In vivo administration of anti-CD3 monoclonal antibody can activate immune responses thus preventing malignant tumor growth.

Anti-CD3 monoclonal antibodies (mAb) have been shown to suppress T cell-mediated immune responses both in vitro and in vivo. However, in vitro studies with these antibodies have also demonstrated that they possess potent mitogenic properties, raising the possibility that they might be capable of potentiating immune responses in vivo. In this regard, we have recently shown that an anti-CD3 mAb can activate murine T cells in vivo. Furthermore, low doses of antibody induce interleukin 2 (IL-2) receptor expression and enhanced proliferation to allogeneic major histocompatibility complex (MHC) antigen without detectable modulation or blocking of the T cell receptor and without suppression of T cell-mediated immune responses. In light of these findings, we investigated the ability of low dose anti-CD3 to enhance an anti-tumor response directed against the malignant murine UV-induced skin tumor, 1591-Pro-4L. Low dose anti-CD3 administration resulted in enhanced in vitro anti-tumor activity and prevented tumor outgrowth in approximately two-thirds of animals treated at the time of tumor inoculation. Furthermore, these animals displayed lasting tumor-specific immunity. These results suggest that anti-CD3 mAb can be utilized for the enhancement of anti-tumor responses in vivo and may have general application in the treatment of immunodeficiency.