CD43s is overexpressed by myeloid malignancies. (A) AT1413 binding to CD34⁺ and CD38⁺ CD45dim AML blasts of patient 101. Bone marrow cells of this patient were isolated using a ficoll gradient and stored at diagnosis, precluding analysis of AT1413 interaction with nonmalignant granulocytes. (B) Representative examples of AT1413 binding to AML blasts obtained from newly diagnosed patients with AML or MDS (Table 2). (C) AT1413 binding to extramedullary AML of 2 patients (myeloid sarcoma [chloroma] of inguinal node [1] and skin [2]). Paraffin-embedded THP-1 and Jurkat cells were used as a positive and negative control, respectively. Biotin immunoreactivity of antibody shown with streptavidin-HRP and the peroxidase substrate DAB. Scale bars, 20 μm. (D) Bone marrow of a patient with concomitant multiple myeloma and therapy-related AML. (Left) Hematoxylin and eosin staining. Asterisk, malignant double-nucleated plasma cell; arrowheads, AML blasts. Original magnification ×100. (Right) AT1413 staining of CD45dim AML blasts; CD138⁺ multiple myeloma plasma cells do not interact with AT1413. (E) AT1413 binding to CD45dim blasts of patients with AML, and to a lesser extent to CD45⁺ granulocytes and monocytes and absence of binding to CD45⁺ lymphocytes. The fold increase MFI of AT1413 compared with the negative control is indicated in gray (AT1002, filled gray histogram). Bone marrow (BL-079, BL-092, BL-095, BL-096, BL-099) or blood (BL-091, BL-106) of patients with AML was freshly obtained and red blood cells lysed before FACs analysis. RAEB, refractory anemia with excess blasts.