CD79b-specific T-cell clones spare healthy nonhematopoietic tissue but demonstrate intermediate and low recognition of T cells, HPCs, and monocytes. CD79b-specific T-cell clones were assessed for their reactivity toward healthy nonhematopoietic tissue and hematopoietic cell subsets. (A) Recognition of HLA-A2–positive fibroblasts (FB) and proximal tubular epithelial cells (PTECs) untreated (–) or pretreated with IFN-γ (+) for 4 days was assessed after coincubation with CD79b-reactive T-cell clones K308 and S100 for 18 hours at an S:R ratio of 5:1. Controls included CD79b-negative K562-A2 cells, CD79b-positive LCL-JY, and T-cell clone HSS12 recognizing a peptide of the ubiquitously expressed USP11 presented in HLA-A2. (B-C) Reactivity toward HLA-A2–positive healthy hematopoietic cells was assessed by coculturing clone K308 with cultured (B) and nonactivated (C) cell subsets at the indicated S:R ratios for 18 hours. Controls included peptide-pulsing of stimulators at a concentration of 100 nM peptide (2:1 + peptide or 6:1 + peptide). CD19⁺ B cells were cocultured with irradiated CD40L-expressing mouse fibroblasts for 6 days before the experiment (CD19 [CD40L]). Immature dendritic cells (imDCs) and mature DCs (mDCs) were CD14⁺ monocyte–derived (see supplemental Data). Activated CD4⁺ cells were generated from CD4⁺ cells that were treated with 0.8 μg/mL PHA and cultured for 10 days. Nonactivated CD19⁺, CD14⁺, CD4⁺, and CD34⁺ cells were isolated from peripheral blood using MACS isolation. (D) Clone K308 was stimulated with primary CD4⁺ or CD8⁺ cells in an S:R ration of 6:1. (E-F) Cytotoxicity of clone K308 was determined for nonactivated CD4⁺ and CD8⁺ T cells and activated T cells (containing CD4⁺ and CD8⁺ T cells), activated and nonactivated CD19⁺ B cells (E), and CD34⁺ HPCs (F). PKH26GL-labeled target cells were coincubated with K308 (K308) at different effector to target ratios for 17 hours. Living PKH26GL-labeled target cells were counted and analyzed by FACS and the percent surviving cells was calculated (see Material and methods). Controls included a CMV-specific T-cell clone (CMV clone) recognizing irrelevant pp65-derived peptide NLVPMVATV presented in HLA-A2. The experiment was carried out in triplicate showing mean ± standard deviation. (G) T-cell clone S100 recognizing peptide CD79b₂₀ in HLA-A2 was stimulated with activated CD4⁺ T cells or CD40L-activated CD19⁺ B cells from 2 HLA-A2–positive individuals in an S:R ratio of 10:1. IFN-γ secretion was assessed by standard ELISA.