Induction of Anti-Cancer Effects by Targeting Alloreactive Intentionally Mismatched T Cells and NK Cells to Tumor Cells Using Bi-Specific Trifunctional Antibodies.

Engraftment of donor stem cells induces host vs graft unresponsiveness thus allowing durable engraftment of donor lymphocytes which can induce graft vs malignancy (GVM) effects following transplantation of MHC compatible donor stem cells. Unfortunately, graft vs host disease (GVHD) frequently results in major toxicity and mortality and limits the clinical efficacy of cell therapy. Although the intensity of GVM effects can be improved by using mismatched donors GVM effects cannot be induced in recipients of haploidentically mismatched allografts because of anticipated lethal GVHD. We have attempted to induce GVM effects by intentionally mismatched donor lymphocytes by targeting donor derived T cells and NK cells activated by rIL-2 to cancer cells, in order to improve the efficacy of the GVL effects on the one hand and prevent or minimize GVHD by targeting alloreactive cells to the tumor cells that need to be eliminated using bispecific tri-functional antibodies, on the other. A trifunctional bispecific antibody (BiLu) directed against murine CD3 and human epithelial-cell adhesion molecule (EpCAM), was administered concomitantly with naïve or IL-2 activated donor splenocytes to mice inoculated with a murine model of melanoma cells transfected with human EpCAM (B16-EpCAM). A total of 10/20 and 32/38 mice treated with BiLu and naïve or IL-2 activated donor splenocytes, respectively, were tumor-free survivors without GVHD for >250 days following tumor inoculation. Out of 28 of the disease free survivors (DFS) without GVHD, treated with IL-2 activated splenocytes and BiLu, 24 mice were resistant to a second tumor inoculum (10⁴) given >250 days following the first tumor inoculation. In contrast, only 8 of the 18 DFS mice treated with naïve splenocytes and BiLu, and 5 of the 10 DFS controls treated with BiLu only, resisted the second tumor challenge. Induction of anti-tumor immunity by IL-2 activated cells and BiLu was more efficient and long-lasting in mice previously injected with a lethal first tumor cell dose (5×10⁴) than in mice inoculated with a sub-lethal tumor cell dose (5×10³). Interestingly, a similar infusion of donor cells labeled with bi-specific anti-EpCAM and anti-CD3 following allogeneic stem cell transplantation for metastatic breast cancer did not result in augmentation of GVHD. In conclusion, concomitant inoculation of alloreactive donor lymphocytes and trifunctional bispecific antibody can be effective for targeting of killer T and NK cells to tumor cells while avoiding GVHD, as well as for induction of long-lasting anti-cancer immunity, most likely due to presentation of tumor antigen to T cells by antigen presenting cells (dendritic cells) expressing Fc receptor binding to the Fc portion of the bi-specific antibody.