The enzyme AID is necessary for the immune response. It changes the antibody genes so that we can efficiently respond to every pathogen and to vaccination. To do this, AID mutates the genome of the lymphocytes that produce the antibodies. However, as a side effect, AID can also mutate the wrong genes and predispose B lymphocytes to become lymphomas or leukemias or make these diseases more aggressive. We have found a mechanism that controls the amount of AID in the cells through the chaperone Hsp90, which keeps AID stable. A number of Hsp90 inhibitors exist and are in clinical trials for cancer treatment but their effectivity is limited by their known and unknown side effects as Hsp90 interacts with multiple proteins. We will investigate how these inhibitors will affect the antibody immune response given that they will destabilize its key enzyme AID. We also propose that these inhibitors could be useful in treating or preventing lymphomas and leukemias that are driven by AID, which we will test using mouse models and human clinical samples.