Effect of SET knockdown or overexpression on NK cell–mediated cytotoxicity. (A) NK-92 cells retrovirally infected using the pSUPER or pSUPER.retro-shSET vector were starved from IL-2 for 48 hours, analyzed for SET protein expression by Western blot (left), and used as effector cells for NK-cell cytotoxicity assays¹⁹  (right). Technical limitations precluded infection of primary human NK cells using the pSUPER or pSUPER.retro-shSET vector. (B) Primary human CD56⁺ NK cells were infected using pNaldini-GFP and pNaldini vector encoding both GFP and SET cDNAs, and next FACS sorted for GFP. Sorted primary human CD56⁺GFP⁺ NK cells were analyzed for SET transcript by real-time RT-PCR (left; n = 4, *P < .01) and used as effectors for NK-cell cytotoxicity assay (right; n = 3, **P < .03). Spontaneous cytotoxicity against K562 cells was tested in a 4-hour ⁵¹Cr release assay. This experiment is representative of 3 performed with similar results. Errors bars represent plus or minus SE.