Tumor-specific immunotherapy holds great promise, but in most cases tumor-specific antigens are not well defined and numerous strategies have been limited in part by the inability to generate functional tumor-specific T cells. In some cases this is due to the low frequency of tumor-reactive T cells. Furthermore, even when they can be isolated they may be anergized, tolerized, or after allogeneic SCT, they may be senescent and unable to expand [20] . The most successful use of targeted cellular therapy has been with the generation of viral-specific T cells to treat viral-associated malignancies such as EBV-associated Hodgkin's disease or post-transplant lymphoproliferative disorders [21] .