ZAP70 and B-cell chronic lymphocytic leukemia: Since i) the phenotype of CLL cells has several features characteristic for activated, antigen experienced B cells, ii) PD-1 expression is present in microenvironment of other B-cell malignancies, iii) CLL has some features of T-cells including ZAP-70, CD-5 and CD38, characterization of PD-1 and PD-L1 expression might give deeper insight into CLL biology [17].