Abstract A058: Bispecific NK Cell Engager Targeting immune checkpoint molecule (ICM) Reverses Drug Resistance Driven by Ligand-Independent Constitutive ICM Signaling in DLBCL

Abstract Diffuse Large B-Cell Lymphoma (DLBCL) is the most common and aggressive B-cell lymphoma, with ∼40% of patients experiencing relapse or refractory disease. Although loss of MHC class expression is frequent and correlates with poor outcomes, we identified aberrant upregulation of the immune checkpoint molecule CD-X (name withheld for patent reasons) as a strong independent predictor of chemoresistance. Unlike its ligand CD-Y, CD-X was selectively induced by B-cell receptor (BCR) signaling and was highly expressed in malignant B cells with constitutive BCR activity. Functional studies using CRISPR-mediated CD-X knockout revealed colocalization of CD-X with BCR complexes and attenuation of MAPK/AKT signaling, BCL2 expression, and pro-survival capacity. CD-X deficiency increased apoptosis and restored sensitivity to vincristine, doxorubicin, and cyclophosphamide, independent of CD-Y. Transcriptional analysis demonstrated that CD-X expression is driven by STAT3 and NF-κB. Pharmacologic inhibition with ruxolitinib effectively suppressed CD-X via JAK–STAT3 blockade and enhanced chemotherapy response. However, in ABC-DLBCL (∼35% of cases) harboring constitutive NF-κB activation, CD-X expression remained high despite ruxolitinib, maintaining drug resistance. To directly target these refractory CD-XHigh cells, we engineered a bispecific NK cell engager (BiKE) linking CD-X to CD16. This BiKE effectively redirected NK cell cytotoxicity against CHOP-resistant CD-XHigh DLBCL cells, eradicating tumors otherwise unresponsive to standard regimens. Our findings uncover a ligand-independent, BCR-associated role of CD-X in sustaining oncogenic survival signaling in DLBCL and demonstrate that a BiKE targeting CD-X provides a promising therapeutic avenue to overcome drug resistance, particularly in ABC-DLBCL. Citation Format: Jaemin Kim, Jaewoong Lee. Bispecific NK Cell Engager Targeting immune checkpoint molecule (ICM) Reverses Drug Resistance Driven by Ligand-Independent Constitutive ICM Signaling in DLBCL [abstract]. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr A058.