Guo, Siqi

Abstract Chimeric antigen receptor (CAR)-T cell therapy has revolutionized the treatment of B-cell malignancies. Despite the clinical success of CD19-targeted approaches, relapsed/refractory (R/R) disease—often driven by antigen loss or immune escape—remains a major challenge. To overcome this, we developed a novel CAR-T cell therapy targeting BAFF-R, a receptor consistently expressed in chronic lymphocytic leukemia (CLL) and other B-cell malignancies. We developed a new anti-BAFF-R monoclonal antibody and engineered the MC10029 CAR construct using its scFv. Antigen-specific cytotoxicity was validated in both in vitro and in vivo models, including Nalm-6 (leukemia) and Z138 (lymphoma), and CD19-knockout tumor cells to model (R/R) disease. MC10029 CAR-T cells were generated from healthy donors and CLL patients, and their cytotoxicity was evaluated against MEC-1, a CLL cell line, as well as autologous CLL patient tumor samples. These studies demonstrated potent and specific antitumor efficacy. We transitioned to clinical-grade production, using GMP-compliant lentivirus to manufacture MC10029 CAR-T cells under regulatory guidelines. With FDA IND approval, we initiated a Phase 1 clinical trial to evaluate safety and dosing. Our first patient, treated with a low-dose, single infusion, achieved a complete metabolic response within 2 months. The therapy is well tolerated, with no severe advent events such as cytokine release syndrome or neurotoxicity, supporting both the safety and efficacy of the therapy. Conclusion: This study represents Mayo Clinic’s first homegrown CAR-T cell therapy, developed entirely in-house—from antibody discovery and CAR design to GMP manufacturing and clinical trial—marking a significant step toward personalized, next-generation immunotherapy for B-cell malignancies. Citation Format: Yan Luo, Shaohua Guo, Yaqing Qie, Martha E. Gadd, Tanya Hundal, Hemant S. Murthy, Mohamed A. Kharfan-Dabaja, Hong Qin. From gene to bedside: Mayo Clinic’s first-in-house BAFF-R CAR-T [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3719.

Abstract Several allogeneic CAR T-cell therapies are in clinical trials to evaluate safety, many of which rely on CRISPR/Cas-based genome editing. However, the Cas enzyme’s random repair mechanism elevates the risk of undesired, off-target effects, posing a challenge for safe allogeneic CAR T-cell generation. To mitigate the risk of therapy-related oncogenesis, we sought to pursue an alternative safe strategy to manufacture allogeneic CAR T-cells distinct from the preexisting ones in the clinic. We have developed a CRISPR RNA (crRNA) targeting T-cell receptor beta constant (TRBC) gene, which in conjunction with AsCas12a Ultra enzyme, causes site-specific editing by eliciting a predictable microhomology-mediated end joining (MMEJ) DNA repair pathway, which mitigates off-targeting risk. Targeted amplicon sequencing was employed to evaluate off-targeting and repair mechanisms. Graft versus host alloreactivity as well as CAR T persistence was evaluated using immunocompromised mice. In vivo tumor challenge study was conducted for over 3 months. Engraftment confirmation was done using immunohistochemistry and flow cytometry. Interestingly while evaluating the edited T-cells, we sequestered a unique T-cell population that showed TCR disruption yet remained CD3-positive and did not cause in vivo alloreactivity. These CD3-Retained, Allogeneically Functioning T-cells (CRAFT-cells) showed a similar growth rate as unedited T-cells and were then used as a platform to produce CD19-targeted CAR T-cells and BAFF-R-targeted CAR T-cells. When compared to the standard CD3-disrupted allogeneic CAR T-cells, CRAFT CAR T-cells displayed an equally robust cytotoxicity while possessing a safer genomic profile. CRAFT CAR T-cells could function as effector cells for bispecific T-cell engager (BiTE) and induce CD3-dependent cytotoxicity against tumor cells. Pertinently, CRAFT CAR T-cells as opposed to CD3-disrupted CAR T-cells, were present in mouse xenografts without alloreactivity. Having the onset of MMEJ-directed repair and minimal off-targeting, positions this CRAFT crRNA to generate safer allogeneic CAR T-cells with an overall reduced genotoxic profile in a clinical setting. This unique CRAFT CAR T-cell population displays in vivo persistence. Additionally, CRAFT CAR T can be combined with BiTE therapy, offering a promising and potentially more durable alternative to preexisting ex vivo allogeneic CAR T-cell therapies. Citation Format: Tanya Hundal, Yan Luo, Yaqing Qie, Martha E. Gadd, Shaohua Guo, Mohamed A. Kharfan-Dabaja, Hong Qin. CD3-positive allogeneic CAR T-cells: A novel platform with persistence, BiTE-capture, and no alloreactivity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4283.