We then delivered this library into the Cas9-expressing murine MLL-AF9 leukemia cells (a well-established AML model driven by a t(9;11) oncogenic fusion protein) (22) using the lentiviral transduction and compared the change of frequency of each integrated sgRNA construct in early (day 0) and late (day 12) time points. The gene discussed is MLLT3; the disease is acute myeloid leukemia.