Enhancing mucosal immunity to Streptococcus pneumoniae by nasal administration of live strains attenuated in virulence

Streptococcus pneumoniae (also called the pneumococcus) is the commonest cause of fatal bacterial infections. The pneumococcus is the commonest cause of pneumonia and a frequent cause of chest infections that are associated with deteriorations in patients with chronic lung disease, and therefore is an important cause of illness in the UK. The present vaccines used in adults and children are very effective at preventing blood borne pneumococcus infection; however they are not effective at preventing adult lung infections and there is a strong need for new methods of preventing pneumococcal pneumonia or chest infections. The pneumococcus is frequently found at the back of the throat causing a low level infection without any associated illness. We and others have shown that colonisation of the throat with the pneumococcus stimulates the host's immune response that can prevent future infection. This suggests a potential strategy to prevent pneumococcal lung infections could be to deliberately spray the nose with live pneumococcal bacteria on an annual basis shortly before the peak period for pneumococcal infections (the winter). To do so the bacteria would have to be genetically altered so they are unable to prevent serious infections such as pneumonia or septicaemia. In this proposal we will use a human model of pneumococcal colonisation to test whether administering genetically altered pneumococci unable to cause severe infection to the nose prevents pneumococcal infection in humans. If so then we could use this as a strategy to prevent pneumococcal lung infections in those people who are particularly susceptible eg the elderly and those with chronic lung disease. The model of pneumococcal carriage has been used in Liverpool for the past 5 years safely with no serious adverse effects, and is a proven method of assessing the immune response to colonisation with the pneumococcus.
Our plan would be to:
1. Make mutants in the pneumococcal strain used for the human colonisation model that prevent it from causing severe infection but do allow it to colonise the throat. These mutants will be tested in mouse models to confirm they are safe to use yet retain the ability to stimulate a significant immune response after colonising the throat.
2. We will then select two of these mutant pneumococci strains to be used in the human colonisation model; young healthy volunteers will have the bacteria inoculated into their noses and then nasal wash fluid and blood samples collected over the next few days and weeks. 35 volunteers will be given for each strain of bacteria, with an additional 35 volunteers given unmutated bacteria and 35 mock infected. These volunteers will then be challenged by intranasal inoculation of wild type pneumococci to see whether the immune response to previous colonisation with pneumococcal mutants reduced in virulence prevents subsequent colonisation with 'normal' pneumococci.
3. The immune response to pneumococcal colonisation in the volunteers will be assessed using conventional tests of antibody and white cell responses and the nasal wash fluid and blood samples. Results will be compared for before and after colonisation. In addition, whether any increases in antibodies after colonisation protects against pneumococcal infection will be tested by injecting the serum from the blood samples into mice before infecting them with pneumococci.
These experiments will provide proof of whether artificial infection of the throat with a safe avirulent pneumococci can cause a strong immune response and therefore could be a strategy for preventing pneumococcal lung infection. If so, the next step would be safety testing and a clinical trial of this approach in older individuals or those at high risk of pneumococcal lung infection.

Despite routine vaccination of adults at risk of S. pneumoniae lung infections, these are still probably the commonest serious infectious disease in the UK. S. pneumoniae causes 40+% of the 189,000 annual admissions due to pneumonia and 25% of the 117,000 admissions due to COPD. New strategies for preventing this huge burden of disease are required. One possible strategy would be to boost mucosal immunity against S. pneumoniae by nasal administration of genetically altered S. pneumoniae strains unable to cause severe infection. We will test this strategy using an experimental human pneumococcal carriage model that has been established in Liverpool by Prof Gordon. Healthy volunteers will be given attenuated S. pneumoniae by nasal administration then challenged with wild type S. pneumoniae bacteria. The primary endpoint is reduction of colonisation rate after rechallenge with wild-type S. pneumoniae strain to 15% for EHPC subjects given the attenuated strains compared to 50% in the negative control group, as assessed by recovery of bacteria from nasal washes. In addition nasal washes and blood samples will be taken for a variety of bacteriological and immunological endpoints including: (i) density and duration of colonisation with attenuated strains; (ii) pre- and post-colonisation local and systemic antibody and cellular responses to S. pneumoniae antigens, looking for equivalence of results between EHPC subjects given attenuated and wild type S. pneumoniae; (iii) functional immune responses using sera for in vitro assays of opsonophagocytosis and for passive vaccination experiments in mice; (iv) bacteriological safety by sequencing and in vitro testing of bacteria recovered from EHPC subjects to ensure genome and phenotypic stability. The data obtained will demonstrate whether immunisation by nasopharyngeal administration of attenuated mutants is a feasible strategy for improving mucosal immunity and therefore for preventing S. pneumoniae lung infections in adults.

Potential beneficiaries from this proposal include:
1. Academic interested in vaccine development, mucosal immunology and pathogenesis of bacterial infection. These groups will be directly interested in the results of the experimental medicine clinical trial that will inform and provide intellectual support for their own future work.
2. Pharmaceutical and biotech companies interested in vaccine development against bacterial mucosal pathogens. The data obtained will directly inform these parties about the potential of the strategy of using live attenuated bacteria to stimulate adaptive immunity to important bacterial pathogens. The potential market for vaccines against these pathogens is enormous, and with the increase in antibiotic resistance amongst bacterial pathogens preventative strategies are of increasing importance.
3. NHS policy makers, clinicians caring for acute medical admissions or patients with chronic organ disease, and adults at risk of S. pneumoniae lung infection ie anyone aged over 65 years, and subjects with chronic lung, cardiac, renal, liver, or neurological disease. An estimated 40 to 50% of the 189,000 annual admissions with pneumonia and 25% of the 117,000 admissions with exacerbations of COPD are caused by S. pneumoniae. Prevention of S. pneumoniae lung infections is therefore an important health priority that could reduce the mortality and morbidity associated with this pathogen. This proposal will directly answer whether the pre-clinical promise of a live attenuated vaccine could be a strategy for preventing S. pneumoniae lung infections. If the answer (as seems likely from the mouse data) is yes then this strategy could be developed very rapidly (within 5 to 10 years) into a cost effective mechanism for preventing S. pneumoniae infections. This will have direct benefits for adults at risk adults of S. pneumoniae infections, and reduce hospital admissions and the use of NHS resources expended on admissions caused by this pathogen.
4. UK plc. As the potential market for a live attenuated S. pneumoniae vaccine is very large (all over 65 year olds, plus most patients with chronic disease), then there would be direct economic benefits to the country if this vaccine strategy were to be developed in the UK. Furthermore, there is a need for mechanisms to assess vaccine efficacy without the considerable expense of a large clinical trial, and this can be fulfilled using the human experimental pneumococcal colonization (EHPC) model. By developing the EHPC model and further demonstrating its utility as a tool for vaccine research the proposal will help attract academic and pharmaceutical investment into the UK for similar future projects.