Lymphodepletion - an essential but undervalued part of the chimeric antigen receptor T-cell therapy cycle.

Lymphodepletion (LD) or conditioning is an essential step in the application of currently used autologous and allogeneic chimeric antigen receptor T-cell (CAR-T) therapies as it maximizes engraftment, efficacy and long-term survival of CAR-T. Its main modes of action are the depletion and modulation of endogenous lymphocytes, conditioning of the microenvironment for improved CAR-T expansion and persistence, and reduction of tumor load. However, most LD regimens provide a broad and fairly unspecific suppression of T-cells as well as other hematopoietic cells, which can also lead to severe side effects, particularly infections. We reviewed 1271 published studies (2011-2023) with regard to current LD strategies for approved anti-CD19 CAR-T products for large B cell lymphoma (LBCL). Fludarabine (Flu) and cyclophosphamide (Cy) (alone or in combination) were the most commonly used agents. A large number of different schemes and combinations have been reported. In the respective schemes, doses of Flu and Cy (range 75-120mg/m2 and 750-1.500mg/m2) and wash out times (range 2-5 days) differed substantially. Furthermore, combinations with other agents such as bendamustine (benda), busulfan or alemtuzumab (for allogeneic CAR-T) were described. This diversity creates a challenge but also an opportunity to investigate the impact of LD on cellular kinetics and clinical outcomes of CAR-T. Only 21 studies explicitly investigated in more detail the influence of LD on safety and efficacy. As Flu and Cy can potentially impact both the

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Copyright © 2023 Lickefett, Chu, Ortiz-Maldonado, Warmuth, Barba, Doglio, Henderson, Hudecek, Kremer, Markman, Nauerth, Negre, Sanges, Staber, Tanzi, Delgado, Busch, Kuball, Luu and Jäger.

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MH and ML: inventors on patents related to CAR T- cell therapy filed by the University of Würzburg. MH is listed as an inventor on patent applications and granted patents related to CAR-T technologies that have been filed by the Fred Hutchinson Cancer Research Center, Seattle, WA and by the University of Würzburg, Würzburg, Germany. MH is a co-founder and equity owner of T-CURX GmbH, Würzburg, Germany. MH received honoraria from Celgene/BMS, Janssen, Kite/Gilead. VO-M: Travel grants: Kite, Celgene-BMS, Novartis, Roche, Takeda & Janssen; Consultant or advisory fees: Kite, Celgene-BMS, Miltenyi Biomedicine, Pfizer, Novartis & Janssen; Honoraria: Kite, Celgene-BMS & Janssen; Employment: Hospital Clínic de Barcelona. UJ: consultant and advisory fees from Novartis, BMS, Gilead, Janssen, Roche, Honoraria from Miltenyi Biomedicine. DB: research projects with Juno/BMS and Repairon Immuno GmbH; consultant and advisory fees from BMS and Immatics. JD: Employment: Hospital Clínic de Barcelona. DH is an employee and shareholder of Bayer AG. HN and RT: are employees of Servier IRIS. PB: Advisory Board and consultancy from Allogene, Amgen, BMS/Celgene, Kite/Gilead, Incyte, Miltenyi Biomedicine, Novartis, Nektar, Pfizer and Pierre FabreKite/Gilead, Incyte, Miltenyi Biomedicine, Novartis, Nektar, Pfizer and Pierre Fabre. JK: Received grants form Novartis, Miltenyi Biotech and Gadeta. JK is inventor and receives revenues on multiple patents on CAR T and TEG engineering. LC was employed by Takeda. AK was employed by ITTM S.A. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.