THE RECEPTOR TYROSINE KINASE P185(HER2) IS EXPRESSED ON A SUBSET OF B-LYMPHOID BLASTS FROM PATIENTS WITH ACUTE LYMPHOBLASTIC-LEUKEMIA AND CHRONIC MYELOGENOUS LEUKEMIA

The class I receptor tyrosine kinase (RTK) HER2 is an oncoprotein that is frequently involved in the pathogenesis of tumors of epithelial or igin, Here we report mRNA expression in peripheral blood and bone marr ow cells from healthy donors in hematopoietic cell lines acid leukemic blasts from patients with acute lymphoblastic leukemia (ALL), acute m yeloblastic leukemia (AML), chronic lymphoblastic leukemia (CLL), and chronic myeloid leukemia (CML). However, cell surface expression of HE R2 protein (p185(HER2)) was found exclusively on a subset of leukemic cells of the B-lymphoblastic lineage, p185(HER2) expression was found on blasts in 2 of 15 samples from infants, 9 of 19 samples from adult patients with C-ALL (CD19(+)CD10(+)), and 1 of 2 samples from patients with pro-B ALL (CD19(+)CD10(-)), whereas none of the leukemic cells f rom patients with AML (0/30), T-ALL (0/7), CLL (0/5) (CD19(+)CD5(+)), or CML in chronic and accelerated phase (0/ 5) or in blast crisis with myeloid differentiation (0/14) were positive for p185(HER2). However, cells from 3 of 4 patients with CML in B-lymphoid blast crisis (CD19( +)CD10(+)) expressed high levels of p185(HER2), which was also found o n the surface of the CML-derived B-cell lines BV-173 and Nalm-1. Our s tudy shows p185(HER2) expression on malignant cells of hematopoietic o rigin for the first time. Aberrant expression of this oncogenic recept or tyrosine kinase in hematopoietic cell types may be an oncogenic eve nt contributing to the development of a subset of B-lymphoblastic leuk emias. (C) 1995 by The American Society of Hematology.