The expression of the ras p21 oncoprotein in the bone marrow smears of children with acute leukemia.

Point mutations of the ras genes have been detected in various hematologic malignancies. This genetic event may either occur in all malignant cells or be acquired by different subclones, which however, cannot be demonstrated adequately by analyzing only DNA derived from patient specimens. The availability of the ras p21 monoclonal antibody (MoAb) Y 13259 makes possible the direct study of the distribution of the ras gene product in human malignant cells. In this report the expression of the ras p21 oncoprotein in the bone marrow smears of 35 children with acute leukemia has been analyzed. The smears were treated with the MoAb Y 13259, biotinylated goat anti-rat IgG, streptavidin, peroxidase and stained with diaminobenzidine (DAB). The intensity of the staining was evaluated by two independent observers as negative or equivocal (-/+), moderate (+) or intense (++), by counting one thousand cells. Patients were also classified according to the percentage of the stained cells into four groups (0, I, II, III). It was found that 22/35 (63%) were (+) or (++) positive as follows: 11/21 (52%) with ALL CALLA (+), 2/2 ALL-B, 3/3 ALL-T and 6/9 AML. In Group 0 (none of the blasts was stained) were 13/35 (37%), as well as in Group I (1 to 25% of the blasts stained 1+ or 2+ positive), while in Group II (26 to 50% positive stained) 3/35 and in Group III (more than 51% stained) 6/35, all of which were AML (6/9). It is concluded that the immunohistochemical analysis of the ras p21 in blast cells of children with acute leukemia may demonstrate that ras gene expression in some subclones, the intensity and percentage of which may be of some clinical importance.