Pathfinder:Experimental Human Challenge with Genetically Modified Commensals to Investigate Respiratory Tract Mucosal Immunity and Colonisation

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We will genetically modify a bacterium and then perform two pilot controlled human infections to road test the technique for investigating human immunity and discovering and testing new vaccines. The proposal is complex - we have to gain regulatory approval both for deliberate release and human work. In the future, vaccines for such diseases as pneumonia, meningitis and whooping cough will be more sophisticated than those in the current schedule, and will likely take the form of nose drops that contain molecules providing nuanced immunity in the nose and throat. This is the critical first entry point of bacteria that cause these diseases, and the key to new generations of vaccines is to understand how natural immunity blocks successful entry. Stopping colonisation by pathogens stops transmission to other people (herd protection). We know that proteins on the surface of bacteria help them gain a foothold. These proteins may also elicit immunity that could be harnessed as vaccines. The `signature` of the bacteria - the proteins on or within the bacterium - vary widely between bacterial families. This variation renders current protein vaccines effective against some, but not all, the pathogens to which we are exposed. To make the future vaccines we need to understand more. Most of our knowledge is from laboratory studies with cells. There are some animal models but they are imperfect. Experimental human challenge is a powerful technique in which people volunteer to be infected with microorganisms in order to study the immune response to the whole organism, and the efficacy of vaccines or treatments. Our group was one of the first to infect the nose and throat with bacteria; we used a commensal Neisseria lactamica (`friendly bacteria`) and have infected over 350 human volunteers and shown it is safe and informative. However, the precision required for experimental medicine will follow if we can control and compare the signature of bacteria that we inoculate. This requires genetic modification.In the first part of the project we will genetically modify N.lactamica. This should be straightforward because we have made a prototype. However we will then need extensive laboratory testing to show that the organism is not more hazardous than the wild type. This will involve seeing how easily it can be killed by antibiotics and human blood, and also how `stable` its genome is (ie is it more likely to be changed genetically into something more dangerous when it is inside the nose). We will need to do this before we approach authorities for permission to allow those people who are challenged to walk out into the community whilst they are still carrying the bacteria in their noses. We contacted DEFRA (the government body concerned with deliberate release) and they have told us what information we will need to provide.On approval, we will enrol participants who will be admitted to our hospital research facility for 48 hours and undergo controlled infections. They will then be discharged with clear instructions how to prevent transmission to others. From the volunteers, samples will be taken of throat and nose fluid, and blood, to isolate carried bacteria (in the throat) and detect the cells and soluble products of the immune response, which will be characterised. Bacteria harvested from the throats will be genome sequenced to check carefully that the bacteria remain stable genetically. Once this is done we will repeat the study - this time to discover whether the natural mechanisms bacteria employ to conceal their signatures (phase variation) cause a different immune response. This is important to know because it informs how to make sure future challenges of this type use the right engineering to address research questions. This study will be a true pathfinder - this technique will fast-track discovery of the bacterial molecules - and the host response to them - that are critical for colonisation of humans by pathogens.