90 percent of people are exposed to the Epstein Barr virus (EBV) at some point in their life. While the immune system’s T cells rapidly clear most EBV-infected B cells, about one in a million infected cells escape. Within these cells, the virus enters a latent phase, kept in check by the watchful eye of so-called memory T cells. This uneasy relationship usually holds steady the rest of a person’s life, unless something -- such as infection with HIV or use of anti-rejection drugs following a transplant -- suppresses the immune system. The virus can then drive the development of B cell cancers. According to new researcher from Children’s Hospital Boston and the Immune Disease Institute, the immune system subdues the virus by watching for a single viral protein called LMP1, knowledge that has already helped suggest two new treatments for the EBV-fueled cancers seen in some immunosuppressed patients.