t(8;21)AML patients with RUNX1e6::RUNX1T19a splice variant have poor prognosis

In t(8;21) AML, the RUNX1::RUNX1T1 fusion gene (also called AML1-ETO or AE for short) exists in multiple splice variants, including RUNX1::RUNX1T19a (also called AML1-ETO9a or AE9a for short), RUNX1::RUNX1T1tr (also called AML1-ETOtr or AEtr for short), and RUNX1::RUNX1T111a (also called AML1-ETO11a or AE11a for short), These splice variants have distinct effects on cellular biological functions, which contribute to variability in patient prognoses.This study identifies a novel splice variant, RUNX1e6::RUNX1T1 (also called AML1e6-ETO or AEe6 for short), which results from the fusion of exon 6 of RUNX1 with exon 2 of RUNX1T1 and demonstrates 100% coexpression with AE. Clinical studies indicate that patients expressing AEe6 exhibit poor prognostic outcomes, however, cellular assays reveal that AEe6 retains functionalities similar to those of AE in promoting apoptosis and inhibiting cellular proliferation. Notably, the splice variant AE9a is recognized as an independent prognostic factor for adverse outcomes. Consequently, this study further investigates the potential synergistic effects between AEe6 and AE9a. In a cohort of 82 patients, we observed a coexpression rate of 97% for these splice variants, referred to as AEe69a. Survival analyses revealed that patients expressing AEe69a exhibited the shortest OS and DFS, with median survival times of 13 and 9 months. Cellular studies demonstrated that, compared to wild-type K562-AE cells, K562-AEe69a cells promoted cell transition from G0/G1 to S/G2M phase and inhibited apoptosis and differentiation. Additionally, drug sensitivity analysis revealed that K562-AEe69a cells were less sensitive to the basic chemotherapeutic agent cytarabine than K562-AE, but more sensitive to the JAK2 selective inhibitor TG101209 than cytarabine.