Transforming growth factor (TGF)-β is produced in most human tumors and markedly inhibits tumor antigen-specific cellular immunity, representing a major obstacle to the success of tumor immunotherapy. TGF-β is produced in Epstein-Barr virus (EBV)-positive Hodgkin disease and non-Hodgkin lymphoma both by the tumor cells and by infiltrating T-regulatory cells and may contribute the escape of these tumors from infused EBV-specific T cells. To determine whether tumor antigen-specific cytotoxic T lymphocytes (CTLs) can be shielded from the inhibitory effects of tumor-derived TGF-β, we previously used a hemagglutinin-tagged dominant negative TGF-βRII expressed from a retrovirus vector to provide CTLs with resistance to the inhibitory effects of TGF-β in vitro. We now show that human tumor antigen-specific CTLs can be engineered to resist the inhibitory effects of tumor-derived TGF-β both in vitro and in vivo using a clinical grade retrovirus vector in which the dominant negative TGF-β type II receptor (DNRII) was modified to remove the immunogenic hemagglutinin tag. TGF-β–resistant CTL had a functional advantage over unmodified CTL in the presence of TGF-β–secreting EBV-positive lymphoma, and had enhanced antitumor activity, supporting the potential value of this countermeasure.