GPRC5D and BCMA bi-specific CAR-T: Ex vivo study to simulate early to late-line multiple myeloma (MM) with elevated soluble BCMA.

7538 Background: GPRC5D and BCMA are near-universally expressed on MM cells, with independent target expression and double-negative cells relatively rare. This profile supports the rationale for developing a bi-specific CAR-T therapy to enhance patient coverage, improve efficacy, and reduce the risk of relapse due to antigen loss. Dual-targeting GPRC5D and BCMA represents a novel advancement in the developed antibody therapies. The clinical outcomes of combination of GPRC5DxCD3 and BCMAxCD3 were highly promising. Tri-specific antibodies (GPRC5DxBCMAxCD3) have exhibited superior preliminary efficacy compared to bsAbs or their combinations, However, these approaches require weekly administrations and may pose potential risk. A recent publication (Freeman et al., Blood, 2024) reported that elevated pre-lymphodepletion soluble BCMA (sBCMA) levels were significantly associated with high-risk characteristics as well as high incidence and severity of CRS & ICANS, and metabolic tumor volume (MTV) were correlated with poor clinical outcomes. To address these challenges, we have developed bi-specific CAR-Ts incorporating novel armors to effectively eliminate heavy MM burdens and enhance efficacy, even in the presence of sBCMA. Methods: Aiming to broadly eradicate MM subsets and reduce heavy tumor burden or extramedullary disease (EMD), we have developed a bi-specific CAR-T with two novel humanized VHH binders specifically targeting either BCMA or GPRC5D. Our design incorporates novel secreted and/or membrane-bound armors. Pre-clinical studies were conducted to evaluate the features and drugability of these armored and non-armored bispecific-CAR-Ts. Results: Targeting dual-Ag, the bi-specific CAR-T showed increased T cell activation, superior functionality, and enhanced expansion under re-stress. Notably, the bi-CAR-T retained its functionality against single-Ag expressing cells and displayed robust potency against MM cells with very low BCMA expression, even in the presence of high concentrations of sBCMA. Compared to industry benchmarks, Oricell’s bi-CAR-T showed superior efficacy in a xenograft mouse model with heterogeneous MM cells. Armored bi-CAR-Ts were potent in eliminating heavy tumor burdens and enhancing T cell infiltration and expansion. Conclusions: The pre-clinical data demonstrated that the bi-specific CAR-T not only outperformed in targeting MM cells mimicking early or middle lines but also reduced the incidence of antigen-negative escape. By enhancing sensitivity and leveraging unique epitopes, the bi-CAR-T maintained robust efficacy in late-line MM models. Future clinical studies will be conducted to validate the safety and efficacy in treating high-risk MM patients.