The purpose of the study was to detect the B7 family members B7.1 (CD80) and B7.2 (CD86) that were expressed in B-ALL patient-derived cells following pre-treatment with Ara-C and to determine whether the combination of the diabody or ds-diabody with Ara-C enhanced the capacity of sub-populations of T cells to kill the tumor cells more effectively in vitro and in vivo. This evidence concerns the gene CD80 and acute lymphoblastic leukemia.