EXPRESSION OF THE C-KIT (CD117) MOLECULE IN NORMAL AND MALIGNANT HEMATOPOIESIS

The c-kit proto-oncogen (CD117) has been shown to be present in severa l cell types including normal and neoplastic hemopoietic cells. Among normal BM cells, CD117 expression has been found in about half of the CD34(+) precursors including progenitors committed to the erythroid, g ranulo-monocytic, and megakaryocytic cell lineages. In addition, stron g CD117 expression is detected in bone marrow mast cells as well as in a small subset of NK cells displaying strong reactivity for CD56, and in a relatively important proportion of CD3(-)/CD4(-)/CD8(-) prothymo cytes. These results suggest that CD117 expression can be detected in both myeloid and lymphoid lineages although for the lymphoid lineage i t would be restricted to a small NK-cell subset and early T-cell precu rsors. In acute leukemias CD117 expression was initially associated wi th AML. Nevertheless, at present it is well established that CD117 exp ression may also be found in a relatively important proportion of T-AL L while it is usually absent in B-lineage ALL. Moreover, recent studie s have shown that in about one-third of multiple myeloma cases and pat ients with monoclonal gammopathy of undetermined significance plasma c ells display reactivity for CD117. The prognostic influence of CD117 e xpression has not yet been clearly established. The analysis of this m arker may also be of value for the investigation of minimal residual d isease (MRD). It has been suggested that CD117 in combination with oth er antigens may be of great help for the identification of leukemia-as sociated phenotypes that could be used to monitor MRD in both acute my eloid leukemias and multiple myeloma patients achieving morphological complete remission.