H2AX and acute promyelocytic leukemia: As γ-H2AX represents a biomarker of the DSB, but not a functional component of the DDR,2, 3, 4 we further analyzed DSBS sensing using 53BP1, a protein that accumulates within PML-NBs and is involved in DSBs repair.41, 42 The time-course analysis of 53BP1 recruitment at the DSBs in in vitro and in vivo models of APL indicated that the disruption of the PML-NBs slows its recruitment at the DSBs after IR.