The evolving role of allogeneic haematopoietic cell transplantation in the era of chimaeric antigen receptor T-cell therapy.

Chimaeric antigen receptor T-cell (CAR T) therapy has revolutionized the management of many haematological malignancies. It is associated with impressive disease responses in relapsed or refractory high-grade B-cell non-Hodgkin lymphoma (B-NHL) and acute lymphoblastic leukaemia (B-ALL) with durable remissions in a subset of patients. Historically, haematopoietic cell transplantation (HCT) has been the standard consolidation strategy for many of these patients who are now being treated with CAR T. Relapses are frequent after CD19 CAR T therapy in B-ALL and consolidation with allogeneic HCT (allo-HCT) may improve survival of patients with high-risk disease. There appears to be a clear difference in B-ALL outcomes between paediatric and adult patients, with the latter having a much higher risk of relapse after CAR T therapy. Late relapses are infrequent in patients with B-NHL and consolidation with allo-HCT may not be needed in patients who achieve a complete remission after CAR T therapy. Future registry-based and prospective studies will hopefully provide the needed data in the future to risk-stratify the recipients of CAR T therapy. Meanwhile, we provide guidance on patient selection and practical issues with performing allo-HCT after CAR T therapy.