In particular, when PBMCs from patients with progressive CLL were cultured with IL15 or scFvB1IL15, we observed the restoration of the direct NK cytotoxic activity to HDs levels (even exceeding them) in both conditions; however, the scFvB1IL15 immunocytokine was more highly effective in increasing the NK-mediated direct cytotoxicity in CLL patients. This evidence concerns the gene IL15 and B-cell chronic lymphocytic leukemia.