Allogeneic Anti-Bcma CAR-T Cells Show Tumour Specific Killing Against Primary Multiple Myeloma Cells from Different Genomic Sub-Groups

Introduction: Autologous anti-BCMA CAR-T cells have been successfully used in clinical trials for the treatment of relapsed refractory Multiple Myeloma (rrMM), achieving high initial response rates (>80%). However, in some patients these therapeutic responses were not sustained long-term and patients relapsed within 12-18 months^1,2. Poor T cell fitness leading to early CAR-T cell exhaustion as well as BCMA negative tumour escape are thought to be factors contributing to treatment failure. In this study we describe for the first time the activity of an allogeneic anti-BCMA CAR-T cell product derived from young healthy donors (HD) against primary MM cells using patient bone marrow (BM) biopsies. In addition, we compare the performance of HD and MM patient-derived anti-BCMA CAR-T cells.

Results: We have developed a clinically relevant model to test the efficacy of allogeneic anti-BCMA CAR-T cells against primary MM cells. This ex vivo platform uses bulk BM biopsies from MM patients to represent the heterogeneity seen in MM tumours in vivo, including their complex genomic background and unique immunosuppressive microenvironment. Newly diagnosed patients and rrMM patients with high risk genetics are included in the cohort. Using this model we show that allogeneic anti-BCMA CAR-T cells efficiently eliminate primary MM cells after 4 hours of co-culture, in a dose-dependent manner (n=9). These allogeneic anti-BCMA CAR-T cells specifically target BCMA-expressing primary MM cells (including samples with low BCMA levels and high risk genomic abnormalities, with specific anti-BCMA CAR-T cell killing of 13-73%), whilst not affecting non-tumour cells in the BM microenvironment. Moreover, we show that anti-BCMA CAR-T cells become significantly activated after exposure to CD138⁺ MM cells (>50% CD25⁺ T cells versus <10% CD25⁺ T cells against negative controls) and release a range of cytokines detected in the cell culture media by Luminex (including IFNγ, TNFα, IL8, GMCSF, IL-13, IL-12, MIP-1α, MIP-1β, RANTES, IL-5, IFN-α and IL-7). Finally, we compare the T cell profile of rrMM-derived anti-BCMA CAR-T cells (n=6) versus HD-derived anti-BCMA CAR-T cells (n=6), showing that HD-derived anti-BCMA CAR-T cells have a higher CD4/CD8 ratio (0.684 vs. 0.334, p<0.05), increased percentage of naïve CD4 T cells (13.6% vs. 5.05%, p<0.05) and naïve CD8 T cells (34.13% vs. 4.43%, p<0.05) and generate an expanded population of activated CD25⁺ T cells after exposure to MM cells. In contrast, MM-derived anti-BCMA CAR-T cells express increased levels of TIGIT (a checkpoint inhibitory molecule involved in MM relapse) and have a large percentage of permanently dysfunctional T cells (CD101⁺CD38⁺CD8⁺), which might affect their T cell fitness and persistence in vivo.

Conclusion: To our knowledge, this is the first study showing that allogeneic anti-BCMA CAR-T cells are therapeutically active against primary MM cells, in a clinically relevant model that includes the BM microenvironment and different MM genomic subgroups. HD-derived anti-BCMA CAR-T cells were shown to have distinct phenotypic and functional characteristics compared to MM-derived anti-BCMA CAR-T cells. This work lends further support to the development of a first-in-human Phase 1 clinical trial for the treatment of rrMM patients using this allogeneic anti-BCMA CAR-T cell therapy.

¹ Raje N et al. N Engl J Med. 2019; 380(18):1726-1737.

² Zhao WH et al. J Hematol Oncol. 2018; 11(1):141.