CD19 is a pan B-cell marker. CALLA (common acute lymphoblastic leukemia antigen) is CD 10. CD45 is known as leukocyte common antigen (LCA). Terminal deoxynucleotidyl transferase (TdT), a specialized DNA polymerase that is expressed only in pre-B and pre-T lymphoblasts, is positive in more than 95% of cases. CD7 is commonly expressed in T-cell ALL.