The frequency of YFP+ leukaemia cells in the peripheral blood of the HCK−/− group was lower than that in peripheral blood of the HCK+/+ group at 32 days after the second transplantation (Fig. 3e), which was consistent with a decrease in the sizes and weights of the spleens of HCK−/− leukaemic recipient mice (Fig. 3f, g, h). The gene discussed is HCK; the disease is leukemia.