Natural killer (NK) cells can be widely applied for cancer immunotherapy due to their ability to lyse tumor targets without prior sensitization or human leukocyte antigens-matching. Several NK-based therapeutic approaches have been attempted in clinical practice, but their efficacy is not sufficient to suppress tumor development mainly because of lacking specificity. To this end, the engineering of NK cells with T cell receptor along with CD3 subunits (TCR-NK) has been developed to increase the reactivity and recognition specificity of NK cells toward tumor cells. Here, we review recent advances in redirecting NK cells for cancer immunotherapy and discuss the major challenges and future explorations for their clinical applications.

Background: t(8;21)(q22;q22) is one of the most frequent chromosomal abnormalities in acute myeloid leukemia (AML), leading to the generation of the fusion protein AML1-ETO. Despite t(8;21) AML being considered as a subtype with a favorable prognosis, approximately 30–50% of patients experience drug resistance and subsequent relapse. N⁶-methyladenosine (m⁶A) is demonstrated to be involved in the development of AML. However, the regulatory mechanisms between AML1-ETO and m⁶A-related enzymes and the roles of dysregulated m⁶A modifications in the t(8;21)-leukemogenesis and chemoresistance remain elusive. Methods: Chromatin immunoprecipitation, dual-luciferase reporter assay, m⁶A-qPCR, RNA immunoprecipitation, and RNA stability assay were used to investigate a regulatory loop between AML1-ETO and FTO, an m⁶A demethylase. Gain- and loss-of-function experiments both in vitro and in vivo were further performed. Transcriptome-wide RNA sequencing and m⁶A sequencing were conducted to identify the potential targets of FTO. Results: Here we show that FTO is highly expressed in t(8;21) AML, especially in patients with primary refractory disease. The expression of FTO is positively correlated with AML1-ETO, which is attributed to a positive regulatory loop between the AML1-ETO and FTO. Mechanistically, AML1-ETO upregulates FTO expression through inhibiting the transcriptional repression of FTO mediated by PU.1. Meanwhile, FTO promotes the expression of AML1-ETO by inhibiting YTHDF2-mediated AML1-ETO mRNA decay. Inactivation of FTO significantly suppresses cell proliferation, promotes cell differentiation and renders resistant t(8;21) AML cells sensitive to Ara-C. FTO exerts functions by regulating its mRNA targets, especially IGFBP2, in an m⁶A-dependent manner. Regain of Ara-C tolerance is observed when IGFBP2 is overexpressed in FTO-knockdown t(8;21) AML cells. Conclusion: Our work reveals a therapeutic potential of targeting AML1-ETO/FTO/IGFBP2 minicircuitry in the treatment for t(8;21) patients with resistance to Ara-C.

The formation of the RUNX1-RUNX1T1 fusion protein, resulting from the t(8;21) translocation, is considered to be one of the initiating events of t(8;21) acute myeloid leukemia (AML). However, the mechanisms of the oncogenic mechanism of RUNX1-RUNX1T1 remain unclear. In this study, we found that RUNX1-RUNX1T1 triggers the heterochromatic silencing of UBXN8 by recognizing the RUNX1-binding sites and recruiting chromatin-remodeling enzymes to the UBXN8 promoter region. Decitabine, a specific inhibitor of DNA methylation, upregulated the expression of UBXN8 in RUNX1-RUNX1T1⁺ AML cell lines. Overexpression of UBXN8 inhibited the proliferation and colony-forming ability of and promoted cell cycle arrest in t(8;21) AML cell lines. Enhancing UBXN8 levels can significantly inhibit tumor proliferation and promote the differentiation of RUNX1-RUNX1T1⁺ cells in vivo. In conclusion, our results indicated that epigenetic silencing of UBXN8 via methylation of its promoter region mediated by the RUNX1-RUNX1T1 fusion protein contributes to the leukemogenesis of t(8;21) AML and that UBXN8 targeting may be a potential therapeutic strategy for t(8;21) AML.

Aberrant DNA methylation is often related to the diagnosis, prognosis, and therapeutic response of acute myeloid leukemia (AML); however, relevant studies on the relationship between bone marrow myeloblast percentage and the DNA methylation level in AML have not been reported. We evaluated the effects of AML blast percentage on DNA methylation level using the MethylC-capture sequencing (MCC-Seq) approach based on next-generation sequencing (NGS) and found that the methylation level of both genome-wide and promoter regions significantly increased when the percentage of AML blasts reached ≥ 40%, indicating that an accurate DNA methylation level in cancer cells can be obtained when the bone marrow samples of AML patients have more than 40% myeloblasts.