Universal protection against Streptococcus pneumoniae by recombinant glycoconjugate vaccines

Vaccines are a critical component of defence against infectious disease, and have eliminated some of the most dangerous diseases that have faced humanity. This is increasingly the case in low income countries, where vaccines can transform the likelihood of healthy childhoods. Streptococcus pneumoniae can cause life-threatening diseases such as pneumonia, septicaemia and meningitis. S. pneumoniae is responsible for significant morbidity and mortality worldwide with over one million deaths of children annually. The emergence and rapid spread of antibiotic-resistant S. pneumoniae strains has further emphasised the need for prevention of S. pneumoniae infections. An inexpensive, broad-range, long-lasting pneumococcal vaccine is a current global imperative, and be of most impact to LMIC countries as this is where existing vaccines are often under utilised and S. pneumoniae infections remain a significant cause of childhood mortality and morbidity. A defining characteristic of a successful vaccine is the ability to evoke long-lasting protective immunity with minimal side effects. The most successful human vaccines are often glycoconjugates, which are combinations of a protein coupled to a sugar glycan, as these provide multiple triggers for the immune system, and increases the lifetime of the vaccine. Examples of current human glycoconjugate vaccines include vaccines against Haemophilus influenzae, Neisserria meningitidis and S. pneumoniae strains. These vaccines are made chemically which is time consuming and expensive. Furthermore, the current pneumococcus glycoconjugate vaccines only protect against a fraction of all S. pneumoniae strains. Ideally, to improve the proportion of all S. pneumoniae strains that the vaccine protects against, a glycoconjugate vaccine against S. pneumoniae should link the sugar component to S. pneumoniae proteins that are present in all strains, but to date this has proved technically challenging to achieve.

Recently, we have developed a new approach for constructing glycoconjugate vaccines involving genetically altering the bacterium E. coli so that they act as cellular factories for the production of glycoconjugate vaccines. This is termed Protein Glycan Coupling Technology (PGCT), and involves making an E. coli strain that can produce the candidate protein and glycan, along with an enzyme that couples the protein and glycan together to produce an inexhaustible and inexpensive supply of vaccine. PGCT can produce purified vaccine in a one-step purification procedure, which reduces costs, and because multiple combinations of protein and glycans can be produced, a greater flexibility in the range of vaccines can be generated and tested. However, as yet we do not know the best S. pneumoniae proteins to use in a vaccine made using PGCT that are able to induce the highest level of protection against S. pneumoniae infections.

In this study we will use new technologies to systematically screen all S. pneumoniae proteins to identify the best candidates for a "double hit" glycoconjugate vaccine consisting of a S. pneumoniae protein coupled to S. pneumoniae glycan (capsular polysaccharide). We will select the top 50 candidates from the screen to test which can be linked using PGCT to S. pneumoniae capsule glycan to make effective recombinant glycoconjugates. The most promising vaccines will then be tested in mouse models of S. pneumoniae infection to find which ones are best able to prevent infections. The new vaccines generated will also be compared to the efficacy of market leading vaccines such as Prevenar13. These experiments will identify the most suitable proteins for inclusion in a novel S. pneumoniae vaccine made using PGCT, or for other novel vaccine approaches. Additionally, the development of PGCT in this study will provide the expertise and knowledge base to make the technology more widely applicable for making glycoconjugate vaccines against other important infectious agents.

