Bispecific antibody fragments with CD20 x CD28 specificity allow effective autologous and allogeneic T-cell activation against malignant cells in peripheral blood and bone marrow cultures from patients with B-cell lineage leukemia and lymphoma

Bispecific antibodies directed against tumor-associated target antigens and to surface receptors mediating T-cell activation, such as the TCR/CD3 complex and the costimulatory receptor CD28, are capable of mediating T-cell activation resulting in tumor cell killing. In this study, we used the B- cell-associated antigens CD19 and CD20 as target structures on human leukemic cells. We found that a combination of bispecific antibody fragments (bsFab₂) with target x CD3 and target x CD28 specificity induces vigorous autologous T-cell activation and killing of malignant cells in peripheral blood and bone marrow cultures from patients with chronic lymphocytic leukemia and follicular lymphoma. The bsFab₂ targeting CD20 were considerably more effective than those binding to CD19. The colony-forming capacity of treated bone marrow was impaired due to large amounts of tumor necrosis factor α produced during bsFab₂-induced T-cell activation. Neutralizing tumor necrosis factor α antibodies were found to reverse this negative effect without affecting T-cell activation and tumor cell killing. CD20 x CD28 bsFab₂, when used alone rather than in combination, markedly improved the recognition of leukemic cells by allogeneic T cells. Therefore, these reagents may be capable of enhancing the immunogenicity of leukemic cells in general and, in particular, of increasing the antileukemic activity of allogeneic donor buffy coat Cells in relapsed bone marrow transplanted patients.