DP069 | PRE-LYMPHODEPLETION SENESCENT AND IMMUNOSUPPRESSIVE TRAITS OF LYMPHOMA SYSTEMIC ENVIRONMENT ASSOCIATED TO CD19.CAR-T CELL THERAPY FAILURE

The therapeutic success obtained with CAR T cells represents the results of many years of research based on the understanding of the interaction between T cells and the tumor microenvironment. Several studies suggest that T cell switch towards an exhausted/senescent phenotype may be a key driver of CD19.CAR T cell failure. In relapsed/refractory (r/r) B-cell lymphoma patients undergoing CAR T cell therapy, a histology-based approach to characterize the inflammatory infiltrate and the tumor tissue is unfeasible in routine clinical practice. In this regard, multicolor flow cytometry was used to characterize the systemic immune repertoire on fresh whole blood and a plasma profile of extracellular vesicles (EVs) as surrogate for lymphoma cells and immunosuppression. A serum panel of 46 mediators and the molecular tracking of the transgenic CAR on whole blood were performed by Luminex 200 platform and digital droplet PCR, respectively. This is a monocentric prospective tissue study conducted on 43 patients receiving AIFA-approved CD19.CAR T cell products, namely axi-cel (N=24), tisa-cel (N=14) and brexu-cel (N=5) for r/r B-cell lymphomas at IRCCS-Azienda Ospedaliero-Universitaria of Bologna. We found a significant increase of senescent CD8+ T cells (Figure 1A), higher levels of senescence-associated mediators (Figure 1B) and immunosuppressive markers (Figure 1C) measured at pre-lymphodepletion (PLD) in patients who did not respond to treatment during the follow up (NDR, n=21) compared to those achieving a durable response at 1-year (DR, n=19). On the contrary, these latter showed a higher percentage of PLD CD8+ cells expressing CD28 activation marker (Figure 1D). Senescent CD8+ T cells positively correlated with PD-L1+EVs and PD-L1+CD19+EVs measured at PLD; negatively with CD4+ TCM (central memory) and CD4+ CAR-TCM measured at peak of expansion. PD-L1+EVs positively correlated with PLD immunosuppressive markers and negatively with CAR-DNA peak and CAR T cells with early-memory phenotype. Our data suggest that pre-lymphodepletion senescent and immunosuppressive traits of lymphoma systemic environment contribute to the poor ability of CAR T cell to kill the target probably through checkpoint immune axis and as consequence to lack of CAR T cell efficacy.