Multi-scale analysis of B cell responses in ageing

The immune system is a complex system, made up of many different types of cells and molecules that interact together to protect us from infectious disease. It has to be able to recognise the many different foreign entities that we come across but without reacting to "self". Hence it is a system that is in very careful balance. With age this balance is disturbed, we become more prone to infectious disease (and when we catch a disease we are more poorly as a result). Vaccination, that normally we rely on to help protect us from disease, does not work as well. On the other hand we also are more likely to suffer from inflammation, and diseases where inflammation may have a part in their aetiology such as cardiovascular disease and Alzheimer's disease. Hence understanding why the older immune system fails with age is a big challenge.
When we are vaccinated the immune system makes antibodies, which bind to the foreign molecule (antigen), have a variety of functions and are the chief readout for many vaccines to decide if the vaccine has worked or not. The antibodies are made by B cells, and after vaccination we are left with memory B cells that know how to make the antibodies we need in case we meet the disease we were vaccinated against. In old age we make less effective antibodies, and some of the antibodies that we do have react to "self" antigens. So somewhere in the antibody - generation process the balanced system has changed.
We have shown that some types of B cell are changed with age, but we don't know what their function is. We will use our unique cell analyser (capable of measuring 35 different parameters per cell) to identify exactly which types of B cell are changed with age.
We have also previously shown that in older people the repertoire of the antibody-producing cells is less diverse. This loss of diversity is associated with poor health. Diversity is important in a vaccine response, as sequencing of thousands of antibody genes in a response shows that many different types of antibody genes are involved. However, we also found that within a population of responding cells there are favoured characteristics of a section of the antibody gene (CDRH3) which codes for the part of the antibody that is important in binding the foreign antigen. So even though the response looks diverse, there are some common sequence characteristics between antibodies - even for different foreign antigens.
We hypothesise that favoured CDRH3 characteristics are ones that make a structure that is capable of binding to multiple foreign antigens (polyspecific), and that these will predominate in a vaccine challenge. However, there needs to be a limit on polyspecificity as this could lead to self-reactivity - we could make an antibody to a foreign pathogen but it might accidentally also bind to a self-antigen and cause autoimmune disease. Since lack of foreign antigen specificity and gain of self-reactivity are features of antibodies from older people, the balanced trade-off between the advantages and disadvantages of polyreactivity may be disturbed in old age.
Many other factors are involved in a vaccine response, and we don't know the details of them all. Hence we will use statistical mechanics to make a model of the B cell response, enabling us to look at events on a population level without knowing the detailed interactions below it. We will model the dynamics of a B cell response, incorporating values determined from laboratory investigation. The data will be carefully looked at to define values for CDRH3 characteristics that might be polyspecific, and we will produce some antibodies in the lab to test our predictions of whether a given CDRH3 sequence would be polyspecific or not. We hope that production and validation of a model that explains the balance between foreign antigen specificity and self-reactivity will then enable us to focus on factors that we might change to redress the balance in older age.

The B cell repertoire is changed with age - having a decreased diversity of Ig genes and altered subsets of B cells. The human immune response is not limited to a few specific antibodies but is diverse. However, there are some common features of Ig genes, in the CDRH3 region, that are favoured in a response regardless of the type of challenge. In naïve B cells the baseline features of Ig genes before challenge show age-related differences that might contribute to reduced efficacy of responses in old age. Our observations challenge the lock and key hypothesis of antibody binding and highlight the requirement for more complex models of antibody responses.
We will investigate possible mechanisms behind age-related B cell change using data on repertoire change at the molecular and cellular levels to build and test models of repertoire responses to challenge. Since Ig gene specificity has a central role in repertoire selection a large part of our work centres on predicting and testing antibody binding characteristics. In addition we have unique access to mass cytometry in order to clarify some of the confusion that exists with respect to cellular population function and age-related changes. Each member of this team has expertise complementary to the others such that the team is uniquely placed to address this question. The unique experimental analyses of high throughput sequencing (HTS) and mass cytometry (CyTOF) have, and will, generate a large amount of data (DDW) that needs to be efficiently explored for extraction of specific age-related immune response fingerprints. Structural bioinformatics will help in the analysis and predictions of the conformational changes and binding specificity observed in the age-specific repertoire (FF). Statistical mechanics can relate end point observation to parameters controlling microscopic stochastic events, and therefore may be usefully employed to help elucidate the reasons for differences in repertoire with age (ACCC)

Academic beneficiaries:
The learning opportunities from this project are invaluable. Close working interactions between the postdocs employed on the project will develop a working appreciation of each other's discipline which will also be felt by other members of the individual labs, including undergraduate and postgraduate students that pass through the labs. Cross-participation in divisional research seminars, together with the fact that all three applicants are involved in undergraduate teaching, will help bring multidisciplinarity to a wider audience.
In addition to researchers in our own academic areas the data available from this program will be of interest to biologists studying vaccine design and basic B cell biology, medics studying autoimmune diseases and B cell lymphomas, or using the CyTOF for analysis of patient samples, biophysicists studying molecular interactions esp of antibody antigen recognition. Analysis software produced during this project will be made publicly available and will facilitate the research of a large number of immunologists.

Industry applications:
Vaccine design. Adjuvant technology has advanced greatly as a result of improved understanding of TLR responses. Coupled with immunological understanding of co-stimulatory molecules and advances in chemical engineering of biocompatible nanoparticles it is now possible to synthesise vaccine nanoparticles that deliver adjuventicity and co-stimulation together with a well-defined B cell antigen. These nanoparticle vaccines (eg Selecta Bioscience's targeted
Synthetic Vaccine Particle, http://www.selectabio.com/product-platform/index.cfm ) have significant advantages over conventional vaccine formulations in that they can be very precise w.r.t. their antigen and target cell and thereby avoid adverse reactions while ensuring the relevant target is not overwhelmed by competing antigens in the same vaccine. Design of the B cell antigen in these systems is crucial to ensure specificity of the response. Data from our project will help understand the dynamics of a responding B cell population as related to common biophysical properties of the antibody interacting sites. This information will be crucial in the design of effective and specific B cell antigens for synthetic vaccines.

Antibody therapeutics. Understanding the characteristics of Ig genes that encode promiscuous antibodies will facilitate antibody discovery by helping choose which antibodies to a particular target will be followed through. Although this is not a drug discovery program we will be characterising and cloning antibodies. Should any of these antibodies be identified as having therapeutic potential we will consider them for patent in conjunction with King's Business.

Public beneficiaries:
Improved vaccine design will benefit public health, particularly the health of older people. More effective vaccines at all ages contributes to herd immunity, and the particular efforts to improve vaccines for older people will substantially reduce morbidity and mortality associated with infectious disease.
A better understanding of the changes in the immune system with age will contribute to the knowledge base upon which health research on age-related diseases is reliant and may therefore contribute to improved public health with regards to diseases such as Cancer, Alzheimer's, Rheumatoid arthritis.