One of the major limitations to the immunotherapy of ovarian carci

One of the major limitations to the immunotherapy of ovarian carci noma based on the use of anti-CD3/antitumor bispecific monoclonal an tibodies (bi-inAb) is the need for preactivation of effector cells ex vivo, because cross-linking of the T cell receptor-CD3 complex per se may lead to T..cellunresponsiveness or even apoptosis. The bi-mAb OCITR, which recognizes the folate-binding protein (FBP) overexpressed in 90% of ovarian carcinomas and the CD3 molecule on T cells, has demonstrated efficacy in a clinical setting. Here we investigated the possibility of deliv ering accessory signals to OCPFR-retargeted peripheral blood mononu clear cells (PBMCs) via an anti-CD2S mAb or an anti-FBP/anti-CD2S bi-mAb. Coculture of resting PBMCs from healthy donors with OCITR, anti FBP/anti-CD28 bi-mAb, and FBP@ tumor cell lines resulted in a highly activated phenotype of effector cells and in a dramatic in vitro growth Inhibition of the target cells without an increase in OCPI'R-redirected lysis Whereas both the CD4 and CDS T cell subsets were involved in the growth inhibition, only the CD8 subpopulation accounted for the cytotoxic activity. The in vitro tumor growth inhibition was mediated mainly by soluble factors, which were active on both FBP' and FBP (“bystander effect―) cell lines. Activation and antitwnor activity were also observed, albeit to a lesser extent, using OCITR and monospecific bivalent anti CD2S mAb. In vitro analysis demonstrated that cross-linking between tumor and effector cells for at least 24 h was needed to achieve T-cell activation and development of antitwnor activities. Thus, ex vivo CD3CD2S costimulation on resting PBMCs might be of therapeutic utility for local treatment of minimal residual disease.