SLAMF7-CAR T cells exert selective fratricide of SLAMF7⁺normal lymphocytes. (A) Expression of SLAMF7 on normal lymphocyte subsets obtained from peripheral blood of myeloma patients (n = 10) analyzed by flow cytometry using the anti-SLAMF7 mAb 162.1. The diagram shows the mean percentage of SLAMF7^+/high CD8 T cells (CD3⁺CD4^–CD8⁺), CD4 T cells (CD3⁺CD4⁺CD8^–), γδ T cells (Vγ9δ2 TCR⁺), NKT cells (CD3⁺CD56⁺), and NK cells (CD3^–CD56⁺), B cells (B) (CD3^–CD19⁺), and monocytes (CD3^–CD14⁺). (B) Expression of SLAMF7 on naive (N) (CD45RA⁺CD45RO^–CD62L⁺), effector memory (EM) (CD45RA^–CD45RO⁺CD62L^–), and central memory (CM) (CD45RA^–CD45RO⁺CD62L⁺) CD4⁺ and CD8⁺ T cells obtained from peripheral blood of myeloma patients (n = 10). (C) CD8⁺ and CD4⁺ T cells were isolated from peripheral blood of myeloma patients, labeled with eFluor670, and used as target cells in 12-hour coculture assays with autologous CD8⁺ SLAMF7-CAR and control CD19-CAR T cells (non–eFluor labeled; E:T ratio = 4:1). The percentage of viable eFluor⁺ target cells before and after coculture was determined by staining with viability dye (top row of histograms); expression of SLAMF7 on viable target cells before and after coculture was determined by staining with anti-SLAMF7 mAb 162.1 (middle row); and the ability of viable target cells to produce IFN-γ in response to stimulation with PMA/ionomycin before and after coculture with SLAMF7-CAR and control CD19-CAR T cells was determined by intracellular cytokine staining (bottom row). The dot plots show overlays of eFluor⁺ target (black) and eFluor^– effector (gray) cells. The numbers in the upper quadrants provide percentages of eFluor⁺ cells. (D) The diagram shows the mean percentage of residual live (7-AAD^–) cells in each of the normal lymphocyte subsets after coculture with SLAMF7-CAR or control CD19-CAR T cells. (C-D) Data shown are representative for 4 independent experiments with SLAMF7-CAR and control CD19-CAR T cells from different donors.