The role of soluble B cell maturation antigen as a biomarker in multiple myeloma

Biomarkers of Efficacy and Safety of the Academic BCMA-CART ARI0002h for the Treatment of Refractory Multiple Myeloma

PURPOSE

B-cell maturation antigen (BCMA)-chimeric antigen receptor T-cells (CART) improve results obtained with conventional therapy in the treatment of relapsed/refractory multiple myeloma. However, the high demand and expensive costs associated with CART therapy might prove unsustainable for health systems. Academic CARTs could potentially overcome these issues. Moreover, response biomarkers and resistance mechanisms need to be identified and addressed to improve efficacy and patient selection. Here, we present clinical and ancillary results of the 60 patients treated with the academic BCMA-CART, ARI0002h, in the CARTBCMA-HCB-01 trial.

PATIENTS AND METHODS

We collected apheresis, final product, peripheral blood and bone marrow samples before and after infusion. We assessed BCMA, T-cell subsets, CART kinetics and antibodies, B-cell aplasia, cytokines, and measurable residual disease by next-generation flow cytometry, and correlated these to clinical outcomes.

RESULTS

At cut-off date March 17, 2023, with a median follow-up of 23.1 months (95% CI, 9.2-37.1), overall response rate in the first 3 months was 95% [95% confidence interval (CI), 89.5-100]; cytokine release syndrome (CRS) was observed in 90% of patients (5% grades ≥3) and grade 1 immune effector cell-associated neurotoxicity syndrome was reported in 2 patients (3%). Median progression-free survival was 15.8 months (95% CI, 11.5-22.4). Surface BCMA was not predictive of response or survival, but soluble BCMA correlated with worse clinical outcomes and CRS severity. Activation marker HLA-DR in the apheresis was associated with longer progression-free survival and increased exhaustion markers correlated with poorer outcomes. ARI0002h kinetics and loss of B-cell aplasia were not predictive of relapse.

CONCLUSIONS

Despite deep and sustained responses achieved with ARI0002h, we identified several biomarkers that correlate with poor outcomes.

Soluble B-cell maturation antigen in multiple myeloma

B-cell maturation antigen (BCMA) has emerged as a promising immunotherapeutic target in multiple myeloma (MM) management, with the successive approval of antibody-drug conjugates, bispecific antibodies, and chimeric antigen receptor T-cell therapies directed to this membrane receptor. Soluble BCMA (sBCMA), a truncated version produced through gamma-secretase cleavage, can be quantified in serum/plasma samples from patients with MM via electrochemiluminescence, fluorescence, or enzyme-linked immunosorbent assays, as well as through mass spectrometry-based proteomics. Besides its short serum half-life and independence from kidney function, sBCMA represents a reliable and convenient tool for MM monitoring in patients with nonsecretory or oligosecretory disease. Numerous studies have suggested a potential utility of this bioanalyte in the risk stratification of premalignant plasma cell disorders, diagnosis and prognostication of MM, and response evaluation following anti-myeloma therapies. In short, sBCMA might be the "Swiss army knife" of MM laboratory testing, but is it ready for prime time?

Safety and clinical activity of autologous RNA chimeric antigen receptor T-cell therapy in myasthenia gravis (MG-001): a prospective, multicentre, open-label, non-randomised phase 1b/2a study

BACKGROUND

Chimeric antigen receptor (CAR) T cells are highly effective in treating haematological malignancies, but associated toxicities and the need for lymphodepletion limit their use in people with autoimmune disease. To explore the use of CAR T cells for the treatment of people with autoimmune disease, and to improve their safety, we engineered them with RNA (rCAR-T)-rather than the conventional DNA approach-to target B-cell maturation antigen (BCMA) expressed on plasma cells. To test the suitability of our approach, we used rCAR-T to treat individuals with myasthenia gravis, a prototypical autoantibody disease mediated partly by pathogenic plasma cells.

METHODS

MG-001 was a prospective, multicentre, open-label, phase 1b/2a study of Descartes-08, an autologous anti-BCMA rCAR-T therapy, in adults (ie, aged ≥18 years) with generalised myasthenia gravis and a Myasthenia Gravis Activities of Daily Living (MG-ADL) score of 6 or higher. The study was done at eight sites (ie, academic medical centres or community neurology clinics) in the USA. Lymphodepletion chemotherapy was not used. In part 1 (phase 1b), participants with Myasthenia Gravis Foundation of America (MGFA) disease class III-IV generalised myasthenia gravis received three ascending doses of Descartes-08 to determine a maximum tolerated dose. In part 2 (phase 2a), participants with generalised myasthenia gravis with MGFA disease class II-IV received six doses at the maximum tolerated dose in an outpatient setting. The primary objective was to establish safety and tolerability of Descartes-08; secondary objectives were to assess myasthenia gravis disease severity and biomarkers in participants who received Descartes-08. This trial is registered with clinicaltrials.gov, NCT04146051.

FINDINGS

We recruited 16 individuals for screening between Jan 7, 2020 and Aug 3, 2022. 14 participants were enrolled (n=3 in part 1, n=11 in part 2). Ten participants were women and four were men. Two individuals did not qualify due to low baseline MG-ADL score (n=1) or lack of generalised disease (n=1). Median follow-up in part 2 was 5 months (range 3-9 months). There was no dose-limiting toxicity, cytokine release syndrome, or neurotoxicity. Common adverse events were headache (six of 14 participants), nausea (five of 14), vomiting (three of 14), and fever (four of 14), which resolved within 24 h of infusion. Fevers were not associated with increased markers of cytokine release syndrome (IL-6, IL-2, and TNF). Mean improvements from baseline to week 12 were -6 (95% CI -9 to -3) for MG-ADL score, -7 (-11 to -3) for Quantitative Myasthenia Gravis score, -14 (-19 to -9) for Myasthenia Gravis Composite score, and -9 (-15 to -3) for Myasthenia Gravis Quality of Life 15-revised score.

INTERPRETATION

In this first study of an rCAR-T therapy in individuals with an autoimmune disease, Descartes-08 appeared to be safe and was well tolerated. Descartes-08 infusions were followed by clinically meaningful decreases on myasthenia gravis severity scales at up to 9 months of follow-up. rCAR-T therapy warrants further investigation as a potential new treatment approach for individuals with myasthenia gravis and other autoimmune diseases.

FUNDING

Cartesian Therapeutics and National Institute of Neurological Disorders and Stroke of the National Institutes of Health.