ChAdOx1 85A Aerosol Versus Intramuscular Vaccination in Healthy Adults (TB039)

Background:

Mycobacterium tuberculosis (M.tb) is a pathogen with worldwide preponderance which infects humans and causes tuberculosis (TB), a transmissible disease resulting in very high mortality and morbidity. A third of the world's population is latently infected with M.tb, and these people carry a 10% lifetime risk of developing active life-threatening disease. In 2015, there were 10.4 million new cases worldwide and 1.8 million people died of TB. Co-infection with human immunodeficiency virus (HIV) greatly increases risk of TB reactivation and death. Diagnosis is challenging and drug treatment can be prolonged, harmful, costly and complex. For these reasons an effective TB vaccine is a global public health priority.

The Bacille Calmette-Guérin (BCG) vaccine is the only licensed TB vaccine and it has been administered globally to several billion people over a 90 year period. Although it does not protect against pulmonary TB in endemic areas, it is effective in preventing disseminated TB disease including tuberculous meningitis in childhood. Recently, heterologous "prime-boost" vaccination strategies, in which two different candidate vaccines expressing antigens in common are given weeks or months apart, have generated strong and sustained cellular immune responses correlating with an M.tb protective effect in preclinical animal models. In such a "prime-boost" strategy, BCG would therefore be an ideal priming vaccine.

ChAdOx1 85A is a new adenoviral vaccine based on a vector that is a chimpanzee adenovirus isolate Y25 expressing the M.tb antigen 85A. Adenoviruses are attractive candidates for use as viral vectors and have been used as vaccine vectors for a number of conditions; however the use has been limited by the high level of anti-vector immunity present in humans in whom adenovirus is a ubiquitous infection. This has led to the consideration of simian adenoviruses, which are not known to cause pathology or illness in humans and to which the prevalence of anti-vector antibodies is low.

The route of M.tb infection is by inhalation of aerosolised infectious droplets containing tubercle bacilli, leading to the establishment of primary infection in the lung, which has a distinct mucosal immune system characterized by bronchus associated lymphoid tissue (BALT), which is well adapted to encounter and process such antigens. Immunising via the airway should therefore have the advantage, over other routes, of eliciting protective immune responses in the lung mucosa. There is data from preclinical animal models with virally vectored vaccines to suggest that immunising the respiratory mucosa may give superior protection against respiratory diseases. The inhaled route is a well-established route of drug delivery for humans and there are numerous perceived advantages of aerosol inhaled vaccination.

This trial will be the first to evaluate the safety and immunogenicity of candidate TB vaccine ChAdOx1 85A given by aerosol inhaled vaccination. Using a paired-placebo design, the trial will investigate aerosol vaccination compared to intramuscular vaccination, the latter for which initial safety data has already been collected and from which the dosing regimen for this trial has been chosen.

Objective:

The study aims to describe the safety and immunogenicity profile for ChAdOx1 85A given by aerosol inhaled vaccination versus intramuscular (IM) vaccination in adult healthy volunteers.

Methods:

Thirty-nine subjects will be enrolled into the trial: 29 BCG-vaccinated and 10 BCG-naïve.

Nine BCG-vaccinated healthy volunteers will receive the ChAdOx1 85A vaccine by aerosol inhaled vaccination at three different dose levels (3 volunteers per dose levels, Groups A-B-C). Based on the safety profile and immunogenicity results obtained in Groups A, B and C, the highest tolerated dose will be determined, and a decision made as to which dose to use for subsequent Groups.

The next 20 BCG-vaccinated subjects will be blinded and randomised in Groups D and E: volunteers randomised to the intervention group (D, inhaled aerosol) will receive a concurrent intramuscular saline injection, while volunteers in the control group (E, intramuscular) will receive a concurrent dose of inhaled saline. This design has the added benefit of allowing a distinction to be made between any adverse events attributable to the method (including nebuliser device) of vaccine delivery and those attributable to the inhaled investigational medicinal product itself.

In parallel to enrolment of Groups D and E, 10 BCG naïve subjects will be enrolled in Group F to receive the highest tolerated dose by aerosol inhaled vaccination.

After vaccination (day 0), volunteers will then follow a schedule of visits over the six months (day 1, day 7, day 14, day 28, day 84 and day 168), for safety and immunological follow-up via blood tests and physical examination. Moreover, at day 14, volunteers will undergo a bronchoscopy to check for signs of inflammation or other damage and to obtain a bronchoalveolar lavage sample and lymph node cytopunction.

Impact:

The overall investigational approach with ChAdOx1 85A trials is to develop an effective prime-boost vaccination strategy to prevent TB infection, with BCG as the priming vaccine.