Hemophagocytic lymphohistiocytosis-like toxicity (carHLH) after CD19-specific CAR T-cell therapy.

Chimeric antigen receptor T-cell (CAR T-cell) therapy is associated with significant toxicities secondary to immune activation, including a rare but increasingly recognised severe toxicity resembling haemophagocytic lymphohistiocytosis (carHLH). We report the development of carHLH in 14·8% of paediatric patients and young adults treated with CD19-specific CAR T-cell therapy with carHLH, occurring most commonly in those with high disease burden. The diagnosis and treatment of carHLH required a high index of suspicion and included multidrug immunomodulation with variable response to therapies. Compared to patients without carHLH, patients with carHLH had both reduced response to CAR T-cell therapy (P-value = 0·018) and overall survival (P-value = < 0·0001).