ZAP70 and B-cell chronic lymphocytic leukemia: In addition to these kinases, CLL cells abnormally express different T-cell markers that are not expressed by normal B cells, such as Lck, Src kinase (a homolog of Lyn) (99), and ZAP70, a protein tyrosine kinase (PTK) associated with the TCR ζ chain (100) (Figure 2).