PMC9296782_01
pDC proliferation within the bone marrow of a patient with T-ALL. (A-C) Representative bone marrow Wright-Giemsa aspirates (x600 magnification), demonstrating blasts, morphologically mature plasmacytoid dendritic cells, and other background hematopoietic cells. (B) Flow cytometry highlighting the abnormal T-lymphoblastic (red) and pDC populations (blue). (C) Immunohistochemical stains (x200 magnification), highlighting small clusters of T lymphoblasts (upper panel) and large aggregates of pDCs (lower panel).
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A subsequent bone marrow aspiration and biopsy demonstrated decreased trilineage hematopoiesis with no morphological evidence of dysplasia to suggest MDS; however, an increase in blasts and atypical plasmacytoid cells were present in a background of other hematopoietic cells ( Figure 1A ). By flow cytometry, the blasts were abnormal T lymphoblasts and expressed cytoplasmic CD3, TdT, CD34, CD1a(subset), CD10(partial), CD5, CD7(bright), CD13(partial), CD33(partial), CD123(dim partial), and CD45(dim) and lacked expression of other lymphoid and myeloid markers including cytoplasmic MPO ( Figure 1B , red, and  Supplemental Figure 1 ). T-cell/B-cell markers ( Figure 1B , blue, and  Supplemental Figure 2 ). To visualize the distribution of T lymphoblasts and pDCs within the bone marrow, immunohistochemistry on serial sections of the core biopsy was performed. T lymphoblasts were seen as clusters of either CD3, TdT (dark brown nuclear staining), LM02, or Ki67-positive cells throughout the bone marrow ( Figure 1C , upper panel). The pDCs expressed CD4, CD123, CD303, and low Ki67 (<5%) and lacked TdT, CD56, and TCL-1 by immunohistochemistry ( Figure 1C , lower panel).
Decreased pDC are frequent in patients with T-ALL. pDC frequency (percentage of white blood cells) in bone marrow aspirates from our index case of MPDCP-T-ALL, and from patients with T-ALL (n = 10) and controls (n = 30). Presents are median +- interquartile range. *p < 0.05 based on unpaired t-test.
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T-cell/B-cell markers ( Figure 1B , blue, and  Supplemental Figure 2 ). To visualize the distribution of T lymphoblasts and pDCs within the bone marrow, immunohistochemistry on serial sections of the core biopsy was performed. T lymphoblasts were seen as clusters of either CD3, TdT (dark brown nuclear staining), LM02, or Ki67-positive cells throughout the bone marrow ( Figure 1C , upper panel).