The Nussenzweig lab explores how the rapid proliferation of immune cells during infection could precipitate cancer. When the body is invaded by viruses, bacteria, or parasites, antibody-producing B cells swiftly expand their ranks to help clear the infection. This vigorous cellular replication comes with a price: When DNA is copied at a rapid pace to produce large numbers of cells, it is at risk of accruing damage, including the sorts of chromosome breaks and rearrangements that may trigger the development of lymphomas. I will stimulate the rapid division of B cells and identify the "fragile sites" within the genome that are prone to breaks and rearrangement. I will also assess whether a protein known to recognize and bind to spots of DNA damage can protect dividing B cells from genomic rearrangements at these sites—work that could point toward novel therapies for cancers that develop in the cells of the immune system.