We deciphered the interaction of RUNX1 with CBFA2T3, and demonstrated that addition of free CBFA2T3NHR2 protein domain inhibits the interaction between RUNX1 and CBFA2T3, and results in reversion of leukemic phenotype by decreasing BCP-ALL cell proliferation. The gene discussed is OPN1SW; the disease is acute lymphoblastic leukemia.