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Acute monocytic leukaemia (AML-M5) disease models are scarce. To address this, we reprogrammed THP-1 cells from a patient into AML-M5-specific induced pluripotent stem cells (AML-M5-iPSCs) and differentiated them into monocytic-like cells. Unexpectedly, reprogramming transgenes Oct3/4, Sox2 and c-Myc were reactivated in the AML-M5-iPSC genome. This study examined how transgene reactivation influences responses to doxorubicin in differentiated monocytic-like cells; MATERIALS AND METHODS: AML-M5-iPSCs were differentiated into monocytic-like cells using hM-CSF and IL-3. Cell morphology, phagocytotic activity and surface markers expression of monocytic-like and THP-1 cells were assessed and compared. Cytotoxicity and apoptotic effects of doxorubicin were investigated with CCK-SK assay and flow cytometry; RESULTS: Monocytic-like cells showed morphology, size, and phagocytosis comparable to THP-1 cells. However, they expressed lower surface markers CD4, CD117, CD33, CD64 and HLA-DR than THP-1 cells. Following 24h doxorubicin exposure, THP-1 cells exhibited an IC ₅₀ of 0.59 μM, while the IC ₅₀ for monocytic-like cells could not be determined. Upon similar treatment conditions, 92.47±3.90% of THP-1 cells underwent late apoptosis. In contrast, only 0.26±0.21% of monocytic-like cells entered late apoptosis, 37.23±1.52% underwent necrosis and 62.47±1.63% remained viable; CONCLUSION: Reactivation of Oct3/4, Sox2 and c-Myc in AML-M5-iPSCs induced lower surface marker expression and doxorubicin resistance in monocytic-like cells. Moreover, the apoptotic effect of doxorubicin had been switched to necrotic effect. Surprisingly, morphology and phagocytic function were unaffected. We postulate that transgene reactivation disrupts epigenetic stability and downstream apoptotic pathways. Further investigations are warranted to clarify mechanisms underlying transgene-mediated drug resistance in iPSC-derived disease models.