1 Introduction Chimeric antigen receptor (CAR) T cell therapy has transformed outcomes for patients with relapsed or refractory hematologic malignancies [1]. By redirecting autologous T cells toward tumor associated antigens, it achieves durable remissions in patients with previously intractable diseases such as diffuse large B-cell lymphoma (DLBCL) [2], mantle cell lymphoma [3], follicular lymphoma [4], B-cell acute lymphoblastic leukemia [5], and multiple myeloma [6].