisting anti-AdHu5 immunity may not be universally applied to all AdHu5-based vaccines against different types of human pathogens.

Parenterally administered Mycobacterium bovis BCG vaccine confers only limited immune protection from pulmonary tuberculosis in humans. There is a need for developing effective boosting vaccination strategies. We examined a heterologous prime-boost regimen utilizing BCG as a prime vaccine and our recently described adenoviral vector expressing Ag85A (AdAg85A) as a boost vaccine. Since we recently demonstrated that a single intranasal but not intramuscular immunization with AdAg85A was able to induce potent protection from pulmonary Mycobacterium tuberculosis challenge in a mouse model, we compared the protective effects of parenteral and mucosal booster immunizations following subcutaneous BCG priming. Protection by BCG prime immunization was not effectively boosted by subcutaneous BCG or intramuscular AdAg85A. In contrast, protection by BCG priming was remarkably boosted by intranasal AdAg85A. Such enhanced protection by intranasal AdAg85A was correlated to the numbers of gamma interferon-positive CD4 and CD8 T cells residing in the airway lumen of the lung. Our study demonstrates that intranasal administration of AdAg85A represents an effective way to boost immune protection by parenteral BCG vaccination.Tuberculosis (TB) is the second leading cause of death by infectious disease worldwide. Mycobacterium bovis bacillus Calmette-Guérin (BCG) has been the vaccine of choice given to humans via the skin for over 80 years and has shown variable efficacies of between 0 and 80% in clinical studies (25). In spite of this fact, over 80% of the world population are BCG vaccinees; this vaccine is still being utilized and will likely continue to be utilized in the majority of the world as a part of childhood vaccination programs because of its efficacy in preventing adolescent and disseminated forms of TB, despite the fact that BCG has been shown to have variable efficacies in preventing adult pulmonary tuberculosis (1, 6). Its limited success in control of adult TB has been attributed at least in part to the fact that immune protection by BCG wanes within 10 to 15 years. Much of the past effort has focused on modifying the current BCG vaccine or identifying new vaccine platforms (11,17,22). However, these strategies are unlikely to accomplish long-term TB protection in humans. Furthermore, replacement of the currently used BCG with a different vaccine platform is increasingly considered an unrealistic goal because of the wide clinical usage of BCG and because any phase III clinical vaccine trial would not ethically be allowed to withhold BCG vaccination (12,26). Therefore, the development of strategies that aim to boost BCG-mediated protection represents a priority (15). In this regard, BCG has been shown to be an ineffective booster vaccine for itself and may even be deleterious to protection against TB, as previously shown in clinical and experimental studies (2,5,8). Increasing evidence suggests that effective booster vaccines for BCG immunization ought to be nonmycobacterial (boosters heterologous to BCG) and may inc...