Cure of Burkitt's lymphoma in severe combined immunodeficiency mice by T cells, tetravalent CD3 x CD19 tandem diabody, and CD28 costimulation

To increase the valency, stability, and therapeutic potential of bispecific antibodies, ne have constructed a tetravalent tandem diabody (Tandab) that is specific to both human CD3 (T-cell antigen) and CD19 (B-cell marker; S. M. Kipriyanov et al., J. Mol. Biol., 293: 41-56, 1999). It was generated b y the functional dimerization of a single chain molecule that contained fou r antibody variable domains (V-H and V-L) in an orientation that prevented intramolecular pairing. Compared with a previously constructed heterodimeri c CD3 x CD19 diabody, the Tandab exhibited a higher apparent affinity to bo th CD3(+) and CD19(+) cells and longer blood retention when injected into m ice. Biodistribution studies in mice bearing Burkitt's lymphoma xenografts demonstrated specific accumulation of the radioiodinated Tandab in a tumor site with tumor-to-blood ratios of 1.5, 8.1, and 13.3 at 3, 18, and 24 h, r espectively. Treatment of severe combined immunodeficiency mice bearing est ablished Burkitt's lymphoma (5 mm in diameter) with human peripheral blood lymphocytes, Tandab, and anti-CD28 MAbs resulted in the complete eliminatio n of tumors in all of the animals within 10 days. In contrast, mice receivi ng human peripheral blood lymphocytes in combination with either the diabod y alone or the diabody plus anti-CD28 MAbs showed only partial tumor regres sion. These data demonstrate that the CD3 x CD19 Tandab may be a promising tool for the immunotherapy of human B-cell leukemias and lymphomas.