S. pneumoniae Polysaccharide Conjugate Vaccines (PCVs) are effective but have limited serotype coverage and are expensive. We propose that a "PCV plus" vaccine consisting of selected S. pneumoniae proteins recombinantly coupled to S. pneumoniae capsules will resolve these limitations, creating a cheap vaccine that would be of most impact to LMIC countries in which S. pneumoniae remains a significant cause of severe disease. We will use protein glycan coupling technology (PGCT) to make recombinant glycoconjugate pneumococcal vaccines. Our hypothesis is that intelligent protein antigen selection can identify carrier proteins for a "PCV plus" vaccine made by PGCT that induces broad serotype-independent protection against S. pneumoniae infections. To identify the best protein antigens for novel S. pneumoniae vaccines we will systematically identify protein candidate antigens capable of inducing IgG and/or Th17 responses using proteome expression technology. An expression library of 1400 conserved S. pneumoniae proteins will be constructed, pooled and used to vaccinate mice. We will identify up to 50 new vaccine candidates by screening sera from vaccinated mice against a protein array to discover antibody-inducing antigens and by using an in vitro assay and CD4 cells to identify antigens inducing Th17 responses. Candidate vaccine proteins will be coupled to serotype 4 S. pneumoniae capsule to produce recombinant glycoconjugates using a high throughput PGCT expression vector. Proteins that are efficiently coupled to capsule will be tested in mice to identify the glyconconjugates that induce the most effective cross-protective immunity against heterologous capsular serotypes and during mucosal infection, whilst maintaining serotype specific immunity. Overall these studies will provide an unbiased screen of S. pneumoniae proteins to identify the best proteins for inclusion in a 'PCV plus' vaccine produced by PGCT for future testing in phase 1 trials.

Given that vaccination is a core public health measure in reducing the infectious disease burden, the proposed studies could have a major impact on the health and well-being of humans. This is particularly the case for pneumococcal disease, where a reported estimate of nearly one million infants die each year and at least an equivalent are burdened with the disease through long-term complications. Our approach promises to break new ground in pneumococcal vaccination to produce an effective and inexpensive glycoconjugate vaccine. This multidisciplinary research proposal fits squarely into several priority research areas identified by the MRC, in terms of reducing the burden of childhood diseases, vaccine candidates and the design of novel treatments.
There will be four main area of impact from this research:
Scientific impact:
The research in this project will provide a platform for the production of recombinant polysaccharide based vaccines. These are likely to be of interest to a wide range of academic researchers looking at bacterial infection. There is also likely to be considerable interest from industry and where appropriate we will exploit our close links with GSK, Pfizer, VaxAlta and Malicisbo, and will use licensing agreements through our respective technology transfer offices to ensure that the platform developed in this proposal can be effectively exploited with these partners. Alternatively, we will explore the option to set up a spin out company focusing on pneumococcal vaccines. The vaccines developed through our proposed study may have important implications for policy makers to future disease outbreaks.
Economic impact:
Our program will primarily offer new vaccine candidates against Streptococcus pneumoniae. It is estimated that the global pneumococcal vaccine market is £5billion. Potentially, this will provide significant benefits to the UK economy. Vaccines, in particular, are proven for the control of infectious diseases in both humans and in animals, and suitably designed vaccines will reduce our reliance on antibiotics and therefore improve control of antimicrobial resistance.
Societal:
The general public will benefit from improved vaccines against S. pneumoniae, with the resultant economic benefit to the UK economy in terms of improved productivity. S. pneumoniae vaccination is strongly recommended in infants and the elderly: maintaining the effectiveness of this vaccination and ensuring protection against pneumococcal meningitis, septicaemia, pneumonia, bronchitis, and otitis media offers a clear benefit to the public. Therefore, the proposal will considerably enhance the quality of life and improve the economic competitiveness of the UK and globally.
Outreach:
It is important that any publically funded research benefits the wider public. The research proposed here is fundamentally basic science; however, the findings of this research have the potential to be taken forward with industrial collaborators e.g. GSK, with which we have established contacts, to form long term development of targeted antimicrobials and prophylactic treatments. We will endeavour to impart this knowledge to the general public utilising the institutes outreach programmes.
Training of researchers:
The project will offer excellent training opportunities for the two PDRAs. The PDRAs will be encouraged to exchange between the two laboratories. They will also be encouraged to present their work regularly at scientific meetings, and to attend advanced training courses. The multidisciplinary experience that they will gain will add to the UK science base in an important and economically vital research area. We currently have an international lead in the development of recombinant glycoconjugate pneumococcal vaccines and require completion of the proposed study to maintain this lead. The research program should give the UK a significant boost in this important and topical health care issue, enhancing the strength of UK science.