To address the urgent need for new therapeutics for MLL‐rearranged leukaemias, we generated a bioluminescence‐engineered MLL‐fusion reporter cell line, called THP1‐MA‐Luc, in which the ratio of FLuc/RLuc is used as a measure of the amount of MLL‐AF9 in these cells (Figure 1A). The gene discussed is MLLT3; the disease is leukemia.