Feavers I M ¹ and Borrow R ²

Characterisation of the immune response to specific antigens in sera following vaccination with OMV vaccines and in sera from patients convalescing from group B disease

Vaccines are available against four (A, C, W and Y) of the five groups of Neisseria meningitidis, the bacterium that causes meningococcal disease, but not against the group B bacteria. Developmental vaccines designed to offer comprehensive protection against all meningococcal groups are based on complex mixtures of bacterial proteins. This makes it difficult to measure the relative importance of the individual components of these mixtures in the immune response of the person receiving the vaccine. This project has successfully developed two approaches to this problem:

1. the production of bacteria that do not produce specific components to test whether they can be killed by a person’s immune response
2. the purification of specific components to test which of them will bind antibodies induced by vaccination.

The first approach was used to investigate immune responses to vaccination with the Norwegian and New Zealand vaccines. Genetic methods were used to construct a collection of bacteria each lacking one specific protein component. The collection was then tested to see whether antibodies from vaccinated mice and vaccinated people were still able to kill the bacteria. The results suggested that two particular proteins, known as PorA and FetA, were important in the immune response to these vaccines.

For the second approach, a collection of purified protein vaccine components was prepared. Each individual protein was then attached to a fluorescent bead. The beads are colour-coded by their fluorescent label enabling a laboratory instrument to distinguish between them. In this way, the proteins are effectively tagged by a specific bead so that they can be resolved, even when mixed together and the instrument can be used to measure antibodies binding to specific proteins. This approach was first tested with specific antibodies and shown to be specific, reproducible and highly sensitive. This approach was subsequently used to examine antibodies produced by mice and people in response to vaccination with the Norwegian and New Zealand vaccines.

As a result of this project we now have two new ways of measuring immune responses to complex protein vaccines. An additional benefit of the project has been the development of a range of useful bacteria and a collection of purified proteins. These resources have proved to be in great demand with other laboratories working on the immune response to complex meningococcal vaccines and meningococcal disease. Some of these resources have subsequently formed the basis of HPA and Wellcome Trust funded projects in which Manchester and at NIBSC laboratories participate.

1. National Institute for Biological Standards and Control, Herts.