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

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, 1x10e6 PFU) aerosol group, 11 in the high dose (HD, 2x10e6 PFU) aerosol group and 9 in the IM (1x10e8 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 <5.39 micrometer 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.