Adult acute myeloid leukemia cells do not express nonfunctional Ikaros isoforms

We read with great interest the article by Yagi et al1 on the expression of nonfunctional Ikaros isoform 6 (Ik6) in childhood acute myeloid leukemia (AML). The authors reported that Ik6 was expressed in 7 of 10 cases of M4 and M5 AML (French-American-British [FAB] classification), but in none with M2 and M7 AML. Their M4 and M5 cases with Ik6 expression had karyotype abnormalities: inv(16), inv(6), inv(9), del(11), +6, +8, +18, +21, or t(9;11). We also determined whether Ik6 was expressed in samples from 24 Japanese adults with AML using reverse transcriptase–polymerase chain reaction2; 7 cases of M1, 5 of M2, 2 of M3, 5 with cessation of M4, and 5 with cessation of M5. As shown in Table1, all AML samples expressed Ik1 and/or Ik2 but not Ik6. Abnormal karyotypes inv(16) (cases 17 and 18) and +8 (case 15) were also found in adult AML M4 cases; however, expression of Ik6 was not detected in these cases of AML. These findings indicate that Ik6 is expressed in childhood AML but not in adult AML, and that expression of Ik6 in AML is apparently not associated with karyotypes. Several reports demonstrated that Ik6 is frequently expressed in B-precursor acute lymphoblastic leukemia (pre-B ALL) in infants, young children,3-6 and adults, and in childhood pre-T ALL.7 We reported that Ik6 was detected in 16 of 36 patients with adult pre-B ALL but not in adult pre-T ALL.2 

Although the role of nonfunctional Ikaros isoforms in leukemogenic mechanisms is not fully understood, it should be kept in mind that the expression manner of IK-6 differs in adult, childhood, and infant acute leukemias.

Supported by research grants from the Ministry of Education, Culture, Sports, Science, and Technology from the Ministry of Health, Labour, and Welfare, Tokyo, Japan.