Biological characteristics of CD7(+) acute leukemia

Eighty six of 430 acute myeloblastic leukemia (AML) patients (20.0%) and forty of 173 acute lymphoblastic leukemia (ALL) patients (23.1%) had CD7 on their leukemia cells. CD7(+)AML occurred at a younger age than CD7(-)AML, and is more frequent in males. Hepatomegaly and central nervous system involvement were also more frequent in CD7(+) AML than in CD7(-)AML. The age of onset of CD7(+) ALL is also younger than that of CD7(-)ALL. Phenotypically, CD7(+) AML expressed CD34, HLA-DR, and TdT more frequently than CD7(-)AML while CD7(+)ALL expressed CD13/33 more often than CD7(-)ALL. CD7(+)AML cells responded most significantly to interleukin 3 (IL-3), whereas most CD7(-)AML cells responded more significantly to granulocyte macrophage-colony stimulating factor (GM-CSF) and/or granulocyte (G)-CSF than to IL-3. CD7(+)sCD3(-)CD4(-)CD8(-)ALL expressed G-CSF receptor and c-kit mRNA more frequently, which is not usual in other types of ALL. P-glycoprotein (P-gp)/multi-drug resistance gene (MDR1), thought to be expressed in hematopoietic stem cells, is expressed in CD7(+)AML and CD7(+)sCD3()CD4(-)CD8(-) ALL significantly more often than in CD7(-) acute leukemias and the CR rate and overall survival of CD7(+)AML was worse than CD7(-) AML. These data, collectively, suggest the close association of CD7(+)AML and CD7(+)sCD3(-)CD4(-)CD8(-)ALL, not only by the common expression of CD7 itself but also because of their phenotypical immaturity, cytokine receptor expression, P-gp/MDR1 expression and clinical manifestations including the frequent occurrence in males and the poor prognosis. We propose that CD7(+) acute leukemia is an hematopoietic stem cell leukemia, which may be separate entity.