Recognition of progenitor cells and viral epitopes by dominant T-cell clones. (A) Frequencies of the 27 dominant CD8⁺ T-cell clones that were selected for reexpression in reporter cell lines. Clones of further mention in the manuscript were labeled individually. (B) Schematic overview of cell and TCR sources for determination of reactivity with hematopoietic precursor cells. (C) Immune phenotypes of hematopoietic progenitor cells (CD34⁺CD45^dim) upon magnetic enrichment and after in vitro expansion. The plots show data of patient 198 as an example. Flow cytometry plots are pregated on live, single cells. (D) Percentage of GFP⁺ reporter T cells after coculture with CD34⁻ and CD34^+exp for all 3 progenitor cell-reactive TCRs. (E) CD34^+exp of patient 230 were cocultured with TCR-transduced or no-transduced (NT) primary human T cells. Bars show percentages of live CD34^+exp after coculture determined by flow cytometry. Coculture details and gating strategy are outlined in supplemental Figure 5. (F-G) Uniform manifold approximation and projection (UMAP) visualization of all index-sorted T-cell clones of the 15 patients. Single data points indicate individual clones. The progenitor cell-reactive T-cell clones are highlighted in orange. (H) Relative frequencies of T-cell clones in the initial and follow-up bone marrow samples of patients 191 and 230 determined by TCRβ repertoire sequencing. Orange triangles indicate progenitor cell-reactive clones. (I) Reactivity of 6 TCRs against viral antigens of CMV (orange, light blue, and blue) and EBV (red). CD34⁻ bone marrow or peripheral blood mononuclear cells of the patients in whom the respective TCRs were identified were used as antigen-presenting cells. The progenitor cell-reactive TCR 11A5 also recognized an epitope within the EBV-PepTivator peptide pools.