This is because significant acidification of the bone marrow micro-environment (as low as pH ∼6.5) occurs during intensive blast production in the progression of leukaemias (Mortensen et al., 1998), suggesting that intracellular acid stress resistance mechanisms are likely required for progression of blood-born cancers and are thus likely also in place in Hap1 cells (see below). Here, HAP1 is linked to leukemia.