Analysis of the surface expression of c-kit and occurrence of the c-kit Asp816Val activating mutation in T cells, B cells, and myelomonocytic cells in patients with mastocytosis

Objective. The Asp816Val c-kit activating mutation is detectable in the per ipheral blood cells of some patients with mastocytosis and in lesional skin biopsies obtained from adult patients with urticaria pigmentosa, These obs ervations led to the conclusion that this mutation is present in mast cells and mast cell precursors that express c-kit, However. the distribution of the Asp816Val mutation among hematopoietic lineages is unknown, To determin e the distribution of the AspS16Val mutation among hematopoietic lineages a nd to explore its relationship to clinical disease, we examined cells beari ng differentiation markers for myelomorlocytic cells as well as T and B lym phocytes, in both peripheral blood and bone marrow obtained from patients w ith mastocytosis. Materials and Methods. The presence of Asp816Val c-kit mutation in cells ma gnetically sorted from peripheral blood or bone marrow according to surface differentiation markers was studied by reverse transcriptase polymerase ch ain reaction (RT-PCR) restriction fragment length polymorphism (RFLP) analy sis, The surface expression of c-kit was determined by flow cytometry. Results. The mutation was detectable by RT-PCR in at Least one cell lineage in the bone marrow in 7 of 7 patients examined and in the peripheral blood of 11 of 11 adult patients with urticaria pigmentosa and indolent disease. The mutation was identified most frequently in B cell?, and myeloid cells. Flow cytometric analysis demonstrated that the differentiated cells expres sing mutated c-kit were negative for surface KIT. Conclusion. These results are consistent with the conclusion that the c-kit Asp816Val mutation occurs in an early progenitor cell and is carried by my elomonocytic cells, T cells, and B cells in addition to mast cells. However , unlike mast cells, these myelomonocgtic cells, T cells, and B cells in ce lls do not concomitantly express surface c-kit and thus may be less suscept ible to the effects of this mutation. (C) 2000 International Society for Ex perimental Hematology. Published by Elsevier Science Inc.