The CD3×CD3 BsAb treats GVHD in mice previously cured of xenograft leukemia without allowing leukemia relapse. (A) Timeline of experiment and treatments. (B) CD19×CD3 BsAb cures mice of CD19⁺ NALM6-luc leukemia. Luciferase (luc)–transduced human leukemia NALM6-luc was monitored using in vivo bioluminescent imaging. n = 5 mice per group. (C-F) GHVD scores for each individual mouse, grouped by treatment. Open triangles represent treatment days. (G) Survival of mice treated with CD3×CD3 BsAb. (H) Standard curve of cycle threshold (ct) values for human CD3 in complementary DNA generated from RNA purified from mouse blood spiked with known numbers of T cells. (I) Calculated number of T cells per mouse. Open circles indicate that the number was incalculably low because the ct value of for human CD3 was >40. (J) Immunohistochemical staining (600× original magnification) showing human CD3⁺ T cells in the lung tissue of the mouse euthanized on day 197, the mouse from the 10-μg group with the highest number of T cells in its peripheral blood. Experiment was repeated 2 times.