CD22 and acute lymphoblastic leukemia: Specific antitumor activity of the SPDP-based immunoconjugates with OARs of 1 : 1, 2 : 1, and 3 : 1 was tested on human Burkitt's lymphoma Daudi and pre-B acute lymphoblastic leukemia Nalm6 cells in comparison with CD22-negative human acute T-cell leukemia cell line Jurkat.