Antibodies are the primary mediators of the protection against infection provided by vaccination. Antibodies become most powerful after the B cells that produce them undergo an evolutionary process called affinity maturation, in which antibodies increase their ability to bind to their targets, and thus neutralize pathogens. Affinity maturation occurs in structures within secondary lymphoid organs (for example lymph nodes or tonsils) known as germinal centers. Germinal centers are well known to be triggered by the first dose of vaccines, generating affinity matured plasma cells (B cells that secrete antibody into serum) and memory B cells, which can be converted into plasma cells by booster doses of vaccine. However, it is not fully understood the extent to which memory B cells can return to germinal centers again upon vaccine boosting. Such return would be very important to allow B cells, for example, to adapt to emerging variants of viruses such as influenza or SARS-CoV-2. This study will involve acquiring samples of B cells from germinal centers that form in response to vaccination with the highly effective hepatitis B vaccine. These cells will be analyzed to determine what fraction of them are memory B cells that returned to germinal centers upon boosting, information that is key to knowledge of how vaccine boosters work. Understanding the rules that govern how and when memory B cells choose to return to germinal centers in an effective vaccine such hepatitis B could help efforts to develop effective vaccination against more challenging, rapidly mutating viruses, such as influenza, HIV, and hepatitis C.