The use of immunosuppressive medications has greatly improved the success of organ transplant because they prevent rejection of the transplant. However, these drugs also greatly increase the possibility of cancer in transplant recipients because they suppress the immune system. One of the most common cancers in transplant patients is caused by a virus, called Epstein Barr virus (EBV). In particular, EBV infection can lead to a type of cancer called B cell lymphoma. A key viral product that contributes to the development of cancer by EBV is called latent membrane protein 1 (LMP1). Studies by our group show that LMP1 exists in different forms, but all the LMP1 molecules found in post-transplant B cell lymphomas have two specific mutations that are not found in other LMP1 molecules. In this study we will expand our analysis of LMP1 molecules from individuals who are infected with EBV. We will also test how LMP1 affects a group of molecules called microRNA, which are known to be involved in controlling how genes are expressed in cells. We believe these studies will help us identify patients who are at particular risk for developing cancer after transplantation and will also help us understand why the cancer occurs. As a result, this will lead to improved management of transplant patients. In the long term, these studies will lead to improved methods of diagnosis and treatment for development of cancer in people who receive organ transplants.