Additional Study Information: Epstein-Barr Virus (EBV) is the virus that causes mononucleosis, also known as mono. Almost all adults have had EBV. For most people, EBV never causes a health problem. However, when their immune system is not working properly (like people who have had a transplant and must be on medications that suppress their immune system), EBV can cause certain diseases where cells grow abnormally. EBV-associated Post-Transplant Lymphoproliferative Disease (EBV-PTLD) is a condition that can occur after a solid organ transplant (SOT) where EBV infects immune cells in your blood, called B cells. In patients who have had an SOT, their immune system is suppressed to prevent the body from rejecting the transplanted organ, and these infected immune cells can lead to cancer. The purpose of this study is to test how well the EBV-CTLs work to treat EBV-PTLD following SOT in patients who have failed rituximab or rituximab plus chemotherapy treatment and to see what side effects happen. Your participation will help us to understand more about EBV-CTLs.