Phase 2b Biomarker Analysis: BCMA CAR-T in Myasthenia Gravis

CAR-T cells that have been redirected to B cell maturation antigen (BCMA) may also be useful for treating myasthenia gravis. A cure for most forms of this debilitating and life-threatening autoimmune disease would require the elimination of long-lived antibody producing plasma cells. In a clinical trial of patients with myasthenia gravis who received BCMA–directed CAR-T cells, patients had significant clinical improvement, targeting of plasma cells, and modulation of relevant immune pathways without general immune destruction. But many questions remain regarding who might benefit from this approach, how to use biomarkers to select patients, and how the health system might be organized to safely bring this expensive treatment to patients.

Recent Research Findings

Descartes-08 (autologous RNA encoded anti-BCMA CAR-T cells) has shown new mechanism of action in relapse/refractory multiple myeloma (MM) patients according to data from the completed placebo-controlled, double-blind, randomized phase 2b trial (NCT04146051). Descartes-08 allows administration in an outpatient setting without preconditioning chemotherapy. The primary endpoint of the trial was met, and in 15 patients treated with Descartes-08, 10 (66.7%) experienced a 5-point or greater improvement in Myasthenia Gravis Composite (MGC) score at month 3. In the placebo group, 4 of 15 (27.3%) patients improved by 5 points or greater at month 3.

Notably, clinical effects persisted for 12 months without further administration of cells. Transiently expressed mRNA CAR-T cells induce a “precision retuning” or “immune reset” that lasts longer than the cells themselves.

Why It Matters

Myasthenia gravis (MG) is a clinically and genetically diverse disease affecting individuals of all ages, marked by fluctuating muscle weakness and fatigue, due to autoantibodies that impede neuromuscular transmission. For a minority of patients, the autoantibodies are produced by and maintained by plasma cells that are not controlled by standard approaches aimed at the B‑cell compartment. The presence of BCMA on plasma cells presents an alternative target for therapeutic development in MG, where the disease is clearly driven by antibody-secreting cells.

Alternative Therapeutic Strategy

Targeting BCMA using CAR-T therapies which redirect a patient’s T cells to attack cancerous plasma cells is a distinct approach to myeloma treatment compared to current therapies. By eliminating or modulating the pathogenic plasma cell populations responsible for myeloma, patients may be able to avoid the life-long daily corticosteroids and other chronic immunosuppressive agents that have toxic side effects and significantly detract from patient quality of life.

What the Data Says

In addition to the clinical results, an exploratory biomarker analysis was conducted to gain better insight in the mechanism of Descartes-08. The data indicate that Descartes-08 decreases the autoreactome (self-reactive antibodies) without inducing general immunosuppression.

• Selective Depletion: The therapy preferentially reduces BCMA-high plasma cells (PCs) and activated plasmacytoid dendritic cells (pDCs), which are primary drivers of autoimmune inflammation.
• Preserving Protective Immunity: Notably, there was no significant decline in vaccine-specific antibodies (such as those for measles, mumps, or tetanus) or total immunoglobulin levels.
• Cytokine Modulation: Treatment led to significant reductions in disease-associated cytokines, most notably IL-6, which is a key indicator of MG severity.

Since mRNA does not integrate into the host genome, this approach provides a level of precision or “on-off switchability” not available with integrating DNA such as DNA A. The CAR RNA is designed to allow for specific and targeted B cell depletion, as the CAR RNA is degraded over time and will not persist after cell division. In contrast, integrating vectors are subject to a proliferative check that results in nonspecific and permanent depletion of B cells.

Rest Hypothesis

Support for the reset hypothesis is also provided by deep molecular profiling studies employing single-cell RNA sequencing (scRNA-seq) and T cell receptor (TCR) analysis.