HTRA2 and myeloid leukemia: However, in THP-1 myeloid leukaemia cells, there was a significant increase in the expression of HTRA2/OMI gene and protein when compared to the vehicle controls and the chemotherapy drugs alone (P ≤ 0.05), but a synergistic response was not observed (Fig. 4A,B) (Supplementary Figs. S1, S2).