To introduce NFKBIE mutations, primary CLL cells from 11 patients were transfected with Cas9 ribonucleoprotein complexes targeting human NFKBIE and were then cultured for 3 days with 3T3-CD40L fibroblasts + IL-4/IL-21 to induce their proliferation, which is required to achieve efficient Cas9 editing [29]. Here, IL4 is linked to B-cell chronic lymphocytic leukemia.