Live cell imaging and imaging flow cytometry analyses suggest that synaptic actin accumulation protects CLL cells against NK cell-mediated killing by reducing intracellular levels of granzyme B. Remarkably, pharmacological inhibition of an actin regulatory pathway in CLL cells was sufficient to prevent actin cytoskeleton remodeling, promote granzyme B accumulation, and restore high susceptibility to NK cell-mediated cytotoxicity. Here, GZMB is linked to B-cell chronic lymphocytic leukemia.