Single‐Cell Dissection Reveals Immune Dysregulation After CD5 or CD7‐Directed Chimeric Antigen Receptor T‐Cell Therapy

Abstract CD5‐ and CD7‐directed chimeric antigen receptor T‐cell (5CAR and 7CAR) therapies for T‐cell malignancies carry the risk of life‐threatening infection. Although depletion of target‐positive lymphocytes is expected, the contribution of residual cell dysfunction to infection risk remains unclear. This work uses single‐cell sequencing to investigate immune dysregulation after 5CAR or 7CAR therapy in patients with T‐cell acute lymphoblastic leukemia. 5CAR induces marked T‐cell exhaustion linked to CD5 loss and B lymphocyte‐induced maturation protein 1 upregulation. This is accompanied by reduced frequency and diversity of Epstein‐Barr virus (EBV)‐associated T‐cell receptors, potentially contributing to the high incidence of severe EBV infection. 5CAR therapy also impairs B‐cell function and diversity while enhancing natural killer cell function and monocyte activation. In contrast, 7CAR reduces the frequency and diversity of multiple pathogen‐associated T‐cell receptors, but causes less T‐cell exhaustion. 7CAR also substantially impairs innate immunity by decreasing monocyte activation and eliminating dendritic cells, which may contribute to the high risk of infection. Thus, unlike CD19 and CD22 CAR therapy, which primarily affects B cells, 5CAR and 7CAR therapies result in broad dysregulation across multiple immune cell types, providing a basis for infection prevention and safer CAR‐T therapy.