Background: The high frequency of relapse after induction chemotherapy of advanced ovarian carcinoma calls for new therapeutic approaches. Lysis of ovarian carcinoma cells can be achieved by retargeting of T lymphocytes using F(ab')2 fragments of the bispecific monoclonal antibody (MAb) OC/TR, which is directed to the CD3 molecule on T lymphocytes and to the folate receptor on ovarian carcinoma cells., Purpose: Our purpose was to assess in ovarian carcinoma patients the antitumor activity of in vitro-activated autologous peripheral blood T lymphocytes retargeted with OC/TR., Methods: Patients with epithelial ovarian cancer (International Federation of Gynecology and Obstetrics stages III and IV) meeting specific criteria were eligible to enter a phase II immunotherapy trial. Before immunotherapy, the 28 patients who entered the trial underwent laparotomy to reduce their tumor load and to allow measurement of all indicator lesions. They then received two cycles of five daily intraperitoneal infusions of autologous in vitro activated peripheral blood T lymphocytes retargeted with OC/TR plus recombinant interleukin 2 (IL-2) with (n = 11) or without (n = 17) a second daily infusion of OC/TR F(ab')2 and IL-2. Response to treatment could be assessed in 26 patients following explorative laparotomy; time to progression could be assessed in 27 patients., Results: Seven patients had clinical evidence of progressive disease after treatment and therefore did not undergo laparotomy. Of the 19 patients evaluated by surgery and histology, three showed complete response, one showed complete intraperitoneal response with progressive disease in retroperitoneal lymph nodes, three showed partial response, seven had stable disease, and five had progressive disease. The overall intraperitoneal response rate was 27% (95% confidence interval [CI] = 10%-44%). The complete responses seen in three patients lasted 26 months in one patient, 23 months in the second, and 18 months in the third. Two patients were not assessable for response. One of these patients had bowel perforation during catheter removal, which precluded further evaluation. The second patient was positive only by cytologic examination before immunotherapy, was tumor free at laparotomy after immunotherapy, and remained so for the entire 21 months of follow-up, as determined by cytologic examination of random biopsy specimens. The median time to disease progression in the 15 assessable patients plus those who had stable disease was 11 months (95% CI = 6-18 months). Immunotherapy-related toxic effects included mild to moderate fever, nausea, emesis, and fatigue. Anti-mouse antibodies were detectable by the end of the treatment in 21 of 25 patients tested., Conclusions: Locoregional immunotherapy of ovarian cancer with bispecific MAb-retargeted T lymphocytes can result in tumor regression. Toxicity was mild to moderate and only transient., Implications: Improvement in systemic antitumor responses is needed before this approach can prove useful as adjunctive treatment following induction chemotherapy in patients with minimal residual disease.