Haematology laboratory parameters to assess efficacy of CD19‐, CD22‐, CD33‐, and CD123‐directed chimeric antigen receptor T‐cell therapy in haematological malignancies

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INTRODUCTION: Chimeric antigen receptor (CAR) T cell products are available to treat relapsed/refractory B-lymphoblastic leukaemia/lymphoma (B-ALL), diffuse large B-cell lymphoma, mantle-cell lymphoma, and myeloma. CAR products vary by their target epitope and constituent molecules. Hence, there are no common laboratory assays to assess CAR T cell expansion in the clinical setting. We investigated the utility of common haematology laboratory parameters to measure CAR T cell expansion and response. METHODS: Archived CellaVision images, absolute lymphocyte counts, and Sysmex CPD parameters spanning 1 month after CD19-CAR, UCAR19, CD22-CAR, CD33-CAR, and UCAR123 therapy were compared against donor lymphocyte infused control patients. Additionally, CellaVision images gathered during acute EBV infection were analysed. RESULTS: CellaVision images revealed a distinct sequence of three lymphocyte morphologies, common among CD19-CAR, CD22-CAR and UCAR19. This lymphocyte sequence was notably absent in CAR T cell non-responders and stem-cell transplantation controls, but shared some features seen during acute EBV infection. CD19-CAR engraftment kinetics monitored by quantitative PCR show an expansion and persistence phase and mirror CD19-CAR ALC kinetics. We show other novel CAR T cell therapies (UCAR19, CD22-CAR, CD33-CAR and UCAR123) display similar ALC expansion in responders and diminished ALC expansion in non-responders. Furthermore, the CPD parameter LY_WY fluorescence increased within the first week after CD19-CAR infusion, preceding the peak absolute lymphocyte count (ALC) by 3.7 days. CONCLUSION: Autologous and allogeneic CAR T cell therapy produce unique changes in common haematology laboratory parameters and could be a useful surrogate to follow CAR T-cell expansion after infusion.