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

This is a pathfinder study to establish the utility of experimental human challenge with a genetically modified commensal bacterium as a future method to investigate pathogenesis, immunity and to discover and test new vaccines. The commensal bacterium Neisseria lactamica (Nlac) does not have a polysaccharide capsule , so any adaptive immune response to this bacterium after colonisation of the nasopharynx must be directed at non-capsular antigens, providing a good platform for assessing non-anti-polysaccharide immunity against colonising bacteria in the upper respiratory tract. A wild-type strain of Nlac Y92-1009 (Nlac), will be chromosomally modified to express the strongly immunogenic meningococcal antigen PorA (GM-Nlac). GM-Nlac will be fully characterised, in particular with respect to enhanced antimicrobial or serum resistance, and altered genome stability cf Nlac. An application will then be made to DEFRA and the National Research Ethics Service to perform a controlled infection study in which non-smoking male participants aged 18-45 will be infected intranasally at a dose of 10,000 colony forming units (selected because we previously have infected >350 volunteers with Nlac at this dose) and then permitted to re-enter the community after challenge and followed up for 4 weeks. In a comprehensive serological and cellular immunological study we will define the nature and kinetics of the PorA-specific immune response to colonising GM-Nlac and measure recombination in carried isolates over the ensuing period of carriage. PorA is phase variable so we will determine the effect of phase variation in a second challenge experiment by comparing the serological and cellular responses to GM-Nlac expressing PorA under a phase variable promoter with one that is constitutively highly expressed. We will also compare the immune response to Nlac antigens between GM-Nlac and Nlac infected participants, to understand the effect of immunodominant antigens on immunity.