Co-stimulation of molecular expression on Nalm-6 cells in vivo and antitumor effect of the anti-CD3×anti-CD19 diabody in xenotransplanted NOD/SCID nude mice. (A) CD80 expression was enhanced when mice were exposed to Ara-C of 1.0 mg/kg/day for 3 days but slightly enhanced for CD86. **p<0.01. (B) For the Nalm-6 xenotransplanted mice, a mixture of T cells and the diabody in different doses (5, 10, and 20 nM/mouse) were injected intravenously 24 hr later and once a week for 2 weeks. PBS, T cells alone, T cells combined with the mixture of anti-CD3scFv and anti-CD19scFv, and T cells combined with the anti-CD3×anti-Pgp diabody served as control groups.