Intracerebral bispecific ligand-antibody conjugate increases survival of animals bearing endogenously arising brain tumors

Bispecific antibodies capable of simultaneously binding a tumor surface antigen and the T-cell receptor/CD3 complex are capable of inducing polyclonal immune effector cells to destroy targeted tumor cells. Bispecific antibody immunotherapies have shown some promise against tumors of hematopoietic origin such as lymphomas, but use of bispecific antibodies for the treatment of solid tumors has been less fully explored. To test the preclinical potential of bispecific antibody therapy against an endogenously arising solid brain tumor, we have utilized a novel variation of conventional bispecific antibodies, referred to as bispecific ligand-antibody conjugates, to target choroid plexus tumors. The bispecific ligand-antibody conjugate described in this study is a chemical conjugate between an anti-CD3 monoclonal antibody (HAh) and folic acid, the ligand for a high-affinity surface receptor expressed on the surface of choroid plexus tumors. SVII mice transgenic for SV40 large T antigen and its promoter develop solid choroid plexus tumors in the brain. We demonstrate that choroid plexus tumor cells are susceptible in vitro to cytolysis mediated by cytotoxic T cells in the presence of the bispecific ligand-antibody conjugate in a folate-inhibitable manner. Adoptive immunotherapy studies demonstrate the potential benefits of the bispecific ligand-antibody conjugate in vivo. The bispecific conjugate is capable of retaining adoptively transferred T lymphocytes specifically within tumor tissue for periods of up to at least I week. Further, following intracerebro-ventricular injection of bispecific conjugate and splenocytes containing activated cytotoxic T cells, T cells were observed to penetrate to interior regions of the tumor. A single treatment of adoptively delivered activated effectors and bispecific conjugate into the brain ventricles was insufficient to produce significant increases in survival of SVII mice, but repeated treatment through indwelling cannulas prolonged survival of animals treated with activated effectors and bispecific ligand-antibody conjugate compared to animals treated with activated effectors or saline alone. Our results demonstrate that the SVl I model may be useful for preclinical evaluation and optimization of bispecific ligand-antibody conjugate treatments of solid tumors.