Prolonged cytopenia following CD19 CAR T cell therapy is linked with bone marrow infiltration of clonally expanded IFNγ-expressing CD8 T cells. Prolonged cytopenia following CD19 CAR T cell therapy is linked with bone marrow infiltration of clonally expanded IFNγ-expressing CD8 T cells

Autologous anti-CD19 chimeric antigen receptor T-cell (CAR T) therapy is highly effective in relapsed/refractory large B-cell lymphoma (rrLBCL) but is associated with toxicities that delay recovery. While the biological mechanisms of cytokine release syndrome and neurotoxicity have been investigated, the pathophysiology is poorly understood for prolonged cytopenia, defined as grade ≥3 cytopenia lasting beyond 30 days after CAR T infusion. By performing single-cell RNA-sequencing analysis of bone marrow samples from healthy donors and rrLBCL patients with and without prolonged cytopenia, we identified a significantly increased frequency of clonally expanded CX3CR1hi cytotoxic T-cells, expressing high interferon (IFN)-γ and cytokine signaling gene sets, associated with prolonged cytopenia. In line with this, hematopoietic stem cells from these patients expressed IFN-γ response signatures. IFN-γ deregulates hematopoietic stem cell self-renewal and differentiation and can be targeted with thrombopoietin agonists or IFN-γ neutralizing antibodies, highlighting a potential mechanism-based approach for the treatment of CAR T-associated prolonged cytopenia. Overall design: Single cell gene expression profiles for 22 bone marrow samples from patients treated with CAR T-cell product, chemotherapy, and healthy donors. Due to patient privacy concerns the raw data is available through the European Genome-Phenome Archive.