Comparison of immunophenotype of CD4⁺ CD56⁺ blastic tumors and plasmacytoid dendritic cells. (A-G) A case of CD4⁺ CD56⁺ BT presenting in skin and lymph node that transformed into monocytic AML at 22 months. Tumor cells in skin show uniform expression of CD56 (A), with a lymphoid morphology (inset). Variable TdT expression was seen in the skin tumor (B), with stronger TdT expression seen in tumor cells from an involved lymph node (inset). Tumor cells in skin show strong nuclear and cytoplasmic staining for TCL1 (C) and CD123 (inset), with marrow tumor cells (D inset; Wright-Giemsa stained smear) also positive for TCL1 (D). Bone marrow blasts in the subsequent myelomonocytic leukemic transformation (E) also show strong TCL1 immunostaining (F) but were negative for CD123 (G). (H-J) Another CD4⁺ CD56⁺ BT of skin with strong CD123 (H) and TCL1 expression (I) but absence of pAKT immunostaining (J). (K-M) Plasmacytoid dendritic cells (DC2s) in a reactive lymph node (inset K) stain for CD123 (K), CLA (L), CD45RA (inset L), and TCL1 (M) and are negative for CD20 (inset M). (N) Western blot analysis with TCL1 antiserum detects a 14-kDa protein in a B-lymphoblastic cell line (NALM-6), T-PLL carrying a chromosome14 inversion, and tumor cells from a case of CD4⁺ CD56⁺ BT. The latter case demonstrated strong immunostaining for TCL1 (I) and absence of pAKT-Ser473 expression (J), both of which were confirmed by Western blot analysis (N). Original magnifications, × 400; insets, × 1000.