Heme Oxygenase-1 Inhibition the Cytotoxicity of NK Cells to AML By Downregulating HLA-C

Backgroud and objective: Acute myeloid leukemia (AML) is a malignant clonal disease of hematopoietic stem cells with abnormal differentiation of myeloid primordial naive cells, which has the highest incidence in adult Acute leukemia with a low cure rate . Clinically, less than one-third of adult AML patients can achieve sustained remission after cytarabine combined with anthracycline chemotherapy, and over 50% relapse after remission. Allogeneic hematopoietic stem cell transplantation (Allo-HSCT) is still the only way to cure leukemia clinically. However, due to age limitation, infection, graft-versus-host disease, and other complications, it is not suitable for all AML patients In recent years, numerous novel drugs have provided more options for the treatment of relapsed and refractory AML while the overall response rate is unsatisfactory and there is no significant advantage in improving overall survival Exploring the mechanism affecting AML relapse and refractory treatment, formulating effective coping strategies are the key to overcome the treatment bottleneck of AML

Methods: Bone marrow nucleated cells were obtained from 15 newly diagnosed AML patients, 15 recurrent AML patients and 15 normal controls. The expressions of HO-1 and HLA-C were detected by quantitative reverse transcription PCR (RT-PCR) and Western blot. In vitro cell experiments, we constructed SiHO-1 lentiviral vector to transfect AML cell lines, cocultured NK cells with it, measured the change of CD107a expression on NK cell surface, and silenced HLA-C expression with small interfering RNA. The silenced AML cell lines were co-cultured with NK cells, and CD107a secretion on NK cells was measured by flow cytometry.

Results: HO-1 expression in AML patients was higher than that in healthy donors (P<0.05), while HLA-C expression was lower than that in healthy donors (P<0.01). Additionally, the plasma HO-1 levels gradually increased, while the HLA-C levels gradually decreased from healthy donors to patients with relapsed AML. In addition, Pearman correlation analysis indicated that HLA-C expression was significantly correlated with HO-1 expression (r=0.635, P<0.001). In AML cell lines, HO-1 silencing enhanced the cytotoxicity of NK cells to AML cells (P＜0.01), while HO-1 overexpression weakened the cytotoxicity of NK cells to AML cells (P＜0.05). The expression of CD107a in NK cells after HLA-C silencing was lower than the control group in U937 and THP-1 cell line. (P＜0.05).

Conclusion: decreased HLA-C expression is associated with increased HO-1 expression during the progression of AML. Besides, the inhibition of HO-1 promotes HLA-C expression, which can therefore promote cytotoxicity of NK cells to AML cells.

No relevant conflicts of interest to declare.