BCMA-directed mRNA CAR-T cell therapy for myasthenia gravis: exploratory biomarker analysis of a placebo-controlled phase 2b trial

Chimeric antigen receptor (CAR)-T cell therapies have the potential to transform treatment of autoimmune disease by resetting the immune system. However, adoption of cell therapies in the autoimmune space is limited by hurdles such as inpatient administration, lymphodepletion and safety concerns around cytokine release syndrome and non-specific immunosuppression. RNA-based cell therapy has potential to address these limitations. Here we report prespecified exploratory analyses from a successful placebo-controlled, double-blind, randomized phase 2b trial in patients with generalized myasthenia gravis who received Descartes-08, an autologous, RNA-encoded anti-B cell maturation antigen (BCMA) CAR-T cell therapy. In 66.7% of patients (n = 10/15), transient targeting of BCMA with Descartes-08 administered in an outpatient setting without lymphodepletion resulted in durable clinical efficacy. Comparison of Descartes-08-treated (n ≤ 19) and placebo (n ≤ 15) cohorts by flow cytometry, serum profiling, multiplexing cytokine analysis and bulk/single-cell transcriptional analysis reveals a precision retuning of self-reactivity demonstrated by increased pro-immune function, decreased activity of BCMA+ plasma cells and plasmacytoid dendritic cells and reductions in disease-associated cytokines, such as IL-6. Furthermore, antibody and T cell receptor analysis revealed altered circulating repertoires of self-reactive antibodies and T cell clones among Descartes-08 participants. These effects occurred without immune suppression, indicated by the lack of decline in vaccine-specific antibodies or hypogammaglobulinemia. Our findings unveil a new type of immune reset and support the development of BCMA-targeted RNA cell therapies as a more accessible therapy for autoimmune diseases. ClinicalTrials.gov identifier: NCT04146051 . Analysis of a placebo-controlled trial of a BCMA-targeting CAR-T cell therapy in patients with myasthenia gravis shows that CAR-T cell infusion selectively remodels the systemic immune environment, with elimination of BCMA-high plasma cells and activated plasmacytoid dendritic cells and changes in the autoreactive B cell repertoire.