Because SCRIB and Dlgh1 were proposed to modulate lymphocyte proliferation [7, 8, 9, 10] , we evaluated whether PALS1 might also participate to T cell activation. To this end, peripheral blood lymphocytes (PBL) were purified on Ficoll-isopaque gradients. Primary human T cells were nucleofected for three days with siRNA targeting PALS1, prior stimulation with anti-CD3 and anti-CD28 antibodies. PALS1 knockdown led to a significant decrease in TCR-mediated induction of the activation markers CD69 and CD25 on cell surface (Figure 2A , B). This was accompanied by a reduction in Carboxyfluorescein Succinimydyl Ester (CFSE) dilution, which reflects cell proliferation ( Figure 2C ). Collectively, these data suggest that PALS1 participates to the optimal lymphocyte activation and subsequent proliferation upon TCR stimulation.