TC688 allows simultaneous detection and enumeration of cells expressing CD15, CD34 and CD64. CD15 is expressed mainly on mature granulocytes and monocytes but also on immature bone marrow cells and on leukemic cells of the myelo-monocytic lineage. Additionally, CD15 is expressed in rare cases of acute lymphoblastic leukemia (ALL), and on adenocarcinoma cells and immature epithelial cells. CD34 is present on human hematopoietic progenitor cells in bone marrow and blood, whereas CD34 is normally not detected on peripheral blood leucocytes and platelets. Approximately 60% of acute B-lymphoid leukemias, 40% of acute myeloid leukemias (AML), and 1-5% of acute T-lymphoid leukemias express CD34. Chronic lymphoid leukemias, lymphomas and multiple myelomas have been found to be uniformly CD34 negative. CD64 is constitutively expressed on monocytes, macrophages and blood dendritic cells, and at very low levels on neutrophils. CD64 is expressed in acute myeloid leukemia with monocytic differentiation (M4 and M5) and in acute promyelocytic leukemia (M3).

The two illustrations show bone marrow from a case of acute myelomonocytic leukemia stained with TC688. Immature blasts (CD34+CD15-CD64-) are shown in red. Partly differentiated cells (intermediate CD34+intermediate CD64+) are shown in magenta. The most mature cells (CD34-CD64+) are shown in green. Cells with granulocytic differentiation (CD15+intermediate CD64+) are shown in blue. Courtesy of professor Peter Hokland.