HTLV-1 infection skews hematopoiesis to the T-cell lineage in HU-NSG mice. Expression of CD19 and CD3 on lymphocytes (gated on human CD45) from the BM (A-B), thymus (C-D), spleen (E-F), and MLN (G-H) of HTLV-1-HU-NSG mouse (14 weeks after injection) in comparison with mock-infected HU-NSG mouse reconstituted with tissue-matched CD34⁺ donor cells. Human CD3⁺ cells were then gated and subsequently analyzed for CD4 and CD8 expression (i-viii). CD4⁺/CD8⁻ single-positive T cells are the predominant population in HTLV-1-HU-NSG mice BM (ii), thymus (iv), spleen (vi), and MLN (viii) in comparison with mock-infected HU-NSG mice. Human lymphocytes in mock-infected donor tissue–matched HU-NSG mice (14 weeks after injection) mice show broader and more diverse hematopoietic lineage development, including the presence of B cells (CD19⁺), mature single CD8⁺ T cells, and immature CD4⁺/CD8⁺ T cells (i,iii,v,vii).