Safety and immunopotency of an adenovirus-vectored tuberculosis vaccine delivered via inhaled aerosol to healthy humans: a dose and route comparison phase 1b study

Summary Background Adenoviral (Ad)-vectored vaccines are typically administered via intramuscular injection to humans, but this route of delivery is unable to induce respiratory mucosal immunity which requires respiratory mucosal route of vaccination. However, inhaled aerosol delivery of Ad-vectored vaccines has remained poorly characterized and its ability to induce respiratory mucosal immunity in humans is still unknown. The goal of our study was to evaluate and compare the safety and immunogenicity of a human serotype 5 Ad-based tuberculosis (TB) vaccine (AdHu5Ag85A) delivered to healthy humans via inhaled aerosol or intramuscular injection. Methods In this open-labeled phase 1b trial, 31 healthy adults between 18 and 55 years of age with a history of BCG vaccination were enrolled at McMaster University Medical Centre, Hamilton, Ontario, Canada. AdHu5Ag85A was administered by a single-dose aerosol using the Aeroneb® Solo Vibrating Mesh Nebulizer or by intramuscular (IM) injection; 11 in the low dose (LD, 1×10 6 PFU) aerosol group, 11 in the high dose (HD, 2×10 6 PFU) aerosol group and 9 in the IM (1×10 8 PFU) group. The primary outcome was safety of a single administration of vaccine delivered to the respiratory tract by aerosol or by IM injection. The vaccine-related local and systemic adverse events were collected from participants from a self-completed diary for 14 days after vaccination and at scheduled follow-up visits. Routine laboratory biochemical and haematological tests were measured at 2, 4 and 12 weeks after vaccination and lung function was measured at 2, 4, 8 and 12 weeks after vaccination. The secondary outcome was comparison of immunogenicity among the different routes and aerosol dose groups. Immunogenicity to aerosol or IM vaccination was measured both in the peripheral blood and bronchoalveolar lavage samples by Luminex, and cell surface and intracellular cytokine immunostaining. Anti-AdHu5 antibodies and neutralization titers were determined before and after vaccination using ELISA and bioassay, respectively. This trial is registered with ClinicalTrial.gov, NCT02337270 . Results The aerosol droplets generated by Aeroneb® Solo Nebulizer were mostly <5.39µm in size, suitable for efficient Ad-vectored vaccine deposition to major human airways. Both LD and HD of AdHu5Ag85A administered by aerosol inhalation and the intramuscular injection were safe and well-tolerated. Respiratory adverse events were infrequent, mild, transient and similar among groups. IM injection was associated with a mild local injection site reaction in two participants. Systemic adverse events were also infrequent, mild, transient and similar among all groups. There were no grade 3 or 4 adverse events reported nor any serious adverse events. Both aerosol doses, particularly LD, but not IM, vaccination markedly induced Ag85A-specific airway tissue-resident memory CD4 and CD8 T cells of polyfunctionality. While as expected, IM vaccination induced Ag85A-specific T cell responses in the blood, the LD aerosol vaccination also elicited such T cells in the blood. Furthermore, the LD aerosol vaccination induced persisting transcriptional changes in alveolar macrophages indicative of trained innate immunity. Interpretation Inhaled aerosol delivery of Ad-vectored vaccine is a safe, economical and superior way to elicit respiratory mucosal immunity. The results of this study encourage further development of aerosol vaccine strategies against not only TB but also other respiratory pathogens including COVID-19. Funding The Canadian Institutes for Health Research and the Natural Sciences and Engineering Research Council of Canada. Research in context Evidence before this study We searched PubMed for published research articles without language or date restrictions by using search terms “adenovirus”, “aerosol” and “clinical trial” or “virus”, “vaccine”, “aerosol”, and “clinical trial”. Our search results indicate that adenoviral-vectored vaccine has rarely been delivered via inhaled aerosol into the respiratory tract of healthy humans. Adenoviral-vectored TB or HIV vaccine was delivered via inhaled aerosol to non-human primates, providing support for its further development for human application. An aerosolized adenoviral vector expressing CFTR was tested as a gene replacement therapeutic in cystic fibrosis patients. Recently, although an adenoviral-vectored COVID-19 vaccine was delivered via aerosol to humans, there were no evidence presented that it induced local mucosal immunity. Given the increased recognition of its value, inhaled aerosol has been explored in humans with non-adenoviral, viral vaccines against respiratory infections of global importance including measles and TB. However, since different aerosol technologies were used in these studies and aerosol characteristics including delivery efficiency vary according to the viral platform, aerosol delivery technology and its efficiency in inducing respiratory mucosal immunity remain to be established for administering adenoviral-vectored vaccine to healthy humans. Added value of this study This represents the first study to demonstrate the characteristics of a single-dose aerosolized human serotype 5 adenoviral-vectored vaccine, and its safety and immunogenicity in BCG-vaccinated healthy humans. It is also the first to show the superiority of inhaled aerosol immunization with this type of vaccine platform, over intramuscular (IM) route of immunization, in inducing respiratory mucosal immunity. Robust adaptive immune memory responses were induced in the respiratory tract with an aerosol vaccine dose up to 100 times smaller than the dose for IM immunization. Besides local mucosal immunity induced by aerosol immunization, it also induces levels of systemic immunity comparable to those by IM immunization. Also for the first time, we show that contrast to IM immunization, aerosol immunization does not increase either local or systemic anti-adenoviral neutralizing antibodies. Implications of all the available evidence Collectively our findings show the technical feasibility, safety and potency of needle/pain-free delivery of a recombinant adenoviral-vectored vaccine to the respiratory tract of healthy adults. This vaccine strategy differs from parenteral route of immunization in its potency to elicit much desired respiratory mucosal immunity consisting of trained macrophages and tissue-resident memory T cells. The study provides the proof of concept to endorse inhaled aerosol vaccine strategies against pulmonary TB. Of further importance, as a number of currently authorized COVID-19 vaccines are also adenoviral-vectored, our study offers important technological details and scientific rationale for the development of inhalable next-generation COVID-19 vaccines aiming to induce all-around protective respiratory mucosal immunity in humans.

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