297 (PB077) - CAR T cells in marginal zone lymphoma (MZL) models with acquired resistance to PI3K and BTK inhibitors

Abstract

Background. MZLs are characterized by an indolent course with median survival over 10 years. However, relapses/progressions are common and if they occur during the during the first 2 years, they heavily impact the median survival. Among the 23 relapsed/refractoryMZL patients treated with the anti-CD19 CAR-T cells axicabtagene ciloleucel (Axi-Cel), the overall response rate was 83% with 73% of complete responses (Jacobson, Lancet Onc 2022; Neelapu, ASH2021). We previously presented MZL-derived models with secondary resistance to BTK/PI3K inhibitors, observing, in some of the resistant cells, an increase in CD19 levels and higher sensitivity to the anti-CD19 loncastuximab tesirine antibody drug conjugate (Arribas, ASH2019, ENA2019, Haematologica 2022). Here, we tested CAR-T cells with costimulatory receptors CD28 or 4-1BB (28z CAR-T and BBz CAR-T), representative of Axi-Cel and tisagenlecleucel (Tisa-Cel), respectively, in these models. Methods: CD19-specific 28z CAR-T and BBz CAR-T produced from 4 healthy donors with retroviral vectors. Transduction efficacy evaluated by protein L staining. MZL models of secondary resistance to PI3K/BTK inhibitors and their parental cells cocultured for 48 h with CAR-T cells (1:1 E: T ratio) after adjusting for transduction efficacy. CAR-T cell-mediated cytotoxicity (CX) calculated as percentage of cell death compared to tumor cells cultured alone. CD19 expression determined by flow cytometry (protein) and RNA-Seq (RNA). Results. We first tested 28z CAR-T and BBz CAR-T against the VL51 cell line and in the 2 derivatives, resistant to various PI3K inhibitors and ibrutinib, respectively. Median CX against parental was 24% and 29% with 28z or BBz CAR-T, respectively. CX was significantly increased against PI3K resistant cells, with a median CX of 62% after coculture with 28z CAR-T and 55% with BBz CAR T cells. Ibrutinib resistant VL51 cells displayed an even higher sensitivity to CAR-T cell killing, with a median CX of 68% after co-culture with 28z CAR-T and 79% with BBz CAR-T cells. Differently from VL51, both parental Karpas1718 and PI3K resistant derivative were equally sensitive to CAR-T cells, with a median 28z CAR-T CX of 72% against parental and 72% against PI3K resistant Karpas1718. Similar results were observed after coculture with BBz CAR-T cells (median CX 67% against parental and 66% against PI3K resistant Karpas1718). The results agreed with CD19 levels, higher in Karpas1718 (parental and derivative) and in the resistant VL-51 derivatives than in parental VL51. Conclusions: Anti-CD19 28z and BBz CAR-T showed maintained or even increased in vitro antitumor activity in MZL models after acquisition of secondary resistance to PI3K/BTK inhibitors. The data support exploring CD19 directed therapeutic modalities for MZL patients. FS, FB: co-senior authors. Work supported by Barletta and Henriette Meyer Foundations. Conflict of interest: Advisory Board: Gilead, AbbVie, Janssen, AstraZeneca, MSD, BMS/ Celgene, Roche, Mei Pharma, Astra Zeneca, Celltrion Healthcare, Incyte, Kite/Gilead. Corporate-sponsored Research: Celgene, Roche, Janssen, Acerta, ADC Therapeutics, Bayer AG, Cellestia, CTI Life Sciences, EMD Serono, Helsinn, ImmunoGen, Menarini Ricerche, NEOMED Therapeutics 1, Nordic Nanovector ASA, Oncology Therapeutic Development, PIQUR Therapeutics AG, Gilead, AbbVie, Janssen.