Despite therapeutic advances, multiple myeloma (MM) remains incurable, especially in relapsed/refractory (R/R) cases. B-cell maturation antigen (BCMA) is a key target for novel immunotherapies, including chimeric antigen receptor T-cell (CAR-T) therapies and bispecific T-cell engagers (BiTEs), which vary in efficacy, toxicity, and accessibility. To compare the efficacy and safety of BCMA-directed CAR-T therapies and BiTEs in R/R MM through a systematic review and meta-analysis. We systematically searched PubMed, Embase, and the Cochrane Library up to October 2, 2024, for studies evaluating BCMA-directed CAR-T or BiTEs therapies in R/R MM. Twenty-six studies comprising 2,246 patients were included. A random-effects meta-analysis and meta-regression were performed to assess pooled efficacy and safety outcomes and examine the impact of CAR-T constructs and patient-level characteristics. CAR-T therapies showed a higher overall response rate (ORR) of 84% and CR/stringent CR (CR/sCR) of 55%, compared to 65% and 41%, respectively, for BiTEs. Dual-targeted CAR-T therapies (e.g., anti-BCMA + anti-CD38/CD19) had the highest efficacy (ORR 92%). CAR-T was associated with more hematologic toxicity and cytokine release syndrome, while BiTEs had fewer severe events but higher infection rates. Meta-regression confirmed CAR-T significantly outperformed BiTEs. Unlike previous analyses, this study integrates interventional and real-world data, evaluates dual-target CAR-Ts, and offers detailed product- and subgroup-level comparisons. BCMA-targeted CAR-T therapies yield deeper responses but greater toxicity. BiTEs offer safer, though less potent, alternatives, supporting more personalized decisions in BCMA-directed immunotherapy for MM.

Background: A bidirectional promoter-driven chimeric antigen receptor (CAR) cassette provides the simultaneous expression of two CARs, which significantly enhances dual antigen-targeted CAR T-cell therapy. Methods: We developed a second-generation CAR directing CD19 and CD20 antigens, incorporating them in a head-to-head orientation from a bidirectional promoter using a single Sleeping Beauty transposon system. The efficacy of bidirectional promoter-driven dual CD19 and CD20 CAR T cells was determined in vitro against cell lines expressing either, or both, CD19 and CD20 antigens. In vivo antitumor activity was tested in Raji lymphoma-bearing immunodeficient NOD-scid IL2Rgamma^null (NSG) mice. Results: Of all tested promoters, the bidirectional EF-1α promoter optimally expressed transcripts from both sense (CD19-CAR) and antisense (GFP.CD20-CAR) directions. Superior cytotoxicity, cytokine production and antigen-specific activation were observed in vitro in the bidirectional EF-1α promoter-driven CD19/CD20 CAR T cells. In contrast, a unidirectional construct driven by the EF-1α promoter, but using self-cleaving peptide-linked CD19 and CD20 CARs, showed inferior expression and in vitro function. Treatment of mice bearing advanced Raji lymphomas with bidirectional EF-1α promoter-driven CD19/CD20 CAR T cells effectively controlled tumor growth and extended the survival of mice compared with group treated with single antigen targeted CAR T cells. Conclusion: The use of bidirectional promoters in a single vector offers advantages of size and robust CAR expression with the potential to expand use in other forms of gene therapies like CAR T cells.

Chimeric antigen receptor (CAR) T cell therapy for B cell malignancies is often limited by T cell exhaustion, which is frequently driven by the PD-1/PD-L1 immune checkpoint axis. To overcome this, we developed an “armored” CAR-T cell strategy using a novel bidirectional promoter system. We engineered a single vector to co-express a CD19-specific CAR alongside a secreted anti-PD1 molecule, in either a full-length antibody or a single-chain variable fragment (scFv) format, using the Sleeping Beauty (SB) transposon system. The sequences for the anti-PD1 modules were derived from the clinical antibody nivolumab. Both armored constructs demonstrated robust CAR expression, comparable to or higher than conventional CAR-T cells, and proliferated significantly more than untransfected controls. The engineered cells successfully secreted their anti-PD1 payloads, with the full-length antibody showing more sustained secretion than the scFv. This autocrine blockade resulted in significantly reduced surface PD1 expression on the armored CAR-T cells. Functionally, the anti-PD1-secreting cells exhibited superior cytotoxicity against PD-L1-positive Raji target cells, particularly at low effector-to-target ratios. Critically, in a serial rechallenge assay designed to simulate chronic antigen exposure, both armored CAR-T cell groups showed markedly enhanced proliferation and persistence compared to conventional CAR-T cells, which failed to expand after repeated stimulation. Our findings validate the bidirectional EF1 promoter as an efficient system for generating multi-functional T cells and demonstrate that armoring CAR-T cells with secreted anti-PD1 antibodies is a potent strategy to enhance their persistence and anti-tumor efficacy.