A preparation of cells, consisting of autologous tumor infiltrating lymphocytes, that are manipulated in vitro and, upon administration in vivo, re-infiltrate the tumor to initiate tumor cell lysis. In vitro, therapeutic tumor-infiltrating lymphocytes (TILs) are isolated from tumor tissue and cultured with lymphokines such as interleukin-2; the therapeutic TILs are then infused into the patient, where, after re-infiltration of the tumor, they may induce lysis of tumor cells and tumor regression. The use of therapeutic TILs is considered a form of adoptive immunotherapy.