Mutations in three amino acids through site-directed mutagenesis of the anti-CD22 variable heavy region enhanced avidity toward the CD22 antigen and lowered the IC50 to 3 × 10–10 M. In vivo evaluation in xenograft mice with established flank Daudi tumors resulted in significant survival of mice that received four 20 μg doses on days 12, 13, 14, and 16 post tumor inoculation. This evidence concerns the gene CD22 and neoplasm.