Eliciting effective affinity maturation is an essential component of efficacious humoral vaccines. Recent findings in vaccine development for influenza and HIV-1 suggest that success in these key areas will depend on the ability to influence affinity maturation to an extent not yet possible. Continuing advances in experimental methods for elucidating cellular interactions in the germinal center reaction now make it possible to understand and model selection in affinity maturation. The specific aims are organized around the major goal of developing and using a mathematical model through cycles of experimentation, development, prediction and validation. For all research aims, the antibodies and antibody clones used will be selected from among those isolated and characterized in human and murine vaccine studies. The model developed will include an accurate model of somatic hypermutation sequence- specific mutation rate. This model will be made possible through the use of mice engineered to express the same rearranged Ig gene in productive and non-productive, but mutating, forms. The model will contain statistically accurate models of the correspondence between amino acid mutations and changes in affinity due to these mutations. These models will be realized through the use of a novel high-throughput B-cell culture system that allows the isolation of light- chain/heavy-chain pairs from individual B cells as well as measurement of the avidity of the antibody encoded by these genes. Furthermore, we will obtain the structures and detailed kinetic binding parameters for selected clonally related antibodies. The Ig variable-region genes to be used in these studies will be selected from genes isolated in a study of affinity maturation in the human response to seasonal influenza vaccine and in murine studies of influenza virus hemagglutinin or Bacillus anthracis protective antigen immunization. The models and methods obtained in these studies will then be used to study 1) the extent to which important features of affinity maturation are conserved in repeated experiments using controlled mouse studies as well as repeated vaccinations in human subjects; and 2) the effects on affinity maturation of modulating the effective selection intensity in mice engineered to overexpress an anti-apoptotic gene. We will provide cross-disciplinary training in our own laboratories and through summer schools and symposia. All models and software will be shared with the scientific community.