A preparation of tumor infiltrating lymphocytes (TILs) that are transduced with a retroviral vector encoding a gene for a dominant-negative form of the transforming growth factor beta (TGFb) receptor, TGFbDNRII, with potential immunomodulating activity. Upon administration, the TGFbDNRII-transduced autologous TILs recognize and kill tumor cells. The expression of TGFbDNRII allows for the TILs to be resistant to TGF-b-mediated inhibition of T cell proliferation and activation, which allows optimal TIL activity. The immunosuppressant TGF-b is produced by tumor cells and plays a key role in the repression of the immune system